I received a post today asking why I thought that renewable energy could only ever account for about 20% of our total requirements. Surely if we cut our total energy use that proportion could be greater? I also said that microgeneration could actually increae co2 emissions. Why?
Here's my answer:
"I suggest you read "Energy beyond oil" by Paul Mobbs which is an excellent review of our energy options - and challenges. It explains all the technical issues in detail but in a very readable form.
Yes, I agree we can go a long way towards reducing our energy demand, but in spite of those people who are already cutting down, UK energy demand continues to grow. We will have to make life-changing decisions to really have an effect. The problem with renewables - wind, wave, tide and solar - is that they are intermittent and cannot be controlled to match the fluctuating demand from the grid. Indeed, if they account for a major proportion of electricity production they provide great difficulties for the grid controllers who have to deal not only with fluctuating demand but fluctuating supply as well. If they can't balance supply and demand the risk is that the grid becomes unstable with cascading failures and power cuts. Biomass and biogas are renewables which can provide power 24/7 and are controllable, but the problem here is that growing biofuel crops competes for land where food is grown (or in some cases where rain forest grows) and the planting, harvesting, processing and transporting of biofuel all takes energy so biofuel is not carbon neutral and some studies have suggested that the process absorbs more energy than it yields.
Microgeneration? Microgeneration of electricity comes from wind or solar. Micro-hydro is possible, but very, very few people will have a suitable water source. In all cases we must look at the total life cycle, which includes the energy used and CO2 emitted in the manufacture, installation and disposal of the turbine or solar panel. Unless the unit saves more CO2 during its useful life than is emitted at these stages, it is actually contributing to CO2, not saving it. A wind turbine needs a steady flow at about 10-12 metres per second. If you go to the DTI wind speed database you will find the average speed for your postcode. The average is only about 6mps. A turbine running at 6mps produces a lot less than half the electricity of a unit at 12mps - it is not a simple straight-line relationship. The other problem - which rules turbines out for most urban locations - is turbulence. Trees, roofs, chimneys and lamposts all cause turbulence which means the airflow - and direction - is constantly changing. The turbine may overspeed, which will damage it, or run too slowly to produce any power. If it is swinging backwards and forwards in the gusts it will not produce a useful output. Once you have the electricity you either have to convert it to ac and transform it to mains voltage (a process absorbing energy) or use it to charge a battery. In the second case you have the additional cost of the battery and of your low-voltage dc lighting circuit or whatever you are using, together with the CO2 emissions involved in manufacturing this kit. In the first case you can sell electricity back to the grid if you aren't using it, but the bit left after transformation and rectification will be subject to further losses in the grid and you will be paid only 4p per unit compared with the 10 or 15p it will cost you to buy it back.
Solar panels have the same problems of rectification and transformation if you go for mains voltage and the same extra costs of batteries etc if you go for low voltage dc. I believe the disposal of solar panels is problematical because of the heavy metals and rare elements they contain. In fact the increasing scarcity of such substances will probably severely limit the availability of solar panels.
Sorry this is such a long answer. Hope it makes sense!"
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