1) “Strict Grid-Tie” Solar Electric Systems
Photons from the sun hit the PV array of modules, the array sends DC electricity to a DC to AC inverter. The inverter sends AC power to the household electric breaker panel. If all the loads within the home are satisfied, the excess energy is sent back to the utility grid. Grid-tie solar electric systems are usually installed on homes and businesses where the electricity grid is reliable and readily available. They interface with the electricity grid, allowing excess power that is produced from the sun during the day to be sold back to the utility company and spinning the meter backwards. At night or during cloudy weather, your home or business takes power from the grid as normal, thereby spinning your meter forwards again. Each day, your electric meter may spin backwards and forwards as part of “net-metering.” Strict Grid tied systems usually require little maintenance, as they have no batteries, battery box, box fans, battery monitors or charge controllers.
A utility intertie battery free system incorporates:
Utility interconnection contract
Residential Sized 1kW to 15 kW System cost rule of thumb: $2.50-$5/watt installed.
2) Stand Alone PV Systems
A stand-alone system is a self contained, independent
power generating system sized for home or business. There are different reasons for installing a stand-alone system on a home, however there are two main reasons for doing so.
The first reason, utility power lines may be too expensive to bring in for hooking up, or they may not even exist in remote locations. When figuring the cost of bringing in the utility, renewable energy can look quite attractive.
The second reason for stand-alone systems for a home is the desire of the home owner to have an independent power source that will not be regulated, is reliable, environmentally safe, allows the consumer to bypass corporate electric bills and ethical beliefs.
A stand alone system incorporates:
A stand alone system in the midwest, is generally sized for the home's loads plus
the battery bank sized for 3-4 days of no sun. After 3 or 4 days of no sun, the batteries need to be charged by either another renewable energy source such as wind or hydro or a gas generator. Stand alone systems require attention to battery fluid levels, connections and charge capacity. These systems tend to be on the upper end of cost per installation.
Residential Sized 1kW to 18 kW System cost rule of thumb: $5-$9/watt installed.
3) Utility Intertie w/Battery Back-up
The third type of system incorporates the best of both worlds in design. The system may operate as a stand-alone system if the utility power goes down or it can operate as a utility intertie system and keep the batteries fully charged for an emergency.
The utility intertie w/battery back up system incorporates:
Utility inter-connection contract
The inverter for this type of system has more tasks to perform than the stand alone or battery free utility intertie inverter. The inverter must be able to operate as both stand-alone and utility intertie, sometimes simultaneously.
This type of system tends to be the most expensive of the three types and requires the same amount of maintenance as the stand-alone system.
Residential Sized 1kW to 15 kW System cost rule of thumb: $5-$9/watt installed