Consumer Center Solar Electric - General Info.

There are two major sources of solar generated electricity. Many people claim that electricity produced from wind turbines is a form of solar electrical production. It is certainly hard to argue against this since wind is a result of the sun' heating. However, for the purposes of this web page, we will only be considering the following two methods of solar electrical energy production. The first uses the sun to generate high temperature heat which is collected by solar collectors. These collectors may be in the form of parabolic troughs that focus the sun's rays onto a center receiving tube that carries a heat collection fluid. A second type of collector, a central receiver, receives concentrated sunlight from many reflecting mirrors. A fluid is heated to high temperatures within this receiver. In both of these cases, the heated fluid is used to generate steam which in turn spins a turbine-generator combination to generate electricity. Such generating facilities are on a commercial scale and will not be covered any further on this page. What we will discuss further, however, is the generation of electricity using solar electric, or photovoltaic (PV) cells or more appropriate, PV modules.

PV modules need the sun to generate electricity. A PV module is comprised of a group of PV cells and are electrically connected to form a module. Modules are wired together to provide power for home usage. Most residential PV systems not tied in with the utility grid will use batteries to store the electrical energy for later use. Before the electricity is used within a home, it usually passes through a charge controller. The charge controller makes sure the PV modules do not overcharge the batteries.

PV modules produce direct current (DC) and batteries store DC electrical energy. Another component of the PV system is the inverter. The job of the inverter is to convert the DC power to alternating current (AC) power. Although most household appliances are available in DC models, they are rather expensive. Some people with PV systems choose to have an all DC house. This does have an advantage of not needing an inverter, but on the other hand, it is more expensive to provide for DC house wiring . However, because of the DC wiring expenses and DC appliances and the easy availability of AC household appliances, most residential PV systems are set up with an inverter for AC operation.

When discussing residential PV systems, several terms are used in these discussions. It is necessary to understand what these terms mean before you can decide whether this technology is for you. So, let's look at some of these terms.

PV sales and installation people talk about off-grid installations. This simply means that the house has no connection to the electrical utility grid, i.e., all electricity used by the home is manufactured by the home electrical generation equipment. Such an installation is also called a stand alone system. The PV system may have some sort (propane, diesel, or gasoline driven) of motor-generator to be used as a backup to the PV generating system. A string of cloudy days or a PV system failure could leave a family in the dark and the generator would then be a welcome insurance policy.

What about a grid-tied PV system? This type of system has a tie in with the electrical utility. When the PV system produces more electricity than the house can use, the excess electricity can be fed back into the utility grid. When the house requires more power than can be supplied by the PV system, power is drawn from the utility grid. Some grid-tied residential systems have a battery back up system, some don't. If for some reason the electrical utility grid goes down, those systems without a back up battery system will also shut down. A back up battery system will allow a grid-tied system to continue supplying power to the house after first disconnecting the house from the utility grid.

And what is this thing called net metering? When a grid-tied system produces more electricity than the house can use, the excess electricity can be fed back into the utility grid. Some electric utilities allow the customer to feed the electricity directly back into the grid and spin the electric meter in the reverse direction. Using this method, the electric utility is buying back the electricity at the same retail price that they are charging the customer, i.e., true net metering. Other utilities require a separate electric meter to monitor the electricity being fed into the electric grid. With this type of set up, the utility charges the customer the retail price and pays the customer a lower price for the electricity fed back into the power grid. The lower price can vary, but some states set this at the "cost avoided" price. Although some utilities like to also call this net metering (good PR), it is not true net metering.

Living in an off-grid/stand along system house does not mean less conveniences than a conventional grid-tied house. Sure, there are some appliances, such as an electric stove, electric water heater, electric clothes dryer , and a conventional air conditioner that are not suited for these types of electrical systems. But natural gas versions for the first three appliances are available, and swamp coolers do a good job of cooling in dryer parts of the country. Energy efficient refrigerators and freezers are available. Remember, the more efficient you can be on the electrical consumption side of the equation, the less you will have to pay on the electrical generation equipment side.

Further in depth descriptions are contained on the Stand alone and Grid-tied systems information pages. Just click on the type of system that is of interest to you for more information.

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This page last updated on 10-3-05