Turning back the clock

Some time ago I dabbled with a solar lighting project, with a small solar panel, which if memory serves is a me 30 watt panel, and an old car battery, no longer capable of holding enough charge for the car, but able to retain few amps/volts or “sparks.” Sparks, in my mind are the important bits, the actual visible bits of electricity, which demonstrates that things are working, or possible not, dependant on where the spark is.


With a little wiring and an extra light fitting and a switch dropped into the office below this battery which sits in the loft, the solar panel worked quite nicely even on the North East facing roof, providing an independent self sufficient 12 volt lighting system for my office. With a low energy 12 volt bulb it would provide three or four hours of free lighting, dropping to maybe an hour if used every night, and as giving as many as 6 hours during the summer months.

Moving the panel onto the extension roof, which faces more Westerly improved matters, but I still didn’t get the best from the system and didn’t feel any real change to the electricity consumed on the bill – it was after all only lighting the office, the rest of the house was still using the mains.

Well, I have now taken the next step and invested in a second hand SGTI (Small Grid Tie Inverter). This converts the 12 volt DC power provided by the solar panel into 240 Volt AC power which can then be plugged into the normal wiring of the house and used around the entire home. This means the solar panel is now working at it’s optimum and not limited by the restrictions of charging a tired old battery.

I have wired things up this afternoon and plugged in the inverter via a digital meter which shows it is producing between 0.7 and 1.4 watts with the panel in the shade. We’ll see what happens later when the sun gets on it.

Now 1.4 watts may not sound a lot, but this is just the start – I’ll be investing in bigger panels later. But for now consider this – without the system turned on my meter took 37 seconds to spin 1 revolution. This is with two computers running, and the TV on standby, plus the fridge and 2 freezers, although I doubt they were in operating mode at the time. With the system turned on the meter now takes 49 seconds to complete a revolution- 25% slower. So can I expect a 25% saving on my bill? Well, no, obviously, because come this evening when the lights are on the panel won’t be working, but there is the chance of bills reducing if daytime consumption is reduced by 25%, maybe a 3 or 4 % saving overall.

The 30 watt panel cost me, about £30 if I remember, so the break even point may be some time off. But, with three more I could make the meter stop during the day – and if I did buy three more they’d be going on the back of the house on the South West slope to get the most sun. Free electricity during the day sounds mighty tempting. I can however source a 250 watt panel for £250. The inverter will take up to 300 watts, so the 250 watt panel would work nicely with that, and that would then start to turn the meter backwards during the day.

As it’s not a professionally fitted system I wouldn’t qualify for any “Feed in Tariff “ payments from the Government, which would have been nice, but simply getting some free electricity and slightly lower bills will be most satisfying.