Saturday, 10 March 2018

How much energy can you get from rain?

Researchers in China have created a hybrid solar panel that can also make electricity from rain [1]. This has obvious advantages, especially for regions where you get more rainfall in winter than in summer because it will help to even out generation through the year. But how much energy can you actually get from rain? How does it compare with solar energy - and is it worthwhile? Here is a back of the envelope calculation.

Sunday, 11 February 2018

Uncertainty about pollution from wood stoves

In my previous post on air pollution, especially fine particulates (PM2.5), in Cambridge I concentrated on traffic, hardly mentioning wood stoves  as a possible source. However, wood burning is cited as an important source of pollution in parts of London [1] so why not Cambridge? To be honest I steered clear of the issue because there is such a huge amount of uncertainty I felt unable to present any facts with confidence. The National Atmospheric Emissions Inventory (NAEI) estimates that 35% of PM2.5 in the air is from domestic wood burning[2] - or it could be 10 times less [3].

The issue is so uncertain that the government is running a call for evidence on the issue. This runs until 27th Feb.  In their call for evidence they say [4]:
  • Burning wet wood (i.e. not properly seasoned wood) generates at least twice the emissions from dry wood.
  • Estimates for the proportion of wood that is burnt wet range from 80% (from the wood industry) to 20% (from a survey by BEIS).
  • Estimates of how much wood is burnt in total range for 3 to 6 million tonnes per year
  • Burning on an open fire generates up to 10 times the emissions from a modern wood stove.

Wednesday, 7 February 2018

Where does air pollution in Cambridge come from?

Air pollution is a big problem for our health, especially very small particles known as PM2.5 (less than 2.5 micrometres in size) that penetrate deep into our lungs. PM2.5 is more closely linked to death rates than the other pollutants [1]. Diesel cars are blamed for a large proportion of air pollution in our cities. But are they the only problem or even the main problem? Traffic is the main source of nitrogen oxides (NOx) in our cities but for particulates the story is more complicated.

  • Most NOx pollution in cities comes from traffic, mainly from burning petrol or diesel (especially diesel).
  • NOx dissipates fairly quickly.
  • Particulates (especially PM2.5) are partly related to traffic (including chemical reactions with NOx) but there are other sources.
  • Particulates can waft around and travel for long distances. Most of the particulates pollution in Cambridge comes from outside the city.

What this means is that while reducing traffic in the city, especially diesel cars, will reduce NOx levels, they will have less of an impact on particulates. Tackling that requires action across the region, not just the city.

Thursday, 25 January 2018

Is waste incineration sensible, a health disaster or a white elephant?

Amey have submitted a planning application for an Energy from Waste plant at their waste handling facility in Waterbeach [1]. Is this a good thing or a bad thing? There are potential concerns about air pollution, carbon emissions and disincentive to reycle. But it will divert stuff from landfill and probably reduce GHG emissions overall.

The facility will process residual waste – the stuff that has come through the Mechanical Biological Treatment and not been picked out as valuable, and the stuff that was rejected from the dry recycling plant, plus construction and demolition waste. This waste would normally go to landfill.

The waste will be burnt in a furnace at 850°C to produce electricity and also heat; they hope to supply district heating for new developments in the area.

Amey's main EfW inputs and outputs [1, section 4]

Friday, 12 January 2018

Would Green Mortgages make energy efficient homes more affordable?

Do you think lenders ought to take into account the energy efficiency of a house (and hence your energy bills) when deciding how much you can afford to borrow? In some parts of the country there appears to be a price premium for a good EPC rating - the overall average for England is an extra £16,000 for 2 levels of EPC grade (D to B or G to E) [1]. This is good news for owners and further encouragement to people thinking of upgrading their homes, but not necessarily good news for buyers. If lenders did take into account your energy bills, how much difference would that make?

Tuesday, 2 January 2018

A bottle deposit scheme is tinkering round the edges.

Much of the news reporting on the parliament report ‘Turning back the plastic tide’ has been about implementing a bottle deposit scheme for plastic bottles. However this is not the most important of the recommendations made.  The key ones, in my view, are those designed to build a market for recycled plastic and to shift the burden of handling packaging waste onto producers.

First a quick recap of the numbers. Annually in the UK
  • 13 billion plastic bottles used
  • 7.5 billion recycled
  • 3 billion incinerated
  • 2.5 billion go to landfill

Thursday, 28 December 2017

Does ordering stuff online increase carbon emissions?

How much of your shopping do you do online? Are you worried about the climate change impacts of online shopping? A recent study of parcel delivery in Central London [1] gives some insights into how this compares with shopping on the high street. London is a bit different from the rest of the country: I have extrapolated these results to Cambridge, with plausible assumptions.

Delivery in Central London is equivalent to driving about 1km in a car, for Cambridge it is nearer 3km. If the parcel is plastic wrapped the carbon emissions for packaging are small but for a medium sized box you need to add another 1.3 km. There are a number of ways in which these emissions could be reduced.