A good read on PV's:
Powering Civilization to 2050
theoildrum.com
My feeling is that photovoltaics are the right answer for the long term future. They don't harm wildlife, don't pollute, people around them don't seem to object to them much, they don't critically depend on anything in ultimately short supply, and they have outstanding energy payback. For example, Nanosolar claims payback of manufacturing energy in less than one month for their state-of-the-art product, but more conventional options still have energy payback in the single digit years, implying an EROEI in the tens to hundreds as we go from current to future PV products.
There are two major issues to overcome: economics, and intermittency. PVs are not yet economically competitive with fossil fuel energy, but there is a long cost history that lends itself to a fairly stable extrapolation that is quite encouraging:
Left panel shows cost of PV panels versus versus cumulative installed capacity. Right panel shows a sensitivity analysis for the learning rate (the percentage drop in the cost due to a doubling of the installed capacity). Source: Fig 3 of McDonald and Schrattenholzer, Learning Rates for Energy Technologies.
The learning rate is the percentage by which some technology drops in cost per doubling of installed capacity. Solar has been dropping at about 22% for each doubling, and this is fairly stable, give or take a few percent. If anything, the learning rate is improving slightly over time. According to the IEA, the installed base of PVs grew at a combined average growth rate (CAGR) of 34.9% from 1990 to 2005. Thus we would expect costs to drop by about 9% per year, which would correspond to halving every eight years. At current costs of about $4/peak watt, unsubsidized PV power costs about 10c/kWhr in sunny places like Los Angeles and about 16c/kWhr in a cloudy place like Seattle (from Solar Revolution, p 110). Thus it is probably already competitive with retail electricity in many sunny places, and will become competitive with wholesale prices of about 5c/kWhr in less than a decade in sunny places and in about 15 years in cloudy places.
With serious policy help, PV installed capacity can grow much faster than the 35% global average. Eg in Germany, PV has grown at a CAGR of 61% over the same 1990-2005 period. However, the global installed base of PV is miniscule - in 2005 it only comprised 0.0033% of marketed primary energy (on a thermal equivalent basis).
The effect of all these trends - tiny current installed base, rapid growth, very fast learning curve, high EROEI tends to mean that PV can be of almost no meaningful benefit to the global situation in the short term, but in a couple of decades from now reaches critical mass, and then will potentially be in a position to provide almost all of society's power within a couple more decades from that. Since PV can be readily fit into all kinds of otherwise unused surfaces on buildings, and also spread out over otherwise low-value desert, and can be applied in installations from a single panel up to thousands of acres or more, it can be ramped up very quickly - there are few barriers to deployment. This is the basis for my selecting it as the backbone of long-term sustainable power for society in my scenario.
The remaining problem that needs to be solved is the intermittency (PV provides no power when it's dark and not much when it's very cloudy). There are basically two possible approaches to this. The first is that we would install enough storage everywhere that the energy stored during the day would be enough to power usage at night. I have not been able to construct a believable story about how current electric storage technology can scale to the required magnitude in a timely way, and thus this approach, as far as I can see at present, faces a critical bottleneck. It's one thing to have a battery that will power a plug-in hybrid for an hour commute. It's another to have enough batteries to get a region through a week of clouds and rain.
The second approach is to construct a global electricity grid. As far as I'm aware, this approach was first proposed by Sanyo under the rubric Project Genesis. Their idea was to install PVs throughout the world's deserts, and connect them up via superconducting cables to the world's cities - they estimated 4% of the world's desert area would be required. To get some feel for the issues, you might want to stare for a while at this screenshot of the planet: |
