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A Plug Into The Sun Install Makes The News

Date: 11 Aug 2010

A Plug Into The Sun install is making the news as a case-study for farmers wanting to invest in solar panels. The 2.96 kWp project at Carhart Mill is being used by the farming industry to highlight the investment opportunities for solar power on agricultural buildings. 

"The average barn roof could be earning more than £20,000 a year by generating electricity through photo-voltaic (PV) panels. That's the claim of British solar power company Solarcentury, which says that the recently-announced arrival of Feed-in Tariffs has shortened the payback period for PV considerably.

A big, barn-roof-mounted array of PV panels totalling 400sq m can produce up to 60kW in ideal conditions, it says. Averaged over a year, that would amount to 51,000 kWh (units) of electricity.

The generation tariff for big solar power installations between 10 and 100kW peak capacity is 31.4p/unit. So that 51,000kWh equates to £16,014 for generated electricity, plus £765 for electricity sold back to the grid and £2295 for savings from not consuming power from the grid. That makes a grand total of £19,074.

The figure assumes that on average you will consume 50% of the solar electricity on the house and farm and export the remainder to the grid. What you use yourself saves you 9p/unit and what you sell earns you 3p/unit.

The example cited is a big PV project, says Solarcentury, which would typically cost £200,000 for equipment and installation. However, farmers in Germany and France (where Feed-in Tariffs arrived some years ago) are beginning to install exactly this sort of set-up.

In the UK, most PV panel arrays are much smaller (see case study below), but Solarcentury expects them to grow in number over the coming years. Also, if you don't want to invest in the equipment itself, there are a number of companies like INRG Solar that will 'rent' your barn roof.

Case study: Carhart Mill, Wadebridge - seven-year PV payback

Stephen Frankel specialises in producing meat from high-husbandry rare breeds on his farm Carhart Mill near Wadebridge, Cornwall - pork from Large Black pigs, beef from Dexters and meat from West Country Geese.

He had already used a solar thermal panel to preheat domestic hot water and has a 6kW wind turbine and woodchip boiler, so he's not new to renewable energy production. He sees the addition of photo-voltaic (PV) panels as part of a range of renewable-energy technologies that together give him protection against rising energy costs.

"We've had a long-standing interest in renewables - we genuinely feel responsible for looking carefully at our carbon balance," he says. "But the main thing that could cause a farm set-up like ours to become no longer viable is a big rise in energy bills."

In March this year he installed an array of Solarcentury photovoltaic panels measuring 8m x 1.5m in total on a south-facing barn roof. The 2.96kW (peak) system is expected to produce 2664 units (kWh) over the year, and the southern location of the farm helps.

Total cost of the panels (plus installation) was about £10,000 and fitting them on a slate barn roof was fairly straightforward. "It is a listed building, but it was no problem getting listed building consent from the planners. Connecting to the grid was straightforward too."

The panels should produce about £1500-worth of electricity each year, made up of a generation tariff, plus power exported to the grid and savings made by using home-produced power instead of paying an energy company for it.

Is PV power production living up to his expectations? "According to the energy meter, we have produced 1231kWh since the panels were installed earlier this year," he says.

Energy production will be lower in winter, of course, but the stronger winter winds mean the 6kW turbine will produce more power at that time of the year to help compensate.

He reckons that the payback period for the PV panels will be about seven years - considerably shorter than it would have been before the feed-in tariffs were brought in. "It means we're completely free of energy costs - and we have an extra income," he says.

Solar power facts

Feed-in Tariffs

• Pay 41.3p/kWh (unit) if less than 4kW system and fitted to an existing building
• Pay 36.1p/kWh if 4-10kW system on existing building

• Pay 31.4p/kWh if 10-100kW system on existing building

• Feed-in tariffs are guaranteed for 25 years, but payment rates for new entrants are to be reviewed every five years

• Feed-in tariff payments will drop for new entrants on 1 April 2011 and 1 April 2012, so the best deals are for those who get stuck in now.

Photo-voltaic panels

• PV panels should be installed at 30-40deg from horizontal

• They can be installed vertically, but will only achieve 60-70% of full potential

• South-facing alignment is best but facing south-east and south-west will give 90% of the power output.

• Panels are guaranteed for 25 years, but should work for at least 40 years.

Costs and generating ability

• Power sold back to the grid gets 3p/kWh

• Using home-produced electricity instead of paying a power company saves 9-12p/kWh.

• 7-8sq m of PV panel is needed to generate 1kW of power

• A 1kW panel should generate 850kWh each year

• Most domestic set-ups are 2-3kW (ie cost between £9000 and £18,000 and produce 1700-2550kWh/yr). Farm ones could be much bigger.

• Typical installed system cost can be less than £4500/kW (peak) for larger systems.

• Typical payback period is 7-12 years

(All figures provided by Solarcentury)"

Courtesy of Farmers Weekly Interactive