One of the biggest complaints I have with the concept of Zero Energy Buildings and with rooftop solar installations is that they do not necessarily reduce overall energy consumption but shifts the source from grid to solar. This is of course a wonderful thing during the day when the sun is shining, but right now, where there are so few ways to store sunshine, there is a big problem at peak times. In fact, “when a building uses electricity can be just as important as how much is being used.”
Utilities in the US today are running at a load factor of about 50 percent, meaning that they are using only half their capacity most of the time, but have to be able to deal with peak loads with a lot of capacity just sitting around most of the day. As more people put solar panels on their roofs, the load factor just gets worse. (more on this on MNN)
In the Sunbelt, a major driver of electricity consumption is air conditioning, consuming as much as 40 percent of peak electrical demand in summer. And while we may not be able to store sunshine, we can actually store coolth, (I never can think of a better word) in the form of ice. Calmac has been doing this for years with their ice storage systems (TreeHugger here) and their VP of sales, Paul Valenta, writes in Consulting Engineer how this can be used to store significant amounts of energy, and is ideal for Net Zero buildings.
A zero energy building can reduce its peak demand through the use of thermal energy storage by making ice during off-peak hours to cool the building during peak periods. Without thermal energy storage, when demand for cooling spikes, renewable energy is used to cool the building. If the sun is no longer available, more expensive energy must come from the grid. The consumer is then charged expensive demand charges to account for use of the grid's standby power, which happens to also be more polluting.
By using thermal energy storage instead, ice is created during low-demand hours using low-cost, low-emission energy. The next day, during peak-demand hours, renewable energy can be used to meet the building's demand for cooling. Energy storage can kick on when the sun isn't shining, thus, reducing the peak demand, flattening the building's electrical profile, and improving the grid's load factor. When there is no increase in energy usage during the high-demand peak hours to the utility, the building appears smaller.
Ice is essentially a battery, made with off-peak power (much of which is solar) and storing a big chunk of the energy needed at peak times. This saves the consumer a lot of money and could take a significant load off the top of the peak. Smart thinking from Calmac.