Review: Housebuilder's Bible

Mark Brinkley's guide to building homes is a best seller and doesn't really need me to tell you how good it is. This is the 14th edition and he doesn't update it regularly only for love. However, he did ask me to check out some of the new content about low carbon heating. So I did, and while I was at it I looked at some other bits too, just because they are interesting. I can't say it is impossible to put down but it is certainly easy to keep turning the pages. I have never built or specified a house and probably never will, but if I did I would do well to start by reading this book. Actually I might want to build an extension one day and it would be useful for that. Also I have done a green retrofit (insulation) project and his section on that would have been helpful. 

 

Do people with PV panels consume more electricity?

Calculations of the benefits of renewable energy usually make the assumption that people will continue to use electricity in the same way they did before. However, a lot of studies show this is not the case. Typically electricity use does increase by up up 20% of the renewable energy generated - a rebound effect of 20% However other studies find that on average electricity use is unchanged. A lot depends on financial incentives, and some on attitudes and some on the technology used. This suggests it is possible to 'nudge' this behaviour to gain the most benefit - how is the UK doing in this respect? It may be that we have, by good luck or judgement, avoided the worst outcomes.

How clean is 'clean' coal?

The G7 summit has agreed to to move away from making electricity from coal plants, unless they have technology to capture carbon emissions [1]. What does this mean in terms of greenhouse gas emissions? Carbon capture and storage  (CCS) is not a perfect solution, sadly. From my calculations, taking into account upstream emissions,  the emissions from a coal power station even with CCS are worse than those for UK grid average electricity now and with little hope of further improvement. In 2019 a little more than a third of UK electricity was from renewable and this continues to increase.  Of course the UK is not representative of the global average, but it shows what is possible, even starting with legacy power infrastructure. By 2050, average UK grid emissions should be down another 90%, but this may not be possible if much of our power comes from coal with CCS. Natural gas with CCS would be more sensible.

Comparing emissions from current UK coal and gas power stations, the same with CCS and average grid emissions. Coal with CCS is slightly worse than grid average, gas with CCS is considerably better. Estimates include emissions upstream of the power station. Data sources and assumptions are described below.

There are several reasons why clean coal is less than 100% clean:

• There are upstream emissions, from mining and handling the coal before it gets to the power station.
• Carbon capture at the power station does not catch all the carbon.
• Carbon capture uses energy which makes the power station less efficient - so you need more coal (and hence more emissions) to make the same amount of energy.

Savings on bills and carbon with TOU tariffs

Converting our heating and transport energy to electricity increases demand which puts strain on the grid. However, it is primarily the peak demand that is the problem, so shifting demand away from the peak times helps a lot. When demand is high, wholesale prices and carbon emissions are usually also high, because we need to use less efficient power sources to top up supply. However there are other factors that affect prices and emissions.

It is possible to take advantage of these differences by switching to an electricity tariff that offers higher prices at peak times and lower prices at times of low demand. In this post I compare two: Tide from Green Energy, which has three tariff levels through the day and Agile from Octopus which follows wholesale prices directly (at least for now). I look at both price differences and the carbon savings from shifting your demand away from peak times to the cheapest times. Shifting demand is easiest with a battery. 

Decarbonising your home or car - which saves more?

The global carbon budget is extremely tight and we all need to do what we can, as soon as we can, to reduce the carbon emissions from our home and other life choices. I was recently asked – will I save more by replacing my gas boiler with a heat pump or replacing my car with an EV? I was surprised to find the results were fairly well balanced. Which saves most depends quite a lot on how much gas you use and how much fuel you typically use in your car. Here are some typical figures and example calculations. 

Also there is at least one other factor to consider: lock-in. If you buy a new gas boiler today you probably will not want to replace it for 15 years. On the other hand you might buy a second hand car and expect to replace it in 5 years. So the decision on a new gas boiler might have more impact over the lifetime of the boiler even if the annual carbon savings are higher for the car.

Field tests on thin insulation for internal wall insulation

There is a new report out: Measuring Energy Performance Improvements in Dwellings Using Thin Internal Wall Insulation [1]. Researchers at Leeds University performed field tests on six kinds of thin internal wall insulation: PIR, aerogel, and EPS (all laminated onto a board), cork render, latex rolls and thermo-reflective aerogel paint. They were all compared to a typical thickness of phenolic foam insulation - the conventional option. The products were installed on three different solid-wall houses (two systems tested in each). The team measured U-values (thermal conduction through the wall) directly and also the impact on air tightness. They used simulations to study the effects on damp and risk of frost damage. They recorded costs of installation, separating out the costs of materials and labour and decorative finishes. They interviewed the installers to find their opinions - you very rarely find these reported! Here I describe the main results. 

A tradeoff between cost thickness and performance.

Reduction in heat loss (percent reduction in measured U-value) obtained from Phenolic foam board and six types of thin insulation. Paint: thermo reflective aerogel paint, Latex: latex roll, Cork: cork render. The thickness is the total thickness including air gap and plaster skim, where appropriate. Data from [1]

Renewable heat installation rates

A friend asked me if I think that heat pumps are still a 'niche' technology or are becoming mainstream. She was surprised by the number of companies able to install in this area - the MCS website finds ten within 30 miles of Cambridge. So I took a look at the statistics for take up of the renewable heat incentive for heat pumps (domestic). Here is a chart showing cumulative installations.

Domestic Renewable Heat Incentive cumulative applications by month, data from [1]. The steep rise up to April 2015 includes legacy applications.