By Dave Elliott
With costs falling rapidly, PV solar is moving ahead fast and some see it as likely to become a major renewable source in the future, if not the dominant one. The World Energy Council notes that in its new Symphony global energy scenario, “by 2050, globally, almost as much electricity is produced from solar PV as from coal,” and Shell’s recent “Oceans” scenario saw solar as being the largest single energy source globally by 2060. So is solar PV going to beat all else? DECC says PV might expand to 20 GW in the UK by 2020, while Germany already has 37 GW of PV, which sometimes supplies nearly 50% of its daytime electricity needs. Globally there’s over 130 GW in place, with China and Japan accelerating their commitments.
Interestingly, PV seems to be expanding slightly faster than wind at present. According to late 2013 estimates by Bloomberg New Energy Finance, 36.7 GW of new PV should have been added globally in 2013, compared to 35.5 GW in new wind (33.8 GW on-land and 1.7 GW offshore). But it’s a close run race. Bloomberg predicted that the wind and PV sectors will contribute almost equally to global new electricity capacity additions between now and 2030: wind will grow from 5% of total installed capacity in 2012 to 17% in 2030, while PV will increase from a lower base of 2% in 2012 to 16 % by 2030.
However the comparison between wind and PV growth rates and capacities has to be put in context. Wind power has already reached around 320 GW globally (nearly three times more than PV) and has several advantages, the most obvious being that it can be available at night and tends to be higher in the winter when energy demand is higher. By contrast, as well as not being available at night, sunlight intensity can vary significantly during the day and across the year, being minimal in winter. If PV is to make a major contribution there will therefore be problems with grid balancing, which means extra costs for energy storage or other balancing systems, more so than for wind. This is reflected in its load factor, typically 10%, compared to 30% for wind, depending on location – it is higher offshore. So you get a lot more energy per MW from wind capacity than from PV.
Nevertheless PV has some specific load-matching advantages. It can meet daytime office loads well and is especially well matched to their summer air-conditioning loads. That will become increasingly important in hot climates around the world as climate change impacts more. Moreover, as costs continue to fall and new technology emerges, PV is likely to be deployed widely as a cheap grid supply option. After all it is easy and quick to install, with relatively few maintenance requirements compared with wind devices. With clever new technologies emerging (for example graphene-based cells and 3-D cell printing) some expect PV costs to fall much faster than for wind, especially offshore wind, so that it becomes the cheapest source available in some locations. In which case the grid balancing/backup cost may not look so economically unattractive.
The solar resource is certainly large – much larger than that for wind, even including offshore locations. There are however some locational constraints. To get to large contributions will mean going beyond rooftop and wall deployment to large-scale solar farms on the land – with potential land-use conflicts. Although there are some novel ideas for PV surfaced roadways and paths: www.solarroadways.com/intro.shtml and there are some floating PV array projects on lakes and reservoirs . Moreover, with large-scale PV arrays in deserts, land use may not be so much of an issue (there are a lot of desert areas). However, for most conventional locations there will be tougher limits. Much more than for offshore wind. The cost of offshore wind may also fall as new technology emerges. For example, floating wind turbines avoid the large cost of seabed installation and can be more easily retrieved for maintenance in ports than sea-bed fixed units. There is also the possibility of aerial devices – flying wind turbines mounted on tethered kites or autogyros. That would open up a very large additional resource, maybe 1000 TWh p.a. some of which could be captured, putting wind and PV in the same league.
For the moment wind clearly leads and it is hard to predict whether or when this will change, in part because, quite separate from the pros and cons of wind and PV, other renewables may challenge both of them. There is already about as much solar thermal heat collecting capacity in place as there is wind capacity globally and that looks likely to continue to grow. Concentrating solar thermal electric (CSP) is also competing with PV in desert areas, although at the moment, in some cases large-scale PV may win. But the advent of hybrid PV-thermal systems (PV-T) may open up a whole new market. Wave and tidal power may also become major players in some locations, as could geothermal, but the contributions in terms of total global capacity of all of these are likely to be relatively small compared to PV and wind. It is conceivable that biomass-fired generation could become widespread, and the potential resource is very large, but there are concerns about the land-use implication of large-scale energy crop growing which may limit the available resource. And of course hydro is already way ahead of all the other renewables in capacity terms (nearly 1000 GW), although the prospects for significant expansion of large hydro projects may be limited by environmental constraints.
Quite apart from their specific merits and demerits, which of the various green energy supply technologies will prosper will also depend on likely changes in the overall energy supply and demand patterns and management systems. For example, it may be that heat supply technologies may be more important, since heat is easier to store than electricity. Alternatively, green power may be converted to (storable) green gas. In either case it’s not clear whether wind, PV or other renewables would then be the best supply option -or a mix. My guess is that wind-to-gas will dominate, but it may depend on what fuel gets selected for transport and of course the whole pathway forward will depend on what happens in the rest of the energy sector e.g. will nuclear revive/survive, will shale gas use spread globally, will climate change policy be ratcheted up more? There are thus a lot of unknowns. And in reality it’s not necessarily a single-winner contest. We need all of the options that prove to be viable – wind, PV and anything else that can meet demands locally and globally at reasonable cost. They each have specific locational pros and cons: it’s a matter of horses for courses. Mind you, some still say that PV will win, and even that it will make grids redundant: see my next post.
* For an interesting comparison of the relative impacts and costs of wind and PV in Germany, which concludes that wind has won hands down, see: http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2477731