Use the Sum of the units of production method to calculate the depreciation expense after 1 year.

Your local government invests into a new wind turbine that costs $4 million with a capacity of 3 MW. The turbine can produce up to 6 million kWh in a year. Over its lifespan of 25 years, it is estimated to produce a total 140 million kWh in energy. Assume the windfarm’s salvageable parts have a residual value of $100,000 based on future steel and copper prices.

The units of production (depreciation) rate is (4 million – 100,000)/140 million kWh = $27,857 per million kWh. 

In the first year, the farm produces 5 million kWh.

What's its depreciation expense?