Solar Electricity
When people think about alternative or renewable energy, the first image that comes to mind is often large blue or black solar panels on rooftops or portable highway signs that have a small panel attached. These panels, also known as photovoltaic modules (or PV modules), convert sunlight into electricity, and they have been the backbone of renewable energy for decades. The Photovoltaic Effect (how sunlight is converted into electrical energy) was discovered over a hundred years ago! Yet widespread implementation of this technology has been very gradual. Only in very recent years has photovoltaics gained wide popularity as an alternative way to produce electricity.
In 1958 the first PV modules were launched into space to power satellites. Even today, solar power is the primary source of energy at the International Space Station. On Earth as well, PV has traditionally been used in areas where there is no practical source of electrical power but there is abundant sunshine. Solar panels are often used for remote applications: like powering cabins, RVs, boats and small electronics when grid service is not available. Recently, “grid-tie” solar electric systems have started gaining momentum as a cost-effective way to incorporate solar electricity into our everyday lives. Now we can take advantage of available solar energy while still enjoying the safety net of the utility grid.
How Solar Panels or PV Modules Work
In very basic terms, a solar panel (PV module) is a device that will produce a flow of electricity under sunlight. This electricity can be used to charge batteries and, with the aid of an inverter, it can power normal household electrical devices, or “loads”. PV modules can also be used in systems without batteries in grid-tie systems.
Most PV modules are framed in aluminum, topped with tempered glass, and sealed by a waterproof backing. Sandwiched between the glass and backing layers are the photo-reactive cells themselves, often made of silicon. On the back of the module is a junction box that may or may not have two cables coming out of it. If the junction box has no cables, it can be opened to access the electrical terminals where wires can be attached to conduct the generated electricity away from the module. If there are cables already in place, the junction box is usually sealed and not user-accessible. Sealed junction boxes are more common.
There are lots of ways to make use of solar electricity. One of the simplest is to charge small electronic devices, like cell phones and music players, with lightweight, portable PV modules. These small battery-charging solar panels are even being integrated into backpacks and clothing for maximum convenience. These panels can be used individually or wired together to form a solar array.
For larger electrical loads, there are two main types of systems for providing electrical power to homes, cabins and offices, etc: stand-alone battery based systems (also called ‘off-grid’ systems) and grid-tied systems (also known as utility-interactive). You’ll want to decide which system is best for your needs by reading more about both.
Solar Cell Technology
There are several technologies used to make solar cells, the building blocks of panels. The main types currently on the market are:
Monocrystalline – Monocrystalline solar panels are often the most expensive due to the manufacturing process, which uses large amounts of highly purified silicon and a great deal of energy. Monocrystalline solar cells are about 13-16% efficient at converting sunlight to electricity.
Polycrystalline (aka multicrystalline) – Polycrystalline cell efficiencies range between 11-14% so solar panels are slightly less expensive than monocrystalline ones on a price-per-Watt basis.
String Ribbon – String ribbon solar panels use less silicon in the cell manufacturing process than the other crystalline types and achieves efficiencies in the 12-14% range.
Amorphous Solar and Thin Film – Amorphous solar panels, or thin-film amorphous silicon, A-si, are not constructed from individual solar cells, but are made by depositing a photo-sensitive compound onto a substrate. While these solar panels have lower efficiencies, (usually 7-10%), they offer certain advantages. They can often be used in hotter climates since they suffer less power loss than other types under hot conditions. Additionally, many models of the the amorphous technology do not use the typical “glass sandwich” construction, allowing for the creation of flexible solar panels which are also very durable.
CIGS – The CIGS technology, or Copper Indium Gallium di-Selenide, uses no silicon at all, and can be made into panels with or without discrete cells. Often this technology is used to make foldable solar panels.
There are also hybrid solar panels which use both crystalline and thin-film technologies to increase energy capture; these modules boast efficiencies up to 19%. Researchers are still working on lower-cost, higher-efficiency alternatives, but for the foreseeable future, these five types represent what is commercially available.
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