How does it work?
A direct electric current (DC) results when sunlight strikes the solar cell. When enough solar cells or panels are wired together, the resulting electric current generated is enough to be used for homes and business. This electric current is “inverted” from DC to the common household alternating current (AC) form of electricity. When the sun is shining, the solar generated electricity is fed into your home's breaker box or service panel. The energy is sent throughout the entire home distributed via the service panel. After satisfying the home's electric load (lighting, appliances, etc.) requirements, any excess energy is sent back to the utility grid or power line. This excess energy will be tracked, spinning the meter backward and credited to your next electric bill. When the sun is not shining or a night, energy is drawn from the “grid” as normal.
Direct grid connected systems operate efficiently with reduced energy loss as compared to battery based PV systems. The advantages are lower carbon footprint associated with no batteries and less expensive per watt installed due to fewer components. Grid connected renewable energy systems can be installed on new and existing homes. Grid connected systems provide all the benefits of abundantly clean renewable energy without the added cost and maintenance required with storage batteries. Generally speaking, if you have the utility grid available utilize the grid to be your "battery bank".
Public electric utilities (Duke, Indianapolis Power and Light) and many electric cooperatives (REMC's) in Indiana now offer net metering and net billing programs to their customers. These programs allow owners of direct grid connected solar electric systems to inter-connect their solar electric system to the utility grid.
Solar System Siting
There are options for mounting and installing solar panels on new and existing homes. The least expensive options include roof mounted rails, ground mounted and pole mounted racking systems. Building integrated designs offer aesthetically pleasing applications that make the PV panels look more natural to the eye.
The most important consideration in locating solar panels is to ensure proper alignment to the sun with little or shading from nearby trees, vegetation or buildings. A site assessment will help determine the best location for solar system placement.
Solar Electric (Photovoltaic or PV) Overview:
Most solar electric systems installed today are direct “grid-tied” systems with no battery backup. Essentially the utility’s power grid acts as the storage (in place of batteries) for any excess power produced by the solar system. This not only eliminates the cost of the batteries, it also eliminates the required monthly maintenance and periodic replacement expenses. This has been a big step forward in generating interest among the general public in installing solar PV systems. By Federal mandate, most utilities must credit the system owner for the excess electricity that their PV system generates. In many States including Indiana, all investor-owned and municipal utilities are required to ‘net meter’, meaning they credit the homeowner at the retail rate for excess energy produced by solar electric systems up to 10kW+ in system size.
A noticeable disadvantage of direct grid-tied systems is that when there is a power outage and the utility power grid goes down, the PV system goes down as well. There is no back up power because there are no batteries. In most areas power outages are not a significant problem and so this is not a major issue, and the reduced maintenance and cost of battery-less grid-tied systems more than makes up for any inconvenience.
It is possible to install a battery backup option for a grid-tied system in order to maintain power to a few critical loads of the clients choosing, however this does add significantly to the cost and reduces the operating efficiency of the system. Retrofitting from a utility interactive system (battery free) to a battery based system is now much more cost effective and efficient. Battery capacity gives you a secure power source when the utility grid goes out.
A PV system is a collection of photovoltaic panels connected together to create an array of the desired size (wattage). For example, a typical residential array may be composed of twenty five (25), 300 watt panels forming a 7500 watt (7.5 kW) system. The black or silver framed PV modules sit side-by-side on a rack and the wires from the individual modules are connected together and then run to a “combiner box” which combines the outputs from the individual strings of modules into one larger output, which is then run to the balance of system components typically located within the home. The PV array produces DC power which, in a normal grid-tied application, is converted into AC power by an inverter and then connected to your load center (breaker box) to power the loads in the home. If more power is being produced than consumed the excess power flows out onto the power grid through the meter, and the utility credits the homeowner’s account in a relationship called net metering. The system size is determined by your electric habits. The more electricity you use the larger the system size is needed to offset that usage. A typical resident in Indiana uses 10,000 kWh / AC per year. A 7-8 KW south facing solar energy system with no shading from trees or buildings will harvest approximately 10,000 kWh AC on average per year.