How Can We Design For Intermittency of Renewables?

There is so much talk about the hydrogen economy these days, and about making "green" hydrogen from renewable electricity, or "blue" hydrogen from natural gas while capturing and storing the CO2 that is released through the steam reformation process. Treehugger has been somewhat skeptical, noting that electric cars are much more efficient for transportation, and modern electric heat pumps are much more efficient for heating and cooling. But another use of hydrogen that has been popping up recently is as a solution to the problem of the intermittency of renewable energy.

Intermittency is what happens when the wind doesn't blow and the sun doesn't shine, and another dependable source of electricity is required to make up the difference between electricity demand and renewable supply. This can be expensive and carbon-intensive, kind of like having a car sitting in your driveway all year for the few times that it's too rainy to ride your bike. Hydrogen has been offered up as a solution to this problem, as explained by Michael Liebreich of BloombergNEF:

"The extra value of zero-emissions hydrogen – be it green, blue, turquoise or whatever – over and above all the other flexible power options listed above, is that it can be stored in unlimited quantities. Hydrogen is therefore the only solution that can provide deep resilience to the highly electrified net-zero economy of the future. To do so, it will need to be pervasively available: stored in salt caverns, in pressure vessels, as a liquid in insulated tanks, or as ammonia. It will be moved around, cheaply via pipelines, or at a higher cost by ship, train, or truck. And it will need to be strategically positioned to cover the risk of supply shocks, whether they be the result of normal weather patterns, extreme weather events and natural disasters, conflict, terrorism or any other cause."

Michael Liebreich is one of my go-to sources for smart discussions about hydrogen, so this drove me to spend my holiday thinking more about intermittency. Clearly, the hydrogen infrastructure that Liebreich is describing here would cost many billions of dollars and take many years, so we can afford to look at a number of options here. But first, let's back up a bit.

Until the Industrial Revolution and the introduction of fossil fuels, intermittency was the way of life. Kris De Decker describes in Low Tech Magazine how people adapted to a world powered by wind and water.

"Because of their limited technological options for dealing with the variability of renewable energy sources, our ancestors mainly resorted to a strategy that we have largely forgotten about: they adapted their energy demand to the variable energy supply. In other words, they accepted that renewable energy was not always available and acted accordingly. For example, windmills and sailboats were simply not operated when there was no wind."

So they would build dams to store water in mill ponds, "a form of energy storage that's similar to today's hydropower reservoirs." They learned the patterns of the trade winds so that they could cross the Atlantic pretty dependably. They adapted business practices accordingly and would work when the wind blew, even on a day of rest. A miller responded after a complaint about working on Sunday: "If the Lord is good enough to send me wind on a Sunday, I'm going to use it." De Decker notes that there could be modern equivalents to this:

"As a strategy to deal with variable energy sources, adjusting energy demand to renewable energy supply is just as valuable a solution today as it was in pre-industrial times. However, this does not mean that we need to go back to pre-industrial means. We have better technology available, which makes it much easier to synchronize the economic demands with the vagaries of the weather."

We Should Design for Intermittency

Before we can design for intermittency, it is helpful to know where our electricity is actually going. According to the Energy Information Administration, heating and cooling are the largest annual uses of electricity in the residential sector.

In the commercial sector, it is broken up a lot more, but the biggest sectors are computers and office equipment (combined), refrigeration, cooling, ventilation, and lighting. Lighting is dropping fast as LEDs take over, and it is likely that office equipment and computers are dropping as well.

Commercial is mostly about running machinery and processes, but industry has often adjusted for intermittency, cutting production when energy costs were high. And when you look at the entire picture, about half of our electrical consumption is going into heating, cooling, and ventilation, and we already know how to deal with intermittency in that sector.

Just as we are redesigning our buildings for a low carbon world, we can also, as our ancestors did, accept that our renewable energy supply is not always available and act (and design) accordingly. Treehugger has previously pointed out that many of Liebreich's worries about extreme weather events and natural disasters can be ameliorated by starting with better buildings, that stay warm or cool as needed if the power goes out. For example, during the infamous polar vortex, this Passive House in Brooklyn stayed warm for a week before they decided to turn on the heat. Hot water tanks could be insulated as well so that they stored heat. This is done now in many power systems, where the utility can turn off the tank when there is not enough power. Properly designed buildings could work the same way, storing heat or coolth with the utility controlling the thermostat.

In the UK, many people have Sunamp thermal batteries – boxes full of phase change materials that store the heat and release it when the electricity is expensive. In the USA, there are Ice Bear thermal storage devices that make ice at night or when electricity is cheaper.

Presenting at a Passive House conference a few years ago, Dr. Es Tressider described how Passive House designs could store wind power as heat. He concluded that if people were willing to live with a few degrees of temperature difference, "up to 97% of heating demand can be shifted to periods of over-supply of wind energy for a small increase in total heating demand."

A few years ago I made this house-as-thermal battery argument in response to all the talk about smart houses and Nest thermostats. The message still applies:

"It is time to get serious and demand radical building efficiency. To turn our homes and buildings into a form of thermal battery; you don’t have to fire up the heat or the AC at peak times because the temperature in them doesn’t change that fast. So a really efficient building can trim the peaks and troughs of our energy production as effectively as any other kind of battery. A properly designed house would need so little cooling or heating that it can be maintained at any time without making a big difference in energy use, without all this complication."

Instead of spending billions on hydrogen production, storage, and delivery, why not spend it on fixing our buildings and reducing demand, turning them all into thermal batteries. The electric car in the garage or the battery on the wall can run the LED lighting and the induction stove. As Dr. Steven Fawkes notes in Rule 9 of his 12 Laws of Energy Efficiency,

"An exciting energy or energy efficiency discovery in a lab somewhere is not the same as a viable technology, which is not the same as a commercial product, which is not the same as a successful product that has meaningful impact in the world."

We can actually design for intermittency on all new structures starting today, just by implementing the Passive House standard. Given how much renewable power has to be added before intermittency is even a problem, we could probably do an Energiesprong retrofit to every existing building in North America for a lot less money than filling caverns with green hydrogen, and we have everything we need to do it right now.