chapter 8- study of solar home system

7/27/2019 Chapter 8- Study of Solar Home System

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Study of Solar Module & Its Efficient Use in Bangladesh

86Study of Solar Home System

Chapter 08

STUDY OF SOLAR HOME SYSTEM

08.1 Introduction

The "green" revolution is upon us. The term "going green" is starting to affect not onlyyoung adults, but seniors and young children. Energy efficiency has ceased to become aplus and is a complete necessity. Hybrid cars, reusable bags, wind energy, Earth-friendly clothing, recycled home decor and low processed foods have contributed to ourgeneration's Earth defense. Alternative-fuel options are target platforms for politicians,proving society's continued interest and desire to change the way we think aboutenergy. Now, solar energy has come into play as one of the most central tactics used tosave energy, money and help the environment.

People use energy for many things, but a few general tasks consume most of the energy.These tasks include transportation, heating, cooling, and the generation of electricity.Solar energy is often used to directly heat a house or building. Heating a buildingrequires much more energy than heating a building's water, so much larger panels arenecessary. Generally a building that is heated by solar power will have its water heatedby solar power as well. The type of storage facility most often used for such large solarheaters is the heat-of-fusion storage unit, but other kinds (such as the packed bed or hotwater tank) can be used as well. This application of solar power is less common than thetwo mentioned above, because of the cost of the large panels and storage system

required to make it work. Often if an entire building is heated by solar power, passivecollectors are used in addition to one of the other two types. Passive collectors willgenerally be an integral part of the building itself, so buildings taking advantage ofpassive collectors must be created with solar heating in mind.

Besides being used for heating and cooling, solar energy can be directly converted toelectricity. Most of our tools are designed to be driven by electricity, so if one can createelectricity through solar power, can run almost anything with solar power. The solarcollectors that convert radiation into electricity can be either flat-plane collectors orfocusing collectors, and the silicon components of these collectors are photovoltaic cells.

08.2 Systems [9]

PV systems fall into two basic categories: stand alone (off-grid) and grid linked. Thegrid is the low AC voltage electricity supply network, also known as utility or themains.


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Due to variation in the solar resources some form of energy is required to be buffer orstored when solar energy is available and later that can be used along with the nationalgrid when production from other means are not sufficient. A battery does this function.It can store energy for later use. It may call grid-intertied with battery backup.

Grid linked or Grid Intertied Solar-Electric Systems

Also known as on-grid, grid-tied, or utility interactive (UI), grid-intertied solar-electricsystems generate solar electricity and route it to the electric utility grid, offsetting ahomes or business electrical consumption and, in some instances, even turning theelectric meter backwards. Living with a grid-connected solar-electric system is nodifferent than living with grid power, except that some or all of the electricity we usecomes from the sun. In many states, the utility credits a homeowners account for excesssolar electricity produced. This amount can then be applied to other months when thesystem produces less or in months when electrical consumption is greater. This

arrangement is called net metering or net billing. The specific terms of net meteringlaws and regulations vary from state to state and utility to utility.

Four configurations of metering are possible for grid connected system

Parallel metering no demand offsetParallel metering with demand offsetReversible or No metering with demand offsetSeries metering with demand offset

A grid connected backup system combines the grid

The following illustration includes the primary components of any grid intertied solarelectric system.

Fig 42: Grid Intertied Solar-Electric Systems


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The main disadvantage of this type of system is that the batteries requirements are largeand expensive to maintain also. Depending on the system design some energy will belost when the batteries are fully charged. The added advantage over a standalone PVsystem is that providing the battery.

Grid-Intertied Solar-Electric Systems with Battery Backup

Without a battery bank or generator backup for our grid intertied system, when ablackout occurs, our household will be in the dark, too. To keep some or all of ourelectric needs (or loads) like lights, a refrigerator, a well pump, or computer runningeven when utility power outages occur, many homeowners choose to install a grid-intertied system with battery backup. Incorporating batteries into the system requiresmore components, is more expensive, and lowers the systems overall efficiency. But formany homeowners who regularly experience utility outages or have critical electricalloads, having a backup energy source is priceless.

The following illustration includes the primary components of any grid intertied solarelectric system with battery backup.

Fig 43: Grid-Intertied Solar-Electric Systems with Battery Backup

Off-Grid Solar-Electric Systems

Although they are most common in remote locations without utility grid service, off-grid solar-electric systems can work anywhere. These systems operate independently


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from the grid to provide all of a households electricity. That means no electric bills andno blackoutsat least none caused by grid failures. People choose to live off-grid for avariety of reasons, including the prohibitive cost of bringing utility lines to remotehome sites, the appeal of an independent lifestyle, or the general reliability a solar-electric system provides. Those who choose to live off-grid often need to make

adjustments to when and how they use electricity, so they can live within thelimitations of the systems design. This doesnt necessarily imply doing without, butrather is a shift to a more conscientious use of electricity.

A simplest stand-alone system consists of a module supplying a load directly. Such asystem could be used to power a pump or to charge a battery. Beyond a certain size of asystem a charge regulator is necessary to protect the battery from over charging. Thisforms of the basic DC PV system and is illustrated in figure, as loads are added thecharge regulator would also serve the service of protecting the battery from being overcharged or from being deep discharged.

The following illustration includes the primary components of any off grid solar electricsystem.

Fig 44: Off-Grid Solar-Electric Systems


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LUX METER

08.3 Instrumentation [18]

A lux meter is a device for measuring brightness. It specifically measures the intensity

with which the brightness appears to the human eye. This is different thanmeasurements of the actual light energy produced by or reflected from an object or lightsource.

The lux is a unit of measurement of brightness, or more accurately, illuminance. Itultimately derives from the candela, the standard unit of measurement for the power oflight. A candela is a fixed amount, roughly equivalent to the brightness of one candle.

While the candela is a unit of energy, it has an equivalent unit known as the lumen,

which measures the same light in terms of its perception by the human eye. One lumenis equivalent to the light produced in one direction from a light source rated at onecandela. The lux takes into account the surface area over which this light is spread,which affects how bright it appears. One lux equals one lumen of light spread across asurface one square meter.

A lux meter works by using a photo cell to capture light. The meter then converts thislight to an electrical current. Measuring this current allows the device to calculate thelux value of the light it captured.

08.4 Balance of System

The balance of system or BOS components consists of everything in a v system exceptfor the PV array and its mechanical mounting. The BOS includes: wiring, batterystorage, PV controllers, battery charge regulators and inverters from dc to ac.


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Cabling

The basic building block of PV system is the low voltage PV module which is installedin the open air and exposed to weather 24hrs.

Cables and fuses

Obviously the system should use weather proof cable specially cable with resistance todegradation from ultra violet radiation and wide variation of temperature. The cableshould also be robust in terms of the voltage and current handling capacity.Fuses are generally used to protect the electrical appliances from passing short circuitcurrent in the event of malfunction and are sized to allow a reasonable margin abovethe expected peak current.

Earthing and lightning protection

Although PV arrays are metallic structures exposed to the element, they are generallyinstalled on or near the ground or building and so present no additional risk oflightning strike to the area. Hence unless installed in a remote location there is no needto include a lightning conductor in a PV arrays.

Batteries

Batteries are used in stand-alone PV system to buffer the energy between the varyingsupplies from the PV array to a varying load demand. Though cost and performanceconsiderations a balance is made between the average generating capacities of the PV.The battery storage capacity and load demand. Two types of battery technology areused in PV system. The lead acid battery and nickel cadmium battery.

Charge Regulation

In a stand-alone system to prolong battery life over charge and deep discharge shouldbe avoided. As indicated above battery state of charge can be roughly determined bymeasuring by thermal measurement condition. In the case of over charge the rise involtage is used to control the charging by shunt regulation or by series regulation. Withover discharge the drop in voltage is used to disconnect loads.

Inverters

An inverter converts the dc voltage from the batteries or PV system to ac voltage topower conventional appliances or to couple the main grid. There are two basic typesinverters stands alone and grid connected. Each has different operation char andperformance. The objective is to deliver various ac loads from the dc battery.


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08.5 System Sizing

In order to design a PV system to meet a particular need in the most cost effective way

information is required on the expected resources, the expected daily load and arrayand BOS characteristics. This data is used to size the PV array and the BOS componentsin several systems configuration to determine the optimum design.

Standalone Systems

Due to the high cost of batteries systems using battery storage should be designedtaking into account the daily load pattern as well as the PV module and batterycharacteristics to optimize the system design. Hence the load assessed first then thearray and the battery are sized in several configuration.

Assessing the Load

The expected load is assessed as followed:

List the loads: grouping the type and operating voltage, quoting the powerdemand and monthly mean daily operating hoursTotal the monthly mean daily power demand and operating hour for each group.For each group calculate the monthly mean daily load demand in kWh per dayfrom the monthly mean daily power multiplied by the total operating hours.

Determine the nominal dc voltage the voltage of the biggest load for dc onlysystems; the input voltage of the inverter for ac or dc/ac systemsCalculate the monthly mean daily load current in the Ah per day for each groupfrom the monthly mean daily load demand divided by the nominal operatingvoltages.Determine the annual mean daily load demand and load and load current at thenominal operating voltage.

Sizing the PV Array

Determine the mean ambient temperature of the site.

Using the proposed module IV data at 1kW/m2 determine the working voltageand the peak current at the maximum power operating point.Determine the number of series connected modules from the sun of the nominaloperating voltage plus diode volt drop divided by the module working voltage.Determine the monthly mean daily string output in Ah by multiplying themodule peak current by the monthly mean daily irradiance.


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Determine the minimum number of parallel strings by dividing the annual meandaily load current by the annual mean daily string output and rounding days ofgroup.Calculate the monthly surplus or deficit from the difference between theminimum monthly output and the monthly mean daily load demand multiplied

by the number of days in the month.

Sizing the Batteries

The battery is sized by follows:

Calculate the battery capacity required for seasonal storage by dividing thewinter deficit by the maximum depth of discharge multiplied by the temperaturecorrection co-efficient.Determine the longest period of consecutive cloudy days likely to be experienced

at the site, with a probability based on the required the level of security.Check that the battery capacity determined in a sufficient to cater for this period,increasing the capacity as necessary.Determine the number of batteries in a series string by dividing the dc operatingvoltage by the nominal voltage of the selected battery.

Costing the Standalone System

The stand-alone PV system costing is determined as follows:

Determine the life cycle cost of the systemRepeat the sizing PV arrays sizing the batteries and assuming more than theminimum number of module strings in the array and two alternative tilt angles.Select the cheapest configuration of array and battery.

Grid Connection System

Grid connected PV system consists of an array and an inverter and a grid connectionthe expected daily load does not have to be known to determine the size of the systemas with stand-alone pv system. It is usually determine by cost consideration and thesystem physical installation. Although with knowledge of the expected load pattern the

proportion supplied by the PV system can also be assessed and the system economicsdetermined in comparison with other energy supplies. Grid connected solar homesystem could be any size in range from 100W-5kW.


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Sizing the Grid Connection System

The steps involved in sizing the grid connected PV system could be as follows:

Calculate the maximum area available for the PV array taking into account

shading and mounting arrangements.Determine the maximum number of modules in the PV array by dividing themaximum area by the module area and rounding to the nearest number. b =a/A.Determine the maximum number of inverters by multiplying the maximumnumber of modules by the module peak power and by dividing 1.2 the selectedinverter power ratings and rounding to the nearest number. c = (b Pp 1.2) /PinvCalculate the inverter peak rating by multiplying the number of inverter by theselected inverter power rating. d = c/ Pinv

Determine the module peak power voltage.Determine the number of series connected modules by dividing the middle of theselected inverter input voltage range by module peak power voltage androunding to the nearest number. f = ((Vmax Vmin ) / 2+ Vmin) / VmppCalculate the string peak power voltage by multiplying the number of seriesmodules by the module peak power voltage. g = fe.Calculate the string peak power by multiplying the number of series modules bythe module peak power. h = f.PpDetermine the number of parallel strings per sub-arrays/inverter by dividingselected inverter power rating by string peak power, dividing by 1.2 and

rounding to the nearest number. Pinv /(h 1.2).Calculate the sub-array peak power by multiplying the number of string per sub-array by the string peak power. j = ih.Calculate the sub-array peak power current by dividing the sub-array peakpower by the string peak power voltage. k = e/g.Determine the total number of sub-arrays.Re-determine the total number of modules. m = ci f.Calculate the array peak power by multiplying the total number of modules bythe module peak output. n = mPp.

Costing the Grid Connected System

The steps involved in costing the grid connected PV system are being as follows:

Determine the total number of modules and the inverter in the system using theabove sizing methodology.Determine the total module and mounting cost by multiplying the number ofmodules by the unit module plus mounting cost.


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Determine the cabling, inverter and grid connection costs.Determine the total installed system cost by summing the above.Calculate the average annual energy generation by multiplying the peak powerin kW by 750-1000 to give energy in kWh/year.Calculate the unit energy cost over twenty years by dividing the total system cost

by twenty times the annual system generation.

The economics of grid connected PV system can be accessed from the daily or monthlyirradiance data, the average of the array, the daily load pattern and the buying andselling price for grid electricity.

08.6 Experimental Data

Table 8

Daytime Data

Time Angle

(C)

Panel

Voltage(V)

Load

Voltage(V)

Battery

Voltage(V)

12:45 pm 51 13 12.8 12.8

12:52 pm 49 13.3 13.1 13.1

01:00 pm 47 13.4 13.1 13.1

01:10 pm 45 13 12.8 12.8

01:20 pm 43 13.6 13.3 13.2

01:33 pm 41 13.4 13.1 13.1

01:40 pm 39 13.1 12.8 12.8

chapter 8- study of solar home system

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