Anyone considered home generation of leccy?

[Ham]

Not that I'm actually considering it, but having just moved energy suppliers I had been looking at the relative cost of fuels, much easier these days everything is in KWh.

Gas is 1/3 the cost of Electricity per Kwh.  Even if the generation is only 60% efficient, that still leaves gas 50% cheaper than electric. Shirley someone is taking advantage of this.....? Like https://www.cclcomponents.com/sdmo-resa-14-tec-standby-residential-generator-natural-gas-lpg ?

There is a problem that it would likely be of most practical use in areas where there is no mains gas (ie, where the generator can be sufficiently remote to address the noise issue), but it is very curious that such a discrepancy CAN exist.

[Kim]

CHP is by far the most efficient way to use gas...

[Canardly]

Has not really taken off for domestic installs tho but, housing density being one of the probs. CHP is more efficient at producing heat than electricity. Now if someone could come up with something fed by plastic .........

[Cudzoziemiec]

District CHP is a thing in most towns in Poland but usually coal fired, for historical, geological and employment reasons. An interesting side effect is where the pipes run slightly shallower, the winter snow can melt in that one spot then refreeze overnight, making slidey slidalicious ice; somehow I don't expect this to be a problem in Ham-ville!

[mrcharly-YHT]

If you can find an ICE that is 60% efficient, wow

I think the best you can expect would be closer to 40% and that is before losses in the electrical generator.

Most of the losses are in heat, which is what makes CHP so attractive.

[edit] now and then people try building stirling engines, even commercially, for CHP in the home. It turns out to be really difficult to make a reliable one.

[Kim]

There was some domestic-scale CHP using high-temperature^[1] fuel cells on Fully charged recently.  A unit that's effectively a drop-in replacement for a normal gas central heating boiler and produces 700W of electricity as a by-product.


_{[1] AIUI fuel cells become massively more practical (no need for exotic metals) if it makes sense to run them hot.  Not the sort of thing you could power a laptop or car with, but fine for CHP.}

[mrcharly-YHT]

There was some domestic-scale CHP using high-temperature^[1] fuel cells on Fully charged recently.  A unit that's effectively a drop-in replacement for a normal gas central heating boiler and produces 700W of electricity as a by-product.


_{[1] AIUI fuel cells become massively more practical (no need for exotic metals) if it makes sense to run them hot.  Not the sort of thing you could power a laptop or car with, but fine for CHP.}

Similar numbers to the Stirling engines. plenty of heat and a bit of power as a byproduct. Not enough to run a house, so you end up needing multiple generators and dumping some of the waste heat.

[Kim]

Similar numbers to the Stirling engines. plenty of heat and a bit of power as a byproduct. Not enough to run a house, so you end up needing multiple generators and dumping some of the waste heat.

Yeah, you still need a grid connection (or BFO battery) to cope with the peak demand, and unless you need the heat all year round (so either somewhere colder than the UK, or a business that involves a lot of hot water), you're going to want an alternative source of electrical power.

It comes down to the difference between "alternative source of electricity" and "a more efficient way to use gas".  CHP seems promising when regarded as the latter.

[Quisling]

Home generation using micro CHP is one option, but the economics generally rely on long running hours to cover baseload electricity demand, and finding a use for all the waste heat.

The fundamental issue with going down the CHP route is that it makes it difficult to decarbonise domestic heating unless you have a source biogas which would at least be theoretically near net zero CO2/kWh.  Accordingly, I'd prefer to work towards an all electric solution for space heating and a solar hot water/electric immersion top-up solution for domestic hot water.

A new Baxi Ecogen wall hung micro CHP has an installed cost of circa £4500, plus you'd probably want to add in some smart controls to ensure various devices around the house make best use of the power/heat.  But as previously discussed it won't produce all your power, and in the summer you'd need to shut it down otherwise you'll have pointless waste heat (unless you have a hot tub, pool or cannabis farm).  It would (currently) earn you some feed-in tariff pennies.

The longer term "green" solution would be a ~4kW solar PV install, which just tucks in under the G83 connection regulations, and a battery storage system (Tesla Powerwall or one of the many similar systems).  Combined with products from companies like http://myenergi.uk/ to manage power use and export in a smart way, this could meet a lot of your daily needs (certainly between spring and autumn).  The combined system might deliver 70% of your power needs over the mid summer, and on average ~50% across the year.  If the battery system can automatically work in "island" mode, this also gives you some resilience in the event of grid power outage whereas a CHP would stop operating if mains power to it's electronics is lost.

There are other products out there like BlueGen which is a fuel cell CHP, the outputs of which are skewed much more towards power generation rather than heat.  But, it's big and really aimed at small commercial needs and as part of a bivalent (hybrid) system in which power demand is >10000 kWh/year.

If you have a high heating demand, year round (e.g. swimming pool) then you could readily combine a small CHP with other systems to really get the benefits.  Consider:
* small CHP to produce electricity and earn a little bit of Feed in Tariff.
* use the electricity produced to power an air source heat pump (to generate additional heat) and use the waste heat from the CHP too.  The ASHP should also qualify for Renewable Heat Incentive.

https://www.renewableenergyhub.co.uk/micro-combined-heat-and-power-micro-chp-information/the-baxi-ecogen-microchp-boiler.html
http://www.solidpower.com/en/bluegen/
https://www.ofgem.gov.uk/environmental-programmes/fit/fit-tariff-rates

[mrcharly-YHT]

I wondered what the Baxi Ecogen was - it looks to be a combi-boiler with a stirling engine.

Hope the warranty is good  . . .

[Wombat]

Quizling, do you mean that after all these years, the Baxi Ecogen is really, actually available?  Its been imminent for at least 8 years to my knowledge.

[Quisling]

Quizling, do you mean that after all these years, the Baxi Ecogen is really, actually available?  Its been imminent for at least 8 years to my knowledge.

They have allegedly installed a few.  Ditto the WhisperGen that TXU (taken over by Powergen, then E.ON) were going to sell.  Back in the day, TXU were going to sell millions of these BUT failed to (a) get the technology right (b) get it into a sensible size unit (c) make it quiet enough.
More realistically though, what stopped micro CHPs flooding the market was a combination of:
* the rapid uptake of solar PV
* the fact that most people buy whatever boiler their plumber recommends and can get hold of as boiler replacements tend to be distress purchases.
* the need to connect a CHP back to the consumer unit which is inevitably nowhere near the boiler therefore likely to cause a lot of extra unsightly surface mounted cabling etc.

If one accepts the need to move to a "post combustion" heating solution for environmental reasons, then micro CHP was only ever going to be an interim technology.  Indeed, as grid power steadily de-carbonises, the carbon benefits of CHP are steadily reducing - although they have other benefits (avoiding the 6% or so transmission and distribution losses in the network etc).

C

[Polar Bear]

I would prefer a combination solar panels with a storage battery and a thermodynamic panel for heating.  On a passivhaus building that should be very effective.

[Pickled Onion]

Out of interest, if one happened to live close to a stream/river, what kind of power could you expect to generate. Eg for a few metre drop like at a water mill?

[philip]

For a water flow of 100L/s falling 2m the maximum power that could be extracted is about about 2000W (height x mass x g).  A waterwheel might be 50% efficient at converting that into mechanical power and an electrical generator might take another 50%, so probably 500W electricity at best.

[Pickled Onion]

Which sounds like an adequate amount: 4.4 MWh per year. Enough to run a house, given careful use and suitable storage to even out the demand. Where did you get the 200 l/s, how big a stream would that be?

[philip]

100L is more than enough to have a bath. 200L/s is probably a small river rather than a stream.

https://nrfa.ceh.ac.uk/

[Diver300]

A waterwheel might be 50% efficient at converting that into mechanical power and an electrical generator might take another 50%, so probably 500W electricity at best.

I suspect that might be overly pessimistic. 1 kW electric motors are about 75 % efficient.

The pump storage at Dinorwig manages 75% overall, so that is motor efficiency * pump efficiency *  turbine efficiency * generator efficiency¹ = 75%

I would expect a lot worse from a waterwheel, but still probably 75%.

The issue with a waterwheel is how much of the flow you can actually capture, and what change of height you can get.

1) I know the motors are the generators, and the pumps are the turbines but the equation stands.

[CarlF]

The Town Mill in Lyme Regis is an old water mill that has had a micro-hydro generator installed. Details here: http://www.townmill.org.uk/the-town-mill-hydro-electric-system/

They give the following numbers:

The heart of the system is a German-built Ossberger cross-flow water turbine fed by a 4.03 metre head of water, average flow rate 0.24m3/s, giving a maximum power output of 7.07kVA. The turbine drives a Brook Crompton induction generator connected for three-phase operation. The hydro system is controlled by a G83-standard digital control system, with connection to the National Grid through an approved export meter. It is estimated the system will produce about 32,000kW annually, with CO2 savings of about 13 tons annually

That "32,000kW annually" is obviously supposed to be "32,000kWH annually". Although the flow they've got is similar to philip's guess (240l/s) they've got a much higher head and they're using a turbine, not a waterwheel. Would anybody actually use a waterwheel for a real system?

The mill leat isn't that big, but it is quite long in order to get that 4m head. You can see it in the lower picture here http://www.lymeregis.org/river-lym.aspx, and in fact they only divert part of the flow for the power turbine and use the rest for the waterwheel that still drives a millstone. This is the pipe for the generator: http://www.geograph.org.uk/photo/5169883

Bad news for a home install....

The total cost of the system was £59,000

[jsabine]

If you've got access to run-off from an existing dam you can think quite a lot bigger ...

https://sites.google.com/site/saddleworthcommunityhydro/home

31m head, 185l/s, 43kW (out of a 51kW turbine) - 90% availability gives 339,012kWh annually.

Possibly useful link re appropriate turbine (and waterwheel) uses: http://www.renewablesfirst.co.uk/hydropower/hydropower-turbines/ - if you've got a 2m+ head it suggests that a crossflow turbine might be suitable, and at lower flows than a waterwheel.

[Karla]

 For the waterwheel/turbine scenario, you've also got to factor in how much of the power you can take out of the water before you stall the flow.  For a wind turbine, the theoretical maximum is about 59% - extract more power than that and you have to put energy back in to move air out of the way of the blades.

My knowledge of fluid dynamics is minimal so I don't know how well this applies to water.

[philip]

I don't think Betz applies to a typical waterwheel as a waterwheel primarily extracts gravitational potential energy rather than kinetic energy (ignoring undershot wheels).

For the Lyme Regis installation: 4m and 240l/s gives about 9.6kW as the "gravitational power" available. To produce the 32,000kWh requires 3.6kW all year, or 38% efficiency.

[philip]

I don't think Betz applies to a typical water turbine either since the flow is constrained in the pipe/duct.

[Karla]

Googling tells me that Betz's law applies to bulk movement (e.g. wind) in Newtonian fluids (e.g. water).  It doesn't apply to constrained flow or flow under gravity though, so you can happily extract more than 59% of the fluid's energy.

[Zipperhead]

I would prefer a combination solar panels with a storage battery and a thermodynamic panel for heating.  On a passivhaus building that should be very effective.

I have a friend who moved to Majorca, and because the property had no mains electricity (or water, or gas, or sewage), the cost of getting connected to the grid was going to be absolutely eye watering.

She has two large solar panels in the field which feed into 24 (very large) lead acid batteries in the barn. There's also a generator in there for periods when the weather is too poor for the solar panels to provide sufficient power.

That produces enough power to power the house (although only one of dishwasher or washing machine can run at once), power the pump that brings water up 90m, power the heat pump to generate hot water and run the swimming pool stuff. LED lights obviously make a big difference.