Solar Harvesting Systems

The Wentworth Project uses several innovative technologies for solar harvesting. These innovations were developed for the site, but they would work equally well anywhere in the world with small adaptations for the latitude in question.

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Solar Convection Windows

The Wentworth Project uses a special window design that boosts passive solar gains by 35% with no need for monitoring or sensor hookups. This design adds a low E thermo-pane to an exterior thermo-pane of low-iron glass.

These windows use heat expansion pistons to control air flow, and maximize and conserve heat gains. Glass is angled in the frame to facilitate solar heating in winter, and to add shading between May and October when excessive sunshine becomes a problem.

Window Construction

The outside glass is a low-iron thermopane with an interior thermopane of low E separated by a gap of 6 to 8 inches. This enables the solar heat to enter the first thermopane and rapidly heat the cavity between the low-iron pane and the heat mirror. The heat causes fluid in a cylinder to expand, which opens vents simultaneously at the top and bottom, allowing the heat to escape and cooler home air to enter the cavity.

This convection flow works as long as the sun shines on the window.

When the sun does not shine, the low E keeps the heat in, conserving any gains. This innovation acts as both a nearly invisible solar harvester and a thermal barrier in a unit that does not cost any more than a premium-priced window.

Easy Maintenance

The windows are engineered to permit opening of "sections" for easy cleaning or ventilation. This design simplicity assures that windows will continue to operate without mechanisms that may break down.

This modular design also facilitates removal and replacement of seals and weather stripping that may deteriorate with time and UV exposure.

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Combination Solar Energy Panels

A combined photovoltaic and solar collector was designed for the Wentworth Project. This innovative panel splits the incoming solar energy into heat and light, and provides both electricity and heat energy to the home.

In this design, a photovoltaic panel sits on top of either an aluminum or translucent sheet, that transmits heat to a fluid core and keeps the electricity-generating upper layer from overheating.

This approach has two benefits: it keeps the panel working at its optimum operating temperature and prolongs its life by preventing degradation due to excessive heat. On hotter days the flow of fluid accelerates, keeping the panels cooler.

Awnings and Overhangs

These combination panels can be incorporated into a fixed awning or overhang to keep south-facing windows from admitting too much heat in the summer. This lessens the need for air conditioning, the third highest use of electricity in the home.

To mitigate any loss of natural light in the interior, the undersides of the awning are covered with a Mylar mirror or polished aluminum to redirect reflected light into the home. Our research indicates that more than 95% of light reflects off snow and 78% off leaves, resulting in the interior being about 25% lighter.

Automatic Snow Removal

Conventional photovoltaic panels are prone to being covered with sticky snow or ice in winter, which can make them useless for days. Snowstorms are often followed by a sunny day, during which power generation is lost while the snow melts.

Freezing rain can coat a panel with a layer of ice several inches thick. This actually happened during Montreal's Great Ice Storm of 1998. At that time, conventional photovoltaic panels could not be scraped or struck to get the ice off; only days of warm and sunny weather melted the ice.

In the Wentworth Project, the combination solar energy panels automatically de-ice themselves. If radically different readings are received from the interior and exterior sensors, a photo-optic switch turns on the fluid pump. This pumps fluid from the reservoir to the panel, and heats the photovoltaic plate.

Snow slides off the heated windows in less than a minute. Ice takes longer to clear, but in either case there is no need for any maintenance to clear sticky snow or ice, as with other types of solar panels.

The Bottom Line

This combination panel design costs 20% more than conventional photovoltaic panels, but provides numerous benefits. It adds 7 to 10% in electricity production due to faster snow clearing and minimal losses to over heating. A panel's life expectancy is anticipated to be 10% longer due to less degradation from overheating. And since one panel produces both heat and 12-volt current, it actually doubles the space available for solar energy harvesting on a home.