Solar energy works by converting the sun's rays into electricity with the use of solar panels, otherwise known as photovoltaics (PV), to supply power to the appliances used in our homes. Solar energy also works by converting the sun's rays into heat with the use of solar thermal collectors for warming water for residential use and for swimming pools. Solar power can be generated with either a grid-connected system or a stand-alone system.
A system where utility supplied electricity is connected to the property, but the owners wish to harvest clean, free energy from the sun is known as a grid connected PV system. Electricity is supplied firstly from the solar energy system, then from the grid if there is still a need. You will not receive monthly checks from your utility company. You can, however, expect to reduce your bills by a high percentage. Money saved is tax free money earned.
UniSource and Mohave Electric offer "net metering" to their residential customers. Since grid-tied solar electric systems don't have any form of storage, if there is any excess power the home is not using (for example, when you're not home during the day), it gets sold back to the utility company at the same rate they charge you. Your meter literally runs backwards, and they simply bill you the net difference at the end of the month. If your meter reads a net negative for the month (you produced more than you used), the utility company provides a wattage credit to your account.
The utility companies have a rollover that you can save up for high summer usage. An example of this follows; say you produce 800 kWh, and use 600 kWh, you wouldn't owe anything for your electrical usage, as they have bought the first 600 kWh at retail prices, and for the last 200 kWh you sold in excess, they will credit your account. Credits accumulate each year, but reset to zero at year end of the year when you are paid a wholesale rate if you generated more power than you used for the whole year.
A grid-tied system generates electricity when the sun is shining and when the utility company is "on-line". If the utility power fails, you have no electricity even though you have solar generated power.
A system not connected to the grid is a stand-alone system. More often than not, these systems are installed in remote areas where there is no utility-supplied power. It is often cheaper to install a solar energy system than lay electricity cables to the site. Excess energy can be stored in a battery for use during times where there is no sunshine. These systems are more expensive due to the battery needs. Batteries are expensive, and need to be replaced every 7-10 years, whether you use them or not.
Appropriate mounting location:
You need space that is not shaded all day during the peak sunlight hours of the day throughout the year for maximum production and economic benefit. Solar electric panels are very sensitive to shade, but do perform with limited efficiency in cloudy weather.
Roof features to take into consideration as potentially shading a solar array include: vents, chimneys, skylights, other roof surfaces, air conditioners, swamp coolers, antennas, satellite dishes, etc. Other things to consider, trees, chimneys, other buildings, etc.
There are four main types of mounting:
- - Pitched Roof Mount (most economical)
- - Tilt Roof Mount (more economical)
- - Ground Mount (more expensive)
- - Trackers (most expensive but highest power output)
For flat roofs
Panels are typically mounted at 15 to 30 degrees.
For ground mounts
Concrete and upright poles are used for mounting. Typically the array is in a single plane that is tilted 20 or 30 degrees. It is also typically necessary to trench and run conduit to the electrical box and meter.
Tracker units are used to gain the maximum output by tracking the sun's movement across the sky all day long. Gains of about 32% can be realized by tracking. Though the units cost more than a fixed mount, you can reduce the number of panels needed by using a tracker, since you get higher output overall. For example a ground mount setup may need 9kW of panels to meet the needs of the user, but the same user could install only 7kW if trackers are utilized.