Energy Payback & Return on Energy
Energy Payback
The energy balance of a wind power plant shows the relationship between the energy requirement over the whole life cycle of the power plant (i.e. to manufacture, operate, service and dispose) versus the energy generated by the wind power plant. This energy payback period is measured in ‘months to achieve payback’, where the energy requirement for the life cycle of the power plant equals the energy it has produced. At this ‘breakeven’ point, our wind turbines become energy neutral.
In high winds, our V117-4.2 MW turbine is energy-neutral within 4.8 months. In medium winds, our V136-4.2 MW turbine hits this breakeven period within 6.1 months and in low winds, the V150-4.2 MW turbine will hit energy neutrality within 7.6 months. As this graph illustrates, a Vestas wind turbine (V117-4.2 MW, 136-4.2 MW, V150-4.2 MW) pays back more energy than it uses after 5 to 8 months. Oil and coal, however, consume more energy than they generate and supply to the grid and never amortise.
Return on Energy
Alternatively, energy payback may be measured by ‘number of times payback’ – meaning, the amount of energy paid back to society versus the energy needed in the lifetime of that turbine. Over the life cycle of a V117-4.2 MW wind power plant, it will return 50 times more energy back to society than it consumed.
That means that when 1 kWh is invested in a wind energy solution, you get 50 kWh in return. For coal, however, if you invest 1kWh you typically get below 0.4 kWh in return.