Unpredictable returns.. of investment

We had a refreshing summer storm yesterday here at Degerö, with gust speeds exceeding 20 m/s. For our house, it meant more than 50% energy surplus as the 5 kW wind turbine generated 2.6kW in average for more than 20 hours. It’s a record this year. Peak power reached 8.2 kW after which the turbine automatically slowed down by turning away from the wind.

The turbine is not connected to the electricity grid, but charges a 235Ah / 240V battery bank which in turn runs the auxiliary power system (APS) of the house. The APS powers all equipment necessary for heating, communications and surveillance systems. During a grid interruption, APS also provides the main power.

BaseN Platform now fetches weather forecasts and opportunistically switches off the grid chargers of the battery bank when 5+ m/s has been forecasted. The battery bank is allowed to drop to 60% capacity, which has always been enough for any surplus energy.

A sad thing about this small wind turbine is that these storm days are very rare, while a windless period can last for a month. According to my calculations, the payback time for the investment is currently some 40 years, even considering the rapid increases in electricity prices. For anyone planning a small wind turbine, I would recommend a full year of accurate wind measurements in the planned location. Otherwise, given all the maintenance and planning costs, the turbine may end up being a nice landmark only.


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