Solar panels have been around for about 40 years now — they evolved from the need to keep spaceships and satellites moving about in outer space without overburdening them with tanks of fuel.
Putting solar panels on buildings and in large fields to farm the energy of the sun is a more recent phenomenon. Most of the bigger projects have taken place only in the last dozen years or so.
The solar panels that power street lamps and calculators work by converting the sun's light rays, not its heat, directly into energy, to be stored in batteries or hooked directly to a power grid. Two thin layers of silicon glass receive a photon charge from the rays that strike the outer surface; the electrons that are shaken loose travel in a current along ultra thin wires to a collector.
That's how electricity is made directly from sunlight but that's not what is happening in the Okotoks solar community south of Calgary, or what is being proposed for the town of Vulcan, a little farther south still.
In both cases, they are looking at direct solar heating for homes and hot-water consumption and so they are more interested in the actual warmth of the sun, and in storing that warmth in underground bunkers.
The circulatory system
Drake Landing Solar Community: How it works (Illustration courtesy Drake Landing Solar Community)
In Okotoks, the engineering breakthrough was to erect the solar collectors on rows of garages and breezeways behind the two-storey family homes, to allow for pre-construction and a relatively unimposing collection system that is not attached directly to the house itself.
During a typical summer day, the heat of the sun pounding down on these collectors is enough to generate approximately 1.5 megawatts of thermal power. The solar panels absorb that energy and heat a system of insulated pipes that contain a solution of glycol, not unlike what you'd find in a car's radiator.
The glycol travels through the pipes to a short-term storage system in the community's energy centre. It basically contains several large tanks of water, like boilers, and the heat from the glycol-containing pipes is transferred to the tanks.
In the warmer months, the heated water in the tanks is distributed through a series of smaller pipes 37 metres below the ground to the longer-term storage area, which is covered over by sand and other insulating material. By the end of the summer the land around this storage site will be heated to approximately 80 C.
When winter arrives, the process is partially reversed. The heated water from the underground storage site is passed back to the boilers in the energy centre from which it is circulated to all the 52 homes in the subdivision via underground pipes, depending on need.
During a sunny winter day, the solar collectors should provide all the heat required by the community. At night the long-term storage pump is turned on to transfer heat from underground back into the system.
In each home, the heated water is passed through a heat exchanger in the basement furnace that turns it into conventional forced-air heating, governed by the home thermostat.
The Vulcan project would be a little different but only on the storage front. It envisions a farm of solar collectors about the size of a football field and the longer-term collection unit would be a massive underground water tank that would hold almost four million litres of water.
In both cases, the solar energy is expected to supply up to 90 per cent of the home heating requirements. The remainder would come from a gas-powered burner, in the case of Okotoks, or a farm waste-burning co-generator in the case of Vulcan. Both would kick in as the need arises.
