Flat Plate SHW collectors in Melbourne « Alternative Technology Assn Forums

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Flat Plate SHW collectors in Melbourne

(17 posts) (8 voices)

Started 11 years ago by dlvb19
Latest reply from hamish05

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SHW water melbourne hot flat plate collectors

dlvb19
Member

Hello fellow green geeks,

I am curious as to the effectiveness of Flat Plate Solar Hot Water collectors at lower latitudes such as Melbourne? I am hoping to provide for 100% of my hot water needs, estimated at approximately 100 Liters per day. Could this be achieved in winter with a average minimum of 1.7 'sun hours'?

With the exception of "Run On Sun" it appears that all Evacuated Tube Solar Hot Water systems require circulation pumps which would likely be the first component to fail. As an aside can anyone comment on the reliability of the circulation pumps and/or other components of their ETSHW systems. Please note brand if possible.

Apologies if this post could have been appended to another forum, I did have a look.

Thank you for your useful comments in advance,

Damien

Posted Monday 21 Feb 2011 @ 9:19:48 am from IP #
OptexSolar
EcoOnline

Hi Damien,

Not sure if this will help, but I've got a 315L three flat plate panel system with instantaneous gas boosting for a three bedroom house. I've stayed alone over winter and had the gas booster completely turned off. Only once did I feel lukewarm water while taking a shower after three days of heavy cloud cover from memory. Should give you some idea.

It's an absolute myth that evac tubes collect more than flat plate collectors, the evac guys like to make a big deal about the efficiency of evac tubes, per absorber (the black part) area. It's true, the efficiency per absorber area for an evac tube is really high but only because they don't count the space (or loss) in between the tubes. If you count this the efficiency drops dramatically to around only 60% at best. What matters at the end of the day is total (gross) area - and as a function of gross area evac tubes are less efficient than flat plate collectors overall.

Posted Tuesday 22 Feb 2011 @ 12:35:25 pm from IP #
Russell Moore
Member

I have had a Beasley FP SHW system in Sydney, for 28 years, and it is still going strong. No motors, no pumps, just good old thermosyphoning and gravity.

It is flat to the roof at 16º, and its winter performance is not great, even with silver vertical reflectors fitted to the south of the collector, in hindsight I should have set the panels at around 40º, and gone with 3 not 2 panels. As with all systems it is the winter performance which will let you down, so you have to set up the panels for maximum output then, and that means higher panel angles.

A lot of people install ETs because there is no roof tank, as with most FPs, and they value the look of a flat fixture. In the end both types are OK, and cost and reliability will be the factors that I would consider when installing.

Posted Wednesday 23 Feb 2011 @ 10:33:41 pm from IP #
sun2steam
Member

"It's an absolute myth that evac tubes collect more than flat plate collectors," ...?
It would be good if you could provide some proof instead of just strong words.

Posted Wednesday 23 Feb 2011 @ 11:56:56 pm from IP #
OptexSolar
EcoOnline

Hi Sun2steam,

Yes I suppose I should qualify that, when I said that I meant that evac tubes collect only slightly less overall.. of course I could be wrong... but I should say I don't have an interest in either technology ... Also I should qualify it by saying it depends on the location, so in Mel on winter it's possible that an evac tube system will collect more (per gross area), however

a good site for testing collectors is the Institut für Solartechnik SPF

http://www.solarenergy.ch/Collectors.111.0.html?&L=6

When you look at some of the test results the evac tubes don't do so well as measured pre gross area, but do really well per absorber area.

Also at one stage i downloaded all the RECs, solar savings and system price data for all the systems on the Australian market from http://www.resourcesmart.vic.gov.au. and plotted evac tubes vs flat plates. (To get RECs you have to go through the AS efficiency standards and hence the solar savings specified there are independently certified.)

I plotted Gross Area vs Solar Savings, the results surprised me and indicated that "overall" flat plate collectors collect more but not by much.

I also plotted System Price vs Solar Savings and flat plate collectors came out on top also.

I guess i formed a negative opinion from that ..and especially from the evac guys making a big deal about efficiency per absorber area but not mentioning efficiency per gross area.

But I could be wrong and things might have changed in the past couple of years with new systems coming on the market... I know U-tube evac tubes are much more efficient than the older heat pipe ones.

At the end of the day I think both technologies are great as they off-set greenhouse gas emissions...

Posted Thursday 24 Feb 2011 @ 6:01:29 am from IP #
franks
Member

the ATA published project a few years ago, flat collector conversion to a electric HWS
The Price of flat collectors are much cheaper can pick up working 1x1.8mtr collectors for under $100 each.
the same in evactated tube collectors over $1000 for a 30 tube system cost $2000 for the tube collectors, pump and controller.
Im looking at converting my Gas Rheem 175lt system to Solar preheated water, total cost $300. (2 collectors & pump)
New flat collectors on ebay $300 each.

Posted Thursday 24 Feb 2011 @ 6:50:56 am from IP #
sun2steam
Member

Thanks OptexSolar,

I agree with your points. We had the same discussion in this forum at least twice before. I supplied a few links at that time, but it is a bit too difficult to find for me now. But as far as I recall your point of effective module area is important and the difference in module performance (in kJ/m^2 per day) in warm climates is negligible and sometimes even to the advantage of flat collectors. However at higher temperature differences between air temperature and hot water temperature (= in winter , that's when it counts) the evacuated tubes are clearly better.

But I agree as a customer what counts is how much does my hot water cost for the hot water I need. And here flat panels are clearly winning. One of the reasons for that is our complicated Australian Standard System which created a high import barrier. I cannot understand why an European Certification is not good enough for solar hot water, if it is sufficient for PV panels. The situation could be quite different. Perfectly OK evacuated tubes can be bought in China for less than $3 each. The few importers that spent a lot of money for the Australian certification have now a kind of oligopoly and can ask for 10 times that price.

As for using the REC's as an indication of efficiency; I have my doubts, as I have found strange examples, for instance a heat pump that got more RECs than a similar size solar hot water system.

Posted Thursday 24 Feb 2011 @ 10:48:27 am from IP #
OptexSolar
EcoOnline

Sun2Steam - I wholly agree, don't even get me started on certifications/regulations and RECs for solar hot water systems and the hoops you have to jump through to get your system certified for rebates. Of course there are safety standards regulations that have to be met, granted - but in my opinion it's all these rebates especially that are absolutely killing innovation in the field. If there wasn't such a HUGE barrier to entry that all these rebates set up i think SHW systems would be less than half price now.

Especially in the field of polymer technology for collectors, which is my pet field, there is huge potential for price decreases for SHW with polymer collectors and tanks. Sure the collectors aren't as efficient, but so what! you make it up by having a greater collector area. But because the standards mandate a minimum efficiency the polymer guys can't even get a look in! They're shot down on the ground.

Why the government is trying to pick winners with these grants is beyond me, it's spending so much money at $250/ton off-set? What a waste! Sure it supports the solar PV industry, but most of it is overseas manufacturing. Does that make sense to you? supporting overseas manufacturing with tax payers money!

I'm sure to ruffly a few feathers here, but I say scrap all these rebates, set a high carbon price per ton and let the market innovate, that's what I say... put a price on what you actually want to decrease - carbon emissions and let the market chose the best and cheapest technology whatever it is.

anyway that's my rant for the day I feel better now

Posted Thursday 24 Feb 2011 @ 11:28:04 am from IP #
sun2steam
Member

100% agreement!

Posted Thursday 24 Feb 2011 @ 12:43:10 pm from IP #
Buzzman
Member

I vaguely recollect that in that previous discussion some wise owl pointed towards a link which demonstrated that altitude also favours the ET HWS over flat plate.

The higher you go, the greater the performance difference between the two, in favour of the ET.

Posted Thursday 24 Feb 2011 @ 11:57:06 pm from IP #
dlvb19
Member

Thanks for the comments,

It seems as if flat-plate collector systems will probably do a reasonable job during winter so long as your hot water demands are low.
Thankyou OptexSolar for your helpful example. Could you tell me what system you have and what part of Victoria your in?

Would anyone care to comment on the reliability of the pumping systems in ET or FP systems?

Posted Friday 25 Feb 2011 @ 11:11:25 pm from IP #
OptexSolar
EcoOnline

Hey Damien,

I'm in the eastern suburbs and I've got an old Solitaire system, can't get them anymore through I think they got bought out by Conergy.

Posted Friday 25 Feb 2011 @ 11:54:27 pm from IP #
sun2steam
Member

The pump is not a big deal. It just consumes 40W in the lowest setting which is sufficient for 'normal' applications. And the pump is only switched on for a part of the time.
In regard of reliability I can look back onto my experience in selling these pumps. I have been selling a couple of hundred pumps and we have a warranty return of about 3 to 4% within the first year. About half of these are caused by application issues like jamming of the rotor by solids or especially water (rain) damage of the pump.

Posted Saturday 26 Feb 2011 @ 3:42:44 am from IP #
hamish05
Member

Yesterday, I asked the Plumber who installed my SHW system about pump performance and reliability. My major reason was that when I measured its energy consumption I was somewhat surprised that it was 90 Watts when running. (Double story house).

He claimed that there were no reliability problems that he was aware of with the "Bianco" pump fitted to my Apricus SHW system.

However, I understand that Apricus are now using a more energy efficient pump with current installs. My Plumber had no knowlege about that.

For the record I measured the total energy consumption of my SHW system (over 48 hrs) at 75kWh/year

Posted Saturday 26 Feb 2011 @ 9:57:33 am from IP #
sun2steam
Member

According to your data your pump consumes 75kWh/365days = 0.2kWh per day. Is that a problem?

If your pump is consuming 90 Watts when running this means that it is just working for a bit more than 2 hours per day.

Posted Saturday 26 Feb 2011 @ 12:00:40 pm from IP #
amun-ra
Member

sun2steam interested in poly I still have a genius shw system out in the backyard they no longer make them to many problems with the poly and heat

Posted Saturday 26 Feb 2011 @ 9:03:16 pm from IP #
hamish05
Member

The 90Watts was considerably more than I had antisipated. Given the sceptism here at times about SHW pumps and that Apricus are now using a more energy efficient pump, I thought the questions were warented.

Yes .2kWh per day is nothing, I agree totally. Given the overall savings in my Hot Water, the change to Solar is a "no brainer" for me.

See my prev post http://www.ata.org.au/forums/topic/shw-savings-measured-1-year-after-instillation

Posted Sunday 27 Feb 2011 @ 12:18:54 am from IP #

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