The other day we were considering the concept of EROI, the amount of energy you get out of a given technology for the amount you have to put in. Specifically we were looking at the figures for solar PV in Spain.
With splendid timing, the Energy Collective has published a post considering EROI for the full gamut of energy technologies. At first glance the story looks not too bad, with wind and solar PV (so long as it's in a desert) above the minimum level of 7 that the article says is needed to sustain a modern society (breakeven EROI of 1 is not really worth the bother). The problem arises when you have to start storing all energy from renewables, which as their adherents suggest is the key to having them compete with fossil fuels.
If we were to store energy in, say, batteries, we must invest energy in mining the materials and manufacturing those batteries. So a larger energy investment is required, and the EROEI consequently drops.
Weißbach et al. calculated the EROEIs assuming pumped hydroelectric energy storage. This is the least energy intensive storage technology. The energy input is mostly earthmoving and construction. It’s a conservative basis for the calculation; chemical storage systems requiring large quantities of refined specialty materials would be much more energy intensive. Carbajales-Dale et al.2 cite data asserting batteries are about ten times more energy intensive than pumped hydro storage.
Adding storage greatly reduces the EROEI (the “buffered” values in the figure). Wind “firmed” with storage, with an EROEI of 3.9, joins solar PV and biomass as an unviable energy source. CSP becomes marginal (EROEI ~9) with pumped storage, so is probably not viable with molten salt thermal storage. The EROEI of solar PV with pumped hydro storage drops to 1.6, barely above breakeven, and with battery storage is likely in energy deficit.