Green Building Forum - Thermodynamic solar panels

Thermodynamic solar panels

DamonHD — Tue, 27 Mar 2012 13:48:37 +0100

I intend to use PVT to pre-heat water for a DHW heater, so it can be quite cool and still useful.

Rgds

Damon

Thermodynamic solar panels

SilverSpray — Tue, 27 Mar 2012 15:01:23 +0100

Nice plan DamonHD:

"I intend to use PVT to pre-heat water for a DHW heater, so it can be quite cool and still useful."

I assume you are going to set the panels to be optomised for electricity production and then grab this "free" pre heating.

Thermodynamic solar panels

JSHarris — Tue, 27 Mar 2012 15:21:48 +0100

The snag is that the panels may well get pretty hot, even when you're heating a big DHW tank. I seem to remember working this out somewhere earlier in this thread.

If you had a typical PVT array sized to give around 4 kWp of PV, then it would deliver around 12 to 15 kWp of heat. It wouldn't take long for a DHW system to get up to temperature with this sort of power input, meaning from then on the panels just get hotter and hotter unless you find a way to dissipate the heat somewhere else.

What would be needed would be a big heat dump somewhere to take all the excess heat from the panels on hot days.

Thermodynamic solar panels

DamonHD — Tue, 27 Mar 2012 17:20:30 +0100

SilverSpray: dunno yet. Poss optimised for heat and then may use energy off-grid and not bother with FiTs (already have 5.2kWp on roof grid-tied).

Rgds

Damon

Thermodynamic solar panels

SilverSpray — Thu, 29 Mar 2012 11:47:33 +0100

I've had an email through from "registering my interest" in the "Thermodynamic Atmospheric Energy Panels"

The email has links to 3 PDFs

http://www.thermogroupuk.com/thermogroup_pdfs/Thermodynamic%20Technical%20Information.pdf
http://www.thermogroupuk.com/thermogroup_pdfs/Thermodynamic%20Case%20Studies.pdf
http://www.thermogroupuk.com/thermogroup_pdfs/Thermodynamic%20Kit%20Retail%20Prices.pdf

I've stripped out, what I see as, the key points and put them at the end of my blog post about these:
http://www.silverspray.co.uk/2012/03/27/ecobuild-thermodynamic-panels-heat-exchanger/

I've emailed them for a rough quote given my outline build plans.

Thermodynamic solar panels

DamonHD — Thu, 29 Mar 2012 12:07:02 +0100

My concern with these panels as a primary source of heating, when mounted on the roof, is how to [cope] with a heavy snowfall.

Rgds

Damon

[Typo edited]

Thermodynamic solar panels

SilverSpray — Fri, 30 Mar 2012 08:39:45 +0100

DamonHD,

Assuming that was a typo, and you mean how to "cope" with heavy snowfall ......
..... as I understand it, the panels can be vertically mounted (and toast rack mounted if there are several). So the snow would only have the potential to build up on the top edge of the panel.

Solar panels must have the same issue, and we know it can be sunny after the initial snow fall, so popping out to scrape the panels clear of any snow would be a sensible plan :-)

Thermodynamic solar panels

DamonHD — Fri, 30 Mar 2012 09:29:32 +0100

Yes, typo, well spotted.

Vertically mounted would need PP, and unlike PV which I can accept simply not generating when it's snowy, I can't do without heating/DHW then. For a supplementary pre-warming app like mine that's OK, and no heat dumping needed in summer if I'm careful, but as a main heating/DHW system?

And attempting to scrape snow off panels on my roof is likely to be lethal, so not a runner.

Some of these systems allow you to recirculate warm fluid through the panels to help clear them, but I'm not sure how effective that would be, never mind the energy cost.

Rgds

Damon

Thermodynamic solar panels

JSHarris — Fri, 30 Mar 2012 10:57:05 +0100

A Canadian friend of mine had a fault in his gutter heaters last year, which cost him a small fortune in repairs from ice load damage. Apparently it's normal practice there to run electric heater cables along the gutters to stop the snow melt that runs off from the underside of the snow on the roof, from freezing solid in the gutters and then creating large ice "waterfalls" that can end up tearing the gutters and associated roof timbers off.

The idea that tens, or even hundreds, of thousands of homes in Canada chuck all that power into their gutters all winter doesn't seem very eco-friendly to me.

Thermodynamic solar panels

tony — Fri, 30 Mar 2012 12:25:19 +0100

It is not so bad when it is hydro power that they use -- death could result from ice falling too.

Thermodynamic solar panels

Ed Davies — Fri, 30 Mar 2012 13:17:57 +0100

Posted By: tonyIt is not so bad when it is hydro power that they use...

Except that that reduces the amount of hydro available to displace coal burning, etc, by their neighbours to the south. It's all one grid (per continent, typically).

More interestingly, there's the question of why the roof in melting the snow in the first place. Is it a lack of sufficient insulation or is it just that even with lots of insulation the amount of snow is such that the melting point is far enough outboard for this to happen.

I've wondered before whether this ice-damming effect is why traditional Scottish houses don't have eves.

Thermodynamic solar panels

DamonHD — Fri, 30 Mar 2012 13:55:55 +0100

The US is itself 3 not-very-well-interconnected grids, and transmission capacity is likely to be a limiting factor even between the Canadian grid and whichever bit of the US grid is is wired into.

So, I agree with you entirely in sentiment (electricity shouldn't be wasted on resistive heating if there are more productive uses or negawatt non-uses such as avoiding burning coal), but I'm in favour of avoiding the wasted energy of injured people and avertible property repairs.

Rgds

Damon

Thermodynamic solar panels

WillInAberdeen — Fri, 30 Mar 2012 14:05:34 +0100

Posted By: Ed DaviesI've wondered before whether this ice-damming effect is why traditional Scottish houses don't have eves.

Like this? (Hope the picture works, not tried posting one before)

This wall is where my ASHP is now mounted, I built a little porch to keep icicles off it.

Cast iron guttering is good - dont know if PVC could hold this much ice!

Think it is just snow melting due to sunshine, despite air <0degC, resulting water runs down roof under snow layer until it hits cold gutter. Have seen same effect on unheated barns.

Thermodynamic solar panels

JSHarris — Fri, 30 Mar 2012 14:17:48 +0100

That photo looks just like one my friend in Montreal sent me last year! In his case it was a two storey house with the ice reaching pretty much down to ground level.

I think that the Canadian problem is that the snow thickness can be massive and provide a fair bit of insulation, so pretty much any small heat leakage to the roof causes the underside of the snow to melt.

Thermodynamic solar panels

Ed Davies — Fri, 30 Mar 2012 15:00:15 +0100

At least in that case the freezing is happening off the actual roof. The big problem is if you get a dam of ice on top of the roof, above eves which are not heated from below, with a pool of water above it which then flows under the slates and into the house. Much worse than just tearing off the guttering.