When considering solar power, there are 3 main reasons people get photovoltaic systems: saving money on electricity, helping the environment, and becoming independent from the electric grid. Your priorities on each of these reasons will help determine what kind of system is best for your situation.
If your goal is to save money on electricity, then a grid-tied system without batteries will save you the most. With this type of system, we size the system to offset 90% to 100% of the electricity you use overall. During the day your panels will produce more electricity than you use, and will sell it to the grid. In the evenings and at night, your panels won’t produce enough electricity and the grid will supply the difference. Because of inexpensive solar panels, an upfront investment can save you thousands of dollars on electricity over the lifetime of the panels. Many customers use financing to pay for the solar panels, and while the interest will reduce the amount of money you save, you can still save thousands of dollars. In addition to money saved on electricity, adding a PV system will protect your roof and add value to your home. Solar panels are designed to be very durable and can handle sizable hail (rated for 1” direct hit).
Next, many people turn to solar power to help the environment. Installing solar in your home will likely help, but it depends on how your local utility generates power. A good metric to look at is pounds CO2 per kWh.
| Source | Pounds CO2 per kWh produced |
|---|---|
| Coal | 2.21 |
| Petroleum | 2.13 |
| Natural Gas | 0.91 |
| Residential Solar | 0.218 |
A kWh, or kilowatt-hour, is a measure of energy typically used for electricity. For example, one gallon of gasoline contains 33.41 kWh. One pound of coal contains about 3 kWh. One AA battery contains 0.0039 kWh. Where the environment is concerned, we want to release the least amount of CO2 we can. If you have a grid tied system, then you average the CO2 cost of solar with the CO2 cost of your utility’s power plant. To cut the utility out of the loop, you can purchase a grid independent system, where you buy batteries and a generator in addition to your panels. Keep in mind that there is a carbon cost to producing the batteries, and batteries waste some of the electricity they store. If your batteries run out, then you will need to provide electricity with a local generator. These small generators are substantially less efficient than power plants. The exact details of how much carbon you save with this type of system is also dependent on how diligently you avoid using the generator, but will almost certainly generate less carbon than relying on a grid supplied by fossil fuel.
Finally, if you are looking to be independent of the electrical grid, then a PV system with battery backup is your best option. Whether you want independence because of physical distance from the grid or otherwise, these systems look the same. As mentioned before, it consists of an array of solar panels that supply your house, a battery bank to store the day’s excess energy, and a gas or propane generator for when the batteries run out. If you use the grid instead of a generator for when your batteries run out, then this system also protects from blackouts, whereas a PV system without batteries does not. Due to the cost of batteries, it is unlikely that you will save money versus connecting to the grid, but not impossible in certain cases. This system works by producing excess electricity during the day, which is stored in batteries. As the sun sets, the average person’s electricity demand goes up, and your batteries will supply the difference between what is generated and what is demanded. We design our systems to store about 3 days of electricity before running out. In cases of high usage, or low generation, these systems have a gas or propane generator. These generators communicate with the system, and are set up to start automatically when the battery is low. You won’t have a loss of power before the generator turns on. This type of system is expensive, but it can be installed anywhere and is the best way to become independent of the electrical grid.