Generating our own electricity — October 2005

FG Wilson diesel generator — control gear to right
Generator Shed

When we arrived at the house all its electricity was supplied by a FG Wilson 16.5KVA diesel generator with a Xantrex SW3024e inverter and 24volts of batteries ( Exide Classic Solar OPzS rated at 985AH at C120). There was no meters to tell what power the house was using so having settled into the house and started to think about power that was the first thing we had fitted (December 2005).

Electricity was fed to the house from the batteries through the Xantrex inverter which converted the 24 volts DC to 240 volts AC.

Xantrex SW3024e inverter
Xantrex inverter

When the batteries became discharged the Xantrex inverter automatically started the diesel engine to recharge the batteries. That cycle repeated indefinitely. The only intervention necessary was to keeping the diesel tank filled up and servicing the diesel engine every 500 hours running time.

Exide OpZs 24V battery bank
24Volt battery Bank

With this set-up and dependent on house load, the diesel generator used to run for three periods of about three hours every day — 9 hours a day. That equates to Over 3000 hours a year. A simple calculation shows how very expensive such a regime is. The engine uses 2 litres of diesel an hour under partial load, that is about 18 litres a day.

Xantrex inverter, change over switch with MCBs and meter
Xantrrex inverter and Change over switch

At 30p per litre for red diesel that is £5.40 per day or just under £2000 per year. And this for a very limited amount of electricity. On top of that there was the cost of servicing the diesel generator six and a half times a year.

There were a number of problems with this set up. Firstly the Xantrex could only deliver 3KW. All power to the house was through the Xantrex. So, even when the 16.5KW diesel engine generator was running the house could only draw 3KW. Massively inefficient. Also the nature of the charging cycle of the batteries meant that there were effectively dead after about three years — badly sulphated. So we had the worst of all possible worlds! Something had to be done.

Man at work revised site under construction