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Off-grid solar electricity: a case study of a field studies centre

Posted by Cathy Debenham on 1 August 2011 at 12:37 pm

Solar generated electricity is the perfect answer for the Stafford Marsh field studies building on the Axe Estuary wetlands in East Devon. Off-grid, and a hard place to get electricity to, it was a "no brainer" according to nature reserve officer, Fraser Rush.

This is the first off-grid installation I've visited, and it was fascinating to see how it works. It's got two inverters. The first converts the DC (direct current) electricity generated on the roof to a battery-friendly voltage. The second inverter converts the electricity supplied by the batteries to mains (AC - alternating current) electricity.

There's a display (see second photo) that shows how much electricity is stored in the batteries, using a traffic light system. Amber gives a warning that's it low, and if it shows red it means turn it off now. The 1kWp solar PV panels were installed by Chris Rudge in February 2011, and so far the light has shown green continuously. However, there is a small generator to cope with the dark days of winter.

The key to the system's design is to maximise the life of the batteries - and so it won't allow anything to be used if it is above or below a safe voltage. A kettle would come in that category, so there's a small gas ring for making the tea. Other than that the solar PV system has coped with everything staff have thrown at it so far.

The field centre building is the nature reserve HQ, an interpretation centre for school groups and other visitors, and venue for events and bird ringing groups.

It's lit by LED work lights, there are pumps for the fish tank and water, a fridge and  microscopes use electricity. Even extended use of a power point projector for teaching hasn't triggered an amber light. It also copes with overnight moth traps, and there's a barn own loft and bat loft wired up for CCTV, should they get occupants.

I found an off-grid installation like this much more exciting than a domestic, on-grid one. While both make a difference, this opens up such opportunities, and means you can avoid the disruption, huge expense and ugly power lines needed to get grid connected. It just makes so much sense.

Stafford Marsh Field studies building received funding from Making it Local.


If you have a question about anything in the above blog, please ask it in the comments section below.

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2 comments - read them below or add one

Rudge Energy

Rudge EnergyComment left on: 4 April 2013 at 3:00 pm

Hi Steve

Unlike other forms of electrical generation such as Wind Turbines or Hydro, which would need a load to send excess power to, Solar PV modules are quite happy to be simply disconnected when the batteries are fully charged as excess power does not need to be used.

For more in depth information on the characteristics of Solar PV module generation, see

You'll see that electrically, the PV module is quite robust and can be left either open circuit or completely short circuit in bright sun with no effect on performance.

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s ward

s wardComment left on: 3 April 2013 at 9:05 pm

hi  can you tell me how do the solar panels cope when the batteries are fully charged  on a stand alone system  thanks.steve

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