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How does a small wind turbine make sense?
A my!WIND supplies in order to cover own demand.
This will work for different applications:
a) On-grid power generation
The small wind turbine will be connected to the residential grid. An inverter converts electricity that is supplied by the wind turbine into constant grid frequency (e.g. 50 Hertz). Generated wind power can be consumed right away and thereby substitutes electricty from the local electric utility. If the wind turbine generates more power than is consumed by the household, then the surplus will be fed into the grid - i.e. bought back from the utility.
b) Power generation for charging batteries
Electricty from the wind turbine will be rectified into direct current in order to supply energy to device charging batteries. These can be used as buffer, e.g. in order to allow constant electricity consumption despite varying wind conditions at a cottage that is not connected to the grid.
c) Wind power for heating
Varying power supplied by the wind turbine can be used for water heating. A heating rod can be inserted into an existing or a new boiler and rise the temperature of water that can be used for heating.
How much power does a my!WIND produce?
The precise number of kilowatt-hours (kWh) very much depends on the individual site. Large wind farms usually achieve capacity factors of around 30%, which small wind turbines can reach very rarely at exceptional spots due to the low mast height. The simple formula below will show the situation:
5 Kilowatt (kW) - (maximum) Rated power of the wind turbine
8760 hours - the number of hours of a standard year (365 days x 24 hours)
8760 hours  x  5 Kilowatt  x  Capacity Factor (%)  =  Kilowatt-hours per average year
It all depends on the capacity factor!
Excellent sites very close to the Northern Sea coast, such as in Northern Germany, can deliver capacity factors of 20% on 10 metres masts. However, for most sites lower values will occur; there may be 8 to 15 percent - objects like local buildings and vegetation will play an enormous role. Accordingly, numbers below are just giving an orientation:
Scenario A)  5 kW x 8760 hours x 15% = 6750 kWh
Scenario B)  5 kW x 8760 hours x   8% = 3504 kWh
If all power from these two examples were be consumed by the turbine owner, then it would substitute electricity from the grid. With a power tariff of e.g. 20 EUR-cent per kWh, scenario A would result in a value of 1,350 EUR, respectively 701 EUR for scenario B. These amounts would vary around average from year to year (less in coastal and more at inland sites).
An own wind turbine pays itself off through saving power from the grid. As soon as investment costs have been earned back the turbines supplies electricity almost for free.
What costs are involved?
"Wind and sunlight are for free" - of course a naive fallacy!
Wind turbine generators do not need fossil or nuclear fuels such as conventional thermal power plants; however, investment in equipment is required to convert energy into electricity. If distributing these costs over a turbine's life time and adding operational expenses, then each kilowatt-hour's costs can be derived. Eventually there will be interest payments, if debt finance is involved. Wind turbine generators are commonly designed for 20 years life expectancy.
Equipment cost (for on-grid operation)
•  5 kW wind turbine incl. 10 metre mast
•  Power inverter and extras
•  Delivery, erection, foundation
•  Various (for permitting, extras)
Value-added-tax (VAT) has to be added. In case of turnover from sales (feeding power into the grid), it will be deducted from sales VAT.
Operation costs
•  Grease bearings (every 2-3 years, 250-350 EUR for work and travel costs of a local service provider)
•  Insurance (if preferred by owner; replacement components typically cost several hundred EUR)
my!WIND OÜ  ·  Soola 1a  ·  EST - 51013 Tartu, Estonia  ·  Email:  ·  Register No 12013166