A recent article by Nafeez Ahmed describes how the rapid growth of renewable energy (RE) is disrupting and transforming the global energy system. The drivers of this rapid transition are technological evolution, rapidly improving RE economics as market size grows, and campaigns for environmental protection, especially mitigating global climate change. A driver of community-owned RE is initiatives to build a society that is more socially just and democratic.

Hence the following axiom:

Specifically, these benefits include:

• reduction and ultimate elimination of greenhouse gas (GHG) emissions from the energy sector;
• reductions in air and water pollution, water use and land degradation;
• reduction in respiratory diseases and cancers from pollution;
• energy security for as long as human civilization exists;
• a cap on energy costs, because most RE sources have no fuel costs;
• more local jobs, per unit of energy generated, than fossil or nuclear power;
• no risk of causing a nuclear war, or radioactive waste escape, or devastating accident.

Furthermore, since household and community-owned RE projects are playing an increasing role, and indeed were the foundation of the energy transition in Denmark and Germany, they increase local self-reliance, reducing the political power of the large energy utilities and the fossil and nuclear power industries, while fostering small businesses. A RE future is much more compatible with a steady-state economy, a healthy environment and social justice than a centralised energy system based on fossil fuels or nuclear energy.

Not all RE sources are equally benign or beneficial. Large hydro-electric dams, that flood pristine environments and displace large populations, must be avoided, as must bioenergy projects that compete with food production, demolish primary forest, and/or generate more GHG emissions than they save. However, pumped hydro based on small dams and bioenergy from crop residues have low environmental impacts and so can be included in the RE mix.

Key questions

The growth of RE and its many benefits raise the questions:

Is it technically feasible to continue the transition all the way to 100% RE?

What are the barriers, real and mythical, and how can they be overcome and refuted, respectively?

Answering these questions involves engineering, economics, sociology, political science and more. I’m a member of an interdisciplinary team of engineers, scientists and social scientists researching these questions at UNSW Sydney.

This article focuses on electricity generation which, together with heat production, is the largest single contributor to global greenhouse gas (GHG) emissions. Although electricity and heat are together responsible for ‘only’ 25% of global emissions at present, electricity is the least difficult part of the energy sector to transform via energy efficiency and RE. Hence, in future almost all heat and transport can be provided directly by renewable electricity. Hence a RE future will be predominantly an electrical future.

The exceptions to an all-electric future are low-temperature heating and cooling, much of which can be provided directly by solar thermal collectors, and transport by air and on long distance rural roads, which could be provided by renewable fuels, comprising biofuels produced sustainably, and hydrogen and ammonia produced by using renewable electricity.

Dozens of detailed national, regional and global scenarios for 100% renewable electricity have been published. Most include efficient energy use and energy conservation, the cheapest and fastest ways of saving energy and cutting GHG emissions. Some scenarios (e.g. by Jacobson and colleagues for the USA and the Centre for Alternative Technology for the UK) describe the transformation to RE of the whole energy sector, that is, electricity, non-electrical heat and transport.

As well as being environmentally and socially desirable, an electricity generating system must be reliable and affordable, and control the fixed frequency of alternating current. These, the main issues raised by RE critics, are now discussed.

Reliable generating systems, based on 90–100% renewable electricity, are already a reality in places which have hydro with large dams, such as Iceland, New Zealand, Norway, Bhutan and Tasmania.

However, providing a reliable 100% renewable electricity system is more challenging in regions with little or no conventional hydro potential.

Nevertheless, several such regions are already generating reliably with 100% of their annual electricity from renewables: for example, two north German states, Schleswig-Holstein and Mecklenburg-Vorpommern, and the Danish island of Samsoe.

Also, in 2016 Denmark as a whole and South Australia generated 42% and 50% respectively of their annual electricity from variable renewable sources, wind in Denmark and wind plus rooftop solar in SA. In each case partial back-up is provided by transmission line connections to neighbours. Although these connections have capacities of only a fraction of the peak demand of the RE regions, the RE systems are reliable.

Both South Australia and Denmark have already operated entirely on renewable electricity for periods of several hours and one day, respectively. This is an indication that the challenges of extending reliable 100% RE to periods of years are much less difficult than claimed by RE critics.

To explore the reliability and affordability of electricity generating systems with high penetrations of RE, many research groups around the world have included in their scenario studies computer simulation models of the operation of large-scale electricity supply-demand systems. This tool is particularly helpful for understanding how regions with little or no hydro and low-capacity (or no) transmission connections to their neighbours, can have reliable generating systems with 100% RE.

Conceptually, the simulations are simple. Each hour, actual electricity demand in the country or region is balanced with real or synthetic data on RE supply. In most studies, the principal renewable sources are wind and solar photovoltaic (PV) power, both variable sources. Many of the studies, including the UNSW research which simulates the Australian National Electricity Market, use only commercially available technologies scaled-up to meet demand.

Contrary to myth, not all RE sources are variable. To achieve reliability, variable renewables are supplemented by flexible, dispatchable RE sources such as hydro-electricity with dams, concentrated solar thermal (CST) with thermal storage, batteries, geothermal and gas turbines fueled on renewable gases or liquids. The mix depends on the availability of RE resources in the region of interest. (The Box gives definitions of ‘flexible’, ‘dispatchable’, ‘reliability’, etc.)

Computer simulations with hourly time-steps spanning 1–6 years show that 100% renewable electricity systems can be as reliable as conventional systems. In particular, the UNSW simulations of the Australian National Electricity Market (NEM) find that a RE mix, in which variable RE provides up to about 80% of annual electricity and dispatchable RE provides as little as about 20%, can still meet the reliability criterion of the NEM (Elliston et al. 2016. Renewable Energy 95:127–139, especially Fig.2).

In addition to choosing an appropriate mix of variable and dispatchable sources/technologies, reliability is increased by dispersing wind and solar farms geographically and connecting them by transmission lines. The wind is almost always blowing somewhere and a cloud drifting over one solar farm does not simultaneously shadow distant solar farms.

The results are based on tens of thousands of hourly simulations. Furthermore, a 2015 study of the USA by Jacobson and co-workers had time-steps of 30 seconds for six years (PNAS vol.112, no.49, p.15060). With a diversity of technologies and geography, only a relatively small amount of storage or back-up is required for reliability.

Many studies find that base-load power stations, such as coal and nuclear, are redundant. Also, they are poor partners for variable RE, because of their relative inflexibility in operation.

Frequency control is a specialised, technically complex topic in electricity power systems engineering. An imbalance between supply and demand results in a frequency change. In the past, the fixed frequency of alternating current was maintained by the inertia of the heavy rotating turbines and generators driven by boilers in conventional base-load power stations. With the gradual phase-out of base-load stations, the following new ways of controlling frequency will be implemented:

All the dispatchable RE sources listed above can contribute immediately.

Contracted rapid demand reduction for critical periods can be expanded.

With minor modifications to hardware and software, wind, solar farms and rooftop solar can contribute.

Synchronous condensers can be installed in the grid.

Improved transmission interconnection between regions will strengthen security.

The first three of these measures are inexpensive and the first four can be rolled out rapidly as required. Next, we consider the costs of 100% renewable electricity systems.

In a 100% RE system the technology mix will vary across regions of the world. Regions with large hydro potential, including off-river pumped hydro, have a low-cost RE source, subject to avoiding major environmental and social impacts. In most other regions, the principal contributors to 100% RE will be the cheapest: wind and solar PV.

Bloomberg New Energy Finance finds that large-scale wind and solar PV can now, or almost, “compete directly with a new coal or gas plants in the absence of subsidies… in all major markets”.

On-shore wind is around half the cost of nuclear power and off-shore wind is becoming competitive with nuclear.

The subsidies to RE have been cut dramatically in many places. Indeed, in several South American countries wind and solar farms are competing without subsidies, in tenders and reverse auctions, with all conventional sources. (See articles published in RenewEconomy.)

In both the scholarly and popular literature, RE critics misrepresent the ongoing transformation of the economics of solar PV and wind: e.g. they halve actual cost of coal or nuclear generation and double actual RE costs, claiming incorrectly that RE requires vast amounts of back-up. Some critics even assert that coal or nuclear stations with the same generating capacity have to be kept running continuously just as back-up for RE systems.

This is refuted by the simulation studies discussed above and by practical experience: e.g. South Australia’s two coal-fired power stations were closed mainly because they couldn’t compete in the market with wind. SA’s remaining base-load station (gas-fired) is expected to close soon. Batteries and, temporarily, gas-fired peak-load stations will maintain reliability.

A technique used by one RE critic, Ted Trainer, is to make Australian wind farms appear more expensive than they really are by choosing their average capacity factor (a measure of annual output, see Box 1) to be much lower (at 20%) than the observed average values of 33–36%. Another Trainer tactic is to assert that “installed capacity in renewable grids can reach three to five times demand, resulting in significant capital cost, and some plant sitting idle for much of the time”.

Although this statement is partly correct, it is irrelevant and misleading, because the capital cost is now quite low and is always included in the economic calculations. Furthermore, excess wind and solar power that’s currently curtailed when demand is low, can in the near future be used to power intermittent loads such as pumping water from a low to a high reservoir during off-peak periods. The potential for installing off-river pumped hydro, a commercially available dispatchable technology, is under active investigation by both the Australian and South Australian governments.

For Australian households and businesses that use most of their electricity in daytime, rooftop solar power is much cheaper than retail electricity from the grid. Battery prices are declining rapidly as the market grows and it’s likely that, within a few years, rooftop solar systems with batteries will be generally competitive with grid electricity too. Suburban owners are likely to remain grid-connected as back-up for occasional long overcast periods.

As a disruptive technology, RE is receiving fierce opposition, mainly from supporters of the politically powerful incumbent industries: fossil fuels, nuclear power, electricity utilities and some very large energy users such as aluminium smelting. Part of this opposition takes the form of disseminating false myths about RE.

The principal myths are that (i) base-load power stations are essential for reliable electricity supply and RE cannot provide them; and (ii) RE is too expensive. For a more detailed refutation of the base-load myth than given above, see this article. For refutations of additional myths disseminated by the nuclear industry, see this article.

Although some politicians, with close links to the fossil or nuclear industries, are still repeating these myths, many RE critics have apparently recognised that they have lost these debates and are now shifting to asserting incorrectly that renewable electricity, apart from large-scale hydro and bioenergy, cannot provide frequency stability.

A tactic used by nuclear campaigner biologists Brook and Bradshaw is to set up a framework to compare RE with nuclear power, choose dubious assessment criteria that favour nuclear power and disadvantage RE, claim falsely that their method is objective, and show that nuclear power satisfies their criteria while RE doesn’t. This particular tactic backfired, because the journal where this article was published, Conservation Biology, subsequently published three peer-reviewed refutations (in volume 30, no.3), including one by the present author, showing that Brook and Bradshaw’s choice of criteria and their scores for the criteria were subjective and biased.

Heard, Brook, Wigley and Bradshaw (2017) used a similar tactic in a recent review article that claimed to be a ‘comprehensive’ critique of simulation modelling of 100% renewable electricity. Several of their assessment criteria are absurd or irrelevant.

Furthermore, instead of assessing the field as a whole, the review authors demanded unreasonably that each individual publication had to satisfy all their criteria chosen for the whole field. In reality, most scholarly research is done in incremental steps. Heard et al. cherrypicked single papers and single topics from research groups, instead of considering their whole body of relevant research, and omitted major recent research from Europe.

Conclusion

Renewable energy has substantial environmental, health and socio-economic benefits compared with fossil fuels and nuclear power. RE contributes to community development and participatory democracy, and is compatible with a steady-state economy.

A 100% renewable electricity system can provide directly, and in future indirectly via renewable fuels, all future energy use, including transport and heat. It is technically feasible, reliable and affordable for many countries and regions of the world. Those regions with insufficient natural RE resources can import RE via transmission line and/or tanker carrying renewable fuels.

Critics, who mostly support vested interests, produce arguments that ignore, misrepresent or deny dozens of detailed scientific and engineering studies. Community groups and the population at large must increase pressure on governments to resist vested interests and achieve an energy efficient, RE future.