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Getting even more energy out of your roof with a PV/T system

How would you like to buy a solar electric (photovoltaic) system for your home or business, and cut the payback time almost in half? PV/T (photovoltaic thermal) systems may offer a way to improve solar payback times by capturing the waste heat energy from the Photovoltaic (PV) system for your building’s water and space heating needs. Of the sun’s energy that falls on the PV modules, about 15% is converted to useful electricity, which leaves 85% of the sun’s energy available as heat. This excess heating of the PV module is wasted and also decreases PV module efficiency.

By Doug Boleyn
Solar Oregon Board Member
Commercial Solar Project Manager, Energy Trust of Oregon

 

How would you like to buy a solar electric (photovoltaic) system for your home or business, and cut the payback time almost in half?

 

PV/T (photovoltaic thermal) systems may offer a way to improve solar payback times by capturing the waste heat energy from the Photovoltaic (PV) system for your building’s water and space heating needs. Of the sun’s energy that falls on the PV modules, about 15% is converted to useful electricity, which leaves 85% of the sun’s energy available as heat. This excess heating of the PV module is wasted and also decreases PV module efficiency.

 DougsHouse

How does a PV/T system work?

 

In a PV/T system, this excess heat is collected from the PV module and put to use. Commonly, a fan pulls warmed air from the backside of the PV modules, and heats water by use of a heating coil.  The cost advantage of a PV/T system is that it uses the same roof, collectors, mounting and racking system to produce both electricity and heat.

 

What can you use the heat output for?

 

The heat can go to domestic water heating year around, and space heating during the heating season. The temperature from the PV modules just needs to be a few degrees higher than the water or indoor air temperature to save money on both.

 

In addition to water heating and space heating, other uses of the heat could include: a) Pre heating make-up air for commercial buildings; b) Process heating for an industrial or agricultural operation; c) Clothes drying; and c) a liquid dessicant cooling (air conditioning) which can use the hot air to provide air conditioning!

 

Are there “off-the-shelf” systems that can be purchased?

 

The most advanced  “packaged” PV/T system is the PVT Solar Echo Solar system. This product has materials and instructions to install a system that efficiently extracts warm air from the PV modules. This consists of a rolled metal roofing on the roof deck, a framework to support the PV modules, and a system of flashing that creates an air- and water-tight plenum that directs the warm air to the fan/control unit to either heat water, heat space, or if excessive, be exhausted. See  http://pvtsolar.com/  for more information. 

 

For commercial/industrial systems, Conserval Corporation offers their Solarduct PVT system.  This is simply black painted perforated metal sheets attached to south building wall with PV modules over them. Fresh air is drawn in behind the PV modules, gets warmed up, and is put into the building, thus saving heating energy. See http://solarwall.com/en/home.php for more details)

 

Are there any incentives for PV/T Systems?

 

As of Fall, 2010, there are no specific incentives for “PV/T” systems. The PV part of the system, however, qualifies for the standard 30% Federal Tax Credit, Oregon Residential or Business Energy Tax Credit, and the Energy Trust of Oregon PV incentives. Both the Energy Trust of Oregon and Oregon Department of Energy are gathering data to find out incremental costs and energy production/savings so that appropriate incentives may be set.

DougPVT

 

Is a PV/T system right for my home or business?

 

Do you and your building meet these qualifications?: 1) a desire for both a photovoltaic and solar water heating system; 2) have a south-facing, unshaded roof area of at least 200 square feet; 3) A building ready for re-roofing; 4) fairly substantial heating and water heating use or a desire for net-zero energy consumption and; 5) Some additional heating loads you’d like served, such as pre-heating for make-up air.

 

Bottom line: For the right building/customer, a PV/T system is worth exploring now.

 

 

 
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