Are the renewables “free”?

This argument is common in debates on renewable energy but is it correct? Let me start by looking at water supply. Is rainwater free? All will agree that it is – no one can charge for rain! So how come we have to pay the utility companies for delivering drinking water to our taps? Well, there are costs involved – dams, pumps, filter stations, chlorination plants, maintenance of water pipes, reading the meters etc. Although rainwater is “free”, water supplied to our tap is not and no one seems to have a problem with it. Well – sun, wind and tides are similarly “free” but the power which can be extracted from them is not. It is in fact expensive. Very expensive.

The technical and logistical complexities associated with harnessing “free” energy are numerous but I will only deal with one issue which, by itself, is enough to challenge the idea that we can all go alternative. Energy storage. To put it simply we do not have the technology to store power in quantities significant for national grids. The available systems are either orders of magnitude too small or similarly too expensive. It is not a matter of making the technology we have got 10, 20 or even 100% more efficient – we would need to make it 100 times more efficient.

The power storage systems which have been used are:

  • Pumped storage. Expensive and limited by the availability of suitable sites. Major environmental impact. Hydro used as storage is viable but has similar siting and environmental issues.
  • Compressed air. Expensive plus major problems with the availability of suitable underground chambers. Issues with the heat required to be supplied during de-compression.
  • Thermal storage (molten salts). Insanely expensive.

The problem is ensuring uninterrupted power supply. Solar, wind and tidal are all intermittent. In the absence of viable energy storage systems they have to be supplemented by other means of generation available on demand. This means hydro, oil, coal or nuclear. When, at the same time, a/ wind does not blow b/ there is no sunlight and c/ tide is turning, the stand-by capacity required to fill in the supply gap must be equal to the “renewable” capacity installed. This means building, commissioning and maintaining fully staffed conventional power stations and… not using them much of the time! I am not sure that all advocates of the on-grid renewable generation realise that.

It is generally accepted that modern national grids can accommodate up to 5-7% ratio of the intermittent renewable generation. I imagine this means driving conventional power stations at 105% of capacity for short periods and occasionally switching off power hungry users like smelteries. Of course the power generation gear driven outside specs wears out faster and if we had to regularly black out smelteries we would need to build more of them so running national grid this way is problematic.

An interesting case study is Denmark which is running 16% on wind generation – how can they do it?

http://incoteco.com/upload/CIEN.158.2.66.pdf

As you will see from the linked article there is no miracle. Being a small player Denmark uses hydro in Norway and nuclear in Germany as power sinks. So, essentially, Denmark’s 16% wind generation is a very small fraction of an integrated trans-national grid which balances the supply. If Sweden, Norway and Germany all wanted to have 16% wind generation they would need to start thinking about back-ups for periods of no wind. There are other interesting bits in the article, for example why the load factor of wind farms has been in steady decline lately.

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