Log Cabin System: A simple 12 volt DC system provides lighting for isolated cabins. Low wattage (<100W) solar panels are connected directly to a battery. The battery is connected to lamps and other 12 volt DC appliances as shown in below figure. The battery life is compromised by unregulated current charging. Available appliances are limited for 12 volt DC power, because wire resistance limits power to a few hundred watts. This system is not connected to AC power lines and is considered to be “off the grid”.
Country Home System:Larger panels providing 24- 96 volts are connected to an inverter to yield 120/240 VAC to operate standard lighting and appliances as shown in below figure. Battery life is improved with a regulated charging module. The higher DC voltages support moderate power levels. This system is not connected to AC power lines and is considered to be “off the grid”.
Urban Home System: Larger panels providing 200- 400 volts are connected to an inverter to yield 120/240 VAC at medium power levels (2-10kW). This system is connected to AC power lines (i.e., connected to thegrid) as shown in Figure 7. The customer sells power to the power company during the day and buys power from the power company during the night. The gridconnected approach eliminates expensive and short lived batteries. A couple of issues exist with this system. One, the inverter has potential as a single point of failure; and two, non-optimal power harvesting from the solar panels, especially in partial shading conditions.
Single Inverter with Multiple DC/DC Converters:The use of DC/DC converters per string provides enhanced power harvesting from solar panels as shown in below figure. The DC/DC converters may be separate modules or reside within the inverter module.This method is still susceptible to single-point-failure of the inverter, and involves the distribution of high voltage DC power – a potentially dangerous situation because direct current power fusing is difficult to achieve.
Urban Home System with String Inverters:Panels providing 200-400 volts are connected to multiple inverters to yield 120/240 VAC at medium power levels (2-10kW). The inverters are connected to the grid as shown in below figure. Use of multiple inverters provides enhanced power harvesting from solar panels and also provides enhanced system reliability.
Module Incorporated Inverters:Each solar panel module incorporates its own inverter. Module-incorporated inverters are also known as microinverters. A micro inverter system is shown in below figure. The incorporation of inverters into the solar panels greatly reduces installation labor costs, improves safety, and maximizes the solar energy harvest.
Note:For the above figures reference taken from Microchip Technology Inc.