Solar Photovoltaics

Photovoltaic systems are solar energy systems thatproduce electricity directly from sunlight.Photovoltaic (PV) systems produce clean, reliableenergy without consuming fossil fuels and can beused in a wide variety of applications.

Photo means light. Voltaic means electricity. Photovoltaic means getting electricity from light.

Photovoltaic

Photovoltaic System

Typical output of a module (~30 cells) is ≈ 15 V, with 1.5 A current

Regardless of size, a typical silicon PV cell produces about 0.5 – 0.6 volt DC under open-circuit, no-load conditions. The current (and power) output of a PV cell depends on its efficiency and size (surface area), and is proportional to the intensity of sunlight striking the surface of the cell.

SOLAR CELL: A typical silicon PV cell is composed of a thin wafer consisting of an ultra-thin layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped (P-type) silicon. An electrical field is created near the top surface of the cell where these two materials are in contact, called the P-N junction. When sunlight strikes the surface of a PV cell, this electrical field provides momentum and direction to light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electrical load

Also called a solar panel or photovoltaic (PV) module, an integrated assembly of interconnected solar cells designed to deliver a selected level of working voltage and current at its output terminals, and suited for incorporation in a solar power system. In addition to the cells, a typical solar module includes the following components: A transparent top surface, usually glass An encapsulate – usually thin sheets of ethyl vinyl acetate that hold together the top surface, solar cells, and rear surface A rear layer – a thin polymer sheet, typically Tedlar, that prevents the ingress of water and gases A frame around the outer edge, typically aluminum Solar modules are normally mounted on top of a roof as part of a roof-mounted solar power system, or a holding rack of some sort, within a frame structure. A solar module is the smallest building block of the power generating part of a solar array.

SOLAR ARRAYThe solar array consists of 14 + 4 parallel connected solar panels with the sections of 196 x 196 mm in size made on the basis of silicon solar cells. Six single-side panels are mounted on the facets of the subsatellite at the distance of 10 mm from metallic surface, 12 panels are to be deployed in space. After deploying their axes have 100 deg angle with respect to subsatellite axis directed toward Sun. Four solar panels are reserved and switched to the system of subsatellite energy supply together with their DC/DC converter-inverter MPC after degradation of the panels initially switched on. The current of the panel being orthogonal to the Sun direction is about 0.2 A at the operation voltage of 14 Volt. The maximum total power of the solar array at the nominal solar orientation is 36 W.

Photovoltaic Cell. Thin squares, discs, or films of semiconductor material that generate voltage and current when exposed to sunlight.

• Module. A configuration of PV cells laminated between a clear superstrate(glazing) and an encapsulating substrate.

• Panel. One or more modules (often used interchangeably with “module”).

• Array. One or more panels wired together at a specific voltage.

• Charge Controller. Equipment that regulates battery voltage.

• Battery Storage. A medium that stores direct current (DC) electrical energy.

• Inverter. An electrical device that changes direct current to alternating current AC).

• DC Loads. Appliances, motors, and equipment powered by direct current.

• AC Loads. Appliances, motors, and equipment powered by alternating current.

Inside a PV Cell

Solar Photovoltaic System uses solar cells to convert light into electricity. A PV system consists of PV modules and balance of systems (BOS). Balance of systems includes module support structure, storage, wiring, power electronics, etc.DC (direct current) electricity is generated when solar radiation strikes the PV module. Power can be used in any DC load directly during this generation. But the generation exists during daytime. So, some storage device is needed to run the system at night or in low sunshine hour. Again this power cannot be used to run any AC (alternate current) load. Inverter has to be used to convert DC into AC.

Solar PV systems are categories into Stand-alone PV systems (also called off-grid systems) Grid connected PV systems (also called on-grid systems) Hybrid systems

Stand-alone PV systems Stand-alone systems are not connected with utility power lines and these are self sufficient systems. These systems could either be used to charge the batteries that serve as an energy storage device or could work directly using the solar energy available in the daytimes. These systems consist of the following: Solar panels mounted on the roof or in open spaces. Photovoltaic modules produce direct current (DC) electrical power. Batteries to store DC energy generated by the solar panels. Charge controller to prevent overcharging the battery. Inverter to convert electricity produced by the system from DC to AC power.

The following diagram shows PV system powering AC loads with battery bank. DC loads can also be connected directly to the battery bank. It is also possible to power the AC load without battery, but in that case it would be confined only to daytime when solar radiation is sufficient to generate required electricity.

Grid connected PV systems A grid connected photovoltaic system will be interacted with utility grid. The main advantage of this system is that power can be drawn from the utility grid and when power is not available from grid, PV system can supplement that power. These grid connected systems are designed with battery or without battery storage. These systems consist of the following: Solar panels mounted on the roof or in open spaces. Photovoltaic modules produce direct current (DC) electrical power. Batteries to store DC energy generated by the solar panels. Charge controller to prevent overcharging the battery. Specially designed inverter to transform the PV generated DC electricity to the grid electricity (which is of AC) at the grid voltage.

The following diagram shows PV system powering AC loads. This system is connected to utility power supply and having battery storage for backup.

Hybrid systems System with more than one source of power is called Hybrid system. It is often desirable to design a system with additional source of power. The most common type of hybrid system contains a gas or diesel powered engine generator. Another hybrid approach is a PV/Wind system. Adding a wind turbine to a PV system provides complementary power generation. These systems consist of the following: Solar panels mounted on the roof or in open spaces. Photovoltaic modules produce direct current (DC) electrical power. Batteries to store DC energy generated by the solar panels. Charge controller to prevent overcharging the battery. Specially designed inverter to transform the PV generated DC electricity to the grid electricity (which is of AC) at the grid voltage.

The following diagram shows PV system powering AC loads. This system is connected to utility power supply & diesel generator and having battery storage for backup.

PV Technology Classification

Silicon Crystalline Technology Thin Film Technology

Mono Crystalline PV Cells Amorphous Silicon PV Cells

Multi Crystalline PV Cells Poly

Crystalline PV Cells ( Non-

Silicon based)

Silicon Crystalline Technology

currently makes up 86% of PV market Very stable with module efficiencies 10-16%

Mono crystalline PV Cells

•Made using saw-cut from single cylindrical crystal of Si

•Operating efficiency up to 15%

Multi Crystalline PV Cells

•Caste from ingot of melted and recrystallised silicon

•Cell efficiency ~12%

•Accounts for 90% of crystalline Si market

Amorphous Silicon PV Cells The most advanced of thin film technologies

Operating efficiency ~6%

Makes up about 13% of PV market

PROS• Mature manufacturing technologies available

CONS• Initial 20-40% loss in efficiency

Poly Crystalline PV Cells

Copper Indium Diselinide

CIS with band gap 1eV, high absorption coefficient 105cm-1

High efficiency levels

PROS• 18% laboratory efficiency• >11% module efficiencyCONS• Immature manufacturing process• Slow vacuum process

Non – Silicon Based Technology

Poly Crystalline PV Cells

Cadmium Telluride ( CdTe) Unlike most other II/IV

material CdTe exhibits direct band gap of 1.4eV and high absorption coefficient

PROS• 16% laboratory efficiency• 6-9% module efficiency CONS• Immature manufacturing

process

Non – Silicon Based Technology

4 TYPES OF STORAGE BATTERY USED IN SOLAR POWERGolf Cart Batteries

Golf-cart batteries, also used in RVs and boats, are suited for small, privately owned solar systems. These batteries are inexpensive, which makes them great for the average homeowner. However, they lack the ability to provide continuous service for a long period of time. This is the battery to use if you are just starting out with solar power and want to experiment a little or if your solar energy needs

are low. They shouldn't be confused with regular car batteries.Gel

Gel solar batteries are solar batteries that are industrial grade and can handle more discharge cycles. According to windsun.com, they have their acid in a gel-like form and have to be charged more slowly than other battery types. They are

safe for use indoors because they don't have any vents that can release gas. This is desirable because gas from batteries may build up in an enclosed space and

pose an explosion hazard.Lead Acid

Like gel batteries, lead acid solar batteries are of industrial quality. However, unlike gel batteries, lead acid batteries have caps through which the user can

add water. This allows the user to "recharge" the electrolyte balance in the battery, leading to better performance.

AGMAbsorbed glass mat (AGM) batteries AGM batteries get their name from the mat of woven glass (boron silicate) that holds the battery electrolyte. these batteries

won't leak and have the advantages of slower discharge and no gas release.

Applications @ PV

• Water Pumping: PV powered pumping systems are excellent ,simple ,reliable – life 20 yrs

• Commercial Lighting: PV powered lighting systems are reliable and low cost alternative. Security, billboard sign, area, and outdoor lighting are all viable applications for PV

• Consumer electronics: Solar powered watches, calculators, and cameras are all everyday applications for PV technologies.

• Telecommunications• Residential Power: A residence located more than a

mile from the electric grid can install a PV system more inexpensively than extending the electric grid

(Over 500,000 homes worldwide use PV power as their only source of electricity)

THANK Q

Solar Domestic Hot Water

Solar Domestic Hot Water

PV Wiring

Series Connections

• Loads/sources wired in series

– VOLTAGES ARE ADDITIVE – CURRENT IS EQUAL

• Loads/sources wired in parallel:

– VOLTAGE REMAINS CONSTANT– CURRENTS ARE ADDITIVE

Parallel Connections

Wire Components

• Conductor material = copper (most common)

• Insulation material = thermoplastic (most common)

• Wire exposed to sunlight must be classed as sunlight resistant

Solar Site & Mounting

Part 6: Learning Objectives

• Understand azimuth and altitude

• Describe proper orientation and tilt angle for solar collection

• Describe the concept of “solar window”

• Evaluate structural considerations

• Pros and cons of different mounting techniques

Altitude and Azimuth

Sun Chart for 40 degrees N Latitude

Solar Pathfinder

• An essential tool in finding a good site for solar energy is the Solar Pathfinder

• Provides daily, monthly, and yearly solar hours estimates

Site Selection – Tilt Angle

Year round tilt = latitudeWinter + 15 lat.Summer – 15 lat.

Max performance isachieved when panelsare perpendicular to thesun’s rays

Solar Access

• Optimum Solar Window 9 am – 3 pm

• Array should have NO SHADING in this window (or longer if possible)

General Considerations• Weather characteristics

– Wind intensity– Estimated snowfall

• Site characteristics – Corrosive salt water– Animal interference

• Human factors– Vandalism – Theft protection– Aesthetics

General Considerations Continued

• Loads and time of use

• Distance from power conditioning equipment

• Accessibility for maintenance

• Zoning codes

Basic Mounting Options

• Fixed– Roof, ground, pole

• Integrated

• Tracking– Pole (active & passive)

Incandescent Lamps• Advantages

– Most common– Least expensive– Pleasing light

• Disadvantages – Low efficiency – Short life ~ 750 hours

Electricity is conducted through a filament which resists the flow of electricity, heats up, and glows

Efficiency increases as lamp wattage increases

FROM THE POWER PLANT TO YOUR HOME INCANDESCENT BULBS ARE LESS THAN 2%

EFFICIENT

Fluorescent Bulbs

• Less wattage, same amount of lumens

• Longer life (~10,000 hours)

• May have difficulty starting in cold environments

• Not good for lights that are repeatedly turned on and off

• Contain a small amount of mercury

Light Emitting Diode (LED) Lights

• Advantages – Extremely efficient – Long life (100,000

hours)– Rugged – No radio frequency

interference

• Disadvantages– Expensive (although

prices are decreasing steadily)

– A relatively new technology

Batteries in Series and Parallel

• Series connections– Builds voltage

• Parallel connections – Builds amp-hour capacity

Functions of a Battery Storage for the night Storage during cloudy weather Portable power Surge for starting motors

**Due to the expense and inherit inefficiencies of batteries it is recommended that they only be used when absolutely necessary (i.e. in remote locations or as battery backup for grid-tied applications if power failures are common/lengthy)

Batteries: The Details

Primary (single use) Secondary (recharged) Shallow Cycle (20% DOD) Deep Cycle (50-80% DOD)

Types:

Unless lead-acid batteries are charged up to 100%, they will loose capacity over time

Batteries should be equalized on a regular basis

Charging/Discharging:

Battery Capacity

Amps x Hours = Amp-hours (Ah)

Capacity:

100 amps for 1 hour

1 amp for 100 hours

20 amps for 5 hours

Capacity changes with Discharge Rate The higher the discharge rate the lower the capacity and vice versa The higher the temperature the higher the percent of rated capacity

100 Amp-hours =

Rate of Charge or Discharge

Rate = C/T

C = Battery’s rated capacity (Amp-hours)T = The cycle time period (hours)

Maximum recommend charge/discharge rate = C/3 to C/5

Grid-Tied System(With Batteries)

• Complexity– High: Due to the

addition of batteries

• Grid Interaction– Grid still

supplements power– When grid goes

down batteries supply power to loads (aka battery backup)

Controllers & Inverters

Grid-Tied System

• Advantages– Low: Easy to

install (less components)

– Grid can supply power

• Disadvantages– No power when

grid goes down

Additional Controller Features• Voltage Stepdown Controller: compensates for

differing voltages between array and batteries (ex. 48V array charging 12V battery)

– By using a higher voltage array, smaller wire can be used from the array to the batteries

Other Controller Considerations• When specifying a controller you must consider:

– DC input and output voltage

– Input and output current

– Any optional features you need

• Temperature Compensation: adjusts the charging of batteries according to ambient temperature

Inverter Basics

• An electronic device used to convert direct current (DC) electricity into alternating current (AC) electricity

• Controller redundancy: On a stand-alone system it might be desirable to have more then one controller per array in the event of a failure

Function:

Efficiency penalty Complexity (read: a component which can fail) Cost!!

Drawbacks:

Specifying an Inverter• What type of system are you designing?

– Stand-alone– Stand-alone with back-up source (generator)– Grid-Tied (without batteries)– Grid-Tied (with battery back-up)

• Specifics:– AC Output (watts)– Input voltage (based on modules and wiring)– Output voltage (120V/240V residential)– Input current (based on modules and wiring)– Surge Capacity– Efficiency– Weather protection– Metering/programming

Solar electricity prices are today, around 30 cents/kWh, but still 2-5 times average Residential electricity tariffs