Systems

Grid-Tied Solar Electric Systems

Grid-tied systems produce direct current (DC) electricity from photovoltaic (PV) panels, which is transformed into alternating current (AC - typical house electrical power). The really fun part of this type of system is that if the PV panels are producing more power than the residence or business is currently using, then the power is fed back out into the electric grid for neighbors' use! When this happens the utility meter spins backward, selling power back to the electric company! This is called "Net Metering". While the utility company does not currently pay for excess generation, in many states credits will be carried forward month-to-month.

Typically, sizing a grid-tied/net metered system starts with determining monthly/yearly electrical usage in kWh's (kilowatt hours - the unit of power electric companies use for billing). This number usually determines the maximum size of a system. Other considerations are:

• available sunny space for PV panels (it is important to avoid most shading)
• aesthetic considerations
• cost of various system sizes
• state incentive/rebate programs locally available
• federal and state tax credits available

One area that can be overlooked in designing systems is thinking about reducing the demand for power. Investments in more energy efficient electrical appliances and equipment, as well as making considered changes in patterns of usage (eg turning off appliances, lights, etc not in use) where feasible, is almost always a much more cost effective and environmentally friendly choice than installing a larger system.

Power can continue to be created during grid outages by installing a system with battery back-up capability. However, without battery back-up, Grid-Tied systems will not produce power when the power grid shuts off (ie during blackouts). This is a requirement by law.

Grid-Tied Solar Electric Systems with Battery Back-up

Grid-Tied solar electric systems with battery back-up are similar to straight Grid-Tied systems, with the added advantage of continuing to produce power during grid outages. Due to the added equipment and complexity, these systems are significantly more expensive. However, they do provide the comfort and security of continuing to produce and provide power during blackouts (as well as a sense of self-satisfaction when your neighbors see your lights on when theirs are out).

Off-Grid Solar Electric Systems

Off-grid solar electric systems are power systems completely independent of outside power sources. They produce power from photovoltaic (PV) panels, which is then converted into usable house power, or stored in batteries for later use. These systems are often coupled with other power generating technologies (gas or diesel generators, wind turbines, hydro turbines, etc), to produce power when there is not enough solar power available for the required power loads. The system typically includes:

• PV panels roof, pole or ground mounted
• An "Inverter" which changes the PV and battery power into AC house power
• A charger which uses generator power to charge the batteries
• A "deep-cycle" battery bank for storage of power from the various generating sources