https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1083857/2022-ghg-cf-methodology-paper.pdfIt's a long read, but the parts I went looking for were the conversion ratios between burning methane (LPNG) for heat and using resistive heating elements (for example). CO2 / kWhe versus CO2 / kWht
There are tables and tables and tables and they all seem to give different values depending on which perspective they are looking at it from. The surprising thing is how rapidly the ratio has been falling.
I find as you get older time seems to go faster and it's easy to get out of date, but the figures they are proposing for the UK fuel mix are something around 170g/kWh burning methane, 190g/kWh burning propane and 191g/kWh electricity.
I'm like, what? (watt?). How? When?
The UK has a fuel mix of about 40-45% natural gas for electric generation. CCGT plants are about 60%-70% thermally efficient and the turbine generators are, what?, 90% efficient? Then (from the report) about 8% grid loss.
I'm probably butchering the maths, but for each kWh electric, 0.45kWh is generated from gas. The overall generation efficiency is 60%*90%*92% = 0.496. So to generate 0.45kWh it will need to consume roughly 0.9 kWh of gas.
That works out. Doesn't it? That 1kWh of electricity, in the UK, currently "costs" 1 kWh of gas. That would not eat into the GOP of heat pumps that much.
I suppose I'm admitting I was wrong for quite a while. I thought it was just 3:1 * carbon fuel mix %.
Either that or there is a large amount of greenwashing going on, or my maths or assumed figures (for generation efficiencies for example) are way out. The others are from the paper.