SolarOne - About Solar Power

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330 Million Terrawatt hours of equivalent energy from the sun hits the earth every year. That’s 30 times more energy from the sun in a single year than all the energy stored in the earth. Photovoltaics transforms the power of the sun into usable electric energy. The first solar panels were deployed in the 1950's for use on U.S. Space Satellites. They have long since proven their reliability and extreme durability, while continuing to improve in efficiency.

On this page:

Direct Conversion AC vs DC Getting Useful Power

Basic Solar Cell Technoligies Applications Why is Interest Growing?

DIRECT VS THERMODYNAMIC CONVERSION

Most electricity today is produced by electrical generators. A generator is a device that spins wire through a magnetic field inducing electricity flow in the wire. The question remains how to spin the generator. Some power plants use hydro or water power, but in most large power plants, fossil or nuclear fuels are used to create steam, which in turn is used to spin a turbine. The turbine then spins the generator. This is called a “thermodynamic” cycle.

A solar cell converts light directly into electricity using the “Photovoltaic Effect”. There is no fuel, steam or thermodynamics involved. When light hits a solar cell, it instantly produces electricity. For more details of the Photovoltaic Effect, visit HowStuffWorks.com. Solar cells today do not store electricity. In other words, when the light is taken away from the cell, it stops producing electricity. It is very common to store the electricity from a solar cell in a battery. There is a neat web page (designed for kids, but good for adults) that illustrates the basics about electricity, energy and renewable energy at the Department of Energy. Back to Top of Page

AC VS DC

Alternating Current (AC) is the type of electricity found in the outlet in your home. DC Direct Current is what you would find in the outlet of your car. DC electricity is also the type of electricity stored in batteries. Generators at big power plants usually produce AC electricity while the alternator (similar to a generator) produces DC. Solar Cells produce DC electricity. Back to Top of Page

FROM SOLAR CELLS TO USEFUL POWER

The basic building block of solar electric systems is the solar cell. Solar cells typically generate somewhere between 0.4 and 0.7 volts when illuminated. A solar cell can be cut or sized to fit into something as small as a watch face. The largest individual solar cells are about 8” square, however in virtually every case, the individual solar cells are ganged into a solar module or solar panel to produce a desired voltage and current. Most solar cells today are wired in such a way as to charge 12 Volt, or 24 Volt batteries, however they can be configured at other voltages. The largest panels are used as overhead skylights or in large fields can be over 25 square feet of area. The modules/panels can again be interconnected to create an even larger “array” of solar panels. There really is no limit to the size of a solar electric system.

In order to get useful power out of a solar cell you must attach wires to it. This may be more difficult than it seems. Solar cells are relatively fragile devices – so the wires must be attached with care. Furthermore, the wires must be attached in such a way that they don’t shadow a large portion of the solar cell. This means that the wires are usually quite small and challenging to work with. Once a solar cell is wired, it usually gets wired to other solar cells in the appropriate series/parallel combination to get the desired voltage and current. Once the solar cells are wired, they are usually put into some protective package to create a solar module/panel. The most common package is to have the solar cells encapsulated in a special polymer with a glass cover and plastic back sheet. Solar modules of this construction are designed to last anywhere from 5 to 40 years.

Once you have solar module, panel or array, it then can be used in an extremely wide range of systems. These units can be connected directly to a load (such as a water pump or fan), they can be used to charge a battery or using a special photovoltaic inverter that converts DC to AC, they can be connected directly into the power grid. Solar panels can be used to “trickle charge” [maintain battery state of charge] or fully charge batteries. In the case of the latter, it is advisable to use a solar charge controller. Back to Top of Page

Basic Solar Cell Technologies

Today most solar cells start with the semi-conductor silicon. They are manufactured in ways similar to the ways integrated circuits (ICs) are produced. Solar cells of more exotic materials are under development. There are two basic silicon type solar cells on the market – crystalline and amorphous. The differences are explained below:

Crystalline – Silicon

Crystalline solar cells have been around the longest. They start out with a silicon “wafer” that is processed into a solar cell. A typical solar cell is a little thinner that a credit card. It is fragile by it self, but very robust inside a solar module. Crystalline solar cells can be “hand soldered” together to form a circuit. These solid-state devices can last for 100 years. They are typically a dark blue or almost black in color. The largest commercial solar panel is rated at 300 watts (under full sun and room temperature).

Amorphous – Silicon

Amorphous silicon (thin film) photovoltaic modules are manufactured by depositing ultra-thin layers (thinner than a light coat of paint) of silicon on a glass or thin stainless-steel substrate. A laser scribing process is used to separate and weld the electrical connections between individual cells in a module. Thin-film photovoltaic materials offer great promise for reducing the materials requirements and manufacturing costs for PV modules and systems. The basic building block of an amorphous silicon system is not the solar cell, instead it is called the “plate” referring to the glass plate on which the amorphous silicon is deposited. Back to Top of Page

Applications

Solar cells are in use across the globe and throughout space. Solar cells were first used to power satellites circling the earth. They have been slowly working their way into all aspects of our daily life. Solar cells are used for small applications such as charging batteries in calculators, watches and toys. They are used to power traffic signs and lighting. On the largest scale they power large radar stations for the military and even feed the electrical grids that deliver the energy to our homes and offices. Because they produce no emissions or noise and they require no fuel, they are very easy to work with. Visit the the Department of Energy for more information on applications. Back to Top of Page

Why is interest in solar growing?

Solar electricity is growing in popularity for several reasons. The industry has been growing steadily at a rate of at least 25% per year for the past 20 years. Last year the industry doubled. Admittedly it started from a small base, but it appears to have reached a point of critical mass. Some factors driving this growth are:

Explosive growth in the “wireless” and personal electronics
Increasing environmental concerns
Desire for energy independence
Utility deregulation
Education about solar in schools, (for more information check out Solar Electric Power Association)
Overall awareness of solar and level of “commitment” in Europe and Japan