Determining the right size wind turbine to power a house depends on several factors, including the average energy usage of the home, the wind speeds in the area, and the size of the turbine blades. In general, a residential wind turbine needs to be quite large in order to generate enough electricity to power a home fully. Small turbines can provide supplemental power, but a minimum 10-15 kW turbine is usually required to meet all of a home’s energy needs.
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Average household energy usage
The average American household uses about 10,600 kWh of electricity per year. This can vary considerably based on the size of the home, number of residents, appliances used, and energy efficiency measures in place. Larger homes or homes with many people will use more energy, while smaller, energy efficient homes will use less. Knowing your own home’s energy profile is important for determining what size wind turbine you need.
Here are some approximate electricity usage figures for common household items:
| Appliance | Average kWh per year |
|---|---|
| Refrigerator | 700 |
| Clothes washer | 100 |
| Clothes dryer | 670 |
| Dishwasher | 300 |
| Air conditioner (window unit) | 500 |
| LED light bulb | 10 |
| Incandescent light bulb | 60 |
| Computer and monitor | 270 |
| Television | 180 |
Adding up the usage of all your appliances and devices will give you an idea of your home’s total energy needs. This determines the minimum size wind turbine you’ll need in order to replace your grid electricity usage entirely.
Average wind speeds
The wind speeds in your area are a major factor in wind turbine output. Turbines need wind of at least 7-8 mph to start generating electricity, with output increasing significantly at higher wind speeds:
| Wind Speed | Power Output |
|---|---|
| 7-8 mph | Minimum needed for turbine operation |
| 9-12 mph | Moderate output |
| 13-17 mph | Rated output |
| 18-24 mph | Maximum output |
| 25+ mph | Shut down to avoid damage |
Check the wind speeds in your area to determine the potential power generation. Coastal areas, mountaintops, and plains tend to be windier, while sheltered valleys and dense urban areas have lower wind speeds. A minimum average wind speed of 10 mph or greater is recommended for residential turbines.
Size of the turbine
The physical size of the wind turbine, including the length of the blades, has a direct impact on power output. Longer blades can harvest more wind energy. Most residential turbines have rotor diameters of 10-25 feet. The larger the rotor, the more electricity the turbine can generate:
| Rotor Diameter | Output |
|---|---|
| 10 feet | 2-3 kW |
| 15 feet | 5-10 kW |
| 18 feet | 10-15 kW |
| 21 feet | 15-20 kW |
| 25 feet | 20-30 kW |
Most homes require a minimum 10-15 kW turbine to meet their total electricity usage. This usually corresponds to an 18-21 foot diameter rotor.
Number of turbines
Sometimes multiple smaller wind turbines are used together instead of one large one. For example, three 5 kW turbines could be installed to provide 15 kW total output. There are a few reasons this might be done:
- Allows installation in smaller spaces: Multiple small turbines can fit on the site when one large one won’t.
- Redundancy for greater reliability: With multiple turbines, the system can still generate some power if one turbine fails.
- Lower initial cost: Smaller turbines are less expensive individually.
The downside is that installing multiple wind turbines adds to the construction and maintenance costs for the system. So in most cases, opting for a single larger turbine is more economical if there is sufficient space available.
Tower height
The height of the wind turbine tower also affects output. Taller towers allow access to stronger and steadier winds, resulting in greater power generation. Most residential turbines are mounted on towers 80-120 feet high. The turbine should be installed at a height at least 30 feet above any obstacles within 500 feet to avoid turbulence.
Batteries for wind energy storage
Wind power output fluctuates based on the wind speeds at any given time. Adding battery storage helps capture excess electricity when wind speeds are high for later use when the wind is lower. This also provides backup power in the event of a grid outage. Most residential systems utilize lead-acid batteries for energy storage. The size and number of batteries should be sufficient to store enough excess power to get through wind lulls.
Connecting to the grid
Most residential wind turbines are connected to the utility grid in addition to powering the home. This allows any excess power generated to be fed back to the grid, credited by the utility company. During periods of low wind when the turbine output is low, the home can draw electricity from the grid. This eliminates the need for oversized batteries to store large amounts of excess power. A grid-connected system only needs enough battery capacity to cover critical backup loads in the event of an outage.
Inverter
Wind turbines produce direct current (DC) electricity. This must be converted to alternating current (AC) for use in a residential electrical system. An inverter performs this conversion and allows the system to seamlessly power household electronics and devices. Most turbine manufacturers provide inverters matched for use with their systems.
Conclusion
Installing a residential wind turbine is a significant project that requires careful planning and consideration of many factors. The location’s wind resource, average household energy consumption, turbine size, tower height, batteries, and grid interconnection all play key roles in determining how big of a wind turbine you need to power a house. In most cases, you will need a minimum 10-15 kW turbine with an 18-21 foot rotor mounted on an 80-120 foot tower. Multiple smaller turbines or larger turbines can also be installed depending on energy needs and site constraints. Consulting with a qualified wind energy expert is highly recommended for selecting the appropriately sized system.
Some key considerations when determining wind turbine size for a residential application include:
- Average annual household electricity usage
- Average wind speeds in the area
- Rotor swept area and rated power output
- Option of installing multiple smaller turbines
- Sufficient tower height for stability and wind access
- Energy storage capacity with batteries
- Ability to connect to the utility grid
- Getting help from a professional installer
With careful planning and sizing, a home wind turbine can provide clean, renewable electricity and energy independence for residential customers.