How much more energy do we get from open cast coal mines compared to solar PV? And how much do the two alternatives cost?
A week ago Northumberland council gave planning permission to a new open-cast coal mine at Druridge on the coastline just north of Newcastle. About 3 million tonnes of coal will be extracted over a five to seven year period from an area of around 350 hectares, including storage space. (350 hectares is about 1.4 square miles)
The environmental objections to the plan are striking. For example, the owners predict about 170 HGV movements a day along local roads during the whole lifetime of the project. The landscape impact is also severe although the developers say they will ensure that the local sandy beaches are unaffected. But what about the benefits of the energy produced? How do they compare to using the land to generate electricity from PV?
The answer is surprising. Burnt in a coal-fired power station, the coal extracted from the mine will deliver only about twice as much electricity as would solar panels installed on the same site over their lives. The UK could get the same energy from the sun on only twice as much land as the coal mine, with very low emissions and limited environmental impact.
Comparison of energy production: the coal mine
1, The total output of the mine is going to be at least 3 million tonnes of coal. (Higher figures are sometimes quoted but these seem to relate to the original mine, now with planning permission, plus several extensions that are not in the current plan).
2, Coal of the type produced at the mine will yield about 8,000 kWh per tonne. (This number is approximate).
3, So the total energy value of the development will be about 24,000 million kWh, or about 24 terawatt hours. (A terawatt hour is a thousand million kWh).
4, Burnt in Drax power station in Yorkshire, the energy value of the coal will be converted to electricity at an efficiency of just less than 40%. The total coal output of the open-cast mine will therefore produce between 9 and 10 terawatt hours of power, or about 3% of one year’s UK electricity output. Let’s call this 10 TWh.
5, The operation of the mine and the shipment of the coal by heavy good vehicle and rail will subtract from the net energy value of the coal produced. But the percentage impact will be quite small - perhaps no more than 5% - so I have ignored it.
A PV farm on the same site
6, The open cast site consists of an area of about 250 hectares of mined land and approximately 100 further hectares that will be used for storage and shipment. The total is about 350 hectares.
7, A tightly packed solar farm of around 170 megawatts capacity could be accommodated on this area. It would last about 35 years. (Future improvements in panel efficiency would increase the amount of power available per unit area. I have not included this).
8, A solar array of one kilowatt facing due south in the Newcastle area will typically produce just over 900 kWh per year. Allowing for losses in the system, the figure may fall to around 850 kWh per year.
9, The total annual output of a huge solar farm on the open-cast site would be about 0.144 terawatt hours a year. Over the life of the farm, just under 5 terawatt hours would be produced, assuming a slow rate of degradation of panel performance.
The coal from the site will therefore produce about twice the energy from PV on the same area. Put another way, the same amount of electrical energy would be produced on a 700 hectare site as from the 350 hectare mine.
a) Vehicle movements
10, The vehicle movements at the coal mine will be about 170 HGV lorries a day over the five to seven years of active mining. The total number of deliveries of PV panels will be 2,000 lorries, or less than 2 weeks of coal movements. For the remainder of the 35 year life, a PV farm would need virtually no large lorries. At the coal mine, there will be one vehicle movement every four minutes for seven years during a 12 hour working day.
11, A 170 MW solar farm would cost about £140m today. The total projected local expenditure by the mine owner is said to be £70m. This figure includes permanent employees and the chain of local suppliers. But the costs involved in converting the coal to electricity are not covered. These missing numbers include the money needed to run the power station at which the coal is burnt. This would probably add at least another £30m (or circa £10 a tonne of coal produced).
12, Electricity suppliers have to pay a tax on their output. The carbon support price imposes a £18 levy per tonne of CO2 emitted when power is produced. This tax is meant to penalise the fossil fuel producers to compensate for the damage CO2 is doing to the global environment, although it is widely regarded as being substantially lower than the true cost of coal. Burning a tonne of standard coal produces about 2.3 tonnes of CO2. The damage caused by the mine in terms of global warming is therefore judged by the UK government to be over £120m (3 million tonnes of coal times 2.3 CO2 multiplier times £18).
13, The total cost to generate the 10 TWh of electricity from the coal will therefore be around £220m. A solar farm on the same site would cost £140m to generate half as much power or £280m to equal the coal power output.
14, Solar power is therefore currently just over a quarter more expensive than the coal from Druridge mine. Druridge has good quality coal close to the surface and near to railway connections. It is therefore perhaps the cheapest fossil fuel available in the UK. If instead of using land in northern England, the country invested in an equivalently sized solar farm on the south coast where yields might be 25% higher in the very best locations, solar power in the UK would now offer electricity at the same cost as cheap coal.