Photovoltaic Thermal System Achieves 86% Efficiency

In April of 2013, SunDrum's Photovoltaic/Thermal (PVT) system achieved 86% efficiency on a Massachusetts home during peak hours. This is a record for a PVT system with a fixed (non-tracking) mount. SunDrum also installed a PVT system at the Inn at Schofield Barracks in Hawaii. That system is expected to pay for itself in less than three years and provide a 30% return on investment. In its first six months of operation, it recouped 25% of its installation cost. High efficiency and short payback periods look pretty cool to me, so let's see how PVT works...



In the sustainable energy industry, it’s commonly known that solar water heating offers a quicker payback period and a higher return on investment than photovoltaics. This is because solar radiation already contains a large amount of heat, so using the heat directly is more efficient than converting it to “high-grade” energy like electricity. Your mileage may vary, but on average a solar water heating system will pay for itself in about 4-7 years, where a photovoltaic system could take 10-20 years.

But the reason electricity is considered “high-grade” energy is that it’s more versatile. Heating water is great, but it’s only one job. Converting sunlight to heat and electricity, and doing both efficiently, would be a double-win. Give it a short payback period and you’ve hit the trifecta!

A PVT system includes a solar thermal collector (as shown above) that mounts underneath a photovoltaic panel. A typical PV cell has an efficiency of 15% under ideal conditions. When a PV panel heats up (as dark objects sitting in direct sunlight tend to do) its efficiency and lifespan will both decrease. Remove some of that heat and the panel will achieve closer to its ideal efficiency and be less prone to heat-related failures. And instead of just radiating that heat away, why not use it to heat your water?

The SunDrum collector is designed to work with a variety of popular PV panels, and its plumbing uses standard off-the-shelf parts to keep costs down.

SunDrum thermal testing shows that the hybrid panels are about 40oF (4.4oC) cooler than standard PV panels. As you can see from the chart below, this produces only a modest increase in electrical production but nearly triples the total usable energy that the system produces, bringing the total efficiency of the system to around 70% without increasing its overall footprint.

SunDrum claims that a hybrid PV/solar water heating system pays for itself in 5-10 years, just slightly longer than a solar water heating system without the PV, and quite a bit faster than a PV system by itself. In places like Hawaii, the payback period is even shorter.

If you’re going to go solar, why not go all the way? (Excerpt from ENGINEERING)


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