Rebound Effect

(N.B. Obviously there is the excellent UKERC report on the rebound effect but don't tell anyone that I actually haven't read it fully, so I might just be repeating what they've said.)

While looking at MacKay's book, one point of discussion that came up was what would be the level of demand in the future. MacKay considered efficiency improvements in electrifying transport and heating, as well as having no electricity conversion losses, bringing demand from 125kWh per day per person down to 68.

Certainly this is possible, however we all know that improvements in energy efficiency can be cancelled out to some degree by increases in energy usage (the rebound effect). So I was thinking whether this would mean 68kWh/d/p is realistically possible and to what extent the rebound effect might reach.

Considering the direct rebound effect (e.g. engine efficiency improvements lead to driving more), I wonder if there are limits to it. For example:

• Insulating your house means you use and spend less on keeping your home warm. However if your home is already at 20 degrees before insulation you're not going to want more heat, so the rebound effect would be small (e.g. only from those in fuel poverty, who don't already have their homes at a comfortable temperature).
  
• Using electric cars rather than internal combustion may bring large energy savings. Although more people would be able to commute further or go on leisure trips more often, there is a limit to how much more driving people need, want or can do. People would obviously tire of 3 hour commutes, have only so much free time for other activities such as shopping and the average occupancy can only drop from 1.6 to 1.
  
• More efficient light bulbs means using and spending less on lighting. There is a limit to how much more lighting someone could want (lighting on all day in every room) and as most people don't currently go around in darkness, the rebound effect would probably also be quite small.
• and so on.

UKERC does estimate that these direct rebound effects might reach only 10-30% so obviously the question shifts to indirect rebound effects (e.g. money saved from fuel costs goes on a transatlantic flight).

Indirect rebound effects are harder to predict because of the multitude of economy-wide effects on different levels, so I'll just say to go read the UKERC report, and that they estimate it can often be over 50% of the reduction or even greater than 100%.

So this suggests that - in a developed country - reductions of energy use in the major categories: transport (domestic at least) and heating, could well reach the estimate of MacKay. However economic growth and the indirect rebound effect could see other sectors, I'd guess most likely electrical goods, would struggle and may well increase.

Considering that energy use (globally or otherwise) has only fallen noticably during recessions (and then by only a few percent) it does seem difficult to see a self-imposed drop from 125kWh/d/p to 100 let alone 68.

Although never say never.

And in the beginning...

Hello, my name is Paul Robins and I'm currently studying a masters in Energy Policy and Sustainability at the University of Exeter. This blog is for my thoughts and feelings about the energy world and its place in society. So first blog and I guess it should be a 'why'.

Energy is fundamentally crucial to humans because (in a rather dry physics definition) energy is required to do work. Whether heating your house, powering a computer or driving your car, you require energy in some form or another. The source of all our energy is ultimately from three resources, the Sun (by far the majority), the heat created by radioactive decay deep inside the Earth (a small bit) and the tides caused by the gravitational pull of the moon (a very small bit). Arguably all of them are finite but although they may last for billions of years, the important factor for us is the finite amount of energy they supply each year,day or second. The amount of work or stuff we can do, from growing crops to generating electricity, is ultimately capped based on this amount.

Current world demand is around 16TW (tera = 10^12) while the amount of sunlight falling on the Earth is around 174PW (peta = 10^15) so it would seem our demands are four orders of magnitude less, i.e. tiny (and that doesn't include fossil fuel reserves or uranium). However it is not as simple as that. Firstly, only around half of the sun's energy reaches the surface, only around a third of which will be over land, a fraction of which is accessible, suitable or near areas of consumption and not to forget plants taking their share of the sunlight. So a rough guess (no figures, just guesstimation) is that about 1% of that energy is capturable for human use, so from being 10,000 times world demand it's now 100 times. That means current demand is 1% of renewables potential and that is a lot less wiggle room than before.

On the consumption side of things, while energy intensity and resource productivity continue to improve, worldwide demand for energy continues to increase as developing countries look to lift many of their citizens from poverty and developed ones to further their prosperity. Population has grown even greater than exponentially over the last 50 years and while this increase is predicted to slow to a maximum of around 9 billion people, there is no certainty that an unforeseen technological invention wont permit an even higher number.

Economic growth is arguably the greater factor in energy consumption, rising 3.8% annually compared to 1.2% for population and shows little sign of slowing or reaching a limit. If this 3.8% growth continued, after around 125 years our demand would breach that estimated renewables limit (fossil fuels are likely to have essentially been exhausted). Using that much energy might appear huge, but imagine 125 years ago when there were almost no cars, electricity grids were in their infancy, aeroplanes didn't exist, nor did televisions or computers and being warm in your house often meant another layer of clothes. 125 years also might appear to be a long time for a single person but it's a relatively short space of time in human society.

But yet again it's not as simple as that, look at this graph below, you can see the approximate exponential growth starting on the left hand side but which tapers off after time. Now cover the right side of the graph and imagine that you are making a prediction while you are some point in time while the graph is still exponential, it seems obvious that the growth will continue when it every situation it will eventually reach a tipping point and start to slow down whether it's population, food yield or percentage of everyone with a mobile phone/car/computer etc. Will we reach technological/financial/social/environmental limits before physical ones in that hypothetical 125 years?




The point here is that very few things, especially energy policy, are simple and easy. One of the first and most important considerations about energy policy is understanding how widespread and complex it can be because of its fundamental role in nature and human society.