Observations no Gas/leccy heating: decarbonising UK

michaels

So within the next 15? years the UK will have to switch away from using gas for household heating if it is to meet its climate change emissions targets.

I have had a boiler problem (again) so having been using electric heaters and immersion for hot water/central heating this month.

It would appear that even using this for of electric heating rather than a more efficient heat pump it take sonly about 1 kwh of electricity to replace two of gas. Our boiler is supposedly highly efficient modulating condensing weather compensation model so it is unlikely that other boilers are likely to be much better. We do probably use less heat and less HW than we would normally but even still it would seem that making the switch may not just be a win because of less carbon fossil fuel burning but will also lead to increased energy use efficiency and thus won't be as costly as some fear.

It also suggests that I would only need a heat pump with an average efficiency of less than 2 for electric heating to cost no more than gas given the relative unit costs (11p/unit electricity, 3p/unit gas). Can this be right - surely if this is the case why would anyone replace a gas boiler with a new one or install a new gas boiler in a new property?

zeupater

michaels wrote: »

So within the next 15? years the UK will have to switch away from using gas for household heating if it is to meet its climate change emissions targets.

I have had a boiler problem (again) so having been using electric heaters and immersion for hot water/central heating this month.

It would appear that even using this for of electric heating rather than a more efficient heat pump it take sonly about 1 kwh of electricity to replace two of gas. Our boiler is supposedly highly efficient modulating condensing weather compensation model so it is unlikely that other boilers are likely to be much better. We do probably use less heat and less HW than we would normally but even still it would seem that making the switch may not just be a win because of less carbon fossil fuel burning but will also lead to increased energy use efficiency and thus won't be as costly as some fear.

It also suggests that I would only need a heat pump with an average efficiency of less than 2 for electric heating to cost no more than gas given the relative unit costs (11p/unit electricity, 3p/unit gas). Can this be right - surely if this is the case why would anyone replace a gas boiler with a new one or install a new gas boiler in a new property?

Hi

You're effectively saying that on environmental impact grounds if it takes 2kWh of gas to produce 1kWh of electricity and that electricity costs 11p/kWh & gas 3p ... however, the point missed is that (using your figures and assuming gas as fuel source) on cost grounds the required SCOP to break even would need to be above 3.0(11/(3/.85)) whilst leaving cost aside and simply looking at environmental impact it needs to be the SCOP of 1.7 (2/(1/.85)).

The issue at hand is that there's a direct relationship between energy source, unit price and efficiency which results in a need for the unit cost of electricity to vary in percentage terms against the unit cost of gas .... assuming that the gas cost remains static, to maintain the environmental impact at current levels requires the cost of electricity to reduce as the SCOP reduces, so to have an installation with a SCOP of 1.7 to maintain balance on environmental grounds, the cost of electricity would need to reduce from 11p/unit to 6.2p ((11/3)*1.7) to stop consumer bills rising, which is particularly unlikely.

The complexity involved to establish a compromise position (how much extra people are willing to pay for energy in order to help the environment) is far beyond what most consumers would attempt to consider when choosing a technology that they're not familiar with, so it's much easier to simply base any decision on it being cost effective and take the benefits to the environment as a given, which a SCOP of ≥3.0 should achieve on your figures ... it's also relevant to note that any increase in efficiency above 3.0 acts to recover the differential cost of the heating source (boiler vs heatpump), so either the SCOP needs to be well above 3 or the cost of heatpump technology needs to fall to levels much closer to that of current boilers! ...

HTH
Z

michaels

So current set up, 10 kwh of electricity costing 110p gives me the same amount of 'heat' as 20kwh of gas costing 60p.

If I had a heat pump that gave '2kwh' of heat for each kwh of electricity I put in then my 10kwh of electricity would give me the equivalent of 40kwh of gas costing 120p.

The first bit obviously sounds wrong - only 50% of gas kwh turn into useful heat kwh - I guess we must be using a lot less heat with the electric heating than we do with the gas or there is something drastically wrong with our boiler efficiency - perhaps that is why I am sitting here shivering....

Using instead a relative efficiency of 85% for gas as per your calc gives the approx. 3 COP needed for the heat pump. Out of interest what is they typical average COP for an ashp in the UK, given that our poorly insulated houses need more heat supplied the colder it is outside and thus the less efficient the heap pump.

Martyn1981

Over a year the average COP for ASHP in the UK is about 2.9. I think GSHP and WSHP are a bit better. So 3.5x better than a gas boiler at around 80-90% efficiency.

I also seem to remember a combined GS/AS HP set up which resembled a half buried fence. That way you get GSHP efficiency in very cold temps, but ASHP efficiency in warm air periods.

Heatpumps are very popular in colder countries without a gas grid as good as the UK's, but they also build super efficiently ..... because they have too.

Lastly, there is the idea of methane fuel cell boilers. These already exist(ish), and I don't think are particularly different to H2 fuel cells, just less efficient at about 50%.

So for 1kWh of gas you get some heat and hot water from the boiler, then 0.5kWh of leccy. But, if you used that leccy for a heatpump, then it could supply on average 1.5kWhs of heat.

So a combination of PV, batts, methane boiler/fuel cell and ASHP would work very well, but I don't know if the fuel cell boiler will get cheap enough to consider. The benefit here is that we'd be using the existing gas grid to help with heating rather than shifting all heating on to the leccy grid. Great use of stored bio-methane from summer excess generation, perhaps!

GreatApe

michaels wrote: »

So current set up, 10 kwh of electricity costing 110p gives me the same amount of 'heat' as 20kwh of gas costing 60p.

If I had a heat pump that gave '2kwh' of heat for each kwh of electricity I put in then my 10kwh of electricity would give me the equivalent of 40kwh of gas costing 120p.

The first bit obviously sounds wrong - only 50% of gas kwh turn into useful heat kwh - I guess we must be using a lot less heat with the electric heating than we do with the gas or there is something drastically wrong with our boiler efficiency - perhaps that is why I am sitting here shivering....

Using instead a relative efficiency of 85% for gas as per your calc gives the approx. 3 COP needed for the heat pump. Out of interest what is they typical average COP for an ashp in the UK, given that our poorly insulated houses need more heat supplied the colder it is outside and thus the less efficient the heap pump.

This was a calculation on a project

Gas:

£4000 capital cost in excess of electric only equating to £400 per year (£4000 depreciated over 20 years at 5% discount rate) and maybe that is too conservative as it assumes the boiler will last 20 years. And maintenance and inspection costs another £50 for the gas system vs the electric system.

Load on all electric: 3MWh for electricity. 1.5MWh base load water 7MWh seasonal heating
Gas&Eletric: 3MWh for eletiricty. 2MWh for gas base load heating 9MWh for gas base load heating


£950 annually for gas and electric version
£1510 Annually for electric only

Seems £560 pa more expensive but reduce the £450 from capital loss and additional maintenance and its closer to £110 more expensive for the electric only version

For well insulated properties or smaller properties or flats its almost certain to be better to be electric only

And in France in particular most new builds are electric only and most of that comes from their nukes at least 9/12 months.

To make things even more rosy, wind power generation is ~1.5-2x as much in Q1/Q4 than it is in Q2/Q3 so works well with seasonal heating demand too. Maybe if we go wind heavy winter eletricity prices could be cheaper than summer prices further incentivising electrical heating.