Sun power for eco-farm

At  Mur Crusto farm, we have completed the final part of the eco jigsaw: we have a photovoltaic system installed and up and running. After a glitch with the wiring, the very professional MGS got our system operational last week. Below are some photos of the installation. Click on them for full sized views:

 Above are the two arrays of nine Schuco panels on the roof. They are supported by a heavily-galvanised robust steel rail system and connected electrically in series so as to generate anything up to 600 volts DC on a good sunny day. The output power is connected to a massive box, the inverter (see below).

 The inverter and its associated safety switches mounted on the board below it, is really the 'brains' of the system, transforming a variable DC input into AC at the voltage and frequency required to feed it into the National Grid or to power appliances in the house. The small white box on the upper right of the board below the inverter records exactly how many kilowatt-hours of power are generated. Our electricity supply company Ecotricity needs to know the total in order to pay us for the power we have generated. With the new feed-in tariffs, this amounts to 41.3 pence per kilowatt-hour. The power is pumped into the Grid via an armoured underground cable which connects to the meter box of Gwyndy, our holiday cottage, which will now be rendered carbon-negative and so can be truly claimed (as we do!) to be an eco-cottage.

Above is one of the simple but rather clever displays on the inverter which tells us how much power is being generated. You can move backwards from Today to Yesterday to the Week or Month and see all the aggregated totals. These include the amount of money generated - always good to know! - and the number of kilograms of CO2 saved by this particular solar powered installation; the feel-good factor.

Are we now carbon-neutral? I don't know but we've

1. insulated everything we can in Gwyndy and Mur Crusto farmhouse
2. have one economical car
3. installed wood-burning stoves for both buildings with all wood sourced from the farm
4. built a solar heat collecting conservatory
5. installed an energy-saving air source heat pump
6. installed the PV system I've described in this post

I think that's about all we can do...


System details

• maximum power the system can generate under ideal conditions - 3.78kWpeak 
• expected generation per year - 2900kW
• saving in CO2 over 1 year - 1.6 tonnes
• system is based on 18  Schuco MPE 215 PS 05 polycrystalline, photovoltaic panels
  mounted on the south facing roof of the barn
• the solar panels are covered by a 25 year manufacturer’s performance guarantee
• total cost - 16,550 GB pounds
• return on invested capital - 8.7 percent in first year rising incrementally to 15 percent in 25 years. Unlike the stock market, this investment payback is guaranteed and in any case generates far more than money held in a bank savings account
• payback time about 10 years
• annual income from sale of power generated - about 1,500 GB pounds

Getting real... about pumps

It's taken some time for the light to dawn: pumping water with 12 volt batteries is an expensive waste-of-time. I've been through several pumps and lugged several generations of heavy lead-acid batteries across the field and finally accepted the blindingly obvious: a mains powered pump is a much easier and more reliable solution to keeping the rainwater tanks (for polytunnel drip irrigation) full. Originally I'd intended to power the whole system by wind or photovoltaics but the expense and complications of doing this meant that I never did it.

So I bit the bullet last week and unrolled a long coil of cable - the run is about 80 metres - and now have an almost-silent submersible pump which pumps the rainwater collection ponds in about one tenth the time of the 12 volt pump (which was twice the price), its predecessor. It also automatically switches itself off with a floating switch. Now I can relax in front of my widescreen telly...

Moral: Avoiding using grid electricity for 'green' reasons can often be a much bigger waste of resources, not to mention a very big waste of money.