Solar Basics

There are a variety of solar PV and solar thermal technologies available for your home or business. Read below to learn more.


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Solar Pv

Solar electric systems, otherwise known as photovoltaic (PV) systems, convert sunlight into electricity. Solar cells, the basic building blocks of a PV system, consist of semiconductor materials. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms. This phenomenon is called the "photoelectric effect." These free electrons then travel into a circuit built into the solar cell to form electrical current. Only sunlight of certain wavelengths will work efficiently to create electricity. PV systems can still produce electricity on cloudy days, but not as much as on a sunny day. For more about the basics of PV, visit the Department of Energy website .

Most PV systems today connect to the local utility system. Using the free electricity from your solar system will lower your electric bills and decrease your carbon footprint.

TECHNOLOGY

PV panels produce DC electricity, which is converted into AC power by an inverter. Generally there is only one inverter for an entire array of panels, but some systems have a newer technology called micro-inverters where each solar panel feeds into a small inverter. Micro-inverters are more efficient, although they can also be more expensive. Appropriate technologies vary depending on the application, and you should consult with a certified solar installer to decide what is right for your needs.

SOLAR CELLS

The performance of a solar cell is measured in terms of its efficiency at converting sunlight into electricity. There are a variety of solar cell materials available, which vary in conversion efficiency.

Semiconductor Materials

A solar cell consists of semiconductor materials. Silicon remains the most popular material for solar cells, including these types:

* Monocrystalline or single crystal silicon
* Multicrystalline silicon
* Polycrystalline silicon
* Amorphous silicon

The absorption coefficient of a material indicates how far light with a specific wavelength (or energy) can penetrate the material before being absorbed. A small absorption coefficient means that light is not readily absorbed by the material. Again, the absorption coefficient of a solar cell depends on two factors: the material making up the cell, and the wavelength or energy of the light being absorbed.


Thin Film

Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Thin film technology has made it possible for solar cells to now double as these materials:

* Rooftop or solar shingles
* Roof tiles
* Building facades
* Glazing for skylights or atria.

Thin-film rooftop or solar shingles, made with various non-crystalline materials, are just now starting to enter the residential market. The following are benefits of these solar shingles:

* Attractive integration into homes
* Dual purpose: serves as both roofing material and electricity generator
* Durability

Commercially-available solar shingles generally have lower efficiencies and greater expense compared with the standard small solar electric system.

For more information on solar PV technologies, visit the Department of Energy website .

COST

Solar PV system cost is generally described in dollars per watt ($/W) of capacity. Capacity refers to the amount of DC power that a PV panel produces when exposed to full sunlight.

Today, the typical cost for PV in New York City is $7-10/Watt . This includes the PV panels, inverter, all equipment, and installation. Without any incentives, a typical 4,000 Watt (4 kilowatt) residential PV installation costs $28,000-40,000.

 

Solar Thermal

In hot and sunny regions, solar thermal systems can be a great decision. But even in New York's relatively cold climate, solar water heaters can provide year-round hot water for homes and swimming pools. The economics of solar water heaters depend largely on the available incentives and on the type of fuel being displaced. For example, a customer that has an expensive source of energy to heat their water, such as electricity or propane, will receive greater benefits from going solar than a customer using relatively lower cost natural gas.

How They Work

Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't.

Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

Three types of solar collectors are used for residential applications:

Flat-plate collector

Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors (typically used for solar pool heating) have a dark absorber plate, made of metal or polymer, without a cover or enclosure.

Integral collector-storage systems

Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.

Evacuated-tube solar collectors

These feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for commercial applications.

For more information on solar thermal systems, please visit the Department of Energy website .

Solar Thermal Applications

Low Temperature (> 30C)
–Swimming pool heating
–Ventilation air preheating

Medium Temperature (30C – 100C)
–Domestic water and space heating
–Commercial cafeterias, laundries, hotels
–Industrial process heating

High Temperature (> 100C)
–Industrial process heating
–Electricity generation

Solar thermal and photovoltaics working together

For more information on Solar Thermal Applications, visit the NREL website .

COST

Without considering available incentives, the total installed cost of a typical solar hot water system for a family of 4 in New York City is approximately $10,000-$12,000 .