The construction of the biggest array of solar PV panels ever seen on a UK barn was finished in Cambridgeshire last week. David Cousins was there

This may not be the first time that solar PV panels have been attached to a barn roof, but it’s certainly the biggest, most serious-looking array so far seen in the UK. And it’s probably not exaggerating to say that this otherwise ordinary-looking farm building ushers in a new age of solar barns in Britain.

The barn’s normal role is providing grain storage at Tim Breitmeyer’s Bartlow Estates in Cambridgeshire. But a visit to the stand of Norwich-based renewable energy company RenEnergy at this year’s Cereals Event made Mr Breitmeyer realise that the grainstore’s roof could support more than just a few pigeons.

RenEnergy had already installed some 100 solar panel arrays on houses, but hadn’t tackled anything of this scale. The good news was the barn faced almost exactly due south and the roof angle was a helpfully steep 22°. And there was 3-phase power on hand as well.

With easily-gained planning out of the way, a series of up-and-down rails were bolted to the roof. Then the 504 Hyundai solar panels, each measuring 0.88m wide by 1.45m long and weighing just under 18kg, were fixed to the rails.

The total weight is 9t, but that’s well within the design capability of the 17-year-old building, points out Ren Energy managing director (and ex-farm manager) Damian Baker.

“Grainstores are ideal for PV panels,” he says, “because both PV power output and electricity usage are at their highest in midsummer.”

Wiring up the 504 individual modules involved almost 3000m of cable. They are grouped into 36 strings of 14 modules, each sending back power individually. Clever equipment downstream monitors the power output of every string and alerts the operator if one or more is down on output.

All the power from the 745sq m of panels – generated in the form of a 60A DC current – is piped to a pair of large cabinets in a metal cabin, each containing 12 Fronius inverter modules. These turn the tidal wave of current (100kW on a sunny summer day) from DC to AC so that it can be used in the grainstore with the remainder sent off to the grid.

Though you can do it yourself, Mr Breitmeyer opted to use the monitoring and management services provided by partner company Esco NRG to get the maximum yield from the system and minimum fuss. Information on performance and output is sent automatically from the barn to Esco NRG’s HQ via the 3G mobile phone network, where it is analysed. Esco NRG also manages the Feed-in Tariff and grid export contracts, as well as co-financing the project with Mr Breitmeyer.

The overall build cost was £340,000, with the revenue from using the electricity in the grainstore, selling it to the grid and getting the Feed-in Tariff expected to amount to £30,000 a year initially. That will increase as the FiT payment rates rise annually with inflation.

What if the sun doesn’t shine? “Though some summers are cloudier than others, when you compare one year to another the amount of usable light is surprisingly similar,” says Mr Baker.

RenEnergy’s tips

* A south-facing barn with a 30-40° roof angle will give you 100% potential panel performance. If the barn is south-west or south-east facing (or has a more normal 20% pitch) you’ll still get 96-98% performance. More northerly latitudes are fine too.

* Though direct summer sun will push power output up to its 100kW design maximum, any bright day will see surprising amounts of power being generated.

* Though simpler (and much easier to get through planning) than a wind turbine, PV projects can still take several months. PV panel and inverter makers are struggling to keep up with worldwide demand, which can slow projects too.

* Don’t forget that any projects completed after 1 April 2012 will see their FiT payment drop from 31.4p/kWh to 28.7p/kWh.

Contacts

RenEnergy 08452 225 2727 www.renenergy.co.uk

Esco NRG 020 7722 9666 www.esconrg.com