Contracts to purchase 200,000 tonnes of bales per year have
been signed with farmers and contractors in East Anglia who
are set to provide fuel for the biggest straw-fired power
station in the world. Mike Williams gives a progress report
THE management team at the Elean Power Station expected some teething troubles when it fired up for the first time last winter, but they hadnt anticipated the difficulty of maintaining a constant supply of dry straw throughout the wettest season in at least 200 years.
The pioneering £60 million project, based at Sutton, near Ely, Cambs is the first British foray into generating electricity exclusively from straw and other crop residues. Though the station has the capacity to produce sufficient electricity to meet the needs of 80,000 households – the equivalent of two towns the size of Cambridge – to meet its production target it needs to burn 40 to 50 Heston type bales per hour, every hour, every day of the year.
All the straw comes from farms within about 50 miles of Sutton, Britains largest grain growing area and traditionally the region with the lowest annual rainfall figures.
Anglian Straw, a subsidiary of the company running the power station, organises the straw procurement and transport to the power station, but operations manager Neil Bond admits the weather has caused some of their biggest problems so far.
"We have to keep the supply going with 30 to 40 truck loads every day. We cant just stop the deliveries for a few days because of bad weather, and that has caused most of our problems," he explains. "Trucks have been bogged down in the field when they collect straw from the stacks, our bale rejection rate is higher than expected because heavy rainfall has penetrated the stacks and, in some cases, the ground has been so soft that the weight of the trucks has damaged farm roads and tracks."
As a result, there have been some hold-ups but the power stations five-day covered storage capacity has kept the generator going.
"We have learnt some lessons, particularly about where to locate the stacks, but trying to protect them from the rain is more difficult," says Mr Bond. "We were expecting to reject the top layer of bales because of rain damage, but on some stacks we are rejecting two layers, and that is more than we had expected."
Most of the fuel Mr Bond buys is wheat straw, but barley and oat straw are also acceptable, and bales of oilseed rape residue, hay from grass seeds production and pea and bean haulm have been used successfully at the plant. Baled linseed straw has also been tried, and the results are said to be good.
The stations preferred bale size is the big 1.2m x 1.2m x 2.5m rectangular pack averaging about 550kg, but smaller bales are also accepted, subject to a 425kg minimum weight. Big round bales are not suitable for the highly automated handling and conveying equipment used at the power station.
Anglian Straw has a flexible approach to its procurement contracts. In some cases the contract is agreed directly with the farmer, but the usual arrangement – covering about 75% of bales supplied – is with a contractor or straw merchant who buys straw in the swath and is responsible for baling and stacking. Anglian Straw is responsible for loading the trucks and transport to the plant.
The period covered by the contract is also flexible, and the company currently has agreements ranging from one to 10 years.
Contract prices are based on £20/t in the stack, but there are adjustments for moisture content and bale density. Longer-term contracts also include a built-in inflation factor.
Moisture content is an important consideration – rotten straw can block some of the handling equipment in the plant and, predictably, bales with excess moisture yield less heat energy when they burn in the power station furnace.
David Mason, commercial manager for Cinergy Global Power, which owns the power station jointly with Energy Power Resources, points out that the straw does not have to look good.
"We are not fussy about the type of straw, and we dont mind if it was sitting in the swath for a long time before it was baled. It doesnt have to be pretty straw, but the moisture content does matter," he says. "Our payments are based on 16% average moisture content, and we do not accept loads averaging above 23.5% or individual bales above 25%."
Although straw and other crop residues will continue to form the principal fuel source for the Elean Power Station, there have also been successful results – albeit experimentally – with bales of miscanthus (elephant grass). It may be that additional equipment will also be installed to burn wood chips from short rotation coppice.
"These deviations apart, the main reason for siting the power station in East Anglia is because of the straw supply, and our long-term future depends on the straw and other crop residues we buy from farmers and contractors in the area," insists Mr Bond. "If the power station did not exist, most of the straw we contracted to buy during our first year would have been chopped behind the combine, so this really is additional income.
In terms of financial matters, Mr Bond explains that the investment in the power station is based on a commitment for a minimum of 13 years. At current prices he is paying about £4m/yr to farmers and contractors involved in the straw supply chain.
"I am surprised we have not had more farmers picking up the phone and saying they want a share of the business, and I believe there are still quite a lot of farmers in the area who have not realised that there is a big new, long term outlet for straw on their doorstep," he says. *
Neil Bond, Anglian Straw, "I am surprised we have not had more farmers picking up the phone and saying they want a share of the business, and I believe there are still quite a lot of farmers in the area who have not realised that there is a big new, long term outlet for straw on their doorstep," he says.