Off-grid, which stores energy in a battery bank, and gridtie, which stores excess electricity in the utility grid. Both off-grid and grid-tied solar power systems convert sunlight to DC electricity, which can be sent through an inverter that converts it to AC current that your solar home can use.
....is used where there is already utility-supplied electricity. Solar panels supplement the electricity that feeds your house or business and sends excess power back into the utility grid. A simple gridtie system eliminates the need for batteries. Typically, the power company will give you credits for the surplus electricity that you feed back into the power grid. In some areas the utility company will actually pay you for the electricity your home sends into the grid.
A grid intertied solar electric system can be sized smaller than an off-grid system because you do not need to produce all the electricity you need. During the day you feed extra electricty into the grid and at night and on cloudy days when your system is not making electricity, you can draw back what you stored from the utility grid without having to pay for it. If you use more electricity than you make, you are able to draw what you need from your utility grid, but you will be charged for it. In areas where the utility charges more for electricity used during peak hours, the cost of use comes out in your favor. You create electricity when the cost is high and "borrow" it back when the cost is low.
Simple Solar Gridtie without Battery Backup.
The simplest gridtie system operates without batteries. The main components are simply solar panels, gridtie inverter, meter and safety disconnects. You make as much electricity from clean, renewable sources as you can afford, and the rest still comes from the utility. Without batteries to store your homemade electricity in, you are without power whenever the utility grid goes down. This method is not about independence from the utility; it's about capping your electricity costs and about using clean energy if possible.
Solar Gridtie with Battery Backup.
If you want to be able to rely on the power company for power over what you produce with solar panels AND you need to have back-up power for when the grid goes down, you can add a battery back-up system. The addition of a charge controller and several batteries will allow you to store enough energy to power essential appliances for a period of time if the grid goes down. The length of time you will be able to use these appliances (radio, computers, cash registers?) depends on the size and number of batteries you add.
Gridtie Wind without Battery Backup.
In areas with more wind than sun, a gridtie wind turbine or generator can be used to make electricity for your home or business. Again, without batteries, you must draw and pay for electricity from the grid when there is not enough wind to produce electricity. Do you have enough wind? Be sure to check the wind speed maps for you area. Then, pay careful attention to the start up speeds of wind generators you consider purchasing.
Gridtie Wind with Battery Backup. Same as with solar, you can add batteries to provide backup power when the grid goes does down.
Solar power and wind power are complementary. In many parts of the country, if the sun is not shining during inclement weather it is very likely that the wind is blowing pretty hard. For these areas, it makes a lot of sense to use both solar and wind. The system is more complex, requires a smarter inverter and may be more costly. Although, with gridtie, again, because you do not have to produce all the energy you use, you can size the system to match your budget.