Farm energy case study: Small-scale AD Norfolk

One of the best ways to assess whether a renewable energy investment would work on your farm is to talk to others who have been through the process.

Paul Spackman quizzed five farmers who have been generating renewable energy for at least a year to hear their experiences and get their tips for others considering entering what is still a relatively new sector.

Stephen Temple has a small-scale anaerobic digester at Copys Green Farm in Norfolk.

Project overview
A combined heat and power (170kW electrical, 198kW thermal) anaerobic digester at Copys Green Farm, Wighton, Norfolk. The digester was designed by Greenfinch (subsequently Biogen Greenfinch, then Biogen) and is fed entirely from on-farm resources (slurry, manure and silage/energy crops).

Ownership
Owned outright by JF Temple and Son, financed from company and family funds.

Timescale
The initial decision to build an AD plant was taken in March 2008, with planning approval given in May that year. The plant began “consistent” gas production in December 2009. The first 140kW combined heat and power unit (CHP) was commissioned in June 2010, but was replaced that winter with a 170kW IET unit, commissioned in February 2011.

Performance
Mr Temple says some elements of the project have performed better than expected, while others were far worse. Technical problems with the original CHP unit (mainly the ignition system and electrical connections) meant it had to be replaced, while digester maintenance costs were also higher than expected until some modifications were made. He is much happier with the replacement CHP and says gas production and returns from electrical/heat generation (see table right) are now better than he expected.

Running costs and net return
Annual returns and feedstock use are summarised in the table left. All feedstocks are produced on the farm.

Payback
Originally projected to be eight years, now more than nine years.

Most difficult part
Mr Temple says that before commissioning, electrical connection and metering were the most difficult hurdles. “Initially EDF, our distribution network operator [DNO] at the time, [it is now UK Power Networks] were very slow with the quotation, and required information I could not provide.

“Then the electrical connection required a new meter for import and export. I could not employ a meter provider until I had an electricity buyer, and could not get a contract with an electricity buyer until I had a meter provider.

“Thanks to help from our buyer, Tradelink Solutions, we eventually got that sorted out. I understand it is all a bit easier now as they are more used to the process.”

Once the system was commissioned, getting the original CHP to work to specification was “impossible”, he says. Retrospective changes in Environment Agency permitting requirements after commissioning were also problematic.

There were some technical issues with getting the feeding equipment to handle flints and rogue bits of metal, and the separator to deal with limescale, but all these problems were rectified using the farm’s own resources, he says.

Easier than expected
Operating the second CHP.

Most useful advice
“We did not get any useful advice.”

Change anything?
“I would have started off from where we are now with many detail changes, but using the same general principles and system.”

Advice to others
“Go to see other systems similar to what you are proposing, and talk to the people who maintain it. When buying equipment, make sure quotes include spare parts costs.”

Rating: 7/10
“The main stresses were sorting out the feeding system and the original CHP.

“Once sorted, benefits were well worthwhile, with more electrical income streams than anticipated, RHI income for heat used, and good digestate value.

“It’s taking more of my time than anticipated, but providing me with an interesting engineering challenge.”

Project cost

Item

Cost (£)

Machinery

131,000

CHP

116,000

Sludge pipework

103,000

Groundworks

96,000

Digester tank

85,000

Silage bunker

81,000

Management/design

73,000

Controls and instruments

46,000

Gas equipment

38,000

Electrical installation

33,000

Hot water system

26,000

Miscellaneous

19,000

Digestate lagoon

17,000

Total

864,000

Production and returns

 

2010

2011

2012

2013

Annual useful heat (MWh)

63

174

Electricity generated (GWh)

0.17

1.03

1.25

1.17

Electricity exported (MWh)

110

773

958

884

Electricity bought (MWh)

69

27.6

4.2

1.7

Generated and used (MWh)

60

257

292

286

Digester electricity (MWh)

96

119

109

122

Digester heat (MWh)

226

293

Spares and repairs (£)

41,569

32,446

39,316

Feed-in Tariffs (£)

19,800

115,300

154,000

152,000

LECs* (£)

728

4,149

5,600

5,500

REGOs* (£)

176

312

292

Electricity sold (£)

3,175

34,045

43,223

43,000

GDUos* (£)

5,611

6,500

Triads* (£)

2,532

2,200

Renewable Heat Incentive (£)

9,259

14,600

Value of electricity used (£)

-3,600

13,800

18,300

16,400

Slurry (tonnes)

2,015

1,836

1,633

1,070

Maize (tonnes)

637

1,877

2,203

2,100

Beet (tonnes)

56

320

449

850

Whey (tonnes)

204

236

Farmyard manure (tonnes)

47

176

107

220

Wholecrop (tonnes)

48

109

120

Value of NPK & S (£)

4,026

3,832

14,023

*Note: LECs: Levy exemption certificates

Regos: Renewable energy guarantees of origin

GDUoS: Generator distribution use of system

Triads: Three half-hour periods during winter with the highest national demand for electricity, separated by 10 clear days.

 

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