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The contradictions of biomass

This week’s Sunday Times magazine featured a spread on Drax, the UK’s largest power station, which is in the process of converting a large part of its capacity from coal to biomass firing (Power Struggle). To quote from the introduction: “Britain’s most toxic power station, Drax in North Yorkshire, is going green — by burning trees ripped from the forests of Mississippi. Is this eco-madness?” Cutting through the journalistic hyperbole, this actually tackles an important issue.

With a capacity rating of just under 4GW, Drax is the largest power station in Western Europe). It plays an important role in the UK economy, contributing on average 7% of the country’s electricity. But it is forty years old and its days would appear to be numbered, as EU and UK policy pushes up the cost of burning coal. The solution from the management team has been to move towards co-firing of the boilers with biomass, mainly wood pellets.

Two out of the six boilers have been converted, and a third conversion is planned. From being labelled as ‘Britain’s worst polluter’ it has become the world’s biggest producer of ‘green’ energy. We actually need to treat these statements with caution. Carbon dioxide is not a pollutant in the true sense, and sulphur and other contaminants are scrubbed out of the flue gases, so the ‘worst polluter’ label is debatable. So also is the factoid about green energy: hydro and nuclear plants produce electricity with zero emissions, and there are some significantly larger examples of these.

But the key issue, and the one which the Sunday Times article addresses, is whether burning biomass in this way is truly environmentally friendly. The philosophy behind this co-firing project is that, although wood or other biomass release carbon dioxide when burnt, in the same way as coal or gas, that CO2 can be recaptured from the atmosphere by planting more trees. Over a period of time, the process is then approximately carbon-neutral.

The problem is that there will be a period of time over which atmospheric carbon dioxide rises in the same way as when fossil fuels are burned, so the system can only work in the longer term, and only if there is a guaranteed replanting programme. This is not going to help stabilised atmospheric carbon dioxide levels in the short term, but Dorothy Thompson, Drax chief executive, claims that, over the cycle, emissions are reduced by more than 80% compared with burning coal.

Another issue – and the reason why Drax is now burning about three shiploads of wood pellets from America every week – is that biomass is both a less concentrated source of energy than coal, gas or oil and not available in anywhere near enough amounts to fulfil the needs of even a single large power plant. Huge quantities are needed, which cannot be sourced locally. To put this in context, there is a purpose-built biomass power station near Ely (Elean). This was designed to burn primarily straw from the neighbouring area, and is rated at just 36MW. For this, 220,000 tonnes of straw are needed annually, sourced from a 60 mile radius.

Wood is a less bulky fuel, but very large quantities are needed. In 2013, the UK imported 4.5 million tonnes. Each of the Drax units needs about 2.3 million tonnes of biomass each year, with a total requirement of about 7.5 million tonnes annually in 2017, mostly in the form of wood pellets from America (although with smaller amounts of other materials sourced locally). This is a vast amount, but would still only provide less than 4% of the electricity use for just one EU Member State. The total contribution of biomass to reducing carbon dioxide emissions seems rather limited. It is also interesting to see that other large Member States do not seem to have followed Britain’s lead with any great enthusiasm.

All this begs the question: is it worth the cost? Drax is investing £700 million in this co-firing project, enough to build about 1.5GW’s worth of efficient new combined cycle gas turbine generating plant. Whereas gas generation receives no subsidy, Drax will receive an estimated £600 million a year for biomass generation, adding about £23 to each household’s electricity bill. This is not something the average consumer would be happy about, and ‘green’ power from biomass is not popular with environmentalists either. Dorothy Thompson acknowledges this but says “I am a believer in biomass, and I honestly believe we are doing the right thing. We have a big problem because it is counterintuitive. We have to make a better case, but we just haven’t found a way to sell it.”

Drax receives double the wholesale price for electricity generated from biomass. This is the price we pay for a small reduction in CO2 emissions which will only become evident once new tree growth has absorbed the emissions. But at least it produces electricity reliably; generating what the industry calls ‘despatchable’ energy. The point made by Thompson is that offshore wind farms receive double the subsidy, but their intermittency means that the cost of backup power also needs to be factored into the equation.

Depending on your point of view, the argument is either that burning biomass is an efficient and effective way to generate green electricity, or that it is a less bad alternative to other renewables. The lesson is surely that, if this is the best we can do at present, we should be putting much more effort into developing cost-effective, low carbon energy generation and storage technologies. Or, on the other hand, we could build more nuclear power stations…

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