Avoiding the rated power fallacy

How much energy does an oven use? Today I have seen examples both on the BBC Food Programme and on the Uswitch website [1] where this question was answered by multiplying rated power by hours of use. This is totally wrong because ovens have thermostats. They turn the power off when they are up to heat. The power of the oven is mainly used during the initial heating phase. After that it turns down the heating and/or cycles on and off. 

Screenshot from Uswitch [1] As well as falling for the rated power fallacy Uswitch has confused watts (power) and watt-hours (energy).

How long can we rely on cheap rate electricity?

A number of my friends are considering or have already installed a Tepeo zero emissions boiler (ZEB) with storage as a low carbon heating solution for their home. This is less disruptive than installing a heat pump but it is only 100% efficient compared to 300% or so for a heat pump. It relies on cheap electricity to keep energy bills at a sensible level – either economy 7 overnight, or similar, or relying on prices fluctuating during the day with a tariff based on wholesale prices, such as Octopus Agile. I shall call all of these tariffs ‘cheap time’, for brevity. 

Cheap time tariffs could become cheaper – or more expensive

Historically, overnight demand is lower than during the day, and hence prices are lower because there is no need to run the expensive peaking plant. This has enabled tariffs such as Economy 7 to work well for homes with storage heating. Hitherto this has been only a small fraction of heating demand: I estimate just 2.2% of domestic heating demand in England [1]. However, there is going to be lots more demand for cheap time power due to switching to low carbon transport and the need for electricity storage to take account of intermittent renewables. Cheap-time tariffs could become cheaper, because renewable power is cheap, or more expensive, because there is more demand for it. On balance I fear the latter is more likely.

Greenhouse Gas Removal – and checking it works

According to the Climate Change Committee (CCC) balanced pathway to net zero, we should be capturing and storing 58 MtCO2e/year by 2050 [1]. This is called greenhouse gas removals (GGR) or sometimes carbon dioxide removals (CDR). It is hard to see how we can get to net zero without some GGR, but there is very little of this happening right now. There are several strategies likely to be deployed. Unfortunately, the ones which are most likely to be permanent tend to be most expensive as well, while with the cheap ones it is harder to measure how well they are working.

In the CCC balanced pathway, 90% of GGR is some form of BECCS – bioenergy with carbon capture and storage. That generally means burning biomass for energy and capturing CO2 from the flue gas. Most of the rest is direct air capture (DAC) which means getting carbon dioxide from the air rather than flue gases. The captured gas must then be stored typically in rock formations or depleted oil and gas wells.

 

Figure from [1] CCC sixth carbon budget

Keeping warm in cold conditions - field studies of personal heating devices

My last post discussed how much we need to heat our homes to keep them healthy. The short answer was, about 8°C warmer than outside. This could mean temperatures as low as 12°C or even less. So how do we keep ourselves comfortable? Wearable devices, warm cushions, portable electric heaters? This post reviews some field studies described in academic literature. It seems to be a hot topic in China.

How warm should your house be to keep it healthy?

During the gas shortage some of us are turning our heating down to save money and some are turning it down to reduce demand and keep prices down generally. How low can we go? There is our own health to consider but fit adults wrapped up warm and with personal heating devices such as jackets and gloves can be comfortable in surprisingly chilly conditions (see the next post). What about the house? Central heating keeps the house dry as well as keeping us warm. How much heating do we need to keep the house safe?

How to recycle solar panels: the cheap and cheerful approach

A recent journal paper suggests a new approach to recycling solar panels [1]. This is very much a cheap and cheerful approach (my words) compared to the gold standard ‘full recovery end of life’ approach. A comparison of the two methods is illuminating. The main author of the paper, Pablo Dias, has since set up a company called Solar Cycle to commercialise his process. It is great to hear of technology progressing from research in a university into the real world. Dias is from the School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, (Sidney, Australia) and some of the contributors to the paper were from other universities in Brazil but Solar Cycle has been set up in Texas, USA. 

The cheap and cheerful approach:

• Involves only mechanical process and electrostatic separation; no high temperatures and no acids
• Produces less pure products – more like metal ‘ore’ than refined metals 
• Is less capital intensive
• Can be economic at small scales

The effect of reducing radiator temperature on room temperature

Heating engineer experts have been complaining for years that condensing boilers were not being installed correctly to achieve the claimed efficiencies. A gas condensing boiler that is supposed to give you 92% could be giving you 85% or even less, if it has been set to heat the radiators at 70°C or hotter. Now that we have an energy crisis, this is one of the few things you can do to make significant savings for no cost and hardly any effort (if you have a combi boiler). Nesta have just launched a campaign on this. However the Heating Hub has been giving similar advice for some time. Some of the savings are from increasing boiler efficiency and some are from indirect effects on the room temperature. There is usually only a small reduction in average temperature but it will vary from one house to another. If you find you are uncomfortable you can tweak the thermostat up a bit to compensate.