Most electricity demand in industrialised countries can be met by solar and wind power, according to scientists.
But the researchers at University of California, Irvine have warned that extra efforts, and new technology, may be needed to fill gaps in a truly zero-carbon future.
Using energy storage will help to meet the demands, the researchers said – as well as countries working together to share resources.
Most reliable systems, which are dominated by wind power, are capable of meeting electricity requirements in the countries studied some 72 to 91% of the time, even without energy storage, according to the study.
With the addition of 12 hours of energy storage capacity, systems become dominated by solar power and can satisfy demand 83 to 94% of hours.
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"Wind and solar could meet more than 80% of demand in many places without crazy amounts of storage or excess generating capacity, which is the critical point," said co-author Steven Davis, UCI professor of Earth system science.
"But depending on the country, there may be many multi-day periods throughout the year when some demand will need to be met by energy storage and other non-fossil energy sources in a zero-carbon future."
The team analysed 39 years’ worth of hourly energy demand data from 42 major countries to work out the adequacy of wind and solar power resources to serve their needs.
They found that a full conversion to sustainable power resources can be easier for larger, lower-latitude countries, which can rely on solar power availability throughout the year.
The researchers highlighted Germany as an example of a relatively smaller country, in terms of land mass, at higher latitude that will make it more challenging to meet its electricity needs with wind and solar resources.
"Historic data show that countries that are farther from the equator can occasionally experience periods called 'dark doldrums' during which there is very limited solar and wind power availability," said lead author Dan Tong, assistant professor of Earth system science at Tsinghua University.
"One recent occurrence of this phenomenon in Germany lasted for two weeks, forcing Germans to resort to dispatchable generation, which in many cases is provided by fossil fuel-burning plants."
Among the approaches the researchers suggested to alleviate this problem was a building-up generating capacity that exceeds annual demand, developing long-term storage capabilities and pooling resources of multiple nations on a continental land mass.
"Around the world, there are some definite geophysical constraints on our ability to produce net-zero carbon electricity," said Davis.
"It comes down to the difference between the difficult and the impossible. It will be hard to completely eliminate fossil fuels from our power generation mix, but we can achieve that goal when technologies, economics and socio-political will are aligned."
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