Given the same sized tank capacity, collector size and climate zone, the RECS figure should be proportionate to relative efficiency. RECS is based on the predicted kWh offset produced by the system.
Tips on Comparing Solar HWS Appreciated
(60 posts) (24 voices)-
fifonik
Member> Need to convince Choice to do a round-up of all the solar hot water systems on
> identical houses... might be hard to do!Not, it's not needed. Even the exact systems under exact hot water consumption will show different results if their electronic is programmed slightly different.
The only panels should be compared, so it could be done by installing the panels with some measuring devices only. Of course, they should be compared in different weather conditions and seasons.
Posted Wednesday 12 May 2010 @ 2:47:29 am from IP # -
Australian Sun Energy
MemberHi
The best SHW system on the Australian market is avaiable from "Australian Sun Energy" they sell and install the only single walled evacuated solar tube on the market.
This tube is 100mm in diametre and a full vaccume and used with a Everlast solar stainless tank.
They only require 16 tubes to heat 320 litres of water were as all other systems need 22-30 tubes.
All REC'S and rebates are available for their systems.Posted Monday 17 May 2010 @ 7:08:23 am from IP # -
"The best SHW system on the Australian market is avaiable from ..." (as in post from 'Australian Sun Energy')
Such a nonsense! Where are independent reports? This is just plain advertising with hollow unqualified claims.
Could the forum moderator please delete the posts of 'Australian Sun Energy' that contain this kind of blunt advertising.
Posted Tuesday 18 May 2010 @ 8:44:34 am from IP # -
Gandini
MemberDon't be hasty deleting posts.
I agree that independently verified facts are important but few if any company websites provide such info, and it's good to hear of new companies and products so let readers assess unsupported claims for themselves.
The Australian Sun Energy website refers to the GreenLand system as using single walled tubes. Is this correct? Aren't all evacuated tubes double walled?
Btw, if the quality of the service from Australian Sun Energy is as good as the quality of the spelling and proof reading of the post from Australian Sun Energy, then look elsewhere. One mistake is unfortunate, two is careless, but three is ...
Posted Tuesday 18 May 2010 @ 11:33:22 am from IP # -
fifonik
Memberthe bigger tube's diameter and vacuum into tubes make them potentially weaker to physical damage (nail).
another important thing -- absorber. it's flat so it doesn't work well during morning/evening. this system is something like flat panels system where the panel is sliced and all these slices are inserted into thermoses. 'old' evacuated tube systems have 'black' _tubes_ which work well under any angle.
also, the web site doesn't contain the comparison with 'old' evacuated tubes' systems. I think, the effectiveness of these tubes may be just slightly higher but complicacy is much higher (every tube is a big thermos). I bet that the price of this 'new' system with 16 tubes only is higher than the price of Hills/Apricus system with 30 tubes
P.S. I also don't like this post. it's simple advert. why author thinks that his system is 'the best'? any proves? if you would like to inform people about new technology/product, it shouldn't be done in such way. imho.
Posted Wednesday 19 May 2010 @ 5:11:26 am from IP # -
dymonite69
MemberFifonik said "old' evacuated tube systems have 'black' _tubes_ which work well under any angle."
This is a fallacy trotted out by the evacuated tube retailers. The arc of the tube that is normal to the radiant path constitutes only a small portion of the collecting area. For any section of the collector that faces the sun, there is a part that gets no sun. The collecting surface receives no more radiation than a flat plate. The irradiance is based on the area of the collecting plane (regardless of the 3-D geometry of the surface) and the angle of the sun. Energy can't be created.
Posted Wednesday 19 May 2010 @ 10:14:13 am from IP # -
But isn't the point that for cylindrical tubes that the collecting area doesn't change (ie, the amount of tube that is normal to the incoming light is constant) so the amount of light hitting the 'black' collectors is steady across a wide range of angles? As long as the angle isn't so fine that the tubes start to shade one another, the tubes should deliver a more constant output across a range of angles?
Posted Wednesday 19 May 2010 @ 11:48:41 am from IP # -
dymonite69
MemberConstant power is not a requirement for an energy storage system. What is important is the total energy captured per day. Hot water use does not have to match instantaneous insolation nor would it be possible with such a small collecting area.
Averaged over a year an evacuated tube produces at the most 10% more energy than a flat plate of similar collector area even in the most challenging climates of Australia. The difference diminishes the sunnier the location.
Posted Wednesday 19 May 2010 @ 12:14:50 pm from IP # -
fifonik
Member2 dymonite69: under 'work well under any angle' I meant 'work similar...'.
as I know (I could be wrong), the angle by itself mean nothing. the key word is 'projected surface area' (I'm not sure if it's correct term in English. sorry, English is my 2nd language). flat panel has smaller projected surface area during morning/evening, tubes have the same projected surface area.
also, if we remember about reflections we'll see that some radiation, reflected from one tube will be collected by its neighbour. with flat collector all reflections will go back to the sky.
as I understand, the main advantage of systems with thermoses is: they don't lose energy by convection so they work much much better in cold climate.
Posted Wednesday 19 May 2010 @ 12:41:21 pm from IP # -
dymonite69
MemberYour last statement is the most correct. Evacuated tubes are more efficient because it is essentially a collector covered by a piece of double glazing. There is less heat loss particularly in cold ambient temperatures
All the other stuff about angles and reflections has little to do with its efficiency.
But for all the sophistication of the design, it gets you 3-10% more heating energy or between 100-300 kWhr per year (a saving of $20-60 per year on your bill compared to a flat plate).
Posted Wednesday 19 May 2010 @ 12:51:27 pm from IP # -
Hy Dymo - I didn't refer to constant power generation as a requirement, merely a result of the physical configuration.
My point is that if an evacuated tube collector has equal collection ability to a flat plate when the the sun is normal to the panel then I would expect it to stay operating at this maximum at angles away from the normal whereas a flat plate won't. This gives the tube collector an advantage in this particular instance. I don't believe this to be a fallacy (though I agree that the market for solar how water is full of other fallacies!)Posted Friday 21 May 2010 @ 3:27:44 am from IP # -
Anonymous
UnregisteredBy installing an electric boosted solar hot water system, the average Australian household would cut greenhouse gas emissions by approximately 34 tons over a 20-year period. This jumps to a saving of over 100 tons over a 20 year period for a gas boosted system. It is a great way to reduce the threat of global warming.
In addition, by using the sun's energy to heat water you will reduce your household hot-water bills by more than 60 per cent each year, a saving of around $200-$300 each year for the average family (so thousands of dollars over the life of the system).
If you also get renewable electricity then all your hot water can be generated from nature, with no impact on our (or our kids') climate.Posted Wednesday 26 May 2010 @ 5:48:13 am from IP # -
swanning_it
MemberOur off peak electric HWS costs us $70/quarter......$280/year, so for us to save $200-$300/year, we'd have to be able to run effectively without any boost. I know Sunshine has stated that is his experience (managing without boost), but has anyone else got any accurate figures (not a guess or assumption) as to how often they have to boost? (locations and system type, too please)!
Posted Wednesday 26 May 2010 @ 8:51:50 pm from IP # -
Russell Moore
MemberLocation, Western Sydney, 28 year old flat plate SHWS.
We have to use electric boost after a day of having full cloudy weather around this time of the year, usually 30 mins of boost is OK on the first day, but after that if the cloudy weather goes on it will be 45 mins of boost per day. Our boost is just a simple on/off switch, so we pay at the standard rate for the electricity.
We don't have connection to 'town' gas, but I would like to know if there is an inline electric boost system that would just heat the water we use on such days?
Posted Wednesday 26 May 2010 @ 11:12:34 pm from IP # -
Solgen
MemberWe (2 people) live in Sydney and have a 30 tube Hills system. It has now been in service for about 18 months and in that time we have only to turn on the OffPeak 1 boost 12 times. The total amount of boost energy used by the HWS in that 18 months is 130kWh.
Swanning_it, considering we were using around 2000 kWh pa before the change and now we use less than 100 kWh pa I think the savings quoted are realistic.
One proviso - don't leave the boost on all the time as you will end up with a solar boosted electric HWS.
We only have to turn on the boost after 4-5 days of rainy cold weather like we are getting now.Posted Thursday 27 May 2010 @ 6:39:11 am from IP # -
Buzzman
MemberOne thing that is often overlooked in discussions about solar HW is the capacity of the tank, and the household's usage figures. If the tank is too small to contain the family's normal usage, then it will need to boost every night, and, as Solgen points out, you then end up with a solar-boosted Off-peak HWS.
Tank size needs to be larger than for comparable OP system *OR* household needs to modify usage to adapt to different type of water-heating regime.
For example, two people having two showers per day (quite common, sadly) will use approx. 200L of hot water (with a 3-star WELS showerhead). So clearly a 250L tank is not going to be adequate for even ONE day of overcast or poor insolation. They'd be better of with a 350-450L tank.
Alternately, look at single shower per day, in the morning, before heading out into the world, leaving the whole day for the tank to reheat.
And dymo is correct - the claims for the improvement factor for tubes over modern flat plate collectors are largely exaggerated, but are vaild for colder climates or higher elevations. But as most of Australia is temperate coastal, or near-coastal, probably not necessary.
And flat plate systems a shedloads cheaper.
Posted Thursday 27 May 2010 @ 7:33:42 am from IP # -
Greenozi
MemberOne more thing for you when considering purchase of split Solar Hot Water system.
Ask you supplier is cylinder on the ground level is vented and no pressure or system is vented on the roof and water level is at solar collectors.
What the difference it makes I know now too late.
1. My system manufactured by Australian Saxon needs 200W circulation pump and another member ( Sun2steam) that has Hills/ Everlast system at similar configuration 2 storey building require only 20W pump.His cylinder is stainless steel and mine is all copper. So for next 20 years I will be paying 20x bigger electric bills to run my HWS that Sun2steam !
Posted Friday 11 Mar 2011 @ 8:44:43 am from IP # -
simple.life2
MemberBuzzman says: "One thing that is often overlooked in discussions about solar HW is the capacity of the tank, and the household's usage figures. If the tank is too small to contain the family's normal usage, then it will need to boost every night"
We looked at the whole evac tube vs flat plate issue, and then realised the tank size was also a important consideration: We came to the conclusion that a smaller tank shouldn't be a huge problem as 1/3 of our hot water usage is about 4pm. So we have a full hot tank by then, use a bit, and it seems to be a full, hot tank again before the sun goes down (NNW facing flat plates). So a smaller tank for 3 people need not be a problem assuming one shower or bath per day per person, if the usage is spread.
We used to have 250 litre off-peak electric hws which used between 4-7kw to reheat each night, and we ran out most of the time by 4pm. We now have a 200 litre Solar HWS tank which takes days to run out, if at all (yes, we did turn the gas boost off just to see what would happen!).
Although we wanted the tube system, the flat plate was $800 cheaper and appeared to do the same job. So we're very happy.
Posted Friday 11 Mar 2011 @ 9:49:56 pm from IP # -
Sunshine
Memberdymo,
Have to disagree on your figures that evac tubes are only 3-10% more efficient than flat plate.
Details of official comparison can be found herehttp://www.energymatters.com.au/renewable-energy/solar-power/solar-hot-water/flat-vs-evacuated.php
Tests performed at National Solar Test Facility Canada, so these were tested in a proper test facility, so aren't a fallacy.
Additionally real world performance of 2 friends in Brisbane with flat plate SHWS confirm they boost considering more than what I do.Posted Saturday 12 Mar 2011 @ 1:21:13 am from IP # -
Buzzman
MemberHere is the critical quote from the (not necessarily unbiased website Energy Matters, who are a retailer of Hills Solar):
<Quote>
Winter: Based upon solar insolation of 426W/m2 and an ambient temperature of 13.1degrees Celsius in Sydney, the Hills Esteem evacuated tube solar collector is on Average 104% more efficient per m2 of aperture compared to flat plate solar collector.Summer: Based upon solar insolation of 840W/m2 and an ambient temperature of 21.3 degrees Celsius in Sydney, the Hills Esteem evacuated tube solar collector is on Average 50.5% more efficient per m2 of aperture.<Unquote>
The KEY phrase here is "per m2 of aperture".
I think it was dymo who, elsewhere here, demonstrated mathematically that the *actual* m2 aperture area of the ET systems is not so great, and that what 'tests' like this DON'T tell you is what one "typical" ET 20 or 30-tube system is like in direct comparison to a *similar spec* flat-plate system.
In other words, an FP collector with the same *roof area* as that of an ET system may be at least equivalent if not actually better. Effectively, you need more roof space covered in tubes to achieve the same "aperture area".
And one of the specific claims is that ET is 'more efficient' heating water 'to 75degC'.
Which we in fact don't need!!!! A max of 50-55 is more than sufficient, and if you review the data sheets, the FP system achieves these temperatures perfectly adequately, even in a chilly ol' Melbourne winter.
While it is CERTAINLY true that ET systems appear to have some 'efficiency advantage' over FP systems, the claims made in this 'report' are patently ludicrous. Or at best, ever so mildly exaggerated.
10% to 40% is considered to be a reasonable 'real world' difference, and this is considered to be the reason why they cost 40-50% more than an FP system.
Like I said, way back, if the tank is SIZED correctly, so that a couple of days without sun can be borne without needing to boost (and remember, the size of the COLLECTOR is determined by the CAPACITY of the storage tank, so the more you have STORED the LONGER it will last before you do need to boost, regardless of which collector system you have.)
Please take such claims with a very large and sceptical pinch of salt.
Dymo can you re-post your calcs from before?
Posted Saturday 12 Mar 2011 @ 2:03:30 am from IP # -
Greenozi
MemberI don't understand this discussion what panel is more efficient Flat or ET.
What difference it makes? None, sun is free.
Main consideration and comparison should be "How much electricity each system require to run" alternatively "What are running costs"
Some split systems needs constant 200W electric motor action to operate but simple thermo-siphon doesn't need electricity at all.
If electricity cost 60c a kWh and pump is running 10 hours it cost
6 dollars a day
or $180 a month
or $2180 per year
$43.600 for lifetime of solar heater !! (20years )or to run 'free solar water heater'
Now you can make conscious decision what solar water heater to buy. With electric circulating pump or without.
Posted Saturday 12 Mar 2011 @ 12:16:42 pm from IP # -
Sunshine
MemberThe big difference between the two is not so much how good they perform in the middle of summer with the sun blazing down, where anything can heat water in those conditions.
It's the performance of the system on marginal days, overcast, rainy, cool weather, whereby an uninsulated flat plate will lose heat, whilst an evac tube system will still gain heat.
I know 2 local friends in Brisbane who need to boost on or after the second day of rainy weather, where I need to only boost on the fifth day. They have similiar sized tank and family, but use flat plate Solarhart and Edwards.
My circulation pump is 22 watts, probably runs 8 hours a day. 176wh a day@20c/kWh= 3.5 cents a day. Not a bit amount.
Whereas an electric boost is 2400w or 3600w, so if you have a 3600 watt electric boost, you would be able to boost for less than 3 mins per day for the same power usage. I can't see electric boost doing much to raise the temperature of a water heater in that time, but the circulation pump will sure keep the water hot, as long as it is installed as per spec sheet.Posted Saturday 12 Mar 2011 @ 10:43:25 pm from IP # -
Greenozi
MemberSmall difference in collector efficiency could be easy wasted if whole design is wrong.
I have 2 flat panel on the roof and possibly 15 meters coper pipes each way to connect circulating water to the cylinder on the ground.Total 30 meters. I imagine the loss of heat in this long tubes must be enormous.
For comparison vacuum tube could be plug into cylinder directly with on obvious lost in transmitting.
No quantum of energy is wasted, everything counts, that why even in dark, rainy day surpassingly they still able to heat water.
So in my opinion Solar Hot Water should be rated as complete setup not a single element by itself.
I would propose for easy comparison test consisting of three differnt condirion and output rated in kwh.
1.Output in kwh (amount of heated water in cylinder0 during whole day in full insulation
2. Moderate condition
3.Rainy ,cloudy dayie S 4,3 M 3.0 C 1.1
Sunny Moderate Cloudy
For standarisation that lighting condition during whole could be measured by solar PV and carefully adjusted, cylinder capacity is known, and water temperature measured before and after test.
This simple test could be applied to any installed SHWS and displayed on the cylinder.Posted Sunday 13 Mar 2011 @ 11:57:41 am from IP # -
Sunshine
MemberMine has around a 20 metre run, but doesn't seem to worry it. I had to prioritise the northern facing roof for the solar pv panels instead.
Make sure your installation has insulation wrapped around the copper pipes all the way from the collector to the tank.
For me, the roof wasn't strong enough to have the tank on the roof, so required extensive engineering work, plus there are power lines on our side of the street, so no crane possible, so having a tank on the roof was not possible for our site. The evac tube collector was carried up a ladder by the installer, so is handy for difficult site installs.Posted Sunday 13 Mar 2011 @ 12:59:59 pm from IP # -
Greenozi
MemberThree weeks and still waiting for installer to show up and resolve problems with not working SolarPower SHWS. I found that my 80W pumps is able to pump a bit warm water in cloudy day but any hotter like today and I can hear whistle and white steam going out of my panels on the roof.
But no circulation to cylinder on the ground.
Funny that I called today only to hear that company is too busy solving other customers complains to attend my installation...
I installed thermometer probe into this monster 400L cylinder and found that during 3 weeks of operation temperature in upper layer of that cylinder never exceeded 40 degree Celsius.
Sadly all my rebates and government grants my builder Dixon wasted on stuff, crap simply that doesn't work since there are so many good solar heaters on the market.Posted Tuesday 15 Mar 2011 @ 11:59:22 am from IP # -
Greenozi
MemberJeff
Booster is not connected as another contractor fail to connect 3 phase connection - again some compliance problem with pole on property (metal one but according to new regulation should be replaced for wooden now. Why nobody that doing their work don't know about standards and requirements? Anyway I have my old windsurfing masts - i can give one to work as a power pole maybe? Good solid steel pole - but now new tree must be cut to replace with wooden one.
Electrician connecting booster mixed up because connected to other 3 phase that are not wired yet. I am on single phase now.
Anyway I am doing big savings because water heater booster will need to work 24/24 to compensate for not working solar heater and also my 25kW air conditioning unit still not
connected, Since winter season will be soon I may not need to waste energy on cooling this summer.
Similarly with Solar PV. Three weeks and still sitting idle on the roof, not plug in anywhere. Possibly I could charge my electric bike battery for now and some battery tools, since I don't have yet electric car.
My example is another proof for advantage of simple thermo-siphon hot water cylinder over split system, Any problem with electicity supply and you are in real mess - no electicity and no hot water.
That also reminds me my old proposal for insulating switch on inverters for domestic solar panels to work independently of the gird. In the case of national disaster every owner or solar PV could easy switch to independent mode (supplemented by moderate battery bank or Electric Vehicle battery plug in)
Recent example from the world could prove that I am right here and this is matter of national security too important to be left to uneducated installers to decide about our future.
Integration of all utilities (water, hot water, electricity, communication, waste) to centralized national grid mean in the disaster scenario total disruption whole country,
but creating independent self sustainable dwelling could be vital - the difference between survival and death.Posted Wednesday 16 Mar 2011 @ 12:01:54 am from IP #
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