Implications of net energy-return-on-investment for a low-carbon energy transition

Abstract

Low-carbon energy transitions aim to stay within a carbon budget limiting potential climate change to 2 ºC-or well below-through substantial growth in renewable energy sources alongside improved energy efficiency and carbon capture and storage. Current scenarios tend to overlook their low net energy returns compared to existing fossil fuel infrastructure. Correcting from gross to net energy, we show that a low-carbon transition would likely lead to a 24 to 31% decline in net energy per capita by 2050, implying a strong reversal of recent rising trends of 0.5% per annum. Unless vast end use efficiency savings can be achieved in the coming decades, current lifestyles might be impaired. To maintain present net energy returns, solar and wind renewable power sources should grow two to three times faster than in other proposals. We suggest a new indicator, 'energy return on carbon' (EROC), to assist in maximizing net energy from the remaining carbon budget. Gross Energy 550 EJ Net Energy 523 EJ 27 EJ reinvested End use energy services 219 EJ Energy losses 304 EJ Consumption on necessities 100 EJ Non-essentials 119 EJ Gross Energy 550 EJ Net Energy 367 EJ 183 EJ Reinvested End use energy services 154 EJ Energy losses 213 EJ Consumption on necessities 100 EJ Non-essentials 54 EJ High EROI Economy (EROI = 20:1) Low EROI Economy (EROI = 3:1)

Comparative net energy analysis of renewable electricity and carbon capture and storage

“…A 2006 CCS and sRE life cycle comparison in the German context did not evaluate net-energy performance but found that, on a lifecycle basis, CCS emissions are considerably greater compared to off-shore wind farms in the North Sea and concentrated solar power (CSP) plants in North Africa per unit of energy delivered 19 . Nevertheless, there are limited studies discussing the EROEI of CCS 20 or comparing the net energy performance of CCS and sRE.…”

Contributions of sociometabolic research to sustainability science

“…One typical finding is that fossil fuels have a relatively high EROI which gradually declines over time, while renewable technologies usually have lower EROIs 68 . This poses substantial challenges for a low-carbon transition because it implies reductions in useful energy 69 .…”

Energy Accounting for a Renewable Energy Future

“…The energy penalty in suitably optimised plants, would probably only be of the order of 25%, but because very few existing plants are so optimised, the energy costs for CCS could be appreciably higher. This energy cost will further lower their EROI [20,21]. Other forms of mechanical CDR include negative emissions technologies (NETs) such as direct air capture of CO 2 or enhanced weathering of minerals.…”

“…The claims for PV cells vary from PV still being an energy sink to PV cells paying back their energy costs in a few days. Some researchers have suggested that actual EROI values for RE are lower than 11, and in some cases even lower than 3.0, especially if storage energy costs are incurred [20,81]. The EROI values discussed here are assumed to be the "standard" EROI [21].…”

“…One exception to low EROI values for RE sources is large-scale hydro; it is not only a dispatchable energy source, but has an EROI estimated to be as high as 84 [20]. However, with a technical potential estimated as low as 30 EJ [66] (although Zhou et al [83] gave an 'exploitable potential' of 57.6 EJ), it can only ever be a minor share of most countries' energy supply-unless there are major overall energy reductions, perhaps through degrowth.…”