Saturday, September 4, 2010

Will the Adoption of Solid State Lighting Lead to an Increase in Energy Use?

The Economist discusses an article in Journal of Physics D: Applied Physics by Tsao et al. on the effects on energy use of the adoption of solid state (i.e. LED) lighting (SSL) on global energy use. The Economist argues that it would be better to keep incandescent bulbs as a result. This seems a bit crazy. The literature on the rebound effect suggests that for energy saving innovations for consumers in developing countries the rebound effect is typically of the order of 30%. In other words, the net energy savings are around 70% of the amount of energy nominally saved by the innovation. Joshua Gans comments on this article taking a direction inspired by the Schumpetarian endogeneous growth literature where new innovations are sold by monopolist innovators.

To understand why the authors posit such a large rebound effect I took a look at the original article. The first key leg of their model is the following relationship between historical data on lighting use and a very simple model:

Most of the early data relies on the work of Fouquet and Pearson. The model treats light consumption as a function of two variables: GDP and cost of lighting. The elasticity of demand with respect to the cost of lighting is minus one and the income elasticity is plus one. Based on this data the model looks pretty plausible. It would be nice though to see this data in per capita terms or to see lighting intensity of GDP plotted against cost of lighting to get a better idea of how robust it is. The way in which the cost of lighting is computed will be very critical too. I'll look at that in a subsequent blogpost.

If the demand elasticity is minus one then any reductions in the cost of lighting will be exactly offset by increases in consumption of lighting services. Both these elasticities seem high in absolute value for developed economies. So it would be nice to at least test a model which allows the elasticities to vary with income level vs. a model which does not if you are going to make big predictions about the future.

Solid state lighting will certainly reduce energy costs of lighting but this is achieved partly by substituting capital for energy. At the moment, LED lights are expensive. This means that the cost of lighting is reduced by less than the energy use is reduced by the innovation currently. Therefore, even if the price elasticity of demand was minus one, adoption of solid state lighting would reduce energy use (ignoring indirect energy costs of capital). The authors argue of course that these costs will reduce rapidly. Historically, they argue that capital costs are typically 1/3 of energy costs of lighting. They assume that by 2030 the capital costs of SSL will be the same so that there is no capital-energy substitution in the adoption of SSL.

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