The case for nuclear is clear!

mech_2

cepheus wrote: »

Problem with MicroCHP is that since the fossil fuel is not centrally combusted it is not feasible to capture the carbon.

That doesn't matter. It replaces gas boilers which don't have carbon capture anyway.

Outside winter months there really should be no need for space heating anyway in a well insulated home or office and all this heat will go to waste anyway.

No it won't because you don't use the CHP unit unless you need heat. You retain a connection to the grid for electricity use outside the heating season. In warmer months with longer days electricity demand is lower anyway.

Meanwhile the electricity will be produced less efficiently in a microplant all year.

It doesn't matter. It's "for free". The waste heat heats the house as it would have done in a boiler.

As a rule heat pumps powered from the mains are more efficient than MicroCHP and have the potential to offer zero carbon emissions. MicroCHP may have a role however if Biogas is used as the fuel.

I'm not sure how easy it is to compare the two. The microCHP is displacing inefficiently generated electricity elsewhere, so its own efficiency isn't the issue. Ground source heat pumps with underfloor heating are efficient, but incredibly expensive to retrofit into existing homes. Air source may be more practical, but I'm still not sure where you would shoehorn it into a Victorian terrace. Air source is less efficient and it's not clear to me that an air source electric heat pump with a COP of around 3 and retro-fitted onto existing radiators can deliver more benefit than a microCHP unit. You would have to show me some sums. My estimates suggest microCHP wins. Don't forget to factor in an immersion heater for hot water - a heat pump can't get the water hot enough.

Electric heat pumps don't consume a primary energy source, so they're clawing back energy wasted elsewhere. Let's say the electricity is generated at 40% thermal efficiency, 7% of that is lost in transmission, so you get electricity at 37% efficiency.

If the property is suitable for a heat pump, another option is a gas fuelled heat pump. Kind of like microCHP coupled to an electric heat pump, but you can eliminate the electrics and just couple them mechanically. I think they have these in Japan. This way you get the advantages of a heat pump and primary energy source in one unit. This design even eliminates any rotary components: http://www.globalcooling.com/documents/HermeticGasFiredResidentialHeatPump_000.pdf

cepheus

Mech Thanks for the heat pump info, never seen anything like it. Suppose the ultimate environmental device is such a heat pump powered by biogas but I digress.

I'm probably coming from a different angle. Looking at the increase in the worlds population, their affluence and hunger for electricity and heat there is no way we can get greenhouse gases down to acceptable levels whilst emitting CO2. This leaves us with Nuclear, renewables and fossil fuel CO2 sequesteration. All these can only produce heat from electricity efficiently via a heat pump, unfortunately CHP is local and must emit CO2 unless it uses biogas. It is actually more efficient overall to use heat pumps than CHP especially if you can generate electricity at 60% efficiency using gas, although I agree retrofitting heat pumps is difficult. I suppose one uses the attic for fitment. COPs of 3 are possible without ground source heat and there is waste warm water to draw on. Perhaps the roof could also be used for low grade solar heat collection that can be pumped up at a later date.

David McKay has a draft report here on how to 'solve' Britains energy problems of which heat pumps is a small part. His take on nuclear is interesting as well. He justifies the CHP v heat pump trade off in terms of energy alone although for the reasons above if you dont want to emit CO2 there is no need for this analysis.

http://www.inference.phy.cam.ac.uk/sustainable/book/tex/cft.pdf

cepheus

I should add that McKay's analysis on the area of wind farm necessary to feed our transport system seems to be wrong, but he does seem to present some innovative ideas and a large number range of energy strategies (one of which relies heavily on nuclear).

mech_2

cepheus wrote: »

Mech Thanks for the heat pump info, never seen anything like it. Suppose the ultimate environmental device is such a heat pump powered by biogas but I digress.

The only reason I can see for it not being suitable in conjunction with a solid fuel stove is the issue of controlling the rate of combustion.

I'm probably coming from a different angle. Looking at the increase in the worlds population, their affluence and hunger for electricity and heat there is no way we can get greenhouse gases down to acceptable levels whilst emitting CO2. This leaves us with Nuclear, renewables and fossil fuel CO2 sequesteration. All these can only produce heat from electricity efficiently via a heat pump, unfortunately CHP is local and must emit CO2 unless it uses biogas.

Well CHP can be centralised via district heating, but I was centring on microCHP because it's feasible in a short timescale (though obviously not instant. Production of the units can't ramp up hugely overnight, but that applies to heatpumps as well). And it's relatively cheap.

Part of the problem that new nuclear reactors are to address is the decommissioning of the existing reactors. Renewables still supply a paltry percentage of our present electricity requirement. Adding more electricity consumption for heatpumps, however efficient, just exacerbates the problems we have trying to replace fossil-fuelled electricity. Mass government-installed microCHP would contribute to electricity generation and use less gas that we are already burning in inefficient boilers to keep warm. Air-source heatpumps could still be offered to people without a gas connection.

It is actually more efficient overall to use heat pumps than CHP especially if you can generate electricity at 60% efficiency using gas,

OK, I checked. You may be right about the efficiency, as the UK's gas fired power stations are currently around 45% efficient. Clearly more is possible, but replacing the UK's gas fired power stations is another long-term aim (as with nuclear). Looking into the future, microCHP will doubtless become more efficient as well.

although I agree retrofitting heat pumps is difficult.

It's expensive. That's the key. MicroCHP will work with current central heating systems. They're now small enough that there are even wall-mounted units coming to market, of a similar size to a wall mounted boiler. It would just be a case of replumbing a few pipes, refilling the system, and fitting an export meter for surplus electricity. Not much more expensive than a new boiler. Maybe £3000 installed. They do already have a reduced rate of VAT (5%) to encourage uptake.

An air source heat pump means moving your heat source into the attic (as long as it isn't a loft-conversion) and probably replacing the whole central heating system as the old radiators would be too small to heat the house in winter at the lower water temperature.

A ground source heat pump means digging up the garden (if there is one) and then probably also needs new radiators or underfloor heating for the same reason as above. I know someone who sank £16,000 into this and rues the day. It still isn't working properly and now they are spending more on bricking up their chimneys to try and reduce heat loss further.

I suppose one uses the attic for fitment. COPs of 3 are possible without ground source heat and there is waste warm water to draw on. Perhaps the roof could also be used for low grade solar heat collection that can be pumped up at a later date.

Yes. A good idea for new builds possibly, where it offsets the cost of not needing a gas connection and can be designed into the building from the start, but new builds are a tiny percentage of the total housing stock. 1% per year?

No energy efficiency policy for the UK can ignore our existing housing stock. Any modifications have to be cost effective and microCHP is easily cheaper than heatpumps. Though without massive subsidy from government, neither heatpumps nor microCHP are likely to displace gas boilers very quickly, even if made mandatory as with SEDBUK 'A' boilers.

David McKay has a draft report here on how to 'solve' Britains energy problems of which heat pumps is a small part. His take on nuclear is interesting as well. He justifies the CHP v heat pump trade off in terms of energy alone although for the reasons above if you dont want to emit CO2 there is no need for this analysis.

http://www.inference.phy.cam.ac.uk/sustainable/book/tex/cft.pdf

Thankyou, that looks interesting. It will take me a while to get around to reading it all. There's a lot there.



Now I'm going to go all geeky and do some sums.

Assumptions:
Average gas consumption presently 20580 kWh per household @ 65% efficiency. Average electricity consumption 3300 kWh.

Gas generated electricity assumed to be 42% efficient after transmission losses. Electricity bill reduction taken to be 40% with

microCHP = 1320 kWh. Gas burning efficiency (for heat) taken to be 82% (a real-world value rather than a peak value).

This would mean 20580+3300/.42 = 28437.1 kWh of gas is burnt currently.

Generated electricity replaces 1320 kWh of grid electricity = 1320/.42 = 3142.8 kWh less gas needed at power station.
Remaining grid electricity generated at 42% efficiency = 0.6*3300/.42 = 4714.3 kWh.
Heating requirements + heat added to replace electricity no longer taken from grid = 20580*0.65 + 1320 = 14697 kWh of heat.
At 82% efficiency this is 17923.2 kWh of gas burnt in the home.
Total gas burnt with microCHP = 17923.2 - 3142.8 + 4714.3 = 19494.7 kWh

So only a 31.4% saving, which is less than I thought, but there are side-benefits such as the reduction of peak electricity demand I mentioned before and installation of an export meter makes it a bit easier to then encourage other forms of microgeneration.
Note that electricity generated outside the heating season when the CHP unit is used for hot water does not actually need to figure in the heat-replacement calculation, but I disregarded this as not significant.

Let's compare with an air source heat pump with COP of 3:
Thermal demand = 20580*0.65 = 13377kWh
Electricity demand = household consumption + heat pump = 3300 + 13377/3 = 7759KWh
From gas fired power station at 42% efficiency = 18473.8 kWh

So a 35% saving compared to the reference household and a 3.6% saving over the microCHP unit, so they are roughly comparable given the limitations of this calculation. Note that I have assumed the heat pump can supply hot water, which may well not be practical. Obviously ground source heat pumps would be more efficient, but impractical in many cases. The relative installation costs of all three options are likely to point to a greater potential take-up of microCHP.

owain.davies

Micro-CHP is almost certainly not the answer to the issues we face, primarily because of a couple of reasons:
(1) Fitting it to an energy efficient home (especially a flat) means that the electricity production is so negigible, it will never pay back in the lifetime of the boiler. And sadly, economics rules green issues every time
(2) As the grid decarbonises through nuclear and renewables (maybe as soon as 10 years time), these micro-CHP units will be emitting more CO2 than equivalent grid electric, so those people who care for the environment will stop using them.

Far more likely to solve some of the issues is macro scale CHP, because although it has the same issues of being higher in emmissions than a potential future grid, only one generator needs to be changed for thousands of houses. Also, sensible use in heat load balancing (commerical premises and ideally swimming pools) means that there is always heat load and therefore always low carbon electricity being produced, meaning these units could actually pay back (all be it in 25-30 year horizons)

As for nuclear vs renewables, nuclear is clearly the more secure supply for grid baseload (still, foggy autumn day anyone? All the lights would go out as PV and wind stop working at the same time!) and don't forget that renewables also take resources from minerals, and in larger quantities than nuclear does! There simply aren;t enough accessible mineral resources for existing photo-volatic technology, and everything else requires large amounts of metals and alloys, which are in themselves energy intensive to produce. Carbon wise, many renewable installations take far more carbon to produce than they ever save! The emissions argument can also be used against nuclear, but at least you can rely on nuclear to provide round the clock power.

andy80085

If you're boiler breaks down your local plumber comes out to fix it. Who do you phone when your CHP unit goes on the blink.

A commercial CHP engine has to run for over 5000 hours per annum recovering all the heatbefore it is worth considering. How many hours does your boiler run in a year?

After 10 years it will need a very expensive overhaul or you have to chuck it in the bin.

andy80085

amcluesent wrote: »

Then you pay 0.1140 Euros per KWH or less than 0.1p per KWh, tariffs here.

I believe that may be 9.1 p/kWh. Therefore Nuclear power argument is nulified.

cepheus

owain.davies wrote: »

As for nuclear vs renewables, nuclear is clearly the more secure supply for grid baseload (still, foggy autumn day anyone? All the lights would go out as PV and wind stop working at the same time!)

This is certainly a problem. Of course this is the advantage of including Tidal on the list of renewables, although even this varies (add neap tide to your list).

For this reason since most of us have a gas/ heating oil boiler already why not just add the heat pump and use the gas/biogas boiler in foggy cold weather? Of course heat pumps can be powered by biogas engine then you can have CHP as well, complicated but perhaps OK for a larger establishment.

With regards to well insulated homes, I guess the solution is is to dispense with the heat pump altogether and just use the (bio)gas boiler for hot water and space heating on foggy days, doubt if it will be cost effective to install anything.

mech_2

owain.davies wrote: »

Micro-CHP is almost certainly not the answer to the issues we face, primarily because of a couple of reasons:
(1) Fitting it to an energy efficient home (especially a flat) means that the electricity production is so negigible, it will never pay back in the lifetime of the boiler. And sadly, economics rules green issues every time

That is only an argument against microCHP in the most limited of cases. The vast majority of the UK's housing stock is not energy efficient. New-build flats tend to be purely electrically heated with no gas connection anyway, so not even relevant. Britain has a long heating season, it has a large percentage of old houses (pre-1970) with a gas connection. MicroCHP is ideal for this country.

(2) As the grid decarbonises through nuclear and renewables (maybe as soon as 10 years time),

All I can say to that is "rofl". 20 years would be wildly optimistic. The government hopes to generate 20% of electricity by renewables by 2020. Nuclear's share is about 19% and will go down before it goes up again - unlikely to be much different from now in 2018. So 60% of electricity will still be fossil fuelled. Crucially, much of this will be during the evening peak that microCHP could contribute to.

these micro-CHP units will be emitting more CO2 than equivalent grid electric, so those people who care for the environment will stop using them.

They can't use more CO2 than grid electricity. They're generating the electricity practically for free as a side benefit. Why do people find this so difficult to understand? You have a gas boiler that generates some electricity, direct gas heat heats the house, the waste heat from using the electricity in appliances also heats the house. You heat the house with gas, but you got some electricity along the way.

Far more likely to solve some of the issues is macro scale CHP, because although it has the same issues of being higher in emmissions than a potential future grid, only one generator needs to be changed for thousands of houses. Also, sensible use in heat load balancing (commerical premises and ideally swimming pools) means that there is always heat load and therefore always low carbon electricity being produced, meaning these units could actually pay back

I can't fathom why you think centralised CHP is better. It needs to be able to be shoehorned in to a neighbourhood so that it's close enough to homes and then all the roads need to be dug up to lay insulated hot water pipes (which will inevitably lose some heat between the power station and the homes). It also needs a totally different metering/billing system. Installation doesn't sound as cheap as microCHP to me.

(all be it in 25-30 year horizons)

Well that's why it isn't popular.

As for nuclear vs renewables, nuclear is clearly the more secure supply for grid baseload (still, foggy autumn day anyone? All the lights would go out as PV and wind stop working at the same time!)

Tidal, wave, biomas, hydro, storage. But your strawman ignores the fact that the weather is never the same over the entire British mainland.

and don't forget that renewables also take resources from minerals, and in larger quantities than nuclear does!

Citation needed.

Nuclear needs tens of thousands of tons of rock to be pulverised per year per reactor and that's before you actually get the fuel out of it.

There simply aren;t enough accessible mineral resources for existing photo-volatic technology,

I think I may have to rofl again.

and everything else requires large amounts of metals and alloys, which are in themselves energy intensive to produce.

Everything else? Every what thing?

Carbon wise, many renewable installations take far more carbon to produce than they ever save!

Such as?

The emissions argument can also be used against nuclear, but at least you can rely on nuclear to provide round the clock power.

Which is why it can never heat your home. Heat demand varies throughout the day. Nuclear can't vary throughout the day. Gas can only realistically be replaced with biomass.

Nuclear provides 6% of the UK's energy (not electricity, all energy) and supply is inflexible. Gas provides 37% and is flexible. 20 years from now the figures could be 13% and 30%, but we will still need to make the most of available fossil fuels.

mech_2

andy80085 wrote: »

If you're boiler breaks down your local plumber comes out to fix it. Who do you phone when your CHP unit goes on the blink.

The heating engineer. I wouldn't call a plumber to fix my boiler. Tried that once. "Beats me", he said, "I've tried all the obvious things. Have you asked the manufacturer? I dunno what makes it tick, I just fit 'em".

A commercial CHP engine has to run for over 5000 hours per annum recovering all the heatbefore it is worth considering. How many hours does your boiler run in a year?

That's probably an internal combustion engine. Have a look at the Stirling engine domestic CHP units. There's really not much on them that can go wrong that can't go wrong on a normal boiler.

After 10 years it will need a very expensive overhaul or you have to chuck it in the bin.

15 years expected lifespan. Paying for itself in about 8.

And repair is probably cheaper than replacement.