How to cut global energy use by three quarters

It will probably be difficult to replace all fossil fuels with sustainable energy. But if we first cut energy demand it will be much easier – and the potential for energy efficiency is huge!

The world could cut energy use by 73 per cent according to a Cambridge team. They claim this is achievable with proven technology, such as better insulation, lightweight cars and using a lid when cooking.

It’s the physics, stupid.

At least you have to start with the physics, because if physics and economics collide, physics will prevail.

While most people agree in principle that energy conservation makes more sense than building new power stations, the influence of neoclassical economists has usually stopped serious conservation effort. The basic economic notions are that a) the present system is in economic balance, i.e. optimised b) that people always makes rational choices and c) that all the choices can be squeezed into one, monetary, dimension.

All empirical evidence shows this to be wrong, but it still represents the conventional wisdom.

If you accept it, the only way to cut energy use is to increase prices, which is political suicide.

The actual success stories of energy conservation, such as the EU ban on incandescent lamps or previous US legislation on car fuel consumption have been achieved by non-economic thinking, though in effect saving a lot of money.

The physical view is taken by a new report “Reducing energy demand: what are the practical limits?”.1

A physical model calculates theoretical efficiency limits based on engineering principles.

The Cambridge team notes the inefficiency of energy conversion devices. If you use coal to produce power and use the power in an oversized motor for an oversized fan, the total efficiency can be ridiculously low.

But their focus is on passive systems. The final energy, as heat, cooling, light or motion, tends to dissipate, but there is great potential to keep it a while longer, so less energy input is needed. Don’t build a new heating system; concentrate on stopping the heat from escaping.

Designing all buildings to Passivhaus standard (see Wikipedia) can save 83 per cent of present energy use for heating, or 179 exajoules (EJ) or 50,000 TWh.

Illuminated space can, they claim, save 95 per cent of energy input. How? Much of it through directing light to where it is needed and wanted, for example to the office desk rather than the office floor. Inferior luminaires steal much of the light instead of sending it to where it is wanted. More losses result from dirty lamps and luminaires. Lighting levels are also often unnecessarily high, to cover future degradation. And cleaner or whiter roofs and walls can cut losses even more. Such detailed information can be found in supporting information, to be retrieved for free here.

Industrial furnaces can, by using better insulation and heat recovery, save 62 per cent of present energy use or 42 EJ.

Industrial drive systems (pumps, fans, refrigeration etc.) can save 59 per cent of energy by using larger diameter tubing and other simple measures.

Cars could save 91 per cent of the 40 EJ they now consume. The passive system here is the motion, which is attacked by air drag, rolling resistance, and braking. As the greatest saving potential is in urban driving – 96 per cent – compared to the more modest 87 per cent in highway driving, one of the most important measures is to cut weight. Based on calculations for Rocky Mountain Institute’s ‘2000 Revolution Hypercar’ they conclude that a 200 kg car would be practical and meet safety requirements. Other contributions come from tyres now on the market and from using an aerodynamic shape, not quite the ideal teardrop shape but halfway there.

Heat losses from cooking are reduced 80 per cent by putting a lid on the boiling pan.

Insulation of cookers and fridges can save a total of 67 per cent from appliances.

The 73-per-cent overall saving would obviously take time to achieve, but on the other hand improvements in conversion efficiency would add to the potential, such as improved light sources compared to business as usual. The total saving, without substantial life style changes, is 85 per cent.

Can we substitute all fossils for renewables? If it looks difficult, subtract 73-85 per cent first!

Unfortunately that is not the politicians’ view. The EU Commission is pouring money into fusion, CCS and gas pipelines, with just a trickle for wind and solar, but the mandatory efficiency target for 2020 is getting nowhere.

Fredrik Lundberg

1 By Cullen, Allwood, and Borgstein of the Department of Engineering, University of Cambridge in Env Sc&Tech 12 Jan 2011.

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