As renewables become cheaper and more ubiquitous, there is a need both to use the power when it’s available and to save some for when that renewable power isn’t operating. We’ve looked at the Aluminium smelters storing and returning energy this way, but that will only return power to the Grid. Sunfire (a German company) look like they’ve been improving the efficiency of using electrical power to synthesise hydrocarbons from the input materials of water and CO2 and though at the moment they’ve got up to 50% efficiency they’re predicting up to 70% (as regards electrical energy put in to chemical energy stored in the fuel). If you then use the fuel in an ICE the end-to-end efficiency goes down to about 28%, but in cases where wind-farms are paying people to use their excess energy (when the wind is stronger than the grid can effectively consume) it could still make economic sense.
You can read what they say about it at http://www.sunfire.de/en/kreislauf/power-to-liquids but to me it looks pretty good. This isn’t really new since the Germans have known how to synthesise hydrocarbons for at least 70 years, but the efficiency has been improved. It’s just good technology. If we have cheap electrical power, from LENR, fusion, fission or from surplus renewable energy, then we can store it in a compact form that we have a lot of experience in handling reasonably safely and that can be used in a myriad of small motors.
For those worried about increasing CO2 in the atmosphere, this is of course carbon-neutral since when you burn the synthesised fuel you only re-release the CO2 it took to make it in the first place. Whether this works out to be economical and a commercial success will of course depend on both the price of mined oil and the various political incentives to not burn that mined oil. For countries with excess wind or solar power and no oil wells, though, it could still make sense. One thing I couldn’t find in their website was the source of the CO2 they used. It’s a by-product of making liquid air, of course, but if you need to process air just to get the CO2 out that’s going to be a bit costly.
In my opinion, this is likely to be somewhat of a niche process, and the current drop in oil costs has probably made it uneconomical for most countries, but it’s good to know that the option is available. Thanks to Anony Mole at Nickelpower for the heads-up.