Is there an optimum level for renewable energy?

Because continued heavy use of fossil fuel will lead to both global climate change and resource depletion of easily accessible fuels, many researchers advocate a rapid transition to renewable energy (RE) sources. In this paper we examine whether RE can provide anywhere near the levels of primary energy forecast by various official organisations in a business-as-usual world. We find that the energy costs of energy will rise in a non-linear manner as total annual primary RE output increases. In addition, increasing levels of RE will lead to increasing levels of ecosystem maintenance energy costs per unit of primary energy output. The result is that there is an optimum level of primary energy output, in the sense that the sustainable level of energy available to the economy is maximised at that level. We further argue that this optimum occurs at levels well below the energy consumption forecasts for a few decades hence.

► We need to shift to renewable energy for climate change and fuel depletion reasons. ► We examine whether renewable energy can provide the primary energy levels forecast. ► The energy costs of energy rise non-linearly with renewable energy output. ► There is thus an optimum level of primary energy output. ► This optimum occurs at levels well below future official energy use forecasts.