controller for solar generation - university of strathclyde project report

Group 3: Controller for Solar Generation

Donald Bryson

Thomas Gibson

Benjamin McIntosh-Michaelis

Adam Stewart

Electrical and Mechanical Engineering

2013 - 2014

EM304

Integrated Design

EM304 Integrated Design Group 3: Controller for Solar Generation 2013/2014 University of Strathclyde

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Abstract This report contains detailed information on a student project undertaken at The University of

Strathclyde as part of 3rd Year Electrical and Mechanical Engineering course EM304: Integrated

Design.

The project had the aim of designing and building a controller for solar generation, implementing a

device to track the position of the sun in the sky at the same time as heating a volume of water for a

practical application.

The project was run between October 2013 and May 2014 and was designed to test and develop the

group’s management and team working skills as well as emphasising investigative, design and

implementation abilities.

Statement of Academic Honesty This submission is entirely the original work of the group. Except where fully referenced direct quotations have been included, no aspect of this submission has been copied from any other source. All other works cited in this submission have been appropriately referenced. Any act of Academic Dishonesty such as plagiarism or collusion may result in the non-award of the degree. The copyright for the material in this report belongs to those named on the cover page.


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Contents Abstract ................................................................................................................................................ 0

1. Introduction .................................................................................................................................. 4

2. Background ................................................................................................................................... 4

3. Specification .................................................................................................................................. 5

4. Roles and Participation ................................................................................................................. 6

5. Mechanical Design and Function .................................................................................................. 7

5.1. Objective ............................................................................................................................... 7

5.2. Design ................................................................................................................................... 8

5.2.1. Concentrator ................................................................................................................. 8

5.2.2. Azimuth ......................................................................................................................... 8

5.2.3. Elevation ....................................................................................................................... 9

5.3. Results/Demonstration of Success ...................................................................................... 12

5.4. Scaling ................................................................................................................................. 12

5.5. Conclusion ........................................................................................................................... 13

6. Electrical Design and Function .................................................................................................... 14

6.1. Objective ............................................................................................................................. 14

6.2. Design ................................................................................................................................. 14

6.2.1. Initial Concept ............................................................................................................. 14

6.2.2. Final Concept ............................................................................................................... 14

6.2.3. Additional Functionality .............................................................................................. 16

6.3. Scaling ................................................................................................................................. 17

6.4. Conclusion ........................................................................................................................... 17

7. Water Heating System ................................................................................................................ 18

7.1. Objective ............................................................................................................................. 18

7.2. Design ................................................................................................................................. 18

7.2.1. Heating Element .......................................................................................................... 18

7.2.2. Tank System ................................................................................................................ 20

7.2.3. Linking the Tank and Heating Element ............................ Error! Bookmark not defined.

7.3. Results/Demonstration of Success ...................................................................................... 21

7.4. Scaling ................................................................................................................................. 22

7.5. Conclusion ........................................................................................................................... 22

8. Procurement ............................................................................................................................... 23

9. Improvements ............................................................................................................................. 25


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10. Conclusion ............................................................................................................................... 26

11. Appendix 1: Fully Integrated Testing ....................................................................................... 27

11.1. Objective ......................................................................................................................... 27

11.2. Procedure ........................................................................................................................ 27

11.3. Results ............................................................................................................................. 28

11.4. Conclusion ....................................................................................................................... 30

12. References .............................................................................................................................. 31


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1. Introduction Reliable water heating is important both domestically and in industry and since water heating takes

significant energy input, hot water supply is a major issue surrounding global energy supply.

Group 3 was made up of four students; Adam Stewart, Thomas Gibson, Donald Bryson and Benjamin

McIntosh-Michaelis. They were tasked with building a Controller for Solar Generation which would

track the movements of the sun and use its infrared radiation to heat water in the interest of killing

legionella bacteria. The timespan of the project was between October 2013 and May 2014 and had

to be completed within a budget of £100. The group’s primary advisor and ’customer’ who created

the initial specification was Dr Bruce Stephen and the secondary advisor was Dr Brian Stimpson, both

from the University’s Department of Electronic & Electrical Engineering.

2. Background The aim of this project is to use solar power to control Legionnaires Disease in water systems. First

discovered in 1976 when 182 US Army Legionnaires contracted the disease which was fatal in 29

cases, it is spread most commonly by the Legionella Pneumophilia bacterium and results in a

pneumonia-like illness. This bacteria accounts for 90% of cases of Legionnaires Disease and has only

ever been discovered in water where it thrives in temperatures between 20 and 45 degrees Celsius.

It can only be contracted by consumption of infected water or inhalation of water droplets

suspended in the air which are contaminated with the bacteria. Common situations for the bacteria

to thrive are in hot water tanks and evaporative condensers used in large air conditioning systems

seen in hotels and office buildings. As well as an appropriate temperature, legionella also thrives

where substances such as rust, sludge or other organic matters are present. Temperatures around

60 degrees Celsius and over will kill the bacteria over time with higher temperatures taking less time

to kill the bacteria.

Solar energy systems in the United Kingdom have taken a slight hit in recent years due to the

downscaling of the feed in tariff offered to contributors in late 2011, but with the reducing cost of

Photovoltaic (PV) panels, solar energy systems are on the rise again. Solar power was in use in over

450,000 UK homes at the end of 2013 with around 2,000 additional installations each week. With

around 1 kW/m2 of thermal power available on a sunny day in the UK, the potential for solar energy

systems is still high. Solar water heating systems are less common in the UK than their Photovoltaic

counterparts but also have their place. They can be used to offset the temperature difference

central heating systems experience on start-up and can save significant amounts of electricity over

the course of a year.


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3. Specification At the start of the project the group was given the task to build a controller for solar generation with

the following objectives:

Must follow the sun in both the azimuth and elevation paths during daylight hours

Will be land based

Will operate in the UK

Will ignore the effect of clouds

Will operate under its own power

Will produce 250L of water at 60°C in a week

Given the above requirements, the group agreed that a

full scale working system would be unfeasible given the

time and budget restraints. It was decided instead to

create a ¼ scale model and it was calculated that this

would correspond to heating 2.5L of water up to 60°C in

an hour on a bright day. Additionally the group decided

to add in a sleep function to the Arduino

microcontroller so that the entire system could be shut down over night and for short but frequent

periods throughout the day. This decision was taken to reduce the overall power consumption of the

project.

The general idea of the solar concentrator would be to reflect sunlight using a parabolic reflector

which would rotate and tilt in order to track the sun and keep the focused sunlight on a heating

element. Water would be cycled between a tank and the heating element in order to heat up the

whole volume of the tank.

From the outset it was obvious that accurately tracking the position of the sun throughout the day as

well as efficiently transferring heat energy from a heating element to a tank full of water would

prove the biggest difficulties that would have to be overcome.

Figure 3.2 System Design Block Diagram

Figure 3.1 Azimuth, Elevation and Zenith Angles


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4. Roles and Participation At the beginning of the project all group members put forward the parts of the project they would

be most interested in working on and those roles have not changed once they were initially agreed

upon. Participation has been evenly spread between the four team members who have been kept in

close contact throughout the academic year and have worked well together as a group, with only

one person working on the project at a time being a rare occurrence.

Adam put himself forward for team leader which was unanimously accepted, in first semester he

organised the weekly group meetings where the group discussed the specification of the project and

how the problems could be solved. The group also discussed resources and where some of the major

components required could be procured. In second semester Adam also took on the role of resource

representative which involved placing all the orders with the electrical workshop. It also involved

submitting work to be done by the mechanical workshop and ensuring it was being completed as

desired by the group to fit in with the rest of the components. The linear actuator which was

produced by the mechanical workshop required a lot of discussions with the staff at the workshop as

they were often inclined to use different materials and were occasionally unsure of the designs.

Adam also helped out with some of the early stages of writing the code required to calculate the

position of the sun but primarily with the integration of the different components to deliver the final

solution.

Tom has performed the role of technical director and has been instrumental in the design and

implementation of the base concept of the project and particularly in the movement sub system. He

has devised the concepts used for many different areas of the project and has played a major part in

the assembly of all the components. Tom has also kept track of the budget throughout the project

and was able to procure the three of the potentially most expensive components in the project, the

satellite dish, Arduino microcontroller and battery, for free which has had a key impact on the

budget.

Donald has worked on the electronic side of the project, writing the code for the motor controller to

drive the pump as well as the motors for the azimuth and zenith angles to ensure that the dish is

always pointing at the sun during daylight hours. He has also constructed a real time clock with more

functions which has enabled the Arduino to turn itself off and then wake itself up. This has helped

the project to save a significant amount of power both at night and throughout the day when it is in

its low power state.

Alongside working with the Vertically Integrated Project, Ben has completed the majority of the

work for the water heating system. He procured the tank where the water will be stored and

insulated it as much as possible with the resources available. He also helped in the implementation

of the pumps, tubing and the bending of the copper pipe used for the heating element. Most

valuably, he has consistently helped in the assembly of the project as a whole and has been involved

with design decisions throughout the project.


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5. Mechanical Design and Function

5.1. Objective The mechanical design of the solar concentrator is concerned with the physical parts requires to

concentrate the sunlight to a point, as well as move the concentrator to be aligned with the sun,

based on signals from the Arduino.

The system must rotate the concentrator to align it with the azimuth angle as well as tilting the

concentrator to align with the sun’s elevation.

By implementing these systems the concentrator complied to the specification of tracking the sun

throughout the day, and provided a much more efficient system as the sunlight is always in direct

sight of the concentrator.

Figure 5.1 below demonstrates how such a system can improve the effectiveness of a solar

concentrator by controlling the focal point.

Figure 5.1 Comparison between Fixed Concentrator (Top) and Solar Tracker (Bottom) in Azimuth Plane

As can be seen above, with a fixed concentrator the focal point moves across the dish relative to the

sun, whereas with the tracker the focal point remains central to the dish. This is favourable when a

collector or heating element is required as it can then remain in the same position relative to the

dish. A similar situation occurs with the elevation angle.

Sun

Focal Point

Concentrator

AM PM


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5.2. Design 5.2.1. Concentrator

To focus the sunlight it was decided that a parabolic reflector would be used, as opposed to a lens.

Where a lens may have produced a more intense focal point, it was considered that a reflector

would be easier to mount and control, and would provide a more useful and traceable focal area.

The reflector was made from a recycled satellite television receiver dish, covered with a reflective

thermal blanket bonded to the dish with PVA glue. The blanket was chosen thanks to its high

reflectivity of both visible light and infrared radiation, so that as much solar energy as possible could

be captured. The thermal blanket was applied in narrower strips, giving a smooth and highly

reflective surface. As seen in Figure 5.2 below, the concentrator was tested using lasers to find the

approximate size and position of the focal area.

Figure 5.2 Laser Testing of Solar Concentrator

The dish had dimensions of 720 mm X 560 mm and an area of approximately 0.317 m2, and since it is

estimated that the sun has a power rating of 1 kW/m2 the concentrator could collect 317 Watts of

thermal power. The dish had a scaling factor of 10, so the reflected light was focused on an area 72

mm wide by 56 mm high.

5.2.2. Azimuth To rotate the concentrator to the azimuth angle it was mounted on

an MDF turntable, using a mounting pole purchased from Onecall,

thus allowing 360° of revolution. MDF was chosen for this and the

base of the assembly since it was available immediately and free of

charge from the EEE mechanical workshop. To reduce friction and

to balance the turntable, castor wheels were added. The turntable

arrangement can be seen in Figure 5.3.

The original plan was to use a small motor and gearbox mounted

on top of the turntable. A shaft would protrude through the

turntable from the gearbox, and drive a pulley against a large gear

wheel fixed to the base of the assembly, as illustrated in Figure 5.4.

Figure 5.3 Turntable Arrangement


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It was soon found that this system was not appropriate, since the motors tried were not capable of

producing a high enough torque, nor could the gearbox transfer enough power when bigger motors

were used. It was also very difficult to align the pulley with the fixed gear, especially with the lack of

space between the base and the turntable.

Therefore the azimuth drive system was redesigned to

incorporate a larger and more powerful motor that

could easily provide the torque required. The motor

was mounted to the assembly base and a Meccano

wheel was used to transfer the power from the motor

to the turntable. A series of spur gears were used

between the motor and the wheel to reduce the

motor speed, so that the turntable had a resultant

speed of around 0.6 rpm, allowing precise control of

the turntable.

A potentiometer was mounted to the axle of the turntable, which remained stationary relative to

the turntable. The body of the potentiometer was mounted to the turntable so that it rotated with

the turntable, feeding a signal back to the Arduino so that the azimuth angle could be calculated.

Figure 5.6 Azimuth Potentiometer

5.2.3. Elevation The control of the elevation angle of the concentrator was one of the more complicated issues

among the mechanical design of the project. An early idea is outlined below, with initial drawings

shown in Figure 5.7 and a card model seen in Figure 5.8.

Turntable

Gear Wheel

Motor/Gearbox

Pulley

Castor Wheel Base

Figure 5.4 Original Turntable Design

Figure 5.5 Motor, Gearing and Drive Wheel


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Figure 5.7 Early Elevation Actuator Drawings

Figure 5.8 Early Elevation Actuator Design

A threaded rod would be placed within the base component, running through a threaded hole in the

strut. As the threaded rod would turn, the base of the strut would travel along the base, in turn

raising or lowering the stand. While this method may have been successful for the project, it was

decided against since it was likely to be a bulky approach and possibly unstable. It would have also

been difficult to attach such a device to the concentrator dish.

Several other approaches were also considered, including using a chain connected between the top

and the base of the dish driven by a motor positioned at the back of the turntable, but it was finally

decided that a linear actuator would be the best approach. The preferred suppliers were searched

for such devices, but it was impossible to find an appropriate device within budget so designs were

drawn up and submitted to the EEE workshop to have an actuator made, as seen in Figure 5.9.

Stand

Strut

Base


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Shaft

Carriage

Threaded

Rod

This design also used a spinning threaded rod as the basis of the actuator. The carriage part has a

threaded hole through the centre so that as the rod is turned the carriage moves along its length. A

shaft connects between the carriage and the dish so that as the carriage moves the base of the dish

is pushed up and out, or is drawn back in. A potentiometer is used as the axle between the carriage

and the shaft, sending a signal to the Arduino relating to the elevation angle of the dish.

The threaded rod was turned using a motor, with a built in gearbox with 100:1 ratio. It was found

that this motor provided an adequate speed for the actuator, so a 1:1 gear ratio was used to connect

between the motor and the threaded rod. To save time and money, the gears for this part of the

project were laser cut using the equipment in the DMEM department, after the appropriate part

files were downloaded from the Rush Gears Website.

Figure 5.10 Linear Actuator (Left) and Gearing (Right)

Figure 5.9 Linear Actuator Design


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5.3. Results/Demonstration of Success Through the implementation of these methods, if was found that both operated very successfully.

The azimuth motor provided enough power to drive the turntable with relative ease, even under

reasonably heavy loading. The range of the turntable was limited to between 30° to 270° from

north, due to the limited range of the axial potentiometer used to measure azimuth angle and the

bolts that secure the linear actuator ends to the turntable since they protrude through the turntable

directly in the path of the drive wheel. To improve this part of the system these bolts may be

countersunk, and a potentiometer with a greater range may be used. An issue also arose with the

first potentiometer used, as the shaft was very stiff to turn there was a tendency for the

potentiometer shaft to shear. To combat this a different potentiometer was used which rotated

much more easily, reducing the shear stress applied to the shaft.

The linear actuator also provided the ideal system for tilting the concentrator dish and proved highly

successful. There were concerns whether the device would function effectively without the use of

bearings in the carriage and end supports, omitted in the interest of saving costs. However it was

found that with appropriate lubrication the effects of friction were minimal. The linear actuator was

designed to have a length of 50 cm, allowing for the full range of elevation of the solar concentrator

(0° – 57°), however to focus the sunlight onto the desired focal point the concentrator had to be

lowered by 25° from the elevation of the sun. Therefore the actuator could have been made

shorter, saving some space and weight on the turntable.

5.4. Scaling This project was concerned with constructing a ¼ scale model in terms of area of the concentrator

dish, i.e. the full scale model would have a dish of around 1.4 m wide by 1.1 m tall. Of course, by this

scaling factor the mass of the concentrator would be greater, so the actuation methods described

above would have to be larger and stronger. Also the full scale system would ideally have a specially

made parabolic reflector with a much smoother surface than the reflector built in this project,

providing a higher reflectivity and efficiency.

The turntable and base would be constructed from a much more durable material such as steel,

aluminium or composite to increase their resistances to weathering, since MDF cannot withstand

water. More suitable castors or bearings would be used between the turntable and the base to

further reduce friction and add support. A skirt may be added around the turntable to prevent

anything from entering the space and blocking the castors. A rack and pinion system may replace

the drive wheel so that the dish cannot move under external influences such as wind.

As well as an increase in size the linear actuator would make use of bearings between all the moving

parts to reduce friction and the effects of wearing. The threaded rod may be enclosed to keep it

clean and to ensure that wires cannot get caught, as well as increasing the safety of the system. If

enclosed the lower part of the actuator could be oil filled to avoid dirtiness and wearing in the

threaded parts. Otherwise weathering may present a significant risk and cause the system to seize.

A professionally made linear actuator could be used but these can come at a much greater cost.

The gearing in each system would also be replaced with metal gears enclosed in oil filled gearboxes.

The motors required would also need to be increased in size, as will the systems for powering these

motors.


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5.5. Conclusion The mechanical aspect of this project was concerned with concentrating the sunlight to a point so

that it could be put to good use, as well as tracking the sun so that as much solar energy could be

captured as possible with high efficiency.

To implement these movement techniques several designs were considered before the turntable

and linear actuator were chosen, and after assessment it can be concluded that these were the best

approaches to take, yielding great results with high positional control and minimal mechanical

losses.

Figure 5.11 Rear View of Final Solar Concentrator Design Showing the main Mechanical Components


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6. Electrical Design and Function

6.1. Objective The electrical system is required to supply power to all the relevant mechanical parts such as the

motors and pump, as well as the Arduino microcontroller. It also concerns the implementation of

solar panels to allow the project to operate under its own power. The electronic side of the project is

necessary to use inputs such as time and geographical position, then use algorithms to calculate

where the sun is in the sky, then send appropriate signals to the motors to ensure the orientation of

the dish is optimal for solar water heating. The Arduino Uno was used for the microcontroller as it

was cheap and has an excellent online community which would aid in the writing of code as there

were many examples which could be adapted for the required uses. The system was supplied power

from a 1.3Ah lead acid battery as this was readily available and an adequate size for the purposes of

the system.

6.2. Design 6.2.1. Initial Concept

The original concept for performing this function was to track the sun with a set of light sensors on

either side of the dish in order to produce an accurate real time position of the sun. However it was

reasoned that this was not practical due to the inherent complexities this would introduce.

6.2.2. Final Concept The final concept tracked the sun the using equations which are very accurate and reliable for many

years. The calculated position of the sun would then be compared with the orientation of the dish. A

few sources were initially used to calculate the position of the sun but they proved inconsistent. In

the end the equations from EEE class EE317: Renewable Energy Technologies were used as these

proved to give results which were consistently accurate. The equations used were as follows:

( )

[1]

[2]

(

) [3]

[4]

[5]

(( ) ( )) [6]

(( ) ( )

) [7]

Table 6.1 below shows the symbols and what they represent in these equations.


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Table 6.1 Position of the Sun Equation Symbols and Meanings

Symbol Meaning

B Placeholder for use in EoT calculation

EoT Equation of Time

δ Declination Angle

Ts Solar Time

λzone Longitude

ω Hour Angle

φ Latitude

α Elevation Angle of the Sun

θ Azimuth Angle of the Sun

When these equations were implemented on the Arduino microcontroller it was found that it

provided wildly inaccurate results, although the equations had been checked using Microsoft Excel.

It was later discovered that the Arduino does not have sufficient arithmetical capabilities to perform

complex equations in one go. They therefore had to be split up into smaller calculations with lots of

intermediate variables introduced to cope with this.

From testing it was found that if the concentrator lined up exactly with the sun then the focal point

would be much higher than the heating element mounted on the dish. Through trial and error the

elevation angle of the dish was lined up with the actual elevation of the sun minus 25 degrees to

focus the sunlight onto the heating element by making changes to the code. To save power the

Arduino would only move the dish West when the azimuth angle of the dish was less than that of

the sun, and would then move to 5 degrees past the actual azimuth angle of the sun. As the heating

element was longer than necessary, this kept the focused light on the heating element at all times

and required the dish to be moved less often. The concentrator would only be moved East if the

azimuth angle of the concentrator exceeded that of the sun by 10 degrees. The elevation angle

would be kept within -25 and -30 degrees of the elevation angle of the sun.

Due to the placement of the potentiometer measuring the angle of the elevation of the dish, the

relationship between the resistance of the potentiometer and the elevation angle of the dish was

non-linear. To resolve this issue, the resistance of the potentiometer was mapped to the

corresponding elevation angle of the dish and stored as a 2D array in the Arduino code. The table

entries give the resistance of the potentiometer at set elevation angles 5° apart. When the elevation

angle is read into the code, the resistance of the potentiometer is compared to the lookup table and

the elevation angle is determined from there. The resistance of the potentiometer is set to the lower

value of the two values it is in-between in the table and the corresponding elevation angle is used.

The time is read into the microcontroller from a Real Time Clock (RTC) which accurately keeps the

time to the second. The RTC originally used was a Maxim DS1302 Real Time Clock which was

purchased on a PCB with a coin battery and relevant resistors. Code to enable the Arduino and the

RTC to communicate was required and downloaded from the GitHub website [vii]. An L293D motor

controller chip was used to drive the motors due to its availability and cost, however as the pump

was sourced after the motors and controller and had a high power demand it was not suitable to be

run directly from the motor controller.


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When the motors were required to move, a signal was sent to the relevant channel of one of the

motor controller chips. One side of the motor controller chip was used to drive the azimuth motor

and the other side of the chip used to drive the elevation motor. Once movement operations were

complete a signal was sent to another motor controller which switched a relay used to provide

power to the pump. This pumped water around the water heating system for a minute before the

system entered a low power state which is explained in detail in part 6.2.3.

6.2.3. Additional Functionality Due to the high power consumption of the pump and the relatively high power consumption of the

Arduino, it was necessary to take measures in order to save power. To combat the issue 2 solar

panels were used to trickle charge the battery, however it was also necessary to put the Arduino into

a low power sleep state while inactive. This would result in the system cycling through operations in

the following way: wake up, move if necessary, pump for a minute and then go back to sleep. Table

6.2 shows the power consumption and duration of each stage in operation.

Table 6.2 Power Consumption of System During an Average Day

Power In (W) Power Out (W) Typical Usage per Day

Arduino (Sleep) - 1.2 21 Hours 29 Minutes

Pump - 24 2 Hours 11 Minutes

Azimuth Motor - 9.6 10 Minutes

Elevation Motor - 4.08 10 Minutes

Solar Panels 8 - 13 Hours

As Table 6.2 shows, the pump is very high powered compared to the other components and on for a

considerable duration of time. Even with 2 solar panels the system still makes a net power loss.

Although the motors are also reasonably high powered they have a very low duty cycle and as a

result the whole system, without the pump, could run off of a single solar panel. By comparing the

net power while the pump is on and while the Arduino is asleep the ratio of time for which the

system is in the two states can be determined. The net power gain while the system is asleep is 6.8W

and the net power loss of the system while the pump is on is 16W. This means that the system

should sleep around 2.5 times longer than the pump is on in order to not lose power over the course

of a day.

For the Arduino to wake up from its low power state it needs to receive a signal to tell it to do so. For

these purposes a new Real Time Clock with a built in alarm function needed to be implemented

instead of the old DS1302 RTC. The new RTC used to fulfil this function was the Maxim DS1306 RTC

chip. The DS1306 chip was set up as shown in Figure 6.1 without the pull up resistor from the 1 Hz

signal output. A 3V coin battery was used to power the RTC and a 10kΩ resistor pulled pin 5 of the

RTC to +5V which was supplied by the Arduino’s voltage regulator. A 32.768 kHz crystal with a 6pF

capacitance was connected to pins 3 and 4 of the RTC as was specified by the chip’s datasheet.


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Figure 6.1 Circuit Diagram of Real Time Clock

New code had to be written to allow the Arduino and the RTC to communicate with each other. This

included changing the registers used to read and write to the RTC and adding new functions to set

the Alarms on the RTC. Once the sun sets, the alarm for sunrise the next day is set and the system

goes into its low power state for the night.

6.3. Scaling Scaling the system up would not affect the electrical control system much, however the accuracies

and tolerances of the system may have to be fine-tuned to be consistent with the new geometry of

the mechanical system. The power required by the motors and the pump would also be affected and

would likely require the implementation of motor controllers which are able to provide a higher

current.

6.4. Conclusion The electrical and electronic system was required to accurately calculate the position of the sun and

send signals to the motor controllers to match the calculated position of the sun with the orientation

of the concentrator within a given tolerance. The control system successfully allowed the

concentrator to be accurately aligned with the sun to produce a focal area on the heating element.

The system made a net power loss on the day of testing the group managed to undertake however,

with a smaller pump that required less power and solar panels that provide more power, this could

be overcome, especially with the recent implementation of the sleep function to the Arduino. A

larger battery could also be used to reduce this problem.


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7. Water Heating System

7.1. Objective The water heating system needs to absorb the heat at the focal point of the concentrator and

transfer the energy to water, raising the temperature. This is done so as to heat 2.5 L of water per

hour from around 20 °C to 60 °C or slightly above during daylight hours with suitable light levels. The

full 2.5 L must be at 60 °C by the end of the hour.

7.2. Design Two basic concepts were initially considered. Holding a vessel with the full 2.5 L in the focal point

and heating the full body at once. The other; heating up a small volume of water, flushing and

refilling the vessel with appropriate timing.

It was decided that a small volume would be heated and flushed. This decision was made because,

whilst 2.5 L was a feasible vessel size at the focal point, 250 L for a full scale system was not. Also

since the overall system design, would, in theory be used as a hot water supply system for a house

or something with similar hot water requirements, the means of taking water away from the system

needed to be considered. This was done by the flushing concept since it could be tapped; whereas a

tank at the focal point of the reflector would be much harder to tap.

The selected concept had three aspects required to be designed. The water needed to be held in a

heating element whilst being heated, it would then need to be held in a tank system which insulated

the water. The tank and heating element needed to be linked in such a way that the turntable could

still turn within the required range.

7.2.1. Heating Element The basic functionality of the heating element is shown in Figure 7.1 where Q is the heat transferred

to the water.

Figure 7.1 Basic Functionality of the Heating Element


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As shown in Figure 7.1 the focused light would be incident with and absorbed by the external

surface of the heating element. The energy would then be conducted through to the internal surface

where it was then transferred to the fluid.

This meant that the heating element needed to be as close to a black body to thermal radiation as

practically possible, and highly conductive. This would ensure that the maximum heat energy was

absorbed by the heating element’s external surface and was then transferred efficiently to the

interface with the fluid. According to the laws of heat transfer, both of these abilities are described

by the coefficients absorptivity, α and thermal conductivity, k.

Research found that common materials used for heating elements in solar water heating systems

are made from copper; α = 0.4 – 0.65 W/m K2, k = 401 W/m K and Aluminium; α = 0.4 – 0.65 W/m K2,

k = 205 W/m K [ii][vi]. Materials such as concrete have a much higher absorptivity but a drastically

lower thermal conductivity therefore copper and aluminium were the most appropriate choices due

to their fairly high values for these coefficients. Copper was the preferred material and was used for

the heating element.

Once the radiation had been absorbed by the external surface of the heating element, and the heat

had been transferred to the internal surface, the energy needed to be transferred to the fluid. This

could be done by forced or natural convection. Forced convection was chosen because it is a more

effective method of heat transfer, capable of transferring around ten times as much energy than

natural convection.

During heating, water needed to constantly flow through the heating element for forced convection.

Therefore the heating element was made from small diameter pipe, making the pipe relatively

simple to bend into a coil which meant that the water spent more time in the focal point. The

heating element covers the full 32 cm2 sized area that the radiation was focused onto.

A recycled copper coolant pipe was sourced from an old fridge and bent into a coil. It was sprayed

with matte black wood stove paint to enhance absorption and mounted at the focal point. The

mounted heating element is shown in Figure 7.2.

Figure 7.2 Mounted Heating Element


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7.2.2. Tank System Two options were considered when deciding where the water in the heating element comes from

and goes to. One option was to use two tanks. One containing colder water and the other, very well

insulated, would contain the heated water. This option presents many problems, if water below 60°C

leaves the heating element, the temperature in the second tank will reduce. Also one cycle through

the heating element is unlikely to be enough to heat the water to above 60°C on a reliable basis. As

the second tank would constantly lose a small amount of heat, the temperature would likely drop to

below 60°C.

The second option was to pump water through the heating element at a constant rate using one

well insulated tank as the source and destination of the water. This meant that the only control

needed was that which turns the pump on and off. This meant that initially the water was gradually

heated up by continually passing through the heating element and remixing. Once the tank was at

60 °C or above, it could be maintained at this temperature by continually passing water through the

heating element.

The tank needed to have the capacity of 2.5 L or slightly above, therefore a 3 L plastic bottle was

sourced for free. There were concerns that this would not have been able to hold its shape at 60°C,

although through experimentation it was found that the plastic bottle used held its shape up to

80°C, and no change was observed at 60°C. For insulation this bottle was covered in the same

thermally reflective material as the satellite dish, before it was Papier Mache’d for rigidity and

covered in foam to insulate. This is shown in Figure 7.3.

Figure 7.3 Insulating the Water Tank


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The heating element was mounted on the satellite dish, which was mounted on the turntable. The

tank was placed off the turntable resulting in relative movement between the tank and heating

element. A suitable way of connecting these two elements was with flexible hosing which was

sourced by the group and had inner diameter 5 mm and outer diameter 8mm.

7.3. Results/Demonstration of Success The system was tested at the Duke Street car park on Friday 18th April 2014 (see Appendix 1 for

more detail).

During testing the water was pumped from the tank and through the heating element, absorbing

heat before returning to the tank. This was continued for four hours but was interrupted due to the

power issues regarding the water pump. It could be observed that the heating element was

appropriately located in the focal point, as shown in Figure 7.4. The surface of the heating element

reached very high temperatures, with a peak of 201°C.

Figure 7.4 Radiation Focused onto the Heating Element

During the first period of testing the tank temperature was raised through 8°C from 24°C to 32°C in

around 20 minutes, demonstrating that the system could heat water. After over an hour with the

reflector covered, the temperature of the water in the tank dropped by 1°C, demonstrating that the

tank was well insulated. After a second period of testing the water in the tank reached 42°C,

however this period was also cut short due to the pump running the battery down to the point

where it could no longer operate.


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7.4. Scaling A full scale system would see 250 L of water heated to 60 °C by the end of one week. The energy

required to heat 1 kg (

) or 1 L of water from 20°C to 60°C was calculated as shown below.

[8]

250 l in one week relates to 35.7 l per day. An average day has approximately 8 hours of sunlight and

of these 8, 4 are assumed to be suitable for effective water heating, though this will vary throughout

the year. Therefore there should be 9 l heated every hour, equating to 2.48 ml heated per second, or

2.48 x 10-3 kg/s. Hence a power of 415 W is required for a full scale system.

Assuming 35 % efficiency of the system, the thermal power required would be 1185 W. The

irradiance of the sunlight is 1 kW/m2 in the UK on a bright day, so the area required for the full scale

system would be around 1.2 m2. The area of the parabolic dish used was 0.32 m2, relating to a ¼

scale model. The scaled system could heat 62.5 l of water per week, meaning about 10 l per day or

2.5 l per hour.

7.5. Conclusion The heating system was successful in heating and storing water. The heating element absorbed

energy at the focal point and then passed it into the water flowing through the element. The

connecting pipes directed the water to and from the heating element. Insulation on the tank was

sufficient to prevent a great temperature drop.

A few improvements could be made, such as adding a coil inside the tank to implement a closed loop

system or insulating the connecting pipes to reduce heat loss as described in section 9. An

additional reflector positioned at the focal point at the back side of the coil would capture reflected

radiation which misses the coil as well as the radiation being emitted by the coil. This secondary

reflector could also be shaped to shield the coil from the wind.


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8. Procurement This project required a large range of parts, materials and equipment to be sourced on a limited

budget, so as much of this as possible was acquired for free or borrowed. Table 8.1 below indicates

the parts that have been used and where they were sourced:

Table 8.1 Items Procured for Project

Qty Item Description Supplier Part Number

Cost Each (£)

Total Cost (£)

1 Arduino Uno RS 715-4081 18.00 18.00

1 32mm Dia. 6-15Vdc Motor 100:1 Gearbox (Elevation)

RS 420-596 15.67 15.67

1* 12 Teeth Timing Belt Pulley 15mm width RS 184-594 5.44 5.44

2 Panasonic 3V CR2032 Coin Battery RS 513-2871 1.16 2.32

1 DS1306 RTC Alarm RS 540-2710 4.00 4.00

1* Motor and Gearbox (Kit Form) Rapid 37-1210 5.62 5.62

2 32.768kHz 6pF 2x6mm Radial Cylindrical Watch Crystal

Rapid 90-3042 0.35 0.70

5 L293D Motor Driver Rapid 82-0192 3.73 18.65

2 L7812cv +12v 1a Voltage Regulator (st) Rapid 47-3292 0.42 0.83

1 4W Solar Briefcase Maplin N05HN 19.99 19.99

1 Loft Mounting Kit 18" Onecall AP02343 4.46 4.46

2 1.75" V Bolt and Nuts Onecall AP02245 0.32 0.65

2 1k potentiometers EEE 1KP 0.49 0.98

1 Linear Actuator Workshop - - -

1 Turntable and Base Workshop - - -

3 Elevation Gears DMEM - - -

5 Azimuth gears/wheel Previous - - -

1* Timing Belt and Gear (Original Azimuth) Previous - - -

1 Satellite Dish Donated [1] - - -

1 Aluminium Foil Tape Donated [2] - - -

1 MFA 919D Motor (Azimuth) Borrowed [2] - - -

1 Small Protoboard Borrowed [2] - - -

1 Large Protoboard Group - - -

1 12V Relay Group - - -

1 12V 1.3Ah Battery Group - - -

1 Water Pump Group - - -

1 Length of Flexible pipe Group - - -

1 Copper Pipe Group - - -

1 Water Tank Group - - -

1 Thermal Insulation Group - - -

1 Thermal Blanket Group - - -

1 PVA Glue Group - - -

3 Insulation Tape (Black, Red, Blue) Group - - -

Total: £97.31


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Various small components (nuts, bolts etc.) were found within the lab or sourced from previous projects.

Items marked * were not used in the final project.

Items marked as “Previous” were reused from previous projects.

Items marked “Group” were sourced separately by or borrowed from group members.

“Workshop” represents the mechanical workshop in the EEE department, University of Strathclyde.

“DMEM” represents the Digital Manufacturing Studio within the Design, Manufacturing and Engineering Management department, University of Strathclyde. With thanks to Mr Duncan Lindsay.

[1] With thanks to Miss Carolyn Gethin, Inverness.

[2] With thanks to Mr John Redgate, University of Strathclyde.


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9. Improvements Given more time and resources, there are a few aspects of the project which the group would like to

improve. First and foremost, a small low power pump would replace the one which is currently in

use in the interest of saving power. Additional insulation would also be added to the system,

primarily to reduce heat loss in the tubing from the heating element to the storage tank. A closed

loop water system could also be implemented which would introduce another coil of pipe within the

water tank. The water in the tank would therefore be completely isolated from the heating system

and a thermal fluid would occupy the piping which would be more efficient at transferring heat from

the heating element to the water stored in the tank. A diagram of this can be found below in Figure

8.1.

An additional reflector could be added to the system so that any radiation reflected from the dish

that misses the heating element would be reflected onto the back of the heating element. This

would also reflect heat energy which is radiating off of the hot surface of the coil. More powerful

solar panels would also be used which would be give the project a net power gain on bright days as

well as being able to generate enough power to be sufficient on bright days with clouds. These solar

panels would be mounted on the turntable so that they also track the sun throughout the day. The

group would also like to implement a relay in series with the solar panels so that the Arduino and

motors would only receive power from the battery if the solar panels are generating enough power,

indicating that it is a nice enough day to be able to heat water with the concentrator. The entire

project would also be weatherproofed so that it could withstand heavy rain as well as moderate

wind. At the moment the base and the turntable are made of MDF which would break up if exposed

to water, this would be replaced with a metal such as steel or aluminium. An electronics box would

also be required to house the Arduino and its connections. Heat shrink tape and Tyco™ connectors

could be used on the wires to completely insulate them and the connections to the motors, pump

etc. Friction could also be reduced by adding bearings to the linear actuator and finding more

suitable casters for the turntable to turn on.

Cold Fluid

Hot Fluid

Parabolic Reflector

Heating

Element

Water Tank

Heat Exchanger

Figure 9.1 Proposed Closed Loop Water System


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The last major thing the group would like to add to this project is temperature monitoring. This

would allow the temperature of the water coming out of the heating element to be checked and the

flow rate of the pump varied depending on this value. A function in the code could also be included

so that the dish could turn away from the sun if the heating element became too hot to the point

where it could cause damage. With these changes made the project could become a permanent, self

sufficient water heating system that would require very little maintenance and could run

autonomously.

10. Conclusion This project should be seen as a success as the group successfully built a device capable of accurately

tracking the position of the sun during the day and using infrared radiation from the sun to heat

water. Although the temperature defined in the specification was not reached on the single test day

available to the group, it can be assumed that the project would have been capable of doing so

without the multiple disruptions to the test day. With a temperature of 201°C measured at the

heating element, this would prove more than adequate to heat the water to 60°C.

The project was well managed with weekly meetings of 3 hours to work on the project. Although the

majority of hours were put into the project outside this scheduled meet, all four members were

always present during this scheduled time which allowed effective communication between the

team members and gave an opportunity for integration problems to be discussed and a compromise

found. A high number of hours in the last few weeks of the project made a very large contribution

towards the success of this project as it was able to be in a reasonable working state two weeks

early. This allowed for the test day on what was one of very few sunny days in the last month of the

project, without which no meaningful results would have been obtained for the water heating

system. The budget was also kept very well throughout the year but took a steep drop in the last

week where component failure necessitated purchase of replacements.

Contacts were made throughout the university in the Electrical, Mechanical and Design,

Manufacture and Engineering Management departments where many members of academic staff

were of invaluable importance. The process of requesting permission to test the project out with the

university also provided valuable experience in producing a risk assessment, method statement,

obtaining insurance and communicating with members of different organisations.

This project has contributed extremely relevant experience of project work to all four of the group

members including resource and time management. The integration of designs from different

technical specialities has also been a valuable lesson which each of the students will be able to carry

on to future projects in university and beyond.


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11. Appendix 1: Fully Integrated Testing

11.1. Objective As each of the project sub systems were created and developed they were independently tested,

including the concentrator dish, azimuth and elevation actuators, and the Arduino coding. However,

fully integrated testing was required to demonstrate the success of the project, to make any

necessary adjustments and to establish what future work would be required.

The objectives of such testing were:

To ensure that the concentrator could effectively track the sun’s position over a day, using

the coded Arduino Uno to calculate the required position based on the feedback from the

azimuth and elevation potentiometers, and operate the motors as necessary.

To confirm that the solar concentrator would focus sunlight onto the heating element.

To find the temperatures that system components could reach in direct sunlight, including

the temperature of 2.5 l of water in the storage tank and the surface temperature of the

heating element.

11.2. Procedure The system was ready for integrated testing shortly after the spring break, so appropriate permission

was acquired for the group members to take the project to the top level of Duke Street multi-storey

car park, Glasgow, chosen for it’s ideal unobstructed view facing south over the city. For this

permission to be granted, a risk assessment and mission statement were written up, and public

liability insurance was secured from the university. Students taking part in the experiment had to

wear appropriate PPE including lab coats, sunglasses and sun cream. The top level of the car park

was closed to the public, this is normal for the car park since it is newly constructed and not yet fully

open.

The experiment was conducted on Friday 18 April 2014, with the equipment assembled on the car

park roof at 09:30. A thermocouple was inserted into the water tank so that the temperature of the

water could be measured, and a GoPro camera was set up to observe the experiment, taking a

photograph every 60 seconds.

Before this experiment, little time had been spent testing the water pump since it was a fairly new

addition to the project. At his stage it was connected directly to the battery, and was independent

from the Arduino.

Figure 11.1 Selection of GoPro Photographs


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11.3. Results The experiment began at 10:00 and almost immediately it was clear that there were power issues,

since the water pump being used was quickly draining the battery, drawing so much current that the

azimuth and elevation motors could not move at the same time the pump was running. As soon as

the pump was unplugged the motors would operate normally. Therefore the system was only run

for around 50 minutes before the pump was disconnected to allow the battery to charge from the

solar panel. During this down time the concentrator was covered to prevent the heating element

from overheating. Before this, however, the temperature of the water had increased from 24°C to

30°C, as illustrated in Figure 11.2.

Figure 11.2 Thermocouple Reading of 30°C after 35 minutes of Experimentation

At 12:00, after 1 hour 10 minutes of downtime, the experiment was restarted, with an extra solar

panel to help provide more power to the battery. Over this time the water temperature had

dropped by only 1°C, and soon regained this heat once the experiment was underway.

Figure 11.3 Thermocouple Reading of 30°C at 12:17

The experiment was then run until 14:00, with a ten minute break around 13:00 to allow the battery

to recharge slightly. The maximum temperature reached just before the end of this phase of the

experiment was 42°C, a significant increase from the starting temperature, but not reaching the

target of 60°C. Figure 11.4 below shows the thermocouple reading just before the maximum was

reached.


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Figure 11.4 Thermocouple Reading of 40°C at 13:40

After 14:00 the water in the tank was replaced with a smaller volume of 1l, and all the electronics

apart from the pump and the solar panels were disconnected from the battery to try and maintain

the experiment for as long as possible. The dish was moved by hand to save power. This however

did not last long since the battery died very quickly, before any useful results could be taken.

Therefore this method was abandoned around 14:30 so that the battery could be charged before

the capabilities of the dish to align to the sun from facing the wrong direction could be tested.

This commenced at 15:00, with the dish moved to face east at maximum elevation and the water

pump switched off the Arduino was powered and controlled the motors to align the dish accurately

with the sun. This was repeated three times and was successful with each attempt.

Throughout the day, the temperature of the heating

element was occasionally measured using the

thermocouple. This temperature was discovered to

be astonishingly high, remaining over 100°C

throughout the day. The highest temperature

recorded on the surface of the element was 201°C.

Figure 11.5 Surface Temperature of Heating Element Reaching 201°C


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11.4. Conclusion This day of experimentation provided many useful results that were applied to the development of

the project, the main outcomes being:

The system could accurately track the sun throughout the day, and could return to the

position of the sun should it become misaligned.

The concentrator effectively focussed the sunlight onto a heating element, the surface of

which reached very high temperatures.

While the solar panel chosen could maintain power for the Arduino and the motors, the

water pump was incredibly power hungry and would have to be adjusted before future

testing. This led to the implementation of the motor controller and relay to control the

pump so that it could be switched off while the motors were running.

In three hours of testing, the water temperature in the tank only rose by around 20°C, but

areas for improvement were identified. These are explained in this report.

The insulation covering the water tank was effective, only losing 1°C in over an hour.

Although there was unobstructed sunlight throughout the day, there was a fairly cool cross wind

blowing. The wind mainly remained gentle throughout the day with occasional gusting, and did have

a cooling effect on the water system. This was particularly noticeable in the afternoon when the

wind was stronger. The concentrator itself withstood this wind and did not become misaligned at

any time.

Figure 11.6 Test set up on Duke Street Car Park Top Level


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12. References

[i] http://www.ijera.com/papers/Vol2_issue1/EF021822830.pdf, Accessed 18/02/14

[ii] http://www.solarmirror.com/fom/fom-serve/cache/43.html, Accessed 18/02/14

[iii] http://www.ijera.com/papers/Vol2_issue1/EF021822830.pdf, Accessed 18/02/14

[iv] http://m.instructables.com/id/Building-a-Parabolic-Solar-Hot-Water-Heater-using-/,

Accessed 18/02/14

[v] http://www.ecogeek.org/component/content/article/3439, Accessed 18/02/14

[vi] http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html,

Accessed 18/02/14

[vii] https://github.com/msparks/arduino-ds1302 Accessed 22/09/13

[viii] http://www.hse.gov.uk/legionnaires Accessed 01/04/14

12.1. With Special Thanks To: Dr Bruce Stephen, Supervisor, University of Strathclyde

Dr Brian Stimpson, Secondary Supervisor, University of Strathclyde

Mr John Redgate, Faculty of Engineering, University of Strathclyde

Mr Duncan Lindsay, Department of Design, Manufacturing and Engineering Management,

Unicersity of Strathclyde

Mr William Arthur, University of Strathclyde

Miss Carolyn Gethin, Inverness

http://www.ijera.com/papers/Vol2_issue1/EF021822830.pdf

http://www.solarmirror.com/fom/fom-serve/cache/43.html

http://www.ijera.com/papers/Vol2_issue1/EF021822830.pdf

http://m.instructables.com/id/Building-a-Parabolic-Solar-Hot-Water-Heater-using-/

http://www.ecogeek.org/component/content/article/3439

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

https://github.com/msparks/arduino-ds1302

http://www.hse.gov.uk/legionnaires


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