The assertion that the fossil fuel-replacing potential of wind power combined with photovoltaics and concentrating solar thermal plants is so utterly guaranteed that consideration of modern nuclear energy is not merely entirely unnecessary, but somehow foolhardy, is often repeated, always implied, but never any more than specious. The survey of over 1200 South Australians that recently revealed only twenty percent of people were actually strongly opposed to nuclear power intimates that it’s only a vocal minority who is convinced that renewable energy is the one true path. The future of energy is a serious matter, and we’re not living in Dirt Girl World where adequate renewable energy solutions can be cobbled together from junk while everyone is content to grow all their own organic veggies.
But popularity is hardly a way to reach sound conclusions, so it’s back to the analysis, which helps us grasp some pretty obvious limitations inherent in variable renewables.
Firstly, although the LCOE of solar is higher, absent cloud cover we at least know for sure when it will be generating. But no so-called 100% renewable energy plan even pretends it will meet our needs without substantial gas back up. No matter how you paint it, the hydrocarbon burning infrastructure is locked in with the intermittent, “clean” technology. If we want to use battery storage instead, the numbers are still against us.
So, OK, by themselves the solar panels would not be able to supply the energy Australia requires but we can always use storage to smooth the power delivered.
Considering that in winter days are shorter let’s add enough storage for 14 hours of the average consumption. That would be 14 x 26 GW = 364 GWh.
Considering Tesla S grade batteries for the above, a total of approximately 2,330,000 tons of batteries would be required. The above would represent ~100 kgs per person. Sure, lithium batteries are among the lowest weight technology, other chemistries would be heavier.
At this point we might want to turn to lower LCOE wind generation but we will quickly wish we hadn’t. The 2013 AEMO wind study included analysis of availability versus demand over a ten year period, highlighting the 10% most demanding periods from summer and winter. For 85% of the time only 8.6 % of installed capacity was firmly available in summer. It was 7.9% for winter. This contribution factor drags wind down below solar for effective availability, and it should be immediately obvious that to increase it would require unavoidable overbuild. To even equal the capacity factor of solar (~20%) in the summertime would require 230% of total 2013 installed capacity.
It’s not just that there are guaranteed to be times when renewables are inadequate. Overproduction has its own problems.
… Increasing the penetration of renewables beyond the point where energy share equals capacity factor would mean the renewable source would begin to regularly produce more electricity than demanded. Without storage or energy sinks willing to buy up excess power, renewable generators would then have to curtail a growing share of their output and waste any associated revenues.
In practice, this ceiling could actually be reached before renewable energy penetration equals capacity factor, as production would begin to regularly exceed demand on high output/low demand days long before this point.
Finally, ultimately, cost will determine what we install, but at the scale we are considering we can’t ignore what we expend for what we’re getting – energy for energy. Analysis by Weißbach and colleagues puts solar and wind, combined with the cheapest required energy storage option (pumped hydro), below the threshold at which they can mathematically contribute economically to the electricity supply of model countries USA and Germany at current prices.
Solar PV in Germany even with the more effective roof installation and even when not taking the needed buffering (storage and over-capacities) into account has an EROI far below the economic limit. Wind energy seems to be above the economic limit but falls below when combined even with the most effective pump storage and even when installed at the German coast.
I still see a substantial role for wind and solar in Australia’s energy future. I actually wish the figures were better for justifying expanding capacity. But it’s simply going to take more than a blind charge down that path.