Time-Shift Your Excess Solar With Ice Storage

Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!

Ice Energy has announced a new model of its thermal energy storage in ice, designed purely with the solar homeowner in mind.


The Ice Cub lets a homeowner time-shift their own excess solar generation by storing solar generated at midday for use in their own air conditioning system.

In the system, refrigerant used in air conditioning is cooled while running inside coils piped throughout a tank of water that was frozen into ice with surplus solar electricity.

“With solar, the worst thing you can do is waste your energy, and that’s the problem with over-generation,” Ice Energy CEO Mike Hopkins told CleanTechnica.

“It’s why utilities put no value on it and they are actually starting to say its a negative value. You created it. You didn’t use it. You’re putting it back in my grid when I don’t want it. I don’t have a use for it, so all you’re doing is creating a problem with it. So we’re getting a spike of supply that we have no use for and we can’t effectively spill it, so it’s energy we need to get off of our grid.”

Ice Energy’s technology is simple. Where a conventional central air conditioning unit has a compressor outside, an Ice Cub adds a tank of water next to that compressor, with refrigerant running in coils through the tank. Excess electricity is used to freeze the water. The ice then keeps the refrigerant cool for hours, making that stored electricity available for cooling the home.

Smart grid product analyst Erich Gunther at the electric power research firm EnerNex praised the concept for its design humility. “It is tempting for many engineers to over-design a system, with complications for the end user,” he said.

The Obama White House has recognized the company for its innovative smart-grid renewable energy storage technology — one of the more elegant ways to make solar work after dark.

Ice Energy’s Ice Bear helped utilities control load on the grid, by owning and remotely switching aggregated storage. Utilities were able to tap excess wind power at night to time-shift daytime load from air conditioning to off-peak night hours. Now they have adapted the concept for the homeowner with solar.

In the same way that a utility was able to remotely control its aggregated storage Ice Bear units, a solar homeowner would be able to schedule when an Ice Cub turns on or off from any computer or smartphone.

You could set a schedule for when to freeze ice or run the air conditioner remotely. If your plans change, you can override it.

Hopkins sees the Ice Cub being used typically to absorb excess solar over-generation at midday and running central air conditioning between about 3:00 to 7:00 pm as families return from school and work, coinciding with the new peak load in California.

Replacing the conventional central air conditioning compressor with an Ice Cub compressor and ice tank would save 95% of the electricity normally used by central air conditioning, he said.

The energy hog aspect of a central air conditioner is the compressor running outside. The interior ducting and fans remain, and take little energy.

The Ice Cub compressor and ice tank is housed in a slim pair of boxes connected to the ducting of central air conditioning units. They will sit on the ground by the side of the house, unlike the company’s hefty commercial Ice Bear which latched onto the A/C ducting on the rooftops of commercial buildings.


Ice Energy expects to be shipping the Ice Cub by the summer of 2017. The cost of the two units making up the Ice Cub storage would be below $6,000 in California with rebates, about the same cost as replacing a conventional central air conditioning compressor.

Compressors typically need replacing every 10 years, as creating cooling is grueling work in hot weather. But the Ice Bear compressor will be guaranteed for 20 years, he said, as it operates in a more benign climate, since ice cools the refrigerant running in piping coiled throughout the ice tank.

The Ice Cub represents Ice Energy’s second foray into storage for homeowners, following its initial utility-owned and remotely operated Ice Bear 20 units for the smart grid.

The Ice Bear 20 was designed for utility-scale load reduction, aggregated as distributed storage. “For our initial home version, we had focused on utilities,” said Hopkins.

“Like our commercial product, a utility would buy it, and they would provide it to homeowners and then the utility would control when the Ice Bank gets used and that’s the way the utility would manage the residential load.”

For its utility business, Ice Energy used off-peak electricity (such as wind power at 3:00 am when nobody wants it) to make ice that cools the refrigerant used in air conditioning in commercial buildings, cutting the electricity needed to run the air conditioning in the heat of the day. Compressors need a lot of power fighting against heat.

Utilities would operate these rooftop units remotely to cut the load near particularly congested substations, autonomously controlling aggregated storage through intelligent software.

The commercial version tapped excess night wind power to cut daytime cooling energy use, and the consumer version could also be used that way, taking power off the grid when prices are low.

As indicated above, the just announced homeowner version, the Ice Cub, aims to run when a homeowner is producing their own excess solar, but the Ice Cub could also freeze the ice with off-peak grid power to eliminate the power draw of the air conditioning next day — in regions with a lot of excess wind power at night resulting in cheap electricity after midnight, for example.

In 2015, when Southern California Edison (SCE) put out requests for energy storage bids, Ice Energy’s was the only clean energy storage technology other than battery storage to be selected.

1,800 Ice Bears, comprising 26 MW of storage, are being installed on host buildings near two high-voltage Orange County substations that SCE identified as contributing a high load to the grid due to their old and inefficient air conditioning.


Utilities can monitor and control the distributed energy storage units. SCE owns and remotely controls the 1,800 Ice Bears as a grid asset, switching them on or off to take the entire group off the grid at once, or incrementally as needed, when it must cut peak demand.

This can be for as little as just a few minutes, and they can be cycled on and off. From the customer’s point of view, there is no impact on cooling. Once loaded with ice, the air conditioning can run for hours with almost no electricity.

Till recently, ice energy storage has been a small market, but as solar and wind increase on the grid, that is changing as utilities increase their opposition to net metering rates that make solar generation a viable investment for home users.

“If you make renewable energy, you actually don’t want to reduce energy use, it is the opposite of fossil energy,” Hopkins said. “You just need a way to use it yourself.”

Have a tip for CleanTechnica? Want to advertise? Want to suggest a guest for our CleanTech Talk podcast? Contact us here.

Latest CleanTechnica.TV Video

CleanTechnica uses affiliate links. See our policy here.