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Land use and energy

By Dave Elliott

By their nature, renewable energy flows are diffuse and the technology for capturing energy from the flows has to cover relatively large areas. It is instructive, and sobering, to revisit Professor David MacKay’s calculations about the areas required to match the energy needed per person from renewable sources:

However, as I noted in an earlier post (on his comparisons between wind/solar and shale gas), some of his analysis is a little limited, and the general conclusions have to be put in perspective. Mankind has happily accepted large areas of land being used for farming, since we need food, and although we do have to avoid conflicts with that, there are many areas of marginal land not usable for cultivation, including deserts (for solar), as well as the sea (for wind, wave and tidal).

Some countries have plenty of space. An early study by the US National Renewable Energy Laboratory (NREL) suggested that to supply the entire US with power with PV would need 0.6% of land area, and noted that in its base case “solar electric footprint is equal to less than 2% of the land dedicated to cropland and grazing in the United States, and less than the current amount of land used for corn ethanol production”.

In the more crowded UK context, in response to claims that the countryside would be “disappearing beneath solar panels”, it was pointed out that the 200 acres of solar farms that had be established in the UK by 2011, were about 0.0003% of the UK land area, and that the 500 miniature “crazy golf” courses in England, which typically covered roughly an acre each, accounted for twice the area covered by solar farms:

If that calculation is expanded to include full-scale golf courses (over 0.5% of UK land area), that gives some idea of what the land use requirement might be for a major UK solar farm programme. Indeed an amusing calculation by a UK PV trade lobbyist group suggested that only 1% of total UK land area would be required for enough solar arrays to meet the UK’s entire electricity needs, though that ignores balancing and (night time) backup requirements;

Many PV arrays have been installed on roofs, taking up no extra land, and there is space for a lot more – the UK is blessed with plenty of suitable houses and other buildings. Putting 2 kW arrays on 10 million domestic roof-tops (about a third of UK dwellings) would give you 20 GW. And there are many industrial and commercial buildings with much larger suitable roof spaces, maybe 250,000 hectares. But if we want PV to make an even larger contribution, then solar farms will have to spread and they do take up land space.

Clearly, with over 200 hundred solar farms in place in the UK and many more planned, there are issues, but in this context, it is interesting to look at a study from India, another densely populated country. The Indian Institute of Science Centre for Climate Change in Bangalore claims that 4.1 % of the total uncultivatable and waste land area in India is enough to meet the projected annual electricity demand of 3,400 TWh by 2070 using solar energy. This assumed present-day PV technology. New solar cells will be more efficient and need less space per kWh produced. The study also did not take account of the fact that roof-top PV does not need any additional land or that some of the land around/under PV farm arrays can be used for other purposes like grazing.

It’s also worth noting that there are several PV projects mounted over areas of water, including a 1 MW array mounted on a gantry over a canal in India, and also a 1.2 MW floating PV system on a reservoir in Japan, where land is equally scarce. In these hot climates, covering water areas with PV arrays reduces evaporation and the cooling effect also improves PV performance, which falls off with rising temperature. Given land constraints, floating systems may also be relevant in the UK: there is now an 800 panel floating PV array on a reservoir near Wargrave in Berkshire.

PV is not the only solar option. Recently the US NREL has looked in detail at land-use issues for Concentrated Solar Power (CSP) as well as PV, at various scales. It found that the total area requirement for a PV plant of 1-20 MW capacity in the US was 8.3 acres/MW. For larger PV plants, the total area needed was 7.9 acres/MW, while CSP needed 10 acres/MW. When weighted by generation rather than capacity, the larger PV plants (3.4 acres/GWh per year) and CSP plants (3.5 acres/GWh/year) do a bit better than smaller PV plants (4.1 acres/GWh/year). But of course many of these plants, of whatever type, could be in desert areas where land-use limits are minimal. And in other locations, it has been argued that solar farms can provide a haven for wildlife and for grazing, since the arrays leave 95% of the land still available:

Wind power is also sometimes seen as needing large areas, with a US NREL study suggesting that it required about 84 acres/MW, much more than PV, although the difference reduces when you look at outputs, given the lower load factor for PV. But, in terms of output comparisons, in his recent study MacKay still has PV taking up 50% less room than wind farms. However, it has to be remembered that the area around wind turbines can still be farmed. On that basis, MacKay says a solar farm takes around 8.5 times more space than the equivalent wind turbines giving the same output:

So wind wins. Moreover, offshore wind takes up no land. And some even look to airborne devices mounted on large kites or balloons, harvesting higher speed wind at altitude – a huge new resource.

Biomass raises more significant land-use issues. Given, basically, the low efficiency of photosynthesis, it is inevitably very land-hungry. One estimate put the requirement at around 533 sq. km/TWha compared to PV at 45 sq. km/TWh, and wind at 72 sq. km/TWh (Gagnon et al 2002, Energy Policy, 30, 14, pp1267-78 ). Even so, it can play a role. To avoid the potentially unsustainable import of biomass, the Pugwash High Renewables Pathway envisaged 10% of UK land being used for biomass cultivation. Around 72% of UK land area is used for agricultural purposes (forestry excluded), and only some of that would be used for energy crops. However, there would have to be changes in farming practice and also perhaps diet:

It cannot be denied however that biomass comes out poorly in land-use terms when compared with just about all other energy options. In 2010, Rutgers University professor Clinton Andrews and colleagues looked at what it would take to produce 10% and 100% of the whole world’s power from various sources, and found nuclear and geothermal at the lowest end of area needs, followed by coal, solar CSP, and natural gas, with wind in the middle and bioenergy at the very high end.

It has to be said, though, that this type of analysis is fraught with bias potentials. As noted above, some solar could be on roofs and so not use any extra land, the land around onshore wind turbines can be used for other purposes so it’s not fair to count the whole wind farm site area, whereas it might be fair to count the security compounds around nuclear plants and their share of linked uranium mines, fuel processing and waste storage sites. In this context it’s interesting to note that US energy expert Amory Lovins claims that the land area/MW needed for nuclear plants, including fuel supply and waste disposal, is much larger than that for PV or wind projects, even leaving aside the very different embedded energy debts/EROEIs. He adds, provocatively, that “a gram of silicon in amorphous solar cells, because they’re so thin and durable, produces more lifetime electricity than a gram of uranium does in a light-water [nuclear] reactor”.


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