Want to produce both hot water and electricity from the sun?
You might want to consider installing Solar Photovoltaic-Thermal, or PV-T for short.
PV-T is a hybrid solar panel combining the functionality of solar thermal collectors and solar PV in one panel. The panels create not only electricity but also produce hot water for use in the home. Two functions from one investment!
Hot solar PV panels produce less electricity
Contrary to popular belief, solar PV panels actually work more efficiently in cold sunny weather. People often assume that hot sunny conditions are the best, but actually as solar PV panels get warmer, they become less efficient. In fact, for an average PV panel, each degree warmer the panel becomes, it will become around 0.5% less efficient. So in the UK, where the dark solar panels regularly hit 70-800c, this could mean a 25% decrease in efficiency at peak time.
This is the reason why many solar installers will try to mount the solar panels on a frame which is slightly raised from the roof to ensure air can circulate around the unit to help keep it cool.
Bearing this in mind, the theory behind running both solar PV and solar thermal through the same panel is sound. The excess heat can be transferred from the solar PV-T panel via a heat exchanger located on the back of the panel and into heat transfer fluid that can used to heat the home.
So not only are you running the photovoltaic cells more efficiently since they are cooler, you are also contributing to your home’s hot water requirements.
Another key advantage of these Solar PV-T hybrid panels they take up less space on your roof. There is no longer the requirement to invest in separate panels to carry out the different functions which can look unsightly. One type of panel will produce both your hot water and electricity.
So what are the issues with solar PVT / Solar Hybrid Panels?
While solar PVT hybrid panels in principal are a fantastic idea, there are 3 major issues with them.
- Solar PVT panels should in theory allow you to benefit from both the feed-in tariff and the renewable heat incentive, since you are producing electricity and renewable heat. Having spoken to the Government teams responsible for these schemes (Aug 2014), in domestic situations they have confirmed that the PV-T hybrid solar panels in domestic installations will only benefit from the Feed-in tariff – not the RHI. However for Non-domestic Solar PV-T installations, one would be able to claim for both the FiT and the RHI. This does mean the payback period for domestic PV-T installations is longer although for commercial applications it still makes great financial sense. The fact that the Government has approved the double income for commercial suggests that it won’t be too long before this is extended to domestic installs too!
- Solar PVT panels are more expensive than the price of traditional solar PV panels. Having said that, Solar PV-T systems can be installed at almost the same cost as the equivalent capacity of separate PV and Solar thermal and so can be a sensible investment where roof space is tight. The PV-T panel is roughly 10% more expensive than the cost of an individual PV panel and solar thermal panel installation but 25% more efficient than the individual technologies. Manufacturers also hope as volume builds the panel costs will come down making them a cheaper option as opposed to the traditional alternative.
- The last issue with PV-T panels is that they produce the majority of the hot water and electricity in the summer months. In the winter months when you need a lot of hot water for space heating, the PV-T panels won’t produce enough hot water so you will need to supplement the heating with a boiler – this however is the same problem with solar thermal too! There are companies with a neat solution to this however, they use the summer heat to charge the ground and then use heat pumps to pull out and upgrade this heat in the winter. This keeps the panels cool in the summer, which maximises their output at the same time as increasing the source temperature for the heat pump in the winter making it run more efficiently.
Do Solar PVT Hybrid Panels have a future?
Yes of course! PV-T can add value even without the domestic RHI. There are a few companies now that offer PV-T hybrid solar panels therefore proofing the commercialisation of this technology is the future.
In time, PV-T panels will surely get the necessary paperwork to profit from the financial incentives like their commercial counterparts in turn boosting their popularity. And with this will come economies of scale which will see a drop in the price of installation. But don’t forgot even now PV-T panels are on a par with the equivalent separate PV and solar thermal system.