Very simply, and I am not near going down this route, I pay 27p/day for gas and 46p/day for electricity. In winter I currently only use gas for DHW but think I only need 4kWh of electricity to satisfy that ( much more gas as it is a non condensing cast iron heat exchanger , a long pipe run to the tank and typically uses 1m3 of gas to heat). Space heating is by a lot of wood.Joeboy wrote: ↑Thu Aug 17, 2023 4:14 pmI would be interested to read the sums on that, keenly so.openspaceman wrote: ↑Thu Aug 17, 2023 3:52 pmYes but I was not thinking about planning for outages, they are few and far between, the longest one was only several hours last year.
I was hypothesising that it may be more economical for me to be offgrid given the high standing charges for gas and electric.
Last year my electricity shortfall was 450kWh and I export electricity from early March till mid October, since 1st March I have produced 2155kWh and exported 915kWh using an immersion for all DHW. Unfortunately I did not log exports before March.
I have a 47kg propane cylinder that costs me £95 to refill including delivery I think, I haven't filled it for years. 1kg of propane burned in a generator liberates 14kWh of heat and at 20% conversion should yield 2.8kWh of electricity, a good proportion of the heat should be recovered for the house.
To make up my shortfall I would need to burn 160kg of gas at £2/kg =£320 but my standing charges are £266.
My shortfall occurs over a 120 day period so I need to produce on average 3.75kWh of electricity to charge my battery, a 2kVA genset for a couple of hours a day for an annual run time of 240 hours.
The main problem is finding a genset that is liquid cooled and plumbing it , via a plate heat exchanger, into the house and if the heat produced would offset the O&M costs of the engine.
There are Totem units but they are way OTT, there are also telecoms sets which are DC chargers by Polar in California but not available here. The marine units are constant running, very expensive and not necessary for this small annual use.
I think it would be better to keep the gas and run the engine from it but that would require Gasafe compliance.
I have mentioned before that the Homach TMG, a commercial product based on the Harwell TMG stirling could be rated at 500W and a conversion efficiency of 10% and ran on propane seems to be a fit but the firm is defunct and I have not seen any of there TMGs which were deployed as ligh buoys. They were rated for 22000 hours with 6 monthy regassing being the only maintenance.