A grid-connected wind turbine can reduce your consumption of utility-supplied electricity for lighting, appliances, and electric heat. If the turbine cannot deliver the amount of energy you need, the utility makes up the difference. When the wind system produces more electricity than the household requires, the excess is sent or sold to the utility. With this type of grid-connection, note that the wind turbine will operate only when the utility grid is available. During power outages, the wind turbine is required to shut down due to safety concerns.

Grid-connected systems can be practical if the following conditions exist:

• You live in an area with average annual wind speed of at least 10 miles per hour (4.5 m/s).

• Utility-supplied electricity is expensive in your area (about 10–15 cents per kilowatt-hour).

• The utility's requirements for connecting your system to its grid are not prohibitively expensive.

• There are good incentives for the sale of excess electricity or for the purchase of wind turbines

Federal regulations (specifically, the Public Utility Regulatory Policies Act of 1978, or PURPA) require utilities to connect with and purchase power from small wind energy systems. However, you should contact your utility before connecting to its distribution lines to address any power quality and safety concerns. Your utility can provide you with a list of requirements for connecting your system to the grid.

Connecting Your System to the Electricity Grid
While renewable energy systems are capable of powering houses and small businesses without any connection to the electricity grid, many people prefer the advantages that grid-connection offers.
A grid-connected system allows you to power your home or small business with renewable energy during those periods (diurnal as well as seasonal) when the sun is shining, the water is running, or the wind is blowing. Any excess electricity you produce is fed back into the grid. When renewable resources are unavailable, electricity from the grid supplies your needs, thus eliminating the expense of electricity storage devices like batteries.
In addition, power providers (i.e. electric utilities) in most states now allow net metering, an arrangement where the excess electricity generated by grid-connected renewable energy systems "turns back" your electricity meter as it is fed back into the grid. Thus, if you use more electricity than your system feeds into the grid during a given month, you pay your power provider only for the difference between what you used and what you produced.
Aside from the major small renewable energy system components, you will need to purchase some additional equipment (called "balance-of-system") in order to safely transmit electricity to your loads and comply with your power provider's grid-connection requirements. You may need the following items:

Power Conditioning Equipment for Grid-Connected Systems
Most electrical appliances and equipment in the United States run on alternating current (AC) electricity, which is also referred to as single-phase, 120-volt AC service in homes, offices and some manufacturing facilities.
The value of AC voltage is continually changing from zero up to the positive peak, through zero to the negative peak and back to zero again

Many available renewable energy technologies, such as wind and photovoltaic (PV), produce direct current (DC) electricity. To run many standard AC appliances, the DC electricity must first be converted to AC electricity using inverters and related equipment.

Inverters condition electricity so that it matches the requirements of the load.
When you size your inverter, be sure to plan for any future additional loads you might have. In the case of a grid-tied system in which you want to enlarge your renewable energy system, it is often cheaper to purchase an inverter with a larger input and output rating than you currently need than to replace it with a larger one later. Please note you cannot just replace an inverter with a larger unit later on. You would need to change wiring, disconnects, fuses, and other aspects of the system, which can be a difficult situation.

Safety Equipment for Grid-Connected Systems
Safety features protect grid-connected small renewable energy systems from being damaged or harming people. Here are the major safety features your system will need:

• Safety disconnects

Automatic and manual safety disconnects protect the wiring and components of your small renewable-energy system from power surges and other equipment malfunctions. They also ensure that your system can be shut down safely for maintenance and repair. In the case of grid-connected systems, safety disconnects ensure that your generating equipment is isolated from the grid, which is important for the safety of people working on the grid transmission and distribution systems.

• Grounding equipment

This equipment provides a well-defined, low-resistance path from your system to the ground to protect your system against current surges from lightning strikes or equipment malfunctions. You will want to ground both your wind turbine or photovoltaic unit itself and your balance-of-system equipment. Be sure to include any exposed metal (such as equipment boxes) that might be touched by you or a service provider.

• Surge protection

These devices also help protect your system in the event that it, or nearby power lines (in the case of grid-connected systems), are struck by lightning.

Meters and Instrumentation for Grid-Connected Systems
Meters and other instruments allow you to monitor your small renewable energy system's battery voltage, the amount of power you are consuming, and the level at which your batteries are charged, for example.

If you are connecting your system to the electricity grid, you will need meters to keep track of the electricity your system produces and the electricity you use from the grid. Some power providers will allow you to use a single meter to record the excess electricity your system feeds back into the grid (the meter spins forward when you are drawing electricity, and backward when your system is producing it).

Power providers that don't allow such a net metering arrangement require that you install a second meter to measure the electricity your system feeds into the grid.

Because grid-connection requirements vary, you or your system supplier/installer should contact your power provider to learn about its specific grid-connection requirements before purchasing any part of your renewable energy system.

Information source; U.S. Department of Energy Wind Energy Program