Solar Query

[openspaceman]

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Depends on what you're planning for!

Yes 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.

I would be interested to read the sums on that, keenly so.

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.

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.

[Joeboy]

Yes 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.

I would be interested to read the sums on that, keenly so.

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.

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.

Wow,.that really is close to being doable, impressed! Just a thought exmod auctions maybe? Thinking RAF gear maybe?

Would you build it yourself if you could find a low gas consumption engine? Could fit the generator of your choice and make up a heat exchanger running off the exhaust. Exciting!

[openspaceman]

https://www.ebay.com/itm/325622697959?h ... R9DbrLikYg

Would have been ideal

If I do pursue the idea I would probably buy a used Yamaha 125cc scooter with variable belt drive, an lpg kit and a axial flux pm alternator from a small wind turbine, a 3ph rectifier running into the same charger you and I currently use with additional panels.

[Joeboy]

https://www.ebay.com/itm/325622697959?h ... R9DbrLikYg

Would have been ideal

If I do pursue the idea I would probably buy a used Yamaha 125cc scooter with variable belt drive, an lpg kit and a axial flux pm alternator from a small wind turbine, a 3ph rectifier running into the same charger you and I currently use with additional panels.

I literally just edited to ask about a diy solution! Then hey presto..

Is the variable belt drive a critical part for the conversion? I'm assuming yes as an easy solution to hook up the engine final drive to the alternator?

[Joeboy]

That was the niggle. We saw loads of tuk tuks in India running lpg. No idea engine size or efficiency but one more source market to think of?

Or maybe Honda 50cc step thru engine. Just saying random things now. Those engines ran forever on almost nothing.

[Stinsy]

Maybe an LPG forklift or golf buggy could be a good starting point? Combined heat and power would be a requirement but water cooled small engines are hard to come by. It all fits nicely with the genny being used only for a few hours a day on the darkest/coldest days of the year.

[openspaceman]

Is the variable belt drive a critical part for the conversion? I'm assuming yes as an easy solution to hook up the engine final drive to the alternator?

No but you need to match the maximum output of the alternator to the sweet spot of the engine and adjusting it via the VEE belt pulleys seems sensible. The liquid cooled engine and plate heat exchanger are to get the heat into the house circuit. For the low run time the engine should be good for a few years.

Nowty's wife's I3 engine is probably configured to run at constant output most of the time for similar reasons, unfortunately though they are cheaply available, used, they are air cooled. Their alternator will be direct coupled. A 2008-10 Honda Civic PMA also has a 13kW pm alternator directly coupled around the flywheel.

[openspaceman]

We saw loads of tuk tuks in India running lpg.

There are a lot of lpg convesrions for small generator engines but all air cooled.Most have a manual gas tap which would not be good enough.

I ran a converted 3.5 V8 Land Rover for 10 years and that was no problem, the oil remained clean between extended oil changes. The only need to change was because the detergent quality of the ingredients got used up. The conversion was very simple, a gizmo on the ignition circuit to sense spark pulses, this then opened the gas solenoid. The gas pressure regulator sensed the depression in the choke tube as the throttle opened to vary the gas,

Because of the power requirement the LPG was liquid feed into a heated vapouriser, this is not necessary for less than 5hp as long as the cylinder is kept warm.

[AGT]

Yes 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.

I would be interested to read the sums

[Joeboy]

Only very vaguely related. Didn't even know these were a thing.

https://www.facebook.com/marketplace/it ... tory_share