Browse Forums Eco Living 1 Nov 20, 2008 10:00 pm Evacuated tube collectors are cited as more efficient than flat plate collectors. What is not often mentioned is how much more so?
ASSUMPTIONS * 300 L tank * Insolation (Adelaide - June): 2.23 kWh * Ground water temperature: 13 C * Off-peak electricity cost: $0.131238 Solahart 302 J Flatplate * Aperture area (2 collectors): 3.72 m2 * Collector efficiency (winter): 45% Hills 30 tube Evacuated tube * Aperture area: 2.844 m2 * Collector efficiency (winter): 80% RESULTS No solar heater * Energy consumed: 16.4 kWh/day * Electricity consumption: $1.18/day Solahart 302 J Flatplate * Hot water potentially heated: 68L/day * Energy offset: 3.7 kWh/day * Electricity consumption: $0.91/day Hills 30 tube Evacuated tube * Hot water potentially heated: 99L/day * Energy offset: 5.1 kWh/day * Electricity consumption: $0.81/day CONCLUSION In an Adelaide winter even a 30 tube ET collector can only heat 1/3 of the tank (FP heats about 1/5). Daily savings of 30 tube ET over Double collector FP (middle of winter in Adelaide) is about 1.4kWh or 10 cents per day. Note that by summer, the insolation is sufficient for either unit to provide 100% hot water needs. Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 2Dec 06, 2008 7:54 am We looked at evacuated tubes for Adelaide (Hills) and found it very hard to get good and accurate advice as no one seems to know much about them.
Solar installers that don't sell them will tell you that they do not give much benefit in Adelaide. They also tell you that they are new and untested etc. In the end out builder would not install it so we had to decide between getting our own plumber to supply and install or go with the builders solar option. We went with the builders option to stop the finger pointing game if anything goes wrong. Given a choice I would still have gone with evacuated tubes. They are now over 40 years old and a well understood technology (except in Australia) and are huge in China. So the argument that they are new and untested is bogus. However they are are new to Australian builders In summer in Adelaide a standard solar panel is more than adequate however it is in the cooler months that evacuated tubes perform well. They can work on days with less sun and because they are round they can absorb radiation efficiently from much greater range of angles, this means that they can work early in the morning and late afternoon. They even absorb heat from behind taking advantage of heat in the roof under them. The result is that they work for more of the year. The greater range of angle also means that they can be mounted on a west or east facing roof without the huge decrease in efficiency that flat plate tubes suffer. This was a driver for us as we planned to put PVs on our small north facing roof area and the evacuated tubes on the west roof. Installation is easier (cheaper) as they can be installed in parts only requiring a single person to do. If any of the tubes fail the remainder of the tubes continue to work and tubes can be replaced individually. Nice if you are worried about hail. The biggest inhibitor to evacuated tubes was finding someone who actually wanted to sell them to us! regards sean Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 3Dec 06, 2008 8:41 am Apparently the selective surface flat panels are just as efficient as evacuated tubes. And cost about the same.
I'm going for flat solar water panels. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 4Dec 06, 2008 9:18 am sdabel We looked at evacuated tubes for Adelaide (Hills) and found it very hard to get good and accurate advice as no one seems to know much about them. The biggest inhibitor to evacuated tubes was finding someone who actually wanted to sell them to us! regards sean There is an Adelaide distributor for Apricus systems at: http://www.comsolar.com.au/ Follow a discussion on: http://forums.envirotalk.com.au/Solar-H ... t8367.html http://forums.envirotalk.com.au/Evacuat ... t7705.html There is no question they are more effective. The question you should ask is byh ow much? In regards to the issues you raised: - ETs are proven technology but I wouldn't go with a cheap brand (leakage at the ends of the tube, loss of vacuum and decrease efficiency) - ETs work better in cold environments but you still need the sun to come out! (no free lunches) - ETs will work better in non-ideal orientations (but see point above) - The tubes can be replaced at about $80 per tube - You need to factor in the complexity of a split system which needs additional plumbing and pumps (maintenance issues) Another consideration is a heat pump if you don't have a ideal facing. It doesn't rely on solar but works like an air-con/heat pump. The figures I gave above were for ideal orientation but I think give a reasonable idea about the actual cost savings gained with the unit. Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 5Dec 06, 2008 9:23 am Casa2 Apparently the selective surface flat panels are just as efficient as evacuated tubes. And cost about the same. I'm going for flat solar water panels. The new selective surfaces are very effective and will narrow the gap between ET and FP. This decreases the incremental benefit of ET. However ET still remains ahead based on collector area. However, the problem is with these super-efficient systems is overheating and boil over in summer. They normally come in standard sizes so you always find there is built in redudancy during the hottest month. Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 6Apr 04, 2009 11:03 am so its definative the tubes are better than panels in adelaide? whats the initial price difference though? are there any aussie made solar gas tube kits? -Nathan 2nd-Fix | Blog Building with Desyn Homes previously with the insolvent [url=https://www.facebook.com/7NewsAdelaide/videos/1162546323776021/]Endeavour Homes[/url] Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 7Apr 04, 2009 1:17 pm FireFox so its definative the tubes are better than panels in adelaide? whats the initial price difference though? are there any aussie made solar gas tube kits? -Nathan It is definitive that tubes are more efficient. They provide about 7 % more heating energy over the course of a year. If you look at this example modelled for Mt. Isa http://forums.envirotalk.com.au/uploads ... 2_9121.jpg 3808 kWh/yr (generated by 30 tube ETT) versus 3555 kwh/yr (for a 2 panel flat plate) This offsets the 6000 kWhr that is needed to heat 300L of water per day. The difference is 253 kWhr/year (or about $32 extra saving per year in energy bills at today's prices) The cost of ET and FP is probably not as quoted on that table. Generally for equivalent size collectors you are look at paying $300-500 more for ET. There are no local manufacturers of ET. They mainly come from China or Europe. Solahart experimented with the idea but abandoned it a few years ago. The important element is the integrity of the insulating glass tube (which is really a sleeve) that sits over the copper heat fin that absorbs the solar energy. If the tube loses its vacuum that most of the efficiency is lost. Good quality tubes have been tested for its durability. Re: Solar HWS Efficiency - Evacuated tube vs Flat plate 8Apr 04, 2009 7:41 pm thanks d69 will prolly go FP then, as looking to build with as much aussie gear as i can. -Nathan 2nd-Fix | Blog Building with Desyn Homes previously with the insolvent [url=https://www.facebook.com/7NewsAdelaide/videos/1162546323776021/]Endeavour Homes[/url] go upvc window frames ensure insulation under colorbond. not just sarking, lighter color roof also not sure if you have seen this viewtopic.php?t=5823 last couple of pages… 4 110592 I would suggest you simply go and talk to council about your proposal, most councils are getting onboard with ancillary dwellings. There is no benefit in keeping it… 1 4124 I think I know the answer but just checking to see if anyone has had experience with it. I want to build a small 20 square metre retreat in my backyard, it will have a… 0 13907 |