Grid Scale, Solar, Storage, Wind Power

Cheap Ice Energy Storage for Solar Homes

By the summer of 2017, solar homeowners could store surplus daytime solar in an ice-based energy storage unit with a 20-year life, for less than half the cost of a battery storing the same solar kilowatt-hours, according to Ice Energy CEO Mike Hopkins. 

“The beauty of the Ice Cub is that if you use it to store solar every day, its capacity doesn’t degrade the way a battery will degrade, and it will last 20 years — twice as long as a battery,” said Hopkins. 

The Ice Cub is the firm’s first energy storage unit designed with the consumer in mind, in particular homeowners who generate solar and use central air conditioning. 

First: Time-shifting Night Wind for Utilities

So far, Ice Energy has made “smart” ice storage units operated by utilities to shift load on the grid. It was almost the only non-battery winner in Southern California Edison’s 2014 tender for energy storage and first partnered in a solar demo with SunPower in 2010.

The firm’s commercial energy storage unit, the Ice Bear, reduces the cost of commercial air conditioning by using off-peak electricity to make ice to cool the refrigerant used in a central air conditioning system during the day.

Then cheaply frozen ice-cooled refrigerant reduces the cost of refrigeration for air conditioning by 95 percent.

Utilities controlling the units remotely can then switch groups of Ice Bears on or off in a smart grid system to reduce distribution bottlenecks. 

New: Time-shifting Residential Solar

Hopkins now sees a growing market for a different application for its ice energy storage. Instead of time-shifting unwanted night wind generation, the Ice Cub will time-shift residential daytime solar spills.

Typically, solar homeowners send daytime solar to the grid and buy electricity back on return home in the evening.

With early net metering rates, this worked. But with net metering under attack in more states, the economics have become less certain for solar homeowners. The Ice Cub addresses this problem.

In most of the sunbelt states, such as Florida, Texas, New Mexico, Arizona, Nevada and parts of California, central air conditioning can account for most of a home’s electricity use.

How It Works

The Ice Cub would enable a solar homeowner to greatly reduce electricity cost by mopping up surplus solar spilled in the middle of the day to run air conditioning when they return home.

This surplus electricity would freeze water to ice, which can cool the refrigerant normally used to run central air conditioning for up to four hours.

Using a smart phone or laptop, the consumer would be able to schedule the Ice Cub to turn on or off remotely, and coordinate it with current solar generation at any time that their solar is generating more than they are using. 

It can be programmed to make and store ice while simultaneously cooling the home during peak heat, or it can be scheduled to hold the cooling for use later. Then if plans or the weather changes, the homeowner can override the setting.

Once loaded with ice, almost no electricity is needed to run the central air conditioning: just for pumping refrigerant through pipes in the ice tank and for a fan blowing the cooled air through the home at an estimated 95 percent energy reduction. 

Easy Substitution

When replacing central air conditioning, all the interior ducting remains; only the exterior compressor is replaced. Similarly, when replacing central air conditioning with an Ice Cub, the interior ducting remains, only the exterior compressor is replaced with the Ice Cub compressor and insulated ice tank. 

Conventional compressors, subject to much more heat stress, need replacement every 10 years, but the Ice Cub is guaranteed for 20 years.

Ice Energy plans deliveries in summer 2017, and the price (with California rebates) is under $6,000, about the same cost as replacing conventional air conditioning.

Initial orders will be through partnerships, not yet announced; but several under consideration include firms that perform energy efficiency upgrades, HVAC companies and solar installers.