Siting of panels for solar water heating

In message , SJC writes

You seem to be so sure of yourself, but you are so wrong. Look up fluid source heat pumps with solar...get a clue.

Sorry top posting dork with a clue (so you reckon)
fluid source heat pumps are not part of your average solar heating system here
I presume you're a septic

"raden" wrote in message In message , SJC writes Solar thermal panels for space heating is one of the ways we can save lots of fossil fuels in the future.
Sorry, this is UK.d-i-y, not alt.bad jokes as practical, as they say, as a chocolate teapot where are you going to get meaningful heat from at 7am ? the best source, I would suggest, would be the hot air emanating from the sales rep -- geoff

-- geoff

In message , raden writes

In message , Curious <no-more-spam@e-mail.net writes
"Will" wrote: We moved into our two storey, reconstituted stone-built, pitched-roof house in April.
We decided early on to get as much of our energy as possible from renewables.
A couple of weeks ago we signed up for a solar heating system. I've looked at a few and this seems like a very good system.
Watchdog 'did' the solar energy industry on BBC 1 last Tuesday evening. Their conclusions were that there a lot of rogue companies, the estimates for equipment and installation are very inflated (�12,000 in one case for a non-working system), the claimed energy benefits are often very exaggerated, the salesmen talk a lot of dishonest rubbish, and a lot of properties are not suitable. My understanding is that the panels need to be mounted on a south-facing aspect. Got a long bargepole?
We also had a discussion in here following my father having signed up to such a system
This was �7000
Say a payback period of 10 years being reasonable, it has to save �700 / year to pay itself back. Given that it's only saving (optimistically ) 70% of hot water, not central heating or gas for cooking, it's patently impossible for it to be viable

Yes, though pay back time is not the only reason people invest in things.
What's the pay back time on a new car or a new kitchen ?
A better question is probably 'could he have got a better deal ?'.
It's hard to know that without knowing the details of the site, the size of the system etc, but the very cheapest systems we do are flat plat 2sqm collectors which under a local authority scheme are a bit over �2,000. At the other end of the domestic scale, we did a 7.2sqm evacuated tube system we did last week was �3,700 ex VAT, ex cylinder change. Guess which was better value.
The main overhead is not buying the panels, it's getting people on site, running the pipes and getting access to the roof with reasonable safety.
Cheers, J/. -- John Beardmore

In message , SJC writes

Solar thermal panels for space heating is one of the ways we can save lots of fossil fuels in the future.

I really doubt it !
Cheers, J/. -- John Beardmore

In message , SJC writes

You seem to be so sure of yourself, but you are so wrong. Look up fluid source heat pumps with solar...get a clue.

OK, but solar is just one of the many things that you can plug onto the front of a heat pump and heat store set, and not necessarily the most appropriate in many circumstances.
Presumably if the collector is going to run cold there won't be any advantage to putting it in a glazed insulated box, but if you run it when the sun isn't shining it reduces to an air source heat pump, and these tend to have crap coefficients of performance when its cold outside compared to ground source and water source.
Or did you have some other arrangement in mind ?
Cheers, J/. -- John Beardmore

In message , Ian Stirling writes

In uk.d-i-y raden wrote: In message , Eric Sears phoneme@025379386.for.email.address> writes
I think the usual assumption is that the building will have significant thermal mass internally, in the form of an insulated concrete slab, or something.

:)
That's not a standard feature of the solar water heating systems we install. You are getting into the realm of the Hockerton Housing Project design strategy here, but this has been criticised because of the environmental impact if making the concrete. Ultra low thermal capacity buildings also have something to commend them as long as they can dump heat when required.
Cheers, J/. -- John Beardmore

In message , Joe Fischer writes

On 16 Nov "Will" wrote:
If this is for space heating,

Optimising the orientation is similar for space heating and SDHW presumably ?

then both the east and west facing slopes are no good unless the panels are mounted at a complex angle so that they face south and up at an angle according to latitude (to get more heat in winter than summer, plus 23 degrees, which at north 50 degrees, approaches vertical).

The heat gathered by a panel also depends on the area. In the UK panels are generally mounted flat to roof, partly because of aesthetics, partly because it reduces the chance of the wind ripping a panel off, and partly because adding is more area is cheaper than making a complex mounting.

Am I wrong? The alternative, according to the surveyor, would be double the number of panels with half on the east pitch and the other on the west. Will.
For a millionaire, sure.

As explained elsewhere in this thread it need not make things hugely more expensive.

But the type of panels might make a difference, air panels without storage might heat certain rooms, like the kitchen and bath in the morning, and other rooms later in the day.

Hmmm... Hard to get in the UK.

Drain-down water panels with thermal storage really should be tracking panels to get the most heat, and tracking is not implemented as much as it should be.

See above. Not sure why you restrict this comment to drain-back/down though ?

In general, east and west facing roof slopes are not good for solar water heating unless the pitch is shallow, and the panels are angled to the south

Not sure that they are so bad if you do the sums.

The roof pitch should be ignored, and the panels mounted so they get the most direct sun,

:)
I started out thinking that, but clients and planners have slowly ground me down.
Cheers, J/. -- John Beardmore

In message , Steve Firth writes

On Fri, 17 Nov 2006 12:58:52 -0000, Mary Fisher wrote:
Your observations about the appearance of the panels also refers really to the style of low-efficiency flat panel that you favour.

:)
Ow ! Pass the tin opener and that huge can of worms !!
Cheers, J/. -- John Beardmore

In message , Joe Fischer writes

On the west slope roof there would be zero efficiency until nearly noon, even if the panels have the north edge of each higher than the south edge with the panels spaced wide apart so they don't shade each other.

Due west certainly isn't great, but they'll go on working into the evening longer, and our measurements of panels 45 degrees west of south show useful heat gain from 9 am on sunny summer days.

The big advantage of the south facing wall mount is the near optimum efficiency in winter, with the possibility of extra reflections to exceed 100 percent rating of the panels, and the reduction of thermal energy in summer.

Hmmm... Little snow here, and only a few polished aluminium driveways...
Cheers, J/. -- John Beardmore

In message , Toby Kelsey writes

Joe Fischer wrote:
Is overheating a big issue?

Not in the UK.

Could you automatically cover the panels?

Generally no need, and other ways to deal with overheating.

Or the circulation and heat transfer may be faster in a vertical orientation.

Are you assuming a convection driven primary circuit.

It's better to do a direct comparison in the field if possible.

See the SPF web site.

And the same for the east side after noon, and with the poor angle you would probably get less than 1/4th the normal heating effect.

Depends on the roof pitch.
Cheers, J/. -- John Beardmore

In message , Richard Bates writes

1.Do not do anything until you have looked at Navitron's website.

Agreed, though I don't think their tubes are Clear Skies / LCBP approved.

2. Solar panels do not have to be high up - I know at least one geezer who has them at ground level and another who has one on his garage.

Yes.

3. Do not believe ignoramuses who suggest that you will not get much heat - that did apply to the old flat panel stuff, still being sold by B&Q, but the vacuum tubes now being used on the continent are vastly superior. I recently went to a demo and noted a cylinder water temperature of 48 c being obtained on a relatively cloudy and cool day.

Yes, though I've seen the same with good flat plat collectors, indeed I've seen a Zen 28S collector with snow on the bottom third of it have a temperature at the top of 116 centigrade in 3pm milky spring afternoon sunlight with thin cloud.

I am reliably advised that on a warm summers day, the tube manifold can reach well over 100 c and hence so much heat is being soaked up that one can have 3 to 4 free baths

Yes.

and still have to dump excess heat into a loft radiator - that's how good they are.

Not quite sure that you'd need a rad. Other ways to skin that cat.

4. If you have already signed up and paid a deposit for a flat panel system do your best to get out of it.

Agreed.

5. I will probably be putting in a Navitron system myself soon with help from plumber brother for around �900.

What area ?

The B & Q deal for �1500 is a total rip off and the energy savings will take at least 15 years to recover.

Agreed ! And don't even get me started on their '10 year safe working life' wind turbines. See for example
http://www.scoraigwind.com/citywinds/index.htm
and
http://www.warwickwindtrials.org.uk/
If anybody is curious about this I can also pass on copies of a report from CREST looking at urban wind turbines.
It seems to me that B&Q risk a backlash from their consumers if the kit doesn't recover its costs or make up for the environmental impact of the manufacturing process.
Cheers, J/. -- John Beardmore

In message , meow2222@care2.com writes

Richard Bates wrote:
First, flat panels give much better ROI than vac tubes

Quick nurse - the tin opener !

Second, British winters are mostly overcast, and flat panels work ok on indirect sun, whereas silvered evacuated tubes work a lot less efficiently under these conditions.

What do you mean by "silvered" ?

3rd, it is all more complex than that,

:) Quite so !

but suffice it to say that flat panels are very much a going concern in Britain.

Yes.

An optimally designed system would have a mix of both flat panel and vac tube, with each heating a separate part of the system.

Yes - been there, got the T-shirt.
Really they need to be on separate primary circuits.

Flat panel is best for mid-temp water, as it gives much more output per �/$. Vac tube is best for the final max temp water, as it gives high output temps that flat panels cant consistently deliver. However, the ROI on the flat tubes will be much poorer, so spending some of the money on flat panels will much improve total annual output.

Hmmm... Have you seen the prices of the Chinese import ETs ?
To be honest, while what you say was true 10 years ago, the difference in cost per area is now pretty small, and the prices we quote to end users are much the same per area for FP and ET, because while ET is slightly more expensive, installation is easier and safer in lifting and handling terms, if not actually quicker.
Cheers, J/. -- John Beardmore

In message , John Beardmore writes

) 70% of hot water, not central heating or gas for cooking, it's patently impossible for it to be viable
Yes, though pay back time is not the only reason people invest in things.
What's the pay back time on a new car or a new kitchen ?

No idea in your circumstances, but it is less well defined than solar
Solar panels have a reasonably well spec'd return
I don't see what my folks signed for as being economically viable
-- geoff

In message , Todd writes

Will,
I too have been experimenting and trying to get all my energy from renewables. First was to have a structure that needed a minimum of energy. I have a simple structure with 12" thick walls filled with fiberglass insulation.
I use no power for heating or A/C.As long as there is light outside it is enough to serve my needs inside ... the roof has clear sections insulated with bubble wrap.

Nice ! I know somebody who lived in an 8' by 12' shed with poly urethane wall insulation from an old container truck, and aluminium foil wall paper. Excellent !

But my experience with solar panels show them to be an abject failure.
1. Cost is high. My 165W high voltage panel cost over $700

Think you were robbed !

2. My 165W panel has never delivered more than 90W

Hmmm... We generally get pretty near peak output for a few hours a year even without OPT regulators.

3. The panel can only supply current about 5 hrs per day

About right.

4. The panel only supply useful power on sunny days

:)
Depends how much you need, but yes, what did you expect ?

5. The panel loses lots of efficiency on hot days

Yes - though it doesn't seem to be much of a problem on open frames in the UK.

6. Any shadow on the panel is the same as complete panel in shade

Pretty much.

7. Can lose 30% or more if panel is not perpendicular to sun's rays

Yes. Do the sums.

8. Charge controller must be very efficient or more is lost

Not hard.

9. For anything practical a huge number of panels and batteries is necessary

Or grid connection where appropriate.

The solution I have arrived at is hybrid. I use my one panel to charge batteries when I'm away. When away, my refrigerator is my only load (about 120W with 30% duty cycle). My battery bank is 10 70AH car batteries. All together they cost about as much as my 1 PV panel. I don't use deep discharge because they are much more expensive

Look for 'leisure batteries'.

and I haven't seen an inverter that works below 10V. Most shut down at 11.5V.

Would trash the batteries if they went lower.

My real power source is a 3hp diesel engine driving a car alternator capable of delivering 40A. I run it on waste vegatable oil (WVO) at low RPM (~1,000).

Good one !

I route it through the same high voltage (up to 53VDC) charge controller that I use with the PV panel. It does a splendid job of keeping the batteries charged and only runs 4 to 5 hours per day. It uses hopper cooling so I get my hot water from it as well.

Interesting ! What's hopper cooling ?
Cheers, J/. -- John Beardmore

In message , raden writes

In message , John Beardmore writes ) 70% of hot water, not central heating or gas for cooking, it's patently impossible for it to be viable
Yes, though pay back time is not the only reason people invest in things.
What's the pay back time on a new car or a new kitchen ?
No idea in your circumstances, but it is less well defined than solar

Yes - but my point is that for people to make a purchase, it need not be defined at all !

Solar panels have a reasonably well spec'd return

Agreed, but some people buy them for other reasons.

I don't see what my folks signed for as being economically viable

No, but I think our clients divide into at least four categories.
People that want to save the world.
People that like interesting toys.
People that want to set an educational example.
People that want to save money.
All three seem worthy in one respect or another. Another category may also creep in.
People that follow fashion.
Still - I suppose their CO2 is as bad as anybody elses, and every little helps !
Cheers, J/. -- John Beardmore

In uk.d-i-y John Beardmore wrote:

In message , Ian Stirling writes In uk.d-i-y raden wrote: In message , Eric Sears phoneme@025379386.for.email.address> writes
I think the usual assumption is that the building will have significant thermal mass internally, in the form of an insulated concrete slab, or something.
:)
That's not a standard feature of the solar water heating systems we install. You are getting into the realm of the Hockerton Housing Project design strategy here, but this has been criticised because of the environmental impact if making the concrete. Ultra low thermal capacity buildings also have something to commend them as long as they can dump heat when required.

I'm not convinced it has no place - you would admittedly need a very large additional thermal mass - a ton or two of water probably, to keep the heating on overnight, with a 10-20C drop.
This is not of itself very expensive, though the places it can be easily installed are of course going to be very limited.