Fridge, lights, TV, computers? YES. Kettle, toaster, hairdryer, washing machine, dishwasher NO. These were the parameters for a minimalist off grid PV system for a friend’s pod. Low power but low price.
They were mostly second hand and we settled on the 300Watt ones from France; defunct solar farm casualties. Apparently there are many solar farms either going bust or upgrading so there will be heaps more cheap panels to come. As panels should last 20 years it makes sense to start off with cheap used ones – who knows what the possible upgrade will be in ten years or so.
20 minutes and £1,740 later we had the kit in the car with batteries to be delivered later. Here’s the kit list:-
4 x 300W PV panels, 4 years old and £99 each.
So this is the 1.2kWp array
40A 12v/24v MPPT charge Controller – New Model Tracer4215BN
This charges the batteries efficiently and safely. Optional MT50 MPPT Display meter for New Tracer BN Charge Controllers 10a 20a 30a 40a. Tells you what is going on with every part of the installation.
Victron Phoenix 1200W, 24V inverter
Much favoured by the boating community this turns 24V DC into 240V AC, up to 1.2kW. The output is pure sine wave AC so good for computers and TV.
Sterling 200Ah Sealed Battery 12v
Two of these in series gives 24V. Big and very heavy there is no doubting the quality and 200Amp.hours is at the top end end of the range.
All the connectors and wires were included and the wiring turned out to be very simple.
To keep the wiring neat and safe I like to use two consumer units; one for the low voltage DC side and another for the 240V mains side. The bus bars and the DIN rail in the consumer unit make wiring quick and convenient and when all the units are board mounted, with wires going behind the board, it all looks neat and tidy.
Once the fridge was turned on the display showed a draw of just under 5 amps for a few minutes at a time. This was not going to tax the 200Ah batteries at all. Every bulb in the place is an LED so no problems there and there will be enough left over for TV and computer and to fire up a gas water heater.
The proposed Rinnai 16i in-line gas water heater draws 68W, when running, which is easily manageable for short periods. This LPG heater will provide instant showers and hot water with twice the power of many combi boilers. If fed by pre-warmed water the unit dials down the gas consumption to produce the same output temperature. This enables any solar heated water to cut down gas use – a project for the future.
Even this starter kit gives a feeling of independence and empowerment and, of course, freedom from price rises for years to come. To run washing machines etc you’d need a 3kW kit which comes to about £5,000. A full 6kW mains equivalent kit would be nearer to £10,000.
There is a section in my book Dream House – Down to the details which discusses the idea of using systems like these as large uninterruptible power supplies, in daily use but keeping the mains as more of a back up. There are charge controllers (e.g. Victron) designed to do just this so the UPS concept is really quite simple to implement.
£1,000 Heat Pumps
The Bimble site is a delight to browse through. I was particularly taken with the circa £1,000 heat pumps at a fifth of the usual prices and looking good value with Toshiba compressors and modern r410a fluid. A heat pump is just like a large fridge, and usually just as reliable, so one of these might be worth a punt at this price but you might need advice on what to connect them to.
In all probability these are Chinese but they often come with quality European components so they should be mechanically sound. Have a look here at a system especially suited to integrating heat pumps.
FYI the UK Renewable Heat Incentive pays 7.63p/kW.hr on air source heat pumps.
Solar Immersion Controller SOLiC 200 – free(ish) hot water from your excess solar
Another find on the Bimble site. If you don’t get much for exporting your PV power to the grid this little box can divert it to your immersion heater. The original kit that could do this disappeared off the market so it looks as though the SOLiC 200 has stepped in to fill the gap. The £200 price will be repaid pretty quickly if you pay a high price for electricity, however if you are defraying gas use in the UK then maybe not. Gas is still really cheap.
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