Sunday, 7 June 2015

Biomass, wind, solar: how our choice of low carbon heating affects our landscape

From our holiday in the New Forest. How will our low carbon heating choices affect our landscape?

I’m just back from holiday in the New Forest - a place we love so much we visit it most years. This spring the deciduous forests and heaths were loud with birdsong and even with our limited expertise we were able to positively identify cuckoo, curlews and skylarks. Wilverley Plain on the other hand was, as always, peaceful with quietly grazing ponies and cattle, and the odd buzzard. In the softwood plantations birds are few and the dominant sound is the whoosh of the wind in the trees. Of course there are many other places in Britain where we can enjoy a rural idyll, shared with wild birds and animals - and they are all at risk to some extent because of the need for low carbon energy. Our choices on how we source energy for homes, transport and business will have a major effect on our landscape.

The choices for domestic heating are biomass, or electricity from wind or solar.
The CPRE report (Warm and Green) [1] for which I was co-author looks at one aspect of this - domestic heating - at the national level. In this post I look at the impact of our choices at a smaller scale. Our low carbon heating options are currently wood (pellets, chips or logs) or heat pumps (driven by electricity) with solar power for hot water in the summer. The main choices for low carbon electricity are wind power and solar power. So what would be the landscape impacts of heating one house, or a city the size of Southampton, next door to the New Forest?

With biomass heating we need 0.3 ha plantation (0.75 acres) per home
A typical home needs 12,000 kWh of energy per year for space and water heating [2]. First let’s consider the wood option, using a biomass boiler. If this were 85% efficient, it would need an area of 0.3 hectares of intensive biomass production such as short rotation coppice [3]. This would be more akin to the pinewood plantations than the mixed deciduous forest, so not so much birdlife but there would at least be trees.

Using biomass, Southampton homes would need 85% the area of the New Forest
The New Forest is 380 km2 [4]. Just as an illustration if we gave over this entire area to biomass, we could heat 118,000 homes. The New Forest is close to Southampton with a population of 240,000 people [5] so say 100,000 homes. That means it would need 85% of the area of the New Forest to heat all the homes in Southampton with biomass. That is a great deal of land.

Using heat pumps, in January, an average home needs 32 kWh/day electricity.
So what about the heat pump option? Using a heat pump we should be able to get 2.5 units of heat for every unit of electricity used so we only need 5000 kWh/year of electricity, even allowing for 5% losses. Electricity storage is expensive - current solutions are suitable for day to day storage but not between summer and winter. So let’s consider the worst month of the year which is January. A typical home needs 75 kWh/day for heat in January [2], so 32 kWh/day electricity using a heat pump.

For Southampton, that would be 5% of the New Forest covered in wind turbines.
Considering wind power, one large 2.5 MW turbine could supply 665 homes. Fortunately, the UK is windier in the winter when there is high heating demand than in the summer, so this calculation is based on a load factor of 35% - rather better than the overall average of about 27% through the year [6]. So, to heat all of the homes in Southampton we need 150 wind turbines. That sounds a lot but if you space them 350m apart you would only need 5% of the New Forest and you can use the space between for other things. You can’t just put wind turbines anywhere, of course, but I must say it always seems to be blowing a gale on Beaulieu Heath so if the birds don’t mind that could be a good spot. As I have said before I am a great fan of wind power.

Wind power can be supplied from offshore rather than onshore turbines, reducing the landscape impact. However offshore wind is more expensive because of the difficulties of offshore engineering. At the last Contract for Difference auction, onshore wind got £80/MWh whereas offshore wind got £117/MWh [9].

Or 6% of the New Forest covered in solar panels
The next option is to use solar power. You can either capture the solar power directly as heat, or convert it to electricity and then use it in a heat pump. The former is a little more efficient but electricity is easier to transport from one place to another, so let’s focus on solar PV panels. To get 32 kWh/day you would need a 33 kWp system [7] - about 130 panels. That is 8 times the size of a typical domestic roof system (4 kWp). You obviously aren’t going to get all this from rooftops in a city. Using ground level solar farms, Southampton would need about 6% of the New Forest [8].

The solar panels option is more costly unless we can use the summer power glut
I expect most of you prefer the solar farm option to the wind turbine because a ground level installation is easier to hide from distant views. Also it is relatively quiet. However this needs dedicated space and, under the current pricing regime, it would also be more costly. The same solar farms would be producing 3.5 times as much electricity in July as in January [7] even though our need for power at that time is much less and under the Feed in Tariffs or the Contract for Difference subsidy regime the guaranteed price is the same at all times of the year. If this summer power is not delivered then the solar panels are uneconomic but if it is delivered then we have to pay full price for it. At the moment we can adjust for the extra solar power by turning off fossil fuel power stations but as we shift to renewables for more of our power this will not be possible. If we could find some other way to use the summer power glut that would be fine. For example we could use the extra power to make fertiliser [9]. However to make this economic we would have to reduce the price of summertime electricity.

Nuclear power has minimal landscape impact but other costs
Finally, we could use nuclear power. The mean heating demand in January for Southampton would be 130 MW so one typical 2 GW nuclear power station could heat 15 cities the size of Southampton. The impact on the landscape would be minimal. However, there are other arguments against nuclear power and at current reckoning the financial costs would be  a little higher than the onshore wind option. The price guarantee for Hinkley C was £90/MWh [10] (and this may or may not go ahead) whereas at the last auction onshore wind was priced at £80/MWh [11].

It's a trade off between cost and landscape - and energy efficiency would help but gets even less investment
Obviously we don't have to all choose the same heating options, but I hope I have convinced you that we can't just all opt for biomass because we simply don't have enough spare land. Of the other options, onshore wind is the cheapest, at least unless we can solve the summer power glut problem with PV. Offshore wind and nuclear power have less landscape impacts but higher costs. All of these impacts would be reduced if we reduced our heating energy need byimproving the insulation and heating management in our homes. Sadly, energy efficiency does not get as much investment or attention as renewable energy (see Is energy efficiency the poor relation?)

[1] Warm and Green (CPRE)
[2] Calculated using the Cambridge Housing Model
[3] 4.4 m2/kWh/year for biomass. ( from Sustainable Energy - without the hot air by David Mackay). This is slightly optimistic considering the Biomass Energy Centre suggests you should get 8-10 tonnes per year.
[4] New Forest (Wikipedia)
[5] 2011 Census Headline Facts and Figures Southampton (
[6] (Characteristics of the UK wind resource: Long-term patterns and relationship to electricity demand. Graham Sinden in Energy Policy.  (This suggests the January resource is typically 10% over the long term average.)
[7] Using the PVWatts calculator
[8] Focus on: Solar PV (Farming Futures) says 200 m2 for 27 kWp
[9] ) Solar ammonia process may spur fertiliser revolution (SciDevNet)
[10] Hinkley Point Contract Terms )(World Nuclear News
[11]UK Renewables auction pushes down costs/ (Carbon Brief)

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