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Solar PVT: can solar PV and solar thermal panels be successfully combined?

Posted by Paul Hutchens on 17 February 2011 at 10:01 am

Most of us are now aware of solar panels that heat water and those that produce electricity. But could we install a panel to do both?

Solar PVT (PV and thermal) is a concept designed to create electricity and use the waste heat (solar PV panels are only about 15% efficient and the rest of the energy has to go somewhere) for heating.

Sound perfect? Well there are some conflicting reports on this subject. Some say PV cells are more efficient at lower temperatures and thermal panels take the heat away from the panel to use elsewhere. So a combined panel should produce more electricity and about the same amount of heated water for the same area of panel.

Others say that solar PV should be operated at less than 30C, solar water heaters at around 50 to 60C and therefore the 2 are simply not compatible.

There is also the "ouch" factor of putting water and electricity quite close together.

There do appear to be products available in the market although they may be expensive and difficult to be sure of their efficiency. It does appear to be the case that the heat produced is "low grade" heat and better suited to underfloor heating (maybe in conjunction with a heat pump) or for heating swimming pools where lower temperatures are required. 

There is also a system becominng available in the USA which uses the heat to heat the air which is drawn under the panels and directed through intake vents to be used for heating or hot water generation through heat exchangers.

It is early days for this technology and probably safer to install the technology that we know works. However we will be keeping an eye on this technology as a company! 

More information about solar thermal and solar PV from YouGen

Solar PV information page

Solar thermal information page

Gas or electric heaters with solar panels?

Solar PV plus air source heat pumps: a case study

Photo by Nasa Godard Photo and Video

About the author: Paul Hutchens is founder and director of Eco2Solar, which installs solar systems around the UK.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

3 comments - read them below or add one

nakedplumber

nakedplumberComment left on: 18 December 2017 at 1:12 pm

I can see the above comments are well out of date as a pioneer and developer of Therma;  stores for domestic use in 1991 and in 2014 my commercial flat pack thermal stores now being assembled in South Africa.

The update to both solar thermal and PVT is that both applications should always begin with the size of the Thermal Store VENTED.

Those who have been in the solar water heating industry since 1990, and know me from my days as the founder of Powertech Solar Ltd until 2009, will know I established a business servicing all the UK, into Ireland, the EU and from China to the USA and Sth Africa with my Apricus heat pipe range.

Its with all this expertise including installations and 5 yrs spent in Cyprus, where I developed my own systems, that I learned all about the failures of mains pressure closed loop systems.

In 2018 I will share with those interested the data from my first PVT system being established in Australia through a British investor business partner.

For to long we have been sold this idea that solar collectors must use glycol to protect the solar collector from Freezing, which resulted in a solar coil being added to a cylinder along with a boiler coil.

If just ONE manufacture had focused on producing ONLY vented thermal store with no solar coil as I have in my loft since 2004, all the solar heated stored water could be used in the day time to keep the house warm as mine is today at 37c (solar input from evacuated tube heat pipes.

PVT is completly different, but still uses a thermal store and no glycol as not needed in my NEW low cost retrofit thermal panel, which has no copper pipe to worry about.

The heated water from over heating PV panels is just a by product in the process of increasing electricity output at its maximum as long as the PV panels remain around 26c

This warm water at 30C max, is used as a pre heat to your existing hot water tank, which is connected to the mains water if unvented

I dont see PVT being idea for a typical house in the UK, as I dont see the point of PV on any roof in the UK, but solar central heating with my latest heat pipe collector, I do see, as supporting the heating of the house in the day time

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Paul Hutchens

Paul Hutchens from Eco2SolarComment left on: 26 February 2011 at 10:36 am

Hi Ian

I think that the heat generated from these systems is unlikely to cause an issue - in fact, if you read my article above, it may be only low grade heat generated i.e. providing a pre-heat only.

 I am not sure I understand your concern about wasting water. This is likely to be a sealed system with antifreeze or a drain back system where the water is stored in a header tank when the pump is off. The only possible waste as I see if is heat that cannot be used - in the unlikely event that there is more than can be stored!

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Ian Smith

Ian SmithComment left on: 25 February 2011 at 7:10 pm

Another issue for me is the incentive to waste water.  As with almost all small CHP generators, one cannot change the ratio between power and heat generation.  If one cannot use the heat, and its operation is electricity led, as PVT will be, one has to dump the heat.  A dump radiator can be used, but if this is in the loft, in summer the sink temperature can be very high - well above 30C.  If outside, the air could still be above 25C but the incoming mains water may only be 12C.  The cost of the increased output available by running the water to waste will be more than offset by the increased FiT income.  How does one stop water being wasted with these systems where there is such an incentive to do so (and one does not have to pay for a closed cycle heat dump either)?

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