Towards 100% renewable-electricity systems

Get real. No way is the world going to obtain sufficient energy from only renewables by 2050. To curb carbon emissions we cannot do without nuclear energy. That was, in a nutshell, the argument set forward by Australian researchers from the universities of Adelaide and Tasmania, Flinders University, and a colleague from the National Center for Atmospheric Research in Boulder (USA).

In a review paper last year in the journal Renewable and Sustainable Energy Reviews, first author Ben Heard and his colleagues presented their case against 100% renewable electricity systems. They doubted the feasibility of many of the recent scenarios for high shares of renewable energy, questioning, amongst others: whether renewables-based systems can survive extreme weather events with low sun and low wind; and the ability to keep the grid stable with so much variable generation.

Another group of scientists, amongst which Delft Professor of Energy Systems Analysis Kornelis Blok of the Faculty of Technology, Policy and Management, has now hit back with a response to the points raised. Blok and his colleagues from the Karlsruhe Institute of Technology, the South African Council for Scientific and Industrial Research, Lappeenranta University of Technology and Aalborg University, analysed hundreds of studies from across the scientific literature to answer the issues raised by the Australians. They believe that there are no roadblocks standing in the way of a 100% renewable future. Their article Response to ‘Burden of proof: A comprehensive review of the feasibility of 100% renewable-electricity systems’ was published in that same journal earlier this month.

So let’s run through some of the issues raised and the counter-argumentation as to why there are no roadblocks.

The electricity demand will be sky high in 2050

Ben Heard et al. believe it is unrealistic to assume that energy demand will not have increased significantly by 2050. “Any future global scenario that presents static or reduced demand in either primary energy or electricity is unrealistic, and is inconsistent with almost all other future energy projections”, they write. “Such an outcome would be at odds with the increase in global population, ongoing economic development for the non-OECD majority, and the firmly established link between industrialization and increased energy consumption.”

Rebuttal

Sure, more people will have larger and more comfortable houses in 2050. And we will also fly more. Still, according to Kornelis Blok, economic development doesn’t automatically mean we will consume more energy. “On the contrary,” says Blok. “Appliances, houses, cars, and industries will become much more energy efficient. We predict that the world energy demand in 2050 will be the same as it is now, although the share of electricity will increase.” What’s more, primary energy consumption automatically goes down when switching from fossil fuels to wind, solar and hydroelectricity, because they have no conversion losses, the researchers write. And renewables-based systems avoid the significant energy usage of mining, transporting and refining fossil fuels and uranium.

Durable energy is too capricious

Up to now, studies have insufficiently demonstrated the capacity of 100% durable energy systems to satisfy consumer demand at any time, Heard et al. write. Wind and sun are capricious. And what happens if, during a period of severe drought, hydro-electric output is seriously impacted and wind and solar energy output is low at the same time? The supply of renewable energy can decrease inconveniently just when local demand is very high.

Rebuttal

We can cope with these variations by to some extent by tweaking the grid. But the variability challenge really starts to be a problem when renewables exceed about 70 to 80%, or so a US company, the Hawaiian Electric Company, recently calculated. That is why some scientists prefer not to rule out other low-carbon sources designed to produce power on demand: nuclear reactors and coal or gas generators that capture the CO2 they produce. These are expensive techniques. But some of the alternatives are also expensive.

For instance, the option to exchange energy between countries. “We have to strengthen the networks between countries,” says Blok. “Some people have suggested putting a big cable around the equator to which all continents can tack on. That way the sun always shines on the grid. This would result in extremely high electrical power (wattage) on that cable. That is not a good idea. But we could exchange much more energy at a continental level.”

One way to deal with daily fluctuations in renewable energy surplus is by finding clever ways to shift demand. “People can, for instance, be encouraged to recharge their cars when supply is high,” says Blok.  And another way is to stockpile the surplus so we can use it when demand peaks. Battery technology is  still very expensive. “But batteries are improving very fast,” says Blok. He has high expectations of lithium-ion batteries becoming cheaper; and other battery technologies that are under development. “And if there are real risks of shortages then we should have electricity plants that run on biofuels or hydrogen ready to jump in.”

Voltage and frequency control and other ancillary services

Ancillary services include reserve power for balancing supply and demand in the short term; rotating inertia to stabilise the frequency in the very short term; synchronising torque to keep all generators rotating at the same frequency; voltage support through reactive power provision; short circuit current to trip protection devices during a fault; and the ability to restart the system in the event of a total system blackout (known as ‘black-starting’). Heard et al. raise concerns that many studies do not consider the provision of these ancillary services, particularly in terms of voltage and frequency control.

Blok and his colleagues believe that these concerns are overblown: “Ancillary services are important, but they can be provided with established technologies (including wind plants), and the cost to provide them is secondary compared to the costs of energy generation.”