How to grow climate friendly food at home

Were you as shocked as I was to hear that growing your own food at home has six times the GHG emissions as conventional agriculture? Surely it does not have to be like this? I looked at the study behind the news [1]. (It came out in January and I do not understand why it has hit the news again now.) The good news is, the main sources of emissions from home grown produce are easily avoided, with a bit of care. 

Compost heaps were one of the main sources of GHG emissions from urban gardens - but good practice can minimise this.

Temperatures in my youth and now

How have external temperatures changed in my lifetime? I have been playing with graphs that show current X (e.g. temperature) as a line versus historic X as typical ranges. Here is one showing temperature in East Anglia in my youth (age 0 to 21) versus the last six whole years. The shaded areas show the range of temperatures seen from 1963 to 1984, with green and blue being below the median while orange and red are above the median. The temperatures are the average, including overnight, The maximum temperature chart actually looks much the same only shifted up a bit.

Mean temperatures by month in East Anglia from 2018 through 2023, versus typical temperatures (shaded) from 1963 to 1984. Click to see this enlarged.

A whole street of heat pumps - noise levels

Heat pumps make noises, of course they do. The question is, will their noise be a nuisance if every house on the street has one? The short answer is - not usually. Here I explain why we are not disturbed by ours, and why a whole street of heat pumps does not sound much louder than a couple. In urban areas, other noises are much more noticeable. In rural areas, you might be disturbed by yours but not so much your neighbour's.

Rainwater harvesting: dammed by regulation

For the whole of the East of England water supply is an increasing problem. Here in Cambridge we need to reduce the amount we take from our aquifers by about half in order to protect the chalk streams. This will be achieved with a combination of reducing leakage, reducing demand and increasing supply (by building large reservoirs). One way to reduce demand is to harvest rainwater for use where it does not have to be drinking quality, such as flushing toilets. 

Eddington in North West Cambridge has a rainwater harvesting system for 3000 homes, the largest in the country. It is often cited as an exemplar for water saving, with every home having two supplies: one from rainwater (non-potable) for use in the garden, in the washing machine and flushing the loo alongside the one from the mains for everything else. As I recall, the pipework has different colours. The rainwater is stored in a rather beautiful lake and is fairly clean but not as clean as the water we get from the chalk aquifer; there is equipment for basic treatment on site. The problem is, the rainwater harvesting supply has never been commissioned due to concerns from the Drinking Water Inspectorate (DWI). 

 

Brook Leys Lake at Eddington – stores rainwater for supply to homes, but not commissioned for use.

Shifting policy costs on energy bills - revisited

As I said in a previous blog post, the current price ratio between electricity and gas means that switching to heat pumps often means bills increase - a major deterrent to many households considering taking on low carbon heating. Part of the problem is because of the way 'policy costs' are loaded mainly onto electricity bills instead of gas so when you switch to a heat pump you end up paying far more policy costs. However, if we were to change this so that policy costs were evenly distributed between gas and electricity, then heat pumps become cheaper. I have updated my previous calculation with a slightly revised method and based on the current price cap as shown in the following chart.

Chart shows the annual bill split into components: policy costs and other for each fuel. Current uses components as computed by OGGEM, 50% split means the variable policy costs are split between gas and electricity. HP costs are with the gas boiler replaced with a heat pump. Assumptions are explained below. Click on this for a larger image

A New Year wish – autonomous cars.

Driverless vehicles are in the news again. (Driverless cars: Tech possible for UK motorways by 2026, transport secretary says). 

The usual justification given for needing driverless cars is safety because most car accidents are caused by human error. I disagree because it seems unlikely driverless cars will ever be demonstrably and significantly more safe than cars driven by humans. However, that does not mean we do not need autonomous vehicles. I think the main reasons are improving equality of access and reducing GHG emissions. That may surprise you as it is often predicted autonomous vehicles will increase car use and emissions. However, driverless cars enable cheaper and more convenient public transport, and also enable policies that can discourage car use. 

Should we shift energy taxes to make heat pumps cheaper to run?

Tariffs vary but averaged across the country, under the current OFGEM price caps, electricity costs four times gas per kWh. This means that by my estimate [1] unless you go off gas completely (hence avoiding the fixed daily charge) you need a heat pump efficiency (SCOP) of 360% to get similar costs. This is not unknown but considerably better than average. If you do go off gas completely, you need 320% which is still better than average. If you only got 300% you would be paying 6% more with the heat pump than gas. This is discouraging for people wanting to switch to low carbon heating.

However, a significant part of the electricity bill is due to environmental and social policies or 'taxes'. If these were removed or shifted, the ratio of electricity to gas price would be smaller, making heat pumps relatively cheaper. Hitherto, policy has been to keep gas cheap because so many of us rely on it for heating which is essential for health. However, doing so penalises households that make the transition to low carbon heating. What are these taxes and how much difference would this make? Here is a graph showing policy costs on gas and electricity as of September. There are more policy costs on the electricity bill than the gas bill and the home with a heat pump uses more electricity, so pays even more policy costs.

 

Policy costs for a typical bill of 12000 kWh gas, 3100 kWh electricity or, with a heat pump, 6650 kWh annually. The policy costs are from OFGEM [3] and the heat pump kWh used is from [1] Costs are taken from the period July/Sep 2023, the latest available. These costs vary little by region. The acronyms are explained below.