Electrical Load Leveling, the Home Front

So as I look through my list of half-finished posts for ideas (I'm not feeling too creative with my workload), I came back to this idea: use heating/cooling to do load leveling of renewables, combined with electric and plug-in hybrid vehicles, for voltage regulation. I actually started this post November 11th, 2005.

The basic idea is to store energy in a heat sink when electricity is available and draw it out as needed to provide heat or cooling for a building. This generally takes the form of either ice, for cooling, or hot water for heat. However it is possible, for example, to use a solid heat sink like granite and then pass a liquid through it to exchange heat.

People who have seen large air conditioning systems will know that they come rated in 'tons', which seems a strange unit of cooling. This nomenclature comes from the olden days when a building would purchase tons of ice from an ice house to provide cooling. Hence a ton refers to the cooling potential of a ton of ice, through the combination of heat of vapourization and the temperature gradient to room temperature. A home typically needs a 1-2 ton AC unit.

There are of course drawbacks to this scheme. One is the sheer volume required. A ton of ice is roughly 1 m³, so a 50 ton unit for a mall will require quite a large room just to house the ice. One doesn't want to directly pass air over moist ice and humidify it in the summer time either. If anything we want to dehumidify the air with a desiccant. Thus a solid-to-liquid heat exchanger is needed, adding cost and complexity. The natural way to heat and cool through this method is to circulate hot or chilled water through radiators or in-floor heating.

On the other hand, we can get away with a smaller air conditioner unit. Instead of an AC unit that needs to meet the peak demand at midday we can install a much smaller one that can continue to operate at night, producing ice to use throughout the day. Also, once installed, a heat pump can provide heating or cooling to an appropriate heat sink. There's no need to have separate components for a well-designed system.

In all cases it is necessary and advantageous for homes and commercial buildings to be well insulated, sealed and with climate appropriate construction methods and window coatings. For example, my south facing apartment has a couple of large elms in front of it. In the winter, the sunlight comes streaming in but when summer rolls around their leaves will provide shade. This is passive heating/cooling in action.

These systems have a relatively high capital cost so it would have the greatest impact to encourage large commercial and residential buildings to operate with flexible load heating/cooling. The advantages would be serious, not just for intermittent electrical sources like wind but also for reducing peak power demand in general for utilities: both their generating capacity and transmission lines benefit. Afterall, a peaking gas turbine is a very expensive operation now.

The intermittent power delivery from renewable sources remains the ultimate drawback of wind, solar, etc. that prevent their full-scale deployment even if we wanted too. Not many nations can be like Denmark and claim to derive 20 % of their power from wind while relying on Norway's dams to smooth out the peaks and valleys. The key to solving renewable intermittency lies with demand side management, not massive energy storage solutions. Modern communication through the Internet is an incredibly powerful device and it's appropriate to use it to our benefit.