Solar panels (photovoltaics) aim to convert solar energy from the sun into usable power for homes, offices, and transportation.
How Does A Solar Panel Work?
A solar cells consist of two plates, one positively charged, and the other negatively charged. The negatively charged plate is composed of Silicon, and another element, commonly Phosphorus. The positively charged plate is composed of Silicon and Boron, and it's the interaction between these to plates that produces energy.
Photons, which arrive from the sun, knock an electron out of the negatively charged plate, which is soon pulled in by the positively charged plate. As electrons are transferred from the negative to positive plates, electricity is generated and extracted from the system.
Solar cells are combined together to create a larger unit, a photovoltaic module which generally uses 36 cells.
Efficiency
Only 15 to 25 percent of the solar energy that strikes a solar panel can be converted to usable energy. This is mostly due to limitations on which wavelengths of light have the right characteristics to knock the free electron from the negative to positive plate.
Life
Solar panels should last 20 years or more.
Using Solar Panels
1. Orientation
Solar panels want to be oriented to true south, and be inclined to an angle equal to the latitude where the solar panel is being used for maximum efficiency. Care should be taken to ensure that no portion of a photovoltaic module are in shade, since even shading one of the 36 cells in a photovoltaic module can cut the efficiency of the entire module by half. Look out for trees, other buildings, and even a chimney, if shading only a small portion of the solar array can have a large impact on how much energy is produced. Ideally, there is no shading on any of the solar panels between 9:00am and 3:00pm.
2. Energy Storage
There are several approaches to storing the energy produced from an array of solar panels; battery storage, and grid storage.
Batteries
Batteries are used to hold the energy created, but add significant cost to the system, as well as chemicals that can be dangerous if not handled properly. The most common batteries are lead-acid and nickel-cadmium batteries. Nickel-Cadmium batteries cost more, but have a longer life. Because over-charging the batteries, or completely draining them, will severely limit their lifespan, charge controllers are needed to control the flow of energy into and out of the batteries.
An inverter is also needed which converts the DC current which is produced by the solar panel into AC current, which can then be used by household appliances. Some PV modules now can also have AC inverters built in, reducing the need for an external inverter.
Grid Storage
An alternative to storing the electricity in batteries, is to sell unused energy from the photovoltaics to the public electricity grid, and then buying electricity back when the solar panels aren't producing energy of their own.
3. How Many Solar Panels Do I Need?
There are several factors that influence how many solar panels are needed to power a home. These include:
1. What are the energy needs of the house?
2. How much sunshine will reach the solar panels?
3. What wattage of panels will be used?
4. How will the solar panels be oriented?
What are the energy needs of the house and how much of the energy do you want to provide from solar?
The first step in determining the total number of solar panels need, as well as the overall square footage of a solar array, is to determine your needs. To do this, you need to know how many kilowatt-hours (kWh) your house consumes in a month, and there are several ways to arrive at this number.
The easiest way to get started is to look at your energy bills, which will list how much energy you have consumed. It's important to keep in mind that one month of information isn't enough to gain a clear understanding of your energy use, you will want a full years worth of information to generate a more accurate average for monthly consumption.
Another method is to determine the energy consumed by all of the appliances, lights, and electronics in your home. Most electronic items and appliances list their wattage on their labels, and light bulbs are pretty easy to find the wattage listed. To generate the monthly usage for a light bulb, multiply it's wattage by how many hours the light will be on during the month (it's easier to do this by the day, and then multiply by 30 to get a good monthly number). This will give you watt-hours (wH). Do this for every device that consumes energy, add them all up, and you will have a total energy usage for your house. Because this number will be in watt-hours (wH), divide by 1000 to convert the number into kilowatt-hours (kWh).
How much sunshine will reach the solar panels?
A variety of factors will affect how much energy producing light will actually reach the solar panels. Your city's latitude and weather will play an large role, as well as the orientation, placement, and tilt of the solar panel.
This will give you Peak Sun Hours, which is the average number of hours of full sunlight per square meter.
What wattage of panels will be used?
Solar panels come in an array of wattages to meet a variety of needs. Common wattages range between 50 and 210 watts per panel.
How will the solar panels be oriented?
The efficiency of the solar array will be affected by their orientation. Obviuosly, panels which face north will not provide the same level of output as those facing south.
Efficiency
Not all energy produced by the solar panels will be available as electricity to power household items. While efficiency has been improving, and will probably continue to do so, electrical systems will always yield less power than what they bring in, due to energy loss in transmission, conversion, and storage. Generally, current solar systems can have efficiencies ranging from 50%-70%, so the overall system wattage needed will have to be nearly doubled to account for inefficiencies within the system.
To arrive at an actual number, the following information must be known:
1. How much supply do you need to create (How much energy does the home use, in kWh per day)?
2. How many hours of Peak Sun Hours reach the site per day (use http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/)
3. How much energy does each solar panel create (in kWh)?
