Optimal Small
Wind Turbine Size

The optimal Wind Turbine Size

The starting point for sizing correctly the small wind turbine is the actual household average electricity consumption. By average I mean:

• One year average for on grid connected home
• Typical day average plus a safety margin for off-grid home

The backup for on grid connected home is the utility; the backup for the off-grid wind turbine are the storage batteries (you might install an off-grid solar system as a backup or use a silent diesel generator for backing up the wind turbine)

For on grid connected home, calculate the average day consumption (consumption over one year divided by 360); On your electricity bill you can view the $$ and the KW-Hour. Now you know how much energy in KW-Hour you need for one day. On the wind turbine spec you can see what the expected energy production of a specific turbine per day is (actually the spec is for one year, so divide it by 360 to see what is it for one day)

With same reasoning, you can calculate the right size for your off-grid wind turbine; since you don't receive electricity bills you can use a home energy monitor to know your consumption.

One big difference though. For off-grid homes, if the wind turbine is your only power source you must install the calculated size.
For on grid homes, you can install a smaller wind turbine if you hit a size limit, weight limit or a budget limit (e.g. 10%, 50%, 70% of your consumption); The utility is always there to provide the balance and it is always there to buy the surplus

Off-grid Wind Turbine System

Most off-grid homes don't have size or weight limitation and they sit on a big enough piece of land. A new connection to the nearest power line is expensive ($15,000 to $50,000 per mile); therefore some sort of power generator is necessary. The alternatives are a silent diesel generator, a solar power generator or a small wind turbine system. (or a combination of these generators).
Typically, the capital investment in a wind turbine is much less than the investment in solar panels with the same power capability; however, a prerequisite is that there are enough hours of wind with velocity above the minimum velocity threshold. Land size must be at least 1 acre.

On grid Wind Turbine System

Most on grid connected homes are sitting on a relatively small piece of land and adding a wind turbine tower is not feasible. The only real option is to install a roof mounted wind turbine, a controversial solution. The maximum size you can think about is around 1000 Watts. A turbine that is rated as a 1000 Watts turbine, its weight is 25 Kg (50 lbs), its diameter (speaking about HAWT – Horizontal Axis Wind Turbine) is 1.75 meter (5.8 feet) and under "normal wind profile" (whatever it means) it will produce 1,100 KWh over one year (91 KW-Hour over one month). 91 KW-Hour is a small fraction of a US household electricity consumption, only 30% of a typical German home or a typical UK home.
VAWT (Vertical Axis Wind Turbine) is claimed to be better for roof mounted situations

The Projected Cost and Life Span

The cost of the turbine itself (not including a mast, inverter, batteries, charge controller) can run between $1.5/Watt to $2/Watt. A complete kit, including wind turbine tower, inverter, batteries charge controller and installation can reach $4 to $6 per watt. Turbine life can reach 20 years with good care, maintenance and insurance cost is higher compared to the maintenance cost of a comparable size solar power generator