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Batteries are a key piece of technology missing on the path to a future of sustainable energy. Homes need a better way to store electricity to avoid peak utility demand periods. If consumers could shift the time of day they use electricity, they could make the grid more sustainable. As electrification moves into mechanical rooms in various markets, sustainability becomes an important topic.
What if consumers already had a big piece of the technology to influence the demand spikes?
My chemistry teacher in high school once said that some local news station would call a water quality expert about once a year after hearing a report that someone dumped a bunch of dihydrogen oxide in the local reservoir. The journalist wanted to know the consequences for consumers. The expert explained that dihydrogen was H2 and oxygen was O, so they described dumping water into water.
The rarely used, extended chemical name for water was the source of confusion and apparently a recurring chemistry prank call of sorts.
In a way, misunderstanding dihydrogen oxide is pertinent today in the battery conversation. Water has always been an excellent battery; it has a higher specific heat capacity than most readily available molecules on earth, meaning it is a great sponge for thermal energy. Hydrogen and helium gas have higher specific heat capacities, but they probably are not piped to a tank in many homes.
As opposed to a lithium-ion battery, water is not for the direct storage of electricity. In cases where homes use electricity to heat water with a heat pump or an electrical resistance element, water is a large indirect battery. Unlike the large lithium-ion batteries entering the market to store electricity directly, most homes already have the water battery tucked away inside the structure. From a usable space perspective, this is different from adding a new Tesla battery into a garage for electricity storage.
How does a tank of water affect the future of the utility industry and national energy goals? U.S. buildings consume about 40 percent of the nation’s energy. Averaged across all homes in the nation, space heating accounts for 43 percent of energy use and water heating uses 19 percent, according to a 2015 Energy Information Administration dataset (https://bit.ly/3MELWZn).
To put that into perspective, if all the nation’s boilers, furnaces, space heaters and water heaters disappeared today, nearly the same energy savings would be achieved as eliminating the entire transportation sector. Space heating and plumbing take up 25 percent of the U.S. annual energy consumption. Cars, planes, trains, trucks and motorcycles consume about 26 percent of the nation’s energy (https://bit.ly/37lyTMf).
In the forgotten mechanical space in homes, behind the broom and dusty storage boxes, are a couple of simple machines responsible for a quarter of the energy used by our nation annually.
If plumbing and HVAC machines are so pivotal, how can we make them more efficient? The good news is that almost all installers can drive to their local supply house and pick up a 90+ percent AFUE boiler, condensing furnace or efficient water heater.
The bad news is that most of those machines are still operated with the simplest of controls. The thermostats and aquastats in the vast majority of homes are simple on/off calls for heat that do not understand the implications of the time of day. If we do not schedule these devices better, we are headed for a utility duck curve.
An electric utility demand dashboard, graphed over 24 hours, will likely show a spike in electricity demand in the morning, rising to a higher spike from about 6 p.m. to 10 p.m. This traditional demand curve has been consistent over many decades (see Figure 1).
As electric utilities add more solar photovoltaics, the graph changes a bit. When the sun is out during the day, the demand for fossil-fuel power shifts. Solar energy gathered throughout the day brings the megawatt burden down for fossil fuels. However, it does not change the spike from 6 p.m. to 10 p.m. much because the sun is generally down by that time and the consumer habits have not changed.
The added solar capacity (duck curve) line in Figure 1 shows this change: a short peak of a tail in the morning, a big dip when the sun is up and a large spike up to the duck’s head when consumers are home from work.
Beware of the duck
If utilities add an enormous amount of solar PV to the grid, it may reduce the need for fossil-fuel power plants during the day. However, if a peak usage time occurs as the sun sets, we are still missing something important. We need to lower the duck’s head to reduce the amount of fossil-fuel power in the utility mix.
One way to fix the problem is to better store renewable energy for evening use. A second option is to let the utility decide when to limit power usage at their customers’ electric heaters and water heaters to avoid spikes. In several utility markets, these load-shedding technologies are available. Markets with high potential for summer brownout scenarios love when consumers allow them to limit air conditioning to push demand down.
Another demand-shifting option is for consumers to stop using as much energy in the early evening. As mentioned before, HVAC and plumbing energy use is an enormous factor in home energy use. If these machines charge a water battery during daylight hours and coast through the evening without cycling on and off multiple times, the demand line starts to look different.
If the machines and systems are more energy-efficient, the curve looks like the added solar and reduced demand line in Figure 1. In a scenario where electric customers lower their energy demands, utilities have more flexibility to take older, expensive-to-operate fossil-fuel plants offline.
Many people reading this article are likely familiar with the problem described previously. What is the solution? If everyone in the industry went door-to-door and told their neighbors, “Do not use a lot of electricity in the evening,” there might be a lot of befuddled looks. It might be too much to ask the general public to understand the flow of kilowatts at all times anyways. The average person wants to come home, watch TV, do laundry and cook dinner.
As industry professionals, we can manufacture, install and commission these electrified space and water heaters to flatten the graph without disrupting homeowners. However, a change is needed to better time electrical heating. With a large volume of water, proper controls and components, designers and installers can change the curve without homeowners noticing a difference.
The standby loss of a modern water heater is so small that “overstoring” it during the sunlight hours, beyond the typical setpoint while letting it coast as far into the evening as possible, is not wasteful. In practice, an electric water heater or heat pump control could adjust the setpoint up 15 degrees from 1 p.m. to 3 p.m. and down 20 degrees from 6 p.m. to 10 p.m.
Proper scald protection valves are always needed if overstoring a tank of domestic water. In a perfect world, this would lower the head of the duck curve. Equipment manufacturers and utility companies are currently working together to figure out a control strategy, but anyone reading this column could likely do the same sequence with a setpoint controller.
In the United States, we love an energy, get-rich-quick scheme. We always have. We badly want some sort of new technology to triple the miles per gallon of our cars, power our phones for days at a time and store energy for our home in a tiny box. Realistically, we should better use the dusty water batteries in our basements as this will be key for the markets pushing electrification.
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