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Heating and cooling: Solar panel sizing

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    • CommentAuthorEdK
    • CommentTimeMar 18th 2009
     
    Hi the local auth here has made some exemptions to the planning laws with effect from April 6th - one of them relates to solar panels - part of the exemption is that they must be in the same plane as the roof and not stick up more than 30cm.
    Would this limit my choices to FP or are most ET's smaller than 30cm deep ? I'm keener to go with ET's for a slightly better winter gain (am still earning so can cough up the extra).

    Have a thermal store with two coils - was going to use one for solar panels. Think that it is 300 litres.

    Any thoughts on best ET's to go for ? What is the ebst way to size them up ?

    Thanks
    Ed in (sunny) Guernsey
    • CommentAuthorstephendv
    • CommentTimeMar 18th 2009
     
    Have a look at the navitron forum www.navitron.org.uk for a bunch of very helpful people
    • CommentAuthordelboy
    • CommentTimeMar 18th 2009
     
    Where have you heard that ET gives better winter gain?

    I thought that generally evac tubes are better all year round.
    • CommentAuthorEdK
    • CommentTimeMar 18th 2009
     
    Long thread on this forum with pros and cons of evac and flatties - guess it is contensious but from looking at it if you have the cash then go with evac tubes - great if they work a bit better. Guess if you are after best value for money then flat panels - but as mentioned I am still working and can afford evacs so even if these cost 50% more and give me 15% better efficiency in winter I would be interested as it is a one off cost (apart from regular maintenance i guess).
    Thanks
    Ed
    • CommentAuthorPeter C
    • CommentTimeMar 19th 2009
     
    Hi EdK,

    From experience I can tell you that Navitron are not the best evacuated tubes on the market and when compared with competitors in their own quality range they are not cheap.

    What they have got is a very informative web site, all prices are displayed and unlike others they do not attempt to hide the fact that the product is manufactured in China unlike some who have products re-badged on the Continent and marketed as made in the E.U.

    In the long term good flat plate panels are better, some have guarantees in excess of 25 years, most have a life expectancy in excess of 40 years against the life expectancy of 20 years for ET, the figure of an extra 15% efficiency for ET is based on the early life of the system.

    It is important to size any system based on the number of people in the home, a guide of 50 litres per person per day is a fair guide, another is one square metre of panel per person, for your cylinder I would expect an average of 3 panels however 2 may be sufficient depending on the number of occupants.

    The biggest difference between the two types is E.T. have more forgiveness when it comes to the orientation of the roof, S.E. or S.W. tubes will generally perform better, south facing there is very little (if any) difference in performance between panels or tubes.

    One maor benefit the flat plate have is they can be integrated into the roof thus spreading the load across the rafters instead of concentrating the load on individual brackets, pipe work is also hidden when the panels are integrated and using a good quality system the flashings are neat / tidy.
    • CommentAuthorEdK
    • CommentTimeOct 15th 2009
     
    Jeez where does time go...been a long summer of work on the house.

    I can get Thermomax solar panels here and am waiting for a quote for the HP200 variety in 2m and 3m panels.

    The roof is 35 degrees and faces due south so I think that this should be good.

    I have two suitable spaces with velux (C04 size) between.
    Space A = 1250mm wide
    Space B = 2080mm wide

    As for height I think that this is about 2400mm.

    I noticed that the Thermomax 3m panel is 2127mm wide and the 2m panel is 1418mm wide.

    Does anyone know whether this is the manifold width at the top ?
    I was hoping to squeeze a 3m panel into space B (2080mm wide) and thought that the main body of the panel might fit with the wider manifold at the top sitting over each velux.

    If not the I guess my choice is limited to just a single 2m panel in space B (with Thermomax).

    They seem well made panels - any comments ?

    Hoping that a 3m Thermomax with my 300l heatstor will go some way to providing all hot water for spring/summer/autumn ?
    Will be using wood burner for winter heating and have specced rads too.

    Thanks
    Ed
  7.  
    Posted By: Peter CFrom experience I can tell you that Navitron are not the best evacuated tubes on the market and when compared with competitors in their own quality range they are not cheap


    Compared with what for e.g...?

    J
  8.  
    • CommentAuthorJulian
    • CommentTimeOct 16th 2009
     
    Hi Ed
    I have Thermomax (made in Ireland and UK I believe) and they are very good. Have outperformed expectations. We have 30 tubes on a single manifold 3m2 and it looks no more than 2,0m wide so you may be ok. I guess you've looked for technical spec. on the Kingspan site?
    • CommentAuthorEdK
    • CommentTimeOct 17th 2009
     
    Hi Julian - thanks - yes, tech specs say 2127mm but the space I have is 2080 - so I'm 47mm out - was wondering if the spec width was the top manifold end and was hoping that the main body was less ... Any one feel like shimmying up onto their roofs and getting the tape out ?! I'll check with KS...might be safer.

    Good to hear that they are good - Julian what is your set up with regards to tank size and DHW usage (number of adults and all that ) ?

    Thanks Ed
    • CommentAuthorEdK
    • CommentTimeJan 28th 2010
     
    Heard back from KSpan and the 3m panel will not fit.

    They also said this : "The number of litres per tube would be 10. We would therefore recommend
    30 tubes to go with your cylinder."

    So looks like I need to find a panel with that output to fit in my available space.

    Ed
    • CommentAuthoracroiso
    • CommentTimeFeb 3rd 2010
     
    Hava a look at the Roth R1. Only 780mm wide.
    • CommentAuthorantiriad
    • CommentTimeFeb 3rd 2010
     
    The Kingspan Thermomax collectors normally recommend a cylinder size of 300 litres to accommodate their 30 tube collector, or a 200 litre cylinder for their 20 tube collector.

    There is no reason why you could not feed a 20 tube collector into a 300 litre cylinder - only difference is that your solar contribution would be less. (i.e. you will only fill 2/3 of your cylinder mid-summer instead of a full cylinder)
    • CommentAuthorJulian
    • CommentTimeFeb 3rd 2010
     
    Hi Ed
    sorry - only just seen your question from October. We're two adults and two children. 300L pressurised cylinder.
    julian
    • CommentAuthorwookey
    • CommentTimeFeb 4th 2010
     
    James: Compared with eco-nomical.co.uk, for example (£320 vs Navitron's £400), and solarsavings.co.uk, and a couple of others who's names I don't have to hand, which all sell very similar chinese panels to Naivtron's, but for less money. Navitron claim minor design differences which will result in longer life (e.g. better frost proofing due to thicker heat pipes). I guess this winter will have been a good test of wether that makes any practical difference. (I have eco-nomical panels and am pleased with the choice so far, but can say nothing much about their lifetime before the first couple of years).
    • CommentAuthortony
    • CommentTimeFeb 4th 2010
     
    If you need more hot water why not increase the area or number of tubes?
    • CommentAuthorantiriad
    • CommentTimeFeb 5th 2010
     
    Hi Tony, you should always size your collector to your demand mid-summer and best-practice is to never over-size your collector unless you have a secondary thermal demand where you can divert any excess energy (best secondary thermal demand is an outdoor swimming pool - unfortunately most of us don't have the luxury of a swimming pool so matching size of collector to demand is very important)....
    • CommentAuthortony
    • CommentTimeFeb 5th 2010
     
    I have grossly oversized my solar collectors in the hope of keeping some of the surplus heat from summer to winter.
    • CommentAuthortony
    • CommentTimeFeb 5th 2010
     
    I also disagree with optimising to summer as the way to go -- I feel that it would be far better to optimise to mid spring/mid autumn and to mount panels much steeper than we generally do.
    • CommentAuthorantiriad
    • CommentTimeFeb 6th 2010
     
    If winter heat is your objective then you should be installing your collectors in a more vertical inclination so that you are maximising you solar gain in the winter periods - if you are doing this you can still size your system to give you 100% of your hot water requirements for mid-summer (though you will require some additional collector area).

    If you have oversized your collector (i.e. to give you more than 100% of your demand mid-summer) I hope you have included a secondary thermal load to deal with the excess energy that you will generate during the summer period, otherwise you could have some problems with this system in the long term.
  21.  
    Doesn't any 100% summer have over capacity to deal with cloudy days...? Other wise how will it achieve 100%...?

    Equally if its all free from the sun you could just overheat to the drain....?

    J
    • CommentAuthortony
    • CommentTimeFeb 6th 2010
     
    What angle should I mount my panels at?
  23.  
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 6th 2010
     
    <blockquote><cite>Posted By: tony</cite>What angle should I mount my panels at?</blockquote>

    This is going to sound a bit dumb but it really depends when you what to maximize your collection time. Best way maybe to work out for your latitude the optimum angles for the 21st of December and 21st June. This gives you your theoretical minimum and maximum (look up what the sun altitude angle for those days at your latitude). Then work out what time of day and altitude angle you will get maximum sunlight on your roof area (assuming the roof is where the collector will be) This will then give you the maximum you can collect. Everything else from will be lower in energy collection and follow the product of the sine of the angles. If you plot it on a chart you can then calculate the area under the curve and estimate your kWh/d for those two days.

    There are a few exception to this, in large cities there is less pollution during the mornings and an east facing panel can collect more than a west facing (marginal and is more for evacuated tubes than flat panel). When using flat plate collectors temperature comes into play because of the larger surface area and associated temperature differences (then west facing is better as warmer in afternoons).

    Think carefully about when you want to use your hot water, your best off using it all up before it is light, then you maximise the collection time.

    Watch out for shadows, the can cause a large percentage of the panels/tubes to not only collect less but also to radiate more.

    Variable speed pumps add little if anything (the controller should be able to be adjusted to suit the response time of your system and in effect becomes a variable flow controller but in discrete steps.

    By maximising for winter you will reduce performance in summer, so reducing overheating. I am lead to believe that the overheating can damage the collectors if extreme.

    Any increase in the temperature in the tank is an energy saving even if it is not at the ultimate temperature you desire. In line supplementary electrical heating can boost the temperature up and may be cost effective for the winter months.
    • CommentAuthorRobinB
    • CommentTimeFeb 7th 2010
     
    I would like to pipe any summer excess in a loop under the patio - I'm met with amused, disparaging looks from would-be installers but I really like the idea of warmed stone on a summer evening. Am I in cloud cuckoo land?
    Robin
    • CommentAuthorJulian
    • CommentTimeFeb 7th 2010
     
    Hi Robin
    What is your patio to be constructed from? There will probably be a good deal of warmth in the stone anyway from solar radiation. Couldn't you do something more creative with any excess? What size will your collector and store be?
    • CommentAuthorRobinB
    • CommentTimeFeb 8th 2010
     
    The patio is a shocking 3m (yes 3metres! ) deep backfill of gravel. I'm planning to add some stone flags to it and I thought that was creative! Store size 300l, plate size TBD.
  28.  
    RobinB what a great idea (each to their own of course Julian) - under patio heating/heat dump! I guess a little bit of optimisation is required to get the best, perhaps some dead cheap 40mm insulation over the gravel otherwise all the heat will dissipate into all the air beneath and some long thin bendy copper pipe laid serpent-wise into the screed the flagstones sit on - all perfectly DIYable.

    Dead cheap and rather cool, in a warm sort of way!
    • CommentAuthorEdK
    • CommentTimeFeb 17th 2010
     
    Spoke to someone at solarsense and they said I could run the 30 tube HP200 with just 29 tubes so that the manifold (2127mm) would be above the velux (space between velux is 2080mm).

    This seems a better solution than the 20 tube array as it will get closer to the ideal of 30tubes/300litres.

    They also mentioned pipework. Said that there was a stainless steel flexible pipe bundle with integral HT insulation and all the wiring and terminated with fittings. i.e you just plug one end into the panel and the other into the heat store and connect up the wiring to the controller. Think it is 15mm rather than 10mm though.
    Anyone used these? Seems easy ?!

    Solarsense OK ? Hopefully getting someone to have a look and depending on price maybe fit it. Cost of the panel and full kit seems to be about the same from them as from the local building merchant.
    Ed

    Thanks
    Ed
    • CommentAuthortony
    • CommentTimeFeb 17th 2010
     
    system installed with new cylinder shouldn't cost more than 3.5k

    I always recon oversizing is a good idea as you get more in spring and autumn -- everyone should get too much in the summer

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