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Like solar electric systems, wind systems fall into three basic categories: (1) grid-connected, (2) grid-connected with battery storage, or (3) stand-alone.
As you may recall from the prev. section, a grid-connected system consists of three main components: (1) a renewable energy source, in this case, a wind machine, (2) an inverter, and (3) a main service panel. DC electricity produced by the wind machine is converted to AC by the inverter, and then travels to the main service panel. From here it travels to various open circuits (loads). Excess power goes on to the grid, and may be “banked” as a credit on your utility bill. When the wind isn’t blowing, electricity you need to power your home comes from the grid. Because the grid is your “storage battery” a grid outage will result in a power outage in your home even if the wind is blowing. This is due to the design of the inverters. (For more details, be sure to read the previous section on grid-connected solar electric systems.)
If you want to store electricity for emergency use — for example, to protect your home, office, or farm from an occasional grid failure — you may want to install a battery bank for back-up power. In these systems, the wind generator supplies electricity to active circuits in the house, Excess electricity is fed into the batteries, When the batteries are full, excess electricity is diverted to the grid. If a blackout occurs, the batteries kick in, supplying electricity to your home to keep the refrigerators running and lights burning. (For more details, check out the section on grid-connected systems with battery backup in Section 7.)
Your third option is a stand-alone system, that is, a system that provides 100 percent of your electricity. Stand-alone systems are not connected to the electrical grid. Because of this, you can't send surplus to the grid in times of excess production, nor can you draw from the grid in times of need. In stand-alone systems, surplus electricity is stored in a bank of batteries, usually lead acid batteries. (This battery bank is much larger than in the previous system.) Electrical demand during windless periods is satisfied by electricity stored in the batteries, as in a stand-alone solar electric system. A back-up electrical generator may also be required. (Again, you can refer to Section 7 if you need to brush up on stand alone systems.)
Because winds don’t blow all of the time, even in windy locations, many homeowners and businesses who want to be off the grid turn to hybrid systems. A hybrid system is a renew able energy system that combines a wind machine with solar electricity (PVs) or some other renewable energy technology. PVs and wind work particularly well together in many parts of the world.
In many locations, during the winter (actually November through March), winds blow frequently and fiercely. Because of this, wind can supply a large portion of a family’s, business’s, or farm’s electrical needs, During this time, the PV array supplements wind generated electricity. During the rest of the year, however, winds continue to blow, but they are often less frequent and milder than winter winds, However, because sunshine is now more abundant, it provides the bulk of one’s electrical power. Wind-generated electricity serves as the backup.
Although wind and solar electricity work well together and can provide nearly all of your electricity, you may still need to install a backup generator. It will supply electrical energy in periods of low wind and low sun shine, You also need to maintain batteries in peak condition, a topic discussed in Section 7.
A Final Note: DC Electricity
As in solar electric systems, wind systems can be designed so that some of the DC electricity bypasses the inverter, Thus, homes and businesses powered by wind energy can utilize DC power directly to pump water, run refrigerators, and even operate household items like ceiling fans, Homeowners can even go entirely DC, although that’s not very practical or economical for most applications.
Bypassing the inverter is an energy-saving measure, inverters require energy to convert DC current into AC current. As alluded to above, this strategy does have some downsides. It’s a topic you should thoroughly understand before designing your system.