A solar cell is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight such as solar panels and solar cells, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, or photovoltaic arrays. Photovoltaics is the field of technology and research related to the application of solar cells in producing electricity for practical use. The energy generated this way is an example of solar energy (also known as solar power).
What you need to know when designing a Solar System
- Solar Power System Overview
- Photovoltaic Solar Panels
- Best Positioning for the Photovoltaic Solar Panels
- Types of Photovoltaic Solar Panel Array Mountings
- Solar Charge Controllers
- Solar Power Inverters
- Storage Batteries
- Solar Power back-up - AC Generators
- Wires and Cables for a Solar Power System
- Meters and Monitors for a Solar Power System
- Battery wiring diagrams for Solar Power Systems
- Watt, Power, Voltage, Current (intensity) Explained
- Consideration When Choosing Free Solar Power
- Costs, Life Expectancy and Minimum Equipment Needed
- Solar Power - Terms and Definitions
Solar electric: Photovoltaic Panels
Say "solar" and most people will think of photovoltaics (PV), the dominant technology in the field. Photovoltaics turn sunlight into electricity, using either silicon (the same type used in semiconductors) or what's called thin-film technology. Typically, when you see a solar panel on a roof, it is a photovoltaic (PV) panel made out of a silicon material and covered with a tempered glass enclosure to protect it from the elements.
Photovoltaic solar panels, also called PV modules, offer a dizzying array of technology choices in terms of cells, panels and configurations. Even the cells themselves can use monocrystalline, polycrystalline, metallurgical grade or a hybrid mix of silicon materials. With so many different manufacturers and so many different panel types, much of the ultimate purchasing decision will be done with the guidance of a trusted professional installer.
Today, the price of the system and the associated cost per kilowatt hour (kWh) of electricity it generates is key. Solar photovoltaics is still an expensive means of generating electricity, especially when compared to coal, which is relatively cheap. Nationwide, retail residential electricity rates averaging $0.10/kWh. The amortized cost of electricity over the course of PV system's lifetime is typically around 25 cents/kWh. On a pure price basis, then, solar can't yet compete with conventional electricity. However, when additional factors are accounted for, a compelling case can be made for solar. Solar PV systems make the most financial sense when:
(1) They are accompanied by government-sponsored incentive programs, which include rebates, tax credits, low-interest loans and grants. For more information, see our U.S. map of solar incentives.
(2) They are deployed to help offset large monthly electricty bills. In many cases, your monthly financing payments will be lower than what you were previously shelling out to your electric utility every month. As a general rule of thumb, solar PV systems make the most sense for individuals and business that are paying a high, per-kWh rate for retail electricity.
(3) They are connected to the electricity grid, or "grid tied." With a net-metering agreement, the PV owner is in many states permitted to sell any excess power back to the utility. As more and more states create renewable portfolio standards (which require that a certain amount of power be generated by renewable resources), more and more utilities will likely be required to purchase renewable energy credits (RECs). By installing a solar PV system, you are becoming equipped to sell RECs to your utility so it can meet state-mandated RPS requirements. While not all states have REC programs in place, there's a good chance the adoption of the REC model will continue.
To get an idea of how much PV panels (also called modules) cost, see the monthly survey posted by SolarBuzz. Bear in mind that these prices are retail prices. In terms of installed costs, you should expect to pay between $9.00 and $10.00 per watt, though this figure will vary depending on your installer, location and project specifications.
For more information, feel free to browse our blog, where we post up-to-date news and commentary about solar PV technology and solar financing.
Thin Film Technologies
Amorphous silicon (a-silicon) cells are the oldest commercial thin-film technology. In contrast to c-silicon, which must be sawed into wafers at great loss of material, a-silicon is directly deposited on a substrate or superstrate. This process produces a continuous random network of bonds, as opposed to the crystalline lattice of c-silicon. This network is less efficient and prone to defects in the form of broken covalent bonds, or "dangling bonds." These defects can be partially remedied by adding hydrogen to bond to the empty "slots" on the silicon, but the addition of hydrogen causes a premature degradation of the material when it is exposed to sunlight, a phenomenon known as the Staebler-Wronski effect. Thus a-silicon cells are not as efficient as crystalline cells, but are less expensive to produce.
Cadmium telluride (CdTe) cells take their name from the cadmium telluride gas that is used in their manufacture. The band gap (essentially the electromagnetic range at which the semiconductor is most efficient at absorbing energy) of the tellurium-based semiconductor is an excellent match for the solar spectrum. There is also a light-transmitting layer of cadmium sulfide in the cell which admits more solar energy. Those two advances combine the efficiency of crystalline silicon cells with the lower manufacturing costs of amorphous silicon processes. While these cells are still in the early stages of development, the technology is evolving rapidly and holds great promise for lower-cost, high-efficiency cells.
Copper-indium-diselenide (CuInSe2, or CIS) cells, like CdTe cells, are named for the semiconductor used to make the solar cell. They also have high efficiency but are at present too expensive for large-scale commercial production.
Solar Tiles are small photovoltaic cells that look like shingles. While less efficient per square unit of area than a solid photovoltaic cell would be, they are more likely to be permitted by local ordinances and neighborhood associations because of their lower aesthetic profile.