This is an innovative self cleaning solar panel system using
the wind and the venturi effect. Being in Ottawa, Ontario, Canada, we
get a lot of permanent snow for two to four months of the year.
The problem here was snow build-up at the base where the panels meet the
roof due to the the dead air space there. This system consisted of four
solar air heating panels
connected in series. However, the panels can also be photovoltaic panels
or solar hot water flat plate or vacuum tube collectors. This system was
designed and installed by
Isolara Energy Services.
The venturi effect is where air flows
through a tube and the tube narrows. As the tube narrows, the air pressure
decreases and the air accelerates, the goal here being to get faster moving
air blowing over the panels to clean off any snow, or in this example, to
blow away snow that was building up at the base of the panels where they
meet the roof. It doesn't always have to be a tube though. In this case the
air flows between the roof and curved length of sheet metal.
For this location there is a large river on the north side, the Ottawa river.
Even though in the winter it is frozen solid, there is still a nice breeze
from it for the intake of the venturi "tube".
Heat removal and results
You might think that the fast moving air flowing over the front of the
solar air heater panel would suck the heat away from the glazing (glass
front) of the panel, and of course it does, just as any wind would.
However, the part of the panel that is heated by the sun is the dark colored
absorber which is separated from the outside by the glazing
and an air gap, both of which act as insulators. Since the addition of this
venturi system, the customer reports no snow build-up at the base of the panels
while still getting plenty of heat.
Other types of solar panels that would benifit
Photovoltaic panels (solar electric/power)
A photovoltaic panel (solar electricity generating panel) decreases in
efficiency the hotter the panel. In this case the glazing is glued directly to the
solar energy collecting material (e.g. silicon solar cells) with no air gap and so
would benefit from any removal of heat by the air flow.
The photo to the right and those below are from installations by
Ottawa Solar Power.
SDHW - vacuum tubes
Solar domestic hot water (solar thermal) systems using vacuum tubes can
especially benefit greatly from this technique since the outside of the tubes
remain cold due to the vacuum between the glazing and the absorber. This is a
major problem in a snowy climate since the snow will not get any heat from the
hot absorber and snow will not melt off them. Instead snow and freezing
rain will happily pile up as on any other cold surface. This happens
with tubes that are not mounted on a sufficiently steep angle and are mounted
close to the roof.
SDHW - flat plate collectors
Solar domestic hot water systems (solar thermal) using flat plate collectors are much
like the solar air heating panels above in that there is glazing and an air gap in
front of the absorber to act as insulators, the majority of the heat
being at the absorber. So air flowing over the glazing will pull heat from
the glazing but not affect the absorber much due to the insulation value of
the air gap and the glazing.
However, these flat plate collectors are typically mounted on a steep enough angle
that snow will fall off naturally. The only concern would be a location where snow
that does fall off has no where to go and instead builds-up at the base of the
panel, eventually beginning to cover it from the bottom up, as was the case with the
solar air heater system it was designed for above. Notice in both photos below
that the angle is steep and in the second photo, there is ample room for snow that
does fall off to pile up without blocking the panel.
Panels as wings or sails
We often refer to solar panels as wings or sails in that if wind gets
behind them a large enough force can be produced to break the panel
away from the roof or the frame that the panel is mounted to or even
to knock over a system of panels mounted on a pole. With the addition of this
venturi system the forces are even greater as metal foil is acting
like a wing, redirecting the wind downward creating lift.
As with any system, this extra amount of force must be taken into account.
Wind gusts of 100 kilometers per hour will become more prevalent in the Ottawa
area as climate change progresses and we are already starting to see this