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PV/Thermal; Hybrid Solar Heating + Electricity

 

SolarWall® PV/T is a hybrid system which provides up to 300% more energy (in the form of solar electricity + solar heat) than a conventional solar PV system.  The heat energy captured from the PV modules is ducted into the building’s HVAC system where it is used to displace the conventional heating load. The secondary benefit is to provide PV cooling by reducing the operating temperature of the PV modules, which improves the electrical performance.  Excess heat buildup behind PV panels is a common problem, and for every 1°C (1.8°F) above 25°C (77°F), the electrical output drops by 0.4 to 0.5 percent.  Read more here.

SolarWall® PV/T Value Proposition

Technology Watt / m2
PV Electrical Output 100 Watts/m2
(10 Watts/ft2)
SolarWall® Thermal Output 200-300 Watts/m2*
(20-30 Watts/ft2)
Hybrid SolarWall® PV/T 300-400 Watts/m2
(30-40 Watts/ft2)

*SolarWall® system output when combined with PV
Note: SolarWall® output without PV is 500-600 Watts/m
2

The hybrid PV/Thermal technology also produces the following additional benefits which collectively help to accelerate the PV system return on investment:

SolarDuct® PV/T

SolarDuct PV/T tech drawingThe technology is also available in a modular roof-top configuration known as SolarDuct® PV/T. In this application, the PV modules are mounted on top of the SolarDuct units, and then heat is drawn off the back of the PV modules and ducted to the nearest rooftop air handling unit.  This “excess heat” is then channeled into the building’s HVAC system where it offsets the heating load.  Since the thermal heating panels do “double-duty” by also acting as the PV racking system, this also contributes to the cost-effectiveness of the hybrid system.  The modular units are easy to install and are angled at an ideal orientation for maximum solar gain.

Capturing the Heat & PV Cooling

SolarWall PVT at CANMET
Above, SolarWall system at Natural Resources Canada's CANMET Buidling in Ottawa. The SolarWall system was upgraded to a hybrid PV/T system in 2010, delivering both solar heated air and electricity to the building.

Conserval Engineering originated the concept of combining PV with the SolarWall technology. The objective was to address some of the problems inherent with conventional photovoltaics, and to develop a solution that would further enhance PV as a viable renewable energy solution for regular commercial and industrial buildings. Two problems that can make PV unattractive are the lengthy payback periods and the low solar efficiencies. The hybrid PV/T system provides a solution to both of these problems.

Typical PV modules have a solar conversion efficiency up to 15%. What happens to the rest of the sun’s energy that shines on the panels? Most of it is converted into heat energy, which normally is lost and provides no value to the system owner. As well, the heat build-up behind PV modules reduces the electrical output by 0.4-0.5% for every 1°C above its rated output temperature, which is 25°C (77°F). For every 1°C (1.8°F) above 25°C, the electrical output drops by 0.4 to 0.5 percent. A typical rooftop PV array may measure 55 to 75°C (131 to 167°F), which means its electrical output would fall by 12 to 25 per cent below the name plate rating. For example, a 10-kW array only generates 7.5 to 8.8 kW under these temperature conditions. A PV/T system lowers the photovoltaic temperature by 10 to 20°C (18 to 36°F), which increases the electrical output by five to 10 per cent, or an extra 0.5 to 1 kW for a 10-kW array.

The performance of the SolarWall PV/T hybrid technology was established through testing at the National Solar Test Facility, in conjunction with the International Energy Agency Task 35.  The results documented that adding the SolarWall thermal component to a PV array boosts the total solar efficiency to over 50%, compared with 10 to 15% efficiency for most PV modules alone. The heat from the PV panels, captured by the SolarWall perforated absorber, was documented to be three times more than the electrical energy generated from the PV modules. This means that by being able to uniformly capture and utilize the excess heat, it becomes possible to realize an energy output improvement in the range of 200-300%, depending on air flow and other design considerations.  The test data also showed that the temperature gain from the PV modules is between 6°C to 20°C or well within the typical range for a conventional single-stage SolarWall solar heating system.

More Information on SolarWall PV/T and SolarDuct PV/T

Below are PV/T leaflets that contain additional information on SolarWall and SolartDuct PV/Thermal cogeneration products.  You can download the PDF (requires a PDF reader; such as Adobe Reader).