The sun has an efficiency problem. Yes, it produces enough energy every hour to power 2,880 trillion light bulbs. And yes, that’s enough to meet the world’s energy requirements for a year. But every night it goes completely dark — at least on one part of the globe. Meanwhile, a few passing clouds can be enough to slow energy production, at least in contemporary solar arrays.
That may sound simplistic, but it’s unfortunately the obstacle preventing solar power from developing into a self-sustained solution to our energy needs. For all our advanced computing and sophisticated data storage, we actually don’t have a proficient way to store electricity without it degrading. Solar batteries exist, but internal resistance makes them less and less efficient over time. That means most solar powered homes either have to stay tied to the grid, rely on a backup diesel generator, or just go dark for a few hours when stored energy peters out. None of those present a very elegant solution to utility-scale energy needs — and powering a single home is obviously a lot simpler than powering a city. Large-scale energy providers deal with imbalances in demand using load switching and management, and have backup sources of energy available to manage grid-stabilization events, something that might be difficult to do with a large wall of industrial batteries.
In fact, switching exclusively to renewable energy would put a huge drain on our grid’s aging infrastructure — with solar power, for instance, we’d not only see issues with storing and supplying demand during low generation periods, like during night, but we’d also face problems during peak yield times as well. A very mild, sunny day could flood the grid with excess electricity, which could just as easily switch off entirely with a passing cloud. Load balancing systems just aren’t designed to handle that kind of rapid fluctuation — they mostly react to widespread, consistent events—high demand on a hot day, for instance.
There may be another solution sitting right under our floorboards though—the humble, unexciting water heater. Recently a report by the National Rural Electric Cooperative Association, Peak Load Management Alliance and Natural Resources Defense Council called this lowly appliance “the hidden battery,” a consensus that’s starting to take off amongst energy professionals and environmental groups alike.
So just, how, exactly can a water heater act like a battery? Well, it starts with grid-interactive smart appliances — instead of consumers and appliances setting demand and utilities responding, grid-interactive appliances are able to communicate with utilities and shift their consumption depending on available supply and grid drain. Water heaters are particularly useful, because they can not only reduce consumption — actually, utilities have been quietly shutting off water heaters to lower use rates during peak periods for many years — but they can also absorb excess energy as heat. Heat far surpasses electricity in terms of the rate of degradation—you can think of it as the tortoise to electricity’s hare. Hot water can be stored for much longer before cooling, and unlike a battery, heat can be steadily pumped into a water heater without the internal resistance that crushes lead acid battery performance.
The only problem there lies on the consumer end. Heat discharge could potentially raise water temperatures to uncomfortable, if not dangerous, levels. But new system designs, like those from Sequentric, could make heat storage a real possibility without affecting residential use. That’s because these systems are built with two storage sections — an upper level that’s designed for conventional use, and a lower portion that holds stored heat from the grid. That would make them more efficient, as well, since heat tends to rise. Grid-interactive water heaters also hold an advantage in speed—they’re some of the most responsive appliances there are, and can be shut off and on in a matter of seconds. Smart bidirectional controls on new devices can expertly shift their charge rate and charge level in real-time. That kind of agility makes them well suited to stabilize a grid with many rapid fluctuations — as long as the grid is smart enough to compute available capacity, that is. But Sequentric is also developing a utility software that can manage residential water heaters in fleets over IP networks. Analytic and dispatching servers track individual charge levels, allowing systems operations centers to shift excess heat to tanks that need it—in the blink of an eye.
All in all, unless there are real advances in photovoltaics, not an unlikely event, battery technology and solar storage will have to evolve to accommodate shifts in the grid. That means thinking about batteries not as electricity containers but merely as energy storage systems—no matter what form that energy takes. In fact, that shift is already starting to take form in California. The popularity of solar there has lead to an edict from the California Public Utilities Commission requiring utilities to build new solar storage into the grid. It will be interesting to see where that takes the technology, but it could very well be that a utility-scale battery solution is hiding right in our basements.