Tuesday, November 18, 2008

wood you believe it?

Turning waste into fuel. It's so appealing that we always want to believe it can solve everything. But we should let the lessons of biofuel for cars be a warning.

Craig White of wood industry lobby body Wood For Gold cites the government's target of generating 20% of our electricity from renewables by 2020 and says

the government is assuming that 50% of that 20% target will be provided by biomass.

So, that means biomass will provide 10% of our electricity.

White further reckons

the UK needs only about 2.7m tonnes a year of wood to meet the biomass 2020 target.


Drax in North Yorkshire is the UK's largest coal-fired power station, supplying 7% of our electricity. They've been 10% 'co-firing'- replacing 10% of their coal with wood in order to reduce carbon emissions - for several years.

Whatever the cyber equivalent of the back of an envelope is, let's get one for a quick calculation.

Drax burns around 10 million tonnes of coal a year(1).

Drax estimate that it takes 1.5 times the amount of biomass to replace a given weight of coal(2), so 1.5 million tonnes of biomass is required to generate 10% of their output.

As they're 7% of the UK's electricity, the biomass accounts for 0.7%.

By this calculation, Craig White's 2.7m tonnes wouldn't generate 10% of our electricity, it would actually be 1.26%.

This could be improved. Drax is an old fashioned, big, cooling-towers power station. The design is hugely inefficient, wasting about 62% of the energy as heat up the chimneys. In other words - and this is something to bear in mind as the government leans towards building a new generation of these things - around two thirds of the coal we dig and the emissions it releases are for nothing.

We could build small localised power stations, Combined Heat and Power (CHP) systems that capture and use the heat. Even this threefold increase in power production wouldn't yield anything like the 10% White talks about.

Also, as CHP would be heating water and space, it would be much more likely to be replacing gas than electricity. That's clearly a very a good thing, but has nothing to do with the renewable electricity target.

To meet White's aim of 10% of the UK's electricity from biomass, by the figures from Drax's real-world test we'd need over 21 million tonnes a year.

White says

Of an estimated 7.5m tonnes of domestic wood waste, much from construction and demolition, some 80% goes to landfill.

So if we were to take the 20% that's being usefully reused (which may have the knock on effect of causing more virgin wood to be bought) and commit all our waste wood to biomass in co-firing with coal, we could generate 3.5% of the UK's electricity.

This is well worth doing (it's very easy for coal-fired power stations to burn wood, although Drax required a consistency of size of wood that waste couldn't provide). But if we are to move to a sustainable society we cannot install systems that are dependent on us generating a high volume of waste.

Even with present levels of waste, to hit White's aim of 10%, we'd need to be growing wood specially. This means that virgin land becomes plantation, or else existing farmland is taken over (with a knock-on effect that people still need to get the food that would have been grown there, so somewhere else virgin land becomes farmland).

How much land are we talking about? Pass me that envelope again, would you?

The willow grown for Drax’s trial yielded just under 10 tonnes per hectare(3), meaning 150,000 hectares was needed.

Grown on three year rotation (the fastest possible) means 450,000 hectares is required to supply Drax with the biomass to generate 0.7% of the UK's electricity.

So to supply 10% would require around 6.5m hectares, or 65,000 square kilometres. The UK's land mass is 241,590 sq km.

On this basis, we'd need over a quarter of the UK planted with willow to supply 10% of our electricity. As we're somewhat unlikely to do that, we'd be importing it.

What is happening on the land we'll be turning into plantations? What wildlife is lost? What people and crops are displaced? What water supplies are diverted? What are the carbon emissions from fertilising, harvesting and transporting all that timber?

In a world of the market, biomass will not be bought from where is most sustainable but from where it's cheapest. Biomass grows quicker where it's warmer. For all Drax's big play to the media about using local willow, they're now importing biomass from Italy. And I'm willing to bet the transportation emissions don't figure in their carbon calculations.

The use of waste wood for power is as worthy as turning waste food oil into biodiesel. That, though, can only supply 3 out of every 1,000 vehicles on the road. The move to biofuels for cars is causing devastating new plantations and food prices to rise.

New biomass plantations for power stations will do exactly the same thing.

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1. Annual Report and Accounts 2006, Drax Group plc, March 2007, p21

2. Alstom to build £50m biomass plant for Drax The Guardian, 20 May 2008

3. Drax Goes Green with Willow, The Guardian, 19 March 2004

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