Posted By: ringiIt all depends on when small CHP become cheap enough to be mass market and what the service costs are.

If it ever does. Is there any reason to expect that it will? Won't scale effects mean it continues to be more efficient in larger plants?

You do have the DWH tank that does not need fully heated until bedtime showers, so can be heated based on the evening usage of electricity.

Perhaps, but for example if fuel cells designed for cars were adapted for home use, they would have enough power to instantaneously heat a shower. No need for storage.

Ceres Power claims to have a small fuel cell that can achieve 50% net electrical efficiency, if this becomes a usable system, then the heat can be considered the bonus, with the fuel cell sized so the electrical output can be used in the home for most of the day. (Let the grid cope with peak usage, as the export payments are so low, so not worth sizing a system that will expert much.)

Such a device would change the baseline. Grid power generation efficiency would necessarily rise to at least the same level.

As soon as electrical storage comes down in price, the fuel cell can be sized to provide most of the electrical needs of the house (and maybe car). (As fuel cells can track electrical demand in near real time, if the capital cost of having a larger fuel cell is not great, then electrical storage is not needed.)

As things stand, it seems likely that electrical storage will never be particularly cheap.

Then it gets interesting, as you have about 10kwh of “free” heat each day, but that is not much more then what a lot of households needs to heat the DHW.....

Well, it seems to be about 3.5 kWh more than we need and I don't think our system is particularly efficient. Any wasted 'free' heat is actually a negative that requires the efficiency calculations to be redone. That's why it's better to look at the electricity as free instead.

Posted By: djhPerhaps, but for example if fuel cells designed for cars were adapted for home use, they would have enough power to instantaneously heat a shower. No need for storage.

The gas pipe coming into most homes does not have a large enough gas flow to heat more then 1 good shower, otherwise combi boilers would have taken over from DHW tanks a long time ago.

Hybrid fuel cell is currently at 65% electrical efficiency and overall efficiency of 95% the only downside is scale the smallest being 1MW. Certainly makes you wonder why anyone would bother with nuclear.

Posted By: ringi

Posted By: renewablejohnHybrid fuel cell is currently at 65% electrical efficiency and overall efficiency of 95% the only downside is scale the smallest being 1MW. Certainly makes you wonder why anyone would bother with nuclear.

The fuel has to come from somewhere......

So long as its renewable does it really matter.

Posted By: SteamyTeaIf a fuel cell is run of natural gas, it still produces CO2 as a by product I think (I hate chemistry but think it is the same as reforming NG to H)

So what is the problem with that. We need to capture CO2 to enable production of bio-methane from excess energy from wind and solar.

<blockquote><cite>Posted By: SteamyTea</cite>You will have to explain that a bit more. The thread title was about reducing CO2, not making more unnecessarily.</blockquote>

Bed time reading Section 4.2

http://www.iea-biogas.net/files/daten-redaktion/download/Technical%20Brochures/Smart_Grids_Final_web.pdf

The way to capture C02 is to Grow More Hemp...

(each ton of hemp grown represents 1.63 tons of CO2 absorption)

The hemp is then used in hempcrete, for slabs and house walls - taking the CO2 clean out of circulation.

gg

Do you have a link to the operational data ?

<blockquote><cite>Posted By: SteamyTea</cite>Do you have a link to the operational data ?</blockquote>

This is the first plant which Audi opened back in 2013.

https://www.audi-mediacenter.com/en/press-releases/world-premiere-audi-opens-power-to-gas-facility-784

A few recent thoughts on carbon intensity. A few have pointed out that it's not average emissions that count, but peak marginal.

Now if there's no coal, the dirtiest generation is coming from gas. Closed cycle stations have a grid intensity of about 360 gCO2/KWh + 7% for transmission losses. So if (when) there's no coal 385 should represent an upper limit for grid intensity. And in practise of course it should be much lower due to the contributions from other, lower emitting power sources. Hence recent averages of 240-325.

Unless we've got lots of more highly polluting open cycle gas power stations. Do we??

Anyway, more good news for heat pumps. If the average conservatively converges on, say 350 gCO2/kWh, a space heating heat pump only needs to manage 1.6 to match gas heating emissions, and a very achievable 3.2 to halve them. Even means their hot water is worthwhile. I think they struggle to better 2.5 COP, but that's still 35% less Co2 to heat water.

Posted By: djh

Posted By: GarethCI was confused too! But basically I'm pretty sure the conversion factors in the 2015 REPORT on UKconversionfactorscarbonsmart are based on -2013- grid carbon intensity DATA. i.e. pretty out of date.

That doesn't make sense. Requiring companies to report actual emissions in 2015 based on rates for 2013 would skew the figures, apparently in a direction that appeared bad for the government. So why would they do that?

I believe that companies -report- their emissions well in arrears (we certainly do). i.e. the latest they are likely to be reporting currently are 2014 figures, so it's ok if the data aren't very timely.

Ah, I think I get it. Thanks ringi. Although you've answered a question I put on a different thread!