Coal and fossil fuels have one advantage over renewable energy sources, and that is a built in storage component. Solar and wind are just energy. It may seem like an obvious observation, but that one characteristic is why fossil fuels are ingrained in our energy infrastructure. Storage provides the grid with the ability to quickly add or decrease capacity for reliable operation. This is also why energy storage is needed to make solar, wind and other "pure" forms of energy a viable, large scale replacement option for fossil fuels.
Take for example a net zero building that is generating enough solar energy in a year to offset the amount consumed from the electricity grid. Without some type of energy storage, the solar energy generated can only be used at the building as it is captured. Rarely, if ever, does the amount of generated energy perfectly match demand. If supply and demand doesn’t match, then either the building is generating too much energy and underutilizing the generated solar energy or it is not generating enough energy and relying on electricity from the grid. In order to match supply with demand on a building-scale and utility-scale, all kinds of energy storage technologies will be needed to decouple when energy is generated from when it is consumed.
Cool energy storage
Comfort cooling is one of the highest energy demands in a building, and the grid for that matter, and yet the least talked about forms of energy storage is distributed thermal energy storage (cool storage), despite its reliability and benefits.
Ice by night, cool by day
While battery storage makes sense for running electronics and lighting within a building, thermal energy storage, specifically ice-based energy storage, makes the most sense for cooling occupants. When using ice-based energy storage, cooling is created and stored in the form of ice. The ice is then discharged as needed during the day to offset or augment a smaller electric chiller to cool building occupants.
It may be possible for solar to power the chiller that is creating the ice in this system, so when a cloud comes over you have stored cooling available instead of drawing power from the grid.
To control system sizing in a commercial building, a smaller partial ice storage system sized for the average load of the building, rather than the peak load, may be used in order to lower daytime energy usage, peak demand and first costs. This targeted strategy makes the most economic sense as it allows a building to lower energy usage during the utility’s most expensive periods of the day.
Ice is created at night when the price of energy from the grid is 50% cheaper than it would be during the day. The ice is then used to cool occupants the next day during peak demand hours.
In a facility that is not using onsite generation, ice is created at night when the price of energy from the grid is 50% cheaper than it would be during the day. The ice is then used to cool occupants the next day during peak demand hours. These are the hours when the grid is reaching its maximum capacity and the price of energy is at its highest. On a utility-scale, high peak demand is responsible for an unfavorable utility load factor.
The current utility load factor for the United States is roughly 50%. This means that on average consumers are using only about 50% of our energy infrastructure. It also means that, theoretically, if energy was consumed at the same rate 24/7 then we could shut down half the power plants in the United States. While relying solely on solar to remove an entire building from the grid has proven difficult, solar working in collaboration with energy storage can provide a solution to reducing peak demand and improving the utility load factor.
Smoothing the grid
The widespread adoption of solar among commercial buildings without energy storage can cause dangerous fluctuations for the power grid. Let’s revisit the net zero example mentioned earlier. Even if that structure is able to generate enough solar energy to operate self-sufficiently during the day, it will still be connected to the power grid as a back-up.
If weather conditions change and daylight is unavailable, in a short amount of time a building will go from needing no energy from the utility to needing enough energy to maintain all the operations that were being powered by solar. This is a drastic spike in demand from one customer. The problem becomes even greater if numerous buildings within the region have the same set up and all instantly start consuming large amounts of power. The utility would need enough reserve capacity to ramp energy generation up and down as needed. More peaking plants which are less fuel efficient would be required to meet demand.
The California Lottery installed both 100 kw PV panels and 2,000 ton-hours of ice-based energy storage.
This scenario would lead to a less energy efficient power grid, a worse utility load factor and much higher energy prices during these spikes in demand. The utility still needs to dedicate a certain amount of capacity to any structure that is not completely off-grid and this is costly to maintain.
With energy storage, the captured solar energy can be used in very targeted ways within a building to lower peak demand, a tactic that will financially benefit the building, replace peaking plants and better stabilize the power grid.
Most structures don’t have enough solar generation to become net zero. A more common implementation is to install enough panels to take the edge off pricey peak demand hours in order to lower utility bills. This approach is what spurred the LEED Gold, California Lottery Building’s Pavilion to install both 100 kw PV panels and 2,000 ton-hours of ice-based energy storage. By targeting peak demand with solar and storage, the facility is helping both the power grid and building.
Written by Mark MacCracken, Chief Executive Officer of Calmac.