PV/T Solar from pvtwins.nl

[DamonHD]

Plotting ahead for next year's renewable project and I'm happy to devote my remaining ~6m^2 of west-spacing roof space to solar thermal with the aim of more or less killing our natural gas usage (other than cooking) outside of winter.

But I could always use more electricity, eg to boost my off-grid system (and/or convert it to 24V), and so I continue to look for PV/T combined solutions.

My PV installer thinks it's a recipe to get two jobs done badly, and at the current state of technology he may well be right, but I live in hope of technical improvements that suck more usable Watts from my remaining roof space.

Does anyone in the UK or elsewhere in the EU have any experience with pvtwins.nl or any other combined EU retail PV/T product for domestic hot water (ie up to 90C) and PV?

Rgds

Damon

[DamonHD]

I've found the UK distributor http://www.eagarenewables.com/ and spoken to a helpful chap there (Steve).

Interestingly the PV efficiency is ~12% (compared to the 18% of my Sanyo HIT panels for example, so still decent) and the thermal efficiency seems to be ~40% compared to ~50% of a normal pure-thermal panel.

So overall, especially given the higher value of the electrical energy over the thermal energy, it does seem like a gain when constrained by space as we are.

I think we'd be the first UK domestic/residential install though!

Rgds

Damon

[Ungrounded Lightning Rod]

Those numbers sound reasonable.

Running at the higher temperature of the thermal panel reduces the efficiency of the solar cells.  Current should be the same but voltage drops.  We should be able to look at the voltage vs. temperature curves for other panels to see what a reasonable drop would be for running at hot-water (plus thermal resistance of the mounting material) temperature vs. air-cooled.  Dropping from 18% to 12% seems reasonable.  (I presume the panel has more extra cells than an air-cooled panel to keep the voltage up when the coolant is hot.)

Meanwhile, the power pulled out by the solar cells as electricity reduces the thermal heating of the output fluid.  With 12% going out as electricity you'd see a 12% drop in thermal efficiency.  So the 40% number says the panel's design as a heat collector is good.

I'll be interested to see how long these panels last, given that they combine water with solar cells and have a greater daily cycle of thermal stress than an air-cooled panel, which could lead to moisture leaks.

[DamonHD]

Hi,

The panels designed to run at a maximum 50C water ("PV-panels" rather than "PV-collectors" in PVTwins terminology), eg for underfloor heating, do claim a higher PV efficiency though not 18% which is the highest in the market and thus atypical and too high to expect.

However, much of the time when I especially care about PV performance, eg in the winter, I don't expect the water to get to anything like the specified 90C and the solar heated water will be the pre-heated feed to my tankless natural-gas combi at that point and maybe closer to 30C or less.  Thus, I'd expect the PV efficiency to often potentially be several points above the 11--12% figure quoted outside of the summer months when I have far more energy than I need!

Rgds

Damon

[Ungrounded Lightning Rod]

Remember that, though the efficiency of the cells will be up, the extra cells that are installed to keep the voltage up so you can charge batteries will have their output wasted.  So the panel's overall efficiency won't go up.  The efficiency will be limited by the cells-in-series count.

Unless you have a voltage-converting max-power-point controller, of course.  That can turn the extra voltage into more amps at the desired output voltage, salvaging far more of the extra power than it consumes for itself.

[DamonHD]

Whatever I do to use the PV it's likely to involve MPPT, either as grid-tie or to batteries!

At the sort of premium I'd be paying I think I have to strain every sinew to use it effectively.

Rgds

Damon

[DamonHD]

Looks like the PVTwins stuff is now supported or sold or taken over by Zen, which has a reasonable reputation AFAIK:

http://www.zen-international.com/technology/solar-thermal-energy/products/pvtwin/

Rgds

Damon

PS.  I did get sent a quote, but it was a little bizarre on the arithmetic front, so I'm not taking much notice of it for now...  B^>