Is the Intermittency of Renewable Energy a Problem?

There are different ways of dealing with it.

Wind Turbines in Girvan, Scotland
Wind Turbines in Girvan, Scotland.

Lloyd Alter

In a recent post, "How Can We Design For Intermittency of Renewables?," I argued that the problem of intermittency – those times when the sun doesn't shine and the wind doesn't blow – could be solved or dramatically reduced by designing our buildings to act as thermal batteries that could coast through these periods. A commenter pointed out that intermittent was probably the wrong word, and that it should be variable.

"Intermittent means having an on-off nature. Variable means that the output varies over time. Quality can mean many things in the power sector, you need to define that a bit better. And that is why you need to combine wind and PV and connect over larger regions than regional weather patterns."

It is an important point; the wind is always blowing somewhere. Many people have claimed that if we have more renewables then we have a bigger problem of variability, but in fact, the opposite may be true. A few years ago, Robert Fares of the U.S. Department of Energy Building Technologies Office explained The Law of Large Numbers in Scientific American:

"The Law of Large Numbers is a probability theorem, which states that the aggregate result of a large number of uncertain processes becomes more predictable as the total number of processes increases. Applied to renewable energy, the Law of Large Numbers dictates that the combined output of every wind turbine and solar panel connected to the grid is far less volatile than the output of an individual generator."

He quotes studies that have shown that the larger amount of renewables, the less one has to worry about the variability and stability of the grid, and the less backup that is needed.

More recently Michael Coren of Quartz reported on the work of Marc Perez, who notes in a published paper that the price of solar has dropped so much that one could overbuild the system to provide enough energy, even on cloudy days.

"In the past decade, solar module prices plummeted more than 90%, according to energy research firm Wood Mackenzie. Meanwhile, the cost to build conventional plants such as coal rose by 11%. Solar panels have become so cheap that the true cost of electricity is shifting from solar arrays themselves to the steel and land needed to house them. ...The low cost overcame renewables’ traditional weakness: the intermittency of supply if the sun or wind fails to appear. Oversizing a system by a factor of three, they found, was optimal."

Given that many electrical systems have other low carbon power sources, like nuclear or hydroelectric to provide a base of constant power, perhaps variability isn't such a big problem.

After reading the earlier post where I quoted Tresidder, he responded with tweets noting that in winter there is a need for long-term storage. He continued:

"For example at the moment we're in the middle of a long, very cold, low wind weather period in the UK. In a future with lots of EVs and lots of heat pumps electricity demand will be high even with better buildings, demand response, and behaviour change. So let's do all of those things, but also push for H2. As far as I can tell it seems essential to getting to very high levels of renewables."

Perhaps. Hydrogen expert Michael Liebreich responds to Tresidder's tweets, agreeing that we need hydrogen backup as well, but it sure seems like it would require a lot of investment; all these electrolyzers and tanks, new distribution networks, and salt caverns to deal with 0.2% of the time. If those pensioners had proper homes, the electricity needed to keep them warm might be so small that they could borrow a cup of electricity from France or somewhere else where the wind is blowing.

Perhaps I should listen to experts like Tresidder and Leibreich; perhaps things have changed since I developed my aversion to the idea of the hydrogen economy 15 years ago. Back then, it was promoted by the nuclear industry as a way of justifying a massive buildout of nuclear plants that would make enough electrolytic hydrogen to power hydrogen fuel-celled cars and buses. That dream died with Fukushima, but now the hydrogen dream is driven by the oil and gas industries, which are promising "blue" hydrogen made from fossil fuels with carbon capture, utilization, and storage.

But then I am trained as an architect, not an engineer. I remain convinced that the answer is to reduce demand through Passive House level standards of efficiency, more multifamily housing with fewer exterior walls, in walkable communities with fewer cars. Work the demand side of the equation, not the supply side. And just in case, build a better, bigger, international grid; the wind is always blowing somewhere.