Burden of proof: A comprehensive review of the feasibility of 100%
renewable-electricity systems
B.P. Heard, B.W. Brook, T.M.L. Wigley, C.J.A. Bradshawhttps://www.scribd.com/document/344418151/Review-for-100-Renewables-SystemsABSTRACT
An effective response to climate change demands rapid replacement of fossil carbon energy sources. This must occur concurrently with an ongoing rise in total global energy consumption. While many modelled scenarios have been published claiming to show that a 100% renewable electricity system is achievable, there is no empirical or historical evidence that demonstrates that such systems are in fact feasible. Of the studies published to date, 24 have forecast regional, national or global energy requirements at sufficient detail to be considered potentially credible. We critically review these studies using four novel feasibility criteria for reliable electricity systems needed to meet electricity demand this century. These criteria are: (1) consistency with mainstream energy-demand forecasts; (2) simulating supply to meet demand reliably at hourly, half-hourly, and five-minute timescales, with resilience to extreme climate events; (3) identifying necessary transmission and distribution requirements; and (4) maintaining the provision of essential ancillary services. Evaluated against these objective criteria, none of the 24 studies provides convincing evidence that these basic feasibility criteria can be met. Of a maximum possible unweighted feasibility score of seven, the highest score for any one study was four. Eight of 24 scenarios (33%) provided no form of system simulation. Twelve (50%) relied on unrealistic forecasts of energy demand. While four studies (17%; all regional) articulated transmission requirements, only two scenarios—drawn from the same study—addressed ancillary-service requirements. In addition to feasibility issues, the heavy reliance on exploitation of hydroelectricity and biomass raises concerns regarding environmental sustainability and social justice. Strong empirical evidence of feasibility must be demonstrated for any study that attempts to construct or model a low-carbon energy future based on any combination of low-carbon technology. On the basis of this review, efforts to date seem to have substantially underestimated the challenge and delayed the identification and implementation of effective and comprehensive decarbonization pathways.
Some interesting points from the paper ...Lack of simulations / realistic simulations"The absence of whole-system simulations from nine of the reviewed studies suggests that many authors and organizations have either not grasped or not tackled explicitly the challenge of ensuring reliable supply from variable sources ... Of the 16 scenarios that provided simulations, only two simulated to intervals of < 1 hour and only two tested against historically low renewable-energy conditions. Historical testing is useful in general, but such tests do not address the high variability of output from renewable resources, let alone the attendant uncertainties associated with future climatic changes. Because of these issues, the system-simulation approaches applied so far mostly cannot demonstrate the feasibility and reliability of 100% renewable energy systems"
Integration cost escalation after certain percentage penetration of variable energy sources"The Mason and colleagues’ studies reinforce the notion that integration of variable renewable energy sources into existing gridscan be cost-effective up to penetrations of around 20%, after which integration costs escalate rapidly [120,121]. An upper threshold to economically rational amounts of wind generation capacity is also found in simulations for the United Kingdom [27]. Any further installed wind-generating capacity makes little difference in meeting electricity demand in times of low wind supply. While the cost-effective threshold for integration of variable renewable electricity will vary among grids, 100%-renewable studies such as these reinforce that penetration thresholds exist and that alternative dispatchable generation supplies are required to meet the balance of supply"
Possibility of sustained coincident low output of solar and wind on a regional basis"There is ample evidence for conditions with sustained, coincident low output from both wind and solar resources in Australia"
Risky assumptions on future possible scale of energy storage technologies, including hydro"It is reasonable to assume a greater range of cost-effective options in energy storage will be available in the future. Such solutions will undoubtedly assist in achieving reliability standards in systems with greater penetration of variable renewable generation. However, whether such breakthroughs will enable the (as yet unknown) scale of storage and associated paradigm shift required for 100% renewable remains unknown and is largely unaddressed in the literature (see
additional discussion in Supplementary Material). To bet the future on such breakthroughs is arguably risky and it is pertinent for policy makers to recall that dependence on storage is entirely an artefact of deliberately constraining the options for dispatchable low-carbon generation [127,128]. In optimal systems for reliable, decarbonized electricity systems that have included generic, dispatchable zerocarbon generation as well as variable renewable generation, the supply
provided by storage is just 2–10% ... . The year-to-year variability of inflows that ultimately determine hydro-electric output is wellknown — the minimum annual US output over 1990–2010 was 23% lower than mean output for the same period"
Assumption of low energy, high environmental impact (hydro and biomass) reality"The demand-reduction assumptions in most of the scenarios considered here, when combined with their dependence on hydroelectricity and biomass, suggest that 100% renewable electricity is likely to be achievable only in a low-energy, high-environmental impact future, where an increasing area of land is recruited into the service of providing energy from diffuse sources."
Undersizing or leaving out transmission grid requirements"Fürsch et al. [81] suggested that a cost-optimized transmission network to meet a target of 80% renewables in Europe by 2050 would demand an additional 228,000 km of transmission grid extensions, a +76% addition compared to the base network. However, this is an underestimate
because they applied a “typical day” approach to assess the availability of the renewable-energy resources instead of using full year or multiyear hourly or half-hourly data. Rodríguez et al. [83] concluded that to obtain 98% of the potential benefit of grid integration for renewables would require long-distance interconnector capacities that are 5.7 times larger than current capacities. Becker et al. [141] found that an optimal four-fold increase in today's transmission capacity would need to be installed in the thirty years from 2020 to 2050. An expansion of that scale is no mere detail to be ignored, as it has been in Elliston et al. [75], all work led by Jacobson [18,24,25,32,112,113], the global proposals from major environmental NGOs [15,108] and many more of the studies we reviewed. Transmission lines are acknowledged as slow projects, taking 5–10 years on average to construct, projects that are vulnerable to social objection that may force even more delay [82]. In one case, a transnational interconnection took more than 30 years
from planning to completion'