The direct grid-tie solar system is the simplest system to install and will meet the needs of most people since the majority of the population lives on a very reliable grid. In areas where commercial power is unreliable, or power is required for critical situations, battery back up and gas or diesel generators can be added to the system. Another fairly simple system is for off grid use where all electrical appliances and lights are 24 volt DC. This is common for boats and trailer homes, but won’t support most folks. The other type of off grid system will have an inverter that converts current to AC and stores power in DC batteries.
Direct Grid-Tie Residential Solar Systems
Direct grid-tie systems need only the solar panels, an inverter and a disconnect switch to shut off power if the grid goes down. The inverter connects to the disconnect and then directly to the main electrical panel. Thus when the sun is shining, the electric meter spins backward when the solar power system is producing more electricity that the home is using. Often the meter needs to be replaced by the power company because older meters weren’t designed for reverse operation and do not read accurately. Of course you want an accurate reading since the electric company will be crediting you for the electricity returned.
Once installed, this system is almost maintenance free and will operate for many years. A promising new type of system uses a micro-inverter which is wired directly to each panel. This makes your system even simpler since your wiring is for AC current, and you can use standard electrical wiring components. This also has the advantage that each panel is wired separately so if one solar panel is shaded, or broken, the rest of the system will work just fine.
As soon as we add batteries to your system, we complicate the design and add extra maintenance. We need a special inverter which in addition to converting to AC power, must feed some DC to charge the batteries, and must be able to instantly switch to battery power if the grid loses power. Batteries also will add 4-5,000 dollars to your system cost, and will add maintenance if you go with less expensive wet cell batteries. You should wire your system so that the backup batteries don’t supply the whole house with power or your battery expense will be even higher. Keep power flowing to refrigerators, furnace, some lights, computers, and other equipment that you must have running..
An off-grid home basically requires the same equipment as the system above designed for battery backup. The only difference is the inverter does not require the circuitry to manage the grid power, and feeds all excess power to the battery charge controller. Depending on the amount of sun you get, you may want to integrate a generator into you system so batteries can get extra charging in winter or periods of bad weather.