Solar 602m6g

Solar Photovoltaics

Photovoltaic Photovoltaic systems are solar energy systems that produce electricity directly from sunlight. Photovoltaic (PV) systems produce clean, reliable energy without consuming fossil fuels and can be used in a wide variety of applications. Photo means light. Voltaic means electricity. Photovoltaic means getting electricity from light.

Photovoltaic System

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

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 , 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

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.

Also called a solar 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 ARRAY The solar array consists of 14 + 4 parallel connected solar s with the sections of 196 x 196 mm in size made on the basis of silicon solar cells. Six single-side s are mounted on the facets of the subsatellite at the distance of 10 mm from metallic surface, 12 s are to be deployed in space. After deploying their axes have 100 deg angle with respect to subsatellite axis directed toward Sun. Four solar s are reserved and switched to the system of subsatellite energy supply together with their DC/DC converter-inverter MPC after degradation of the s initially switched on. The current of the 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. • . One or more modules (often used interchangeably with “module”). • Array. One or more s 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 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 s 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 s. 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 s 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 s. 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 s 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 s. 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 PV Cells

Amorphous Silicon

Multi Crystalline PV Cells Cells

Poly Crystalline PV ( Non-Silicon based)

Silicon Crystalline Technology  

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

Mono crystalline PV Cells

Multi Crystalline PV Cells

•Made

using saw-cut from single cylindrical crystal of Si

•Caste

•Operating

•Cell

efficiency up to 15%

from ingot of melted and recrystallised silicon efficiency ~12%

•s

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 Non – Silicon Based Technology Copper Indium Diselinide CIS with band gap 1eV, high absorption coefficient 105cm-1 



High efficiency levels

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

Poly Crystalline PV Cells Non – Silicon Based Technology Cium 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

4 TYPES OF STORAGE BATTERY USED IN SOLAR POWER Golf 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 gellike 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 can add water. This allows the to "recharge" the electrolyte balance in the battery, leading to better performance. AGM Absorbed 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 •

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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

Parallel Connections • Loads/sources wired in parallel: – VOLTAGE REMAINS CONSTANT – CURRENTS ARE ADDITIVE

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 Max performance is achieved when s are perpendicular to the sun’s rays

Year round tilt = latitude Winter + 15 lat. Summer – 15 lat.

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 & ive)

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 Types:

 Primary (single use)  Secondary (recharged)  Shallow Cycle (20% DOD)  Deep Cycle (50-80% DOD) Charging/Discharging:  

Unless lead-acid batteries are charged up to 100%, they will loose capacity over time Batteries should be equalized on a regular basis

Battery Capacity Capacity:

 Amps x Hours = Amp-hours (Ah) 100 Amp-hours

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 

=

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

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 Function:

• An electronic device used to convert direct current (DC) electricity into alternating current (AC) electricity Drawbacks: Efficiency penalty • Complexity Controller redundancy: On a stand-alone (read: a component which cansystem fail) it might be desirable to have more then one controller per array in  Cost!! the event of a failure 

Specifying an Inverter • What type of system are you deg? – – – –

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