Grid-Tied Solar Power System Change to Time Of Use billing and save an additional 15 to 40%: Where utility power is available, a grid-tied solar power system can supply some of the energy needed and use the power from the utility in place of batteries. Because these grid-connected systems are much less expensive to purchase and operate than battery backup systems - and because the owners can effectively sell power back to the utilities - these systems are becoming very popular. Note that inverters used with grid-connected solar electric systems do not have battery backup capability, and this backup capability cannot be added at a later date unless the inverter is changed.     The owner of a grid-connected solar energy system may not only buy, but may also sell, electricity each month. This is because electricity generated by the solar energy system can be used on-site or fed through a meter into the utility grid. California's net metering law provides that all utilities must allow customers with solar electric systems rated up to 1.5 MW to interconnect with the local utility grid and receiving retail value for the electricity produced. When a home or business requires more electricity than the solar (photovoltaic) array is generating (for example, in the evening), the need is automatically met by power from the utility grid. When the home or business requires less electricity than the solar power array is generating, the excess is fed (or sold) back to the utility -- and your electric meter actually spins backwards. Used this way, the utility serves as a backup to the solar power system similar to the way in which batteries do in stand-alone (off-grid) systems. Utilities are required to buy power from owners of solar energy systems (and other independent producers of electricity) under the Public Utilities Regulatory Policy Act of 1978 (PURPA). An approved, utility-grade inverter converts the DC power from PV modules into AC power that exactly matches the voltage and frequency of the electricity flowing in the utility line, and also meets the utility's safety and power-quality requirements. Safety switches in the inverter automatically disconnect the solar energy system from the line if utility power fails. This safety disconnect protects utility repair personnel from being shocked by electricity flowing from the solar power electric array into what they would expect to be a "dead" utility line. Here is how the billing works. Every month you will receive a monthly statement showing how much electricity you have "sold" back to the utility (effectively running the meter backwards), or how much net electricity you have consumed; you will also get billed a nominal (about $5) standby charge. Then, once a year on the anniversary of your system's interconnection, the utility will send a reconciliation statement to you and bill you for the net power you have used during the year. Effectively you will go on annual billing for your electricity. In addition to cooperating under PURPA, utilities are establishing rate structures that make solar power grid-connected systems even more economical. For example, PG&E's Time Of Use rate allows you to run your electric meter backwards at up to $0.44 per kwh during summer weekday afternoons (when your solar energy system generates its maximum amount of power), and purchase electricity at all other times at $0.12 per kwh! This Time Of Use billing method effectively improves the economics of your solar power electric system by 15 to 40%.