Energy “autarky” — a term that roughly means self-sufficiency — has obvious social and community advantages. They include reducing the reliance on centralized suppliers and power imports from far-off destinations as well as aiding local development. While the political ramifications of decentralized energy supply is much debated, there are cost issues. It can be less efficient and so more costly to use smaller, local-generation schemes. In addition, local energy self-sufficiency, at whatever level, may also not be viable for all areas, especially given the local variations of renewable supply.
There is certainly a debate over the relative merits of national grids versus local autarky. For example, while the European Commission and the European Network of Transmission System Operators for Electricity “do not oppose local generation”, they both emphasize the benefits of grids, especially when it comes to the “cost-decreasing effect of integration and electricity trading among European countries”.
A new study led by the Potsdam Institute in Germany seeks to clarify the issues. It looks at the possibilities for local, regional and national autarky in renewable electricity generation/use in Europe. It assumes that area-based electricity independence/autonomy is only possible when the technical potential of renewable electricity exceeds local demand.
Electricity autarky below the national level is often not possible in densely populated areas in Europe
The work assesses the technical potential of roof-mounted and open-field photovoltaics as well as on- and off-shore wind turbines at all scales and locations — including at continental, national, regional and municipal levels — taking competing land use issues into account. It found that most regions across Europe were likely to be able to satisfy their electricity needs by using solar and wind power and that the renewable electricity potential exceeds demand at continental and national levels, with the total potential at a Europe-wide level of 15 000 TWh per year — over four times current demand. But it warns that developing these systems would increase pressure on land-use around large cities and towns while some municipalities might have to import power from outside.
Local shortages
The report found that the “technical-social potential” of renewable electricity beats demand on the European and national levels. For more local autarky, however, the situation is different. Here, demand exceeds generation in several regions — an effect that is stronger when the population density is higher. To reach electricity autarky below the national level, regions would need to use “very large fractions or all of their non-built-up land” for renewable electricity generation.
That might be hard given there may be competing uses for the land. Indeed, the study concludes that electricity autarky below the national level is often not possible in densely populated areas in Europe. In fact, it found more than 3000 European municipalities that cannot be self-sufficient due to insufficient land area.
The bottom line of the report is that large cities may lack enough renewable potential with the only way to self-sufficiency being to co-operate with surrounding regions or assign all their undeveloped land to generating renewable electricity — an outcome that may not be desirable. “Ultimately, it is a balancing act between self-sufficiency and more intensive local land use on the one hand and the acceptance of imports together with greater cooperation with other municipalities, regions and countries in Europe on the other,” says the report’s co-author Tim Tröndle from the Potsdam Institute.
Rural options
It is a useful study, even if it only covers power and not other energy needs. Yet it does not look at way to balance competing demands for land, which could be a key issue for local-level autarky. Certainly, as the study admits, even without balancing issues, it may be hard to achieve local autarky in high-density urban areas. Some might say it is foolish to try. Indeed, that view may be reinforced by another interesting study, which suggests that PV solar — usually seen as well-suited to use on urban roof tops — is in fact better deployed in rural areas.
That may seem counter intuitive, given that there could be conflicts between solar farms and land for growing crops. However, the US-based study suggests that the two can be compatible — via PV arrays on stands or semi-transparent PV materials — to allow crops to grow underneath. Moreover, PV cells’ efficiency falls off significantly with rising temperature so local rural micro climates can help with cooling. Hot urban roof tops, and indeed hot deserts (another common choice for big arrays), are not ideal.
The study suggests that growing crops in the intermittent shade cast by the PV panels “does not necessarily diminish agricultural yield’. It concludes that the potential for “agrivoltaic” globally could be met if less than 1% of agricultural land at the median power potential of 28 W/m2 were suitable candidates for agrivoltaic systems and converted to dual use. But it warns that the lack of energy storage and the “temporal variance” in the availability of solar energy will restrict this expansion.
So we have not escaped the balancing problem, although trading power via the grid from solar farms (and wind farms) dotted widely around the country might be part of the solution- with cities taking in their share.
The roof-top solar resource
While PV cooling issues are important, it obviously makes sense, in terms of avoiding environmental intrusion, to use domestic or commercial roof-tops for PV wherever possible rather than on land sites. Indeed, various PV cooling options are being developed for roof mounted PV including hybrid PV thermal systems (PVT) that make use of the collected heat.
The EU’s cost competitive roof-top solar PV resource has been put in a recent study at 680 TWh — 25% of EU power. Interestingly, in that study, France is seen as having the largest potential in solar power output while Portugal leads in terms of the potential solar power percentage of total generation (around 40%). That is based on a projected future Levelised Cost of Energy (LCOE) in the range €6–21 per MWh, the lowest cost obviously being in the the sunnier south.
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Another recent study has looked in more detail at projected likely PV costs across the EU, although this is for larger utility schemes, most of which are likely to be land based. It suggests that by 2030, utility scale PV LCOE will range from €14 per MWh in Malaga to €24 per MWh in Helsinki with 7% weighted average cost. And that this range will be €9–15 per MWh by 2050.
Projecting costs so far ahead is obviously fraught with uncertainty, but it does seem clear that PV solar is likely to get very cheap and boom across the EU. A new report by the International Energy Agency says that PV will lead the rest, with 60% of the huge 1 200 GW of new renewable capacity expected globally by 2024 being PV solar. The best specific site deployment choice for PV however remains a matter of debate. Even leaving cooling issues aside, large utility schemes, most of which are on the ground, are usually much more competitive than smaller roof-top domestic schemes. Yet the eco-impacts for ground mounted schemes are higher and they can’t easily be located in dense urban areas. Urban energy autarky clearly isn’t going to be easy.
