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Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 5:59 pm
by offgridCBR
A cloudy canberra winter might not be as suitable as the sunshine coast sadly... The house won't be connected to the grid. Could be an option if I could pick up a few cheap 2nd hand panels but would still need some form of boosting heme the wet back.

Re: Solar hot water systems with a wetback

PostPosted: Wed Jul 20, 2016 7:45 pm
by 34by151
There are 2 factors that apply regardless of the type of solar collection used

First is the efficiency of the collection and second is the size of the tank

The second part is obvious but often overlooked. The bigger the tank the more power need to heat it. The overall efficiency of the collection more effects the amount of roof space you need to dedicate to the job.

Take a read of the info on the controllers page but I doubt you would need more than 3-4 panels

If you take the average 3000W element, when it comes on it will run for 10-15 mins
If we say 15 mins (0.25 hours) thats 3000 * .25 = 750 watts consumed each hour
So the number of 250W panels needed is 3 as the system will run for the full hour not 15 mins
Allowing for cloudy Canberra and just chuck a few more panels at it say 4 or 5 up to a max of 2kw

Re: Solar hot water systems with a wetback

PostPosted: Tue Aug 02, 2016 3:31 pm
by offgridCBR
Is there a high failure rate with on ground storage tank pumps? Currently debating the merit of an in roof 315L tank using thermosyphon and a on ground (outside or in a cupboard) storage tank. I have found some alternatives for the split systems and am interested to hear your views

Cheers

Re: Solar hot water systems with a wetback

PostPosted: Tue Aug 02, 2016 3:47 pm
by australsolarier
well, if you buy a cheap chinese made circulation pump the failure rate will be way higher than if you invest in a grundfos or other quality made pump. the price will be 3 times higher, or more, so will be the reliability and your ease of mind.
i have 3 grundfos pumps, no problem, two of the chinese pumps failed shortly after installation. i could tap them with the screw driver and they would stall and after more taping unstall again. i suppose that is alright if you sit next to the pump 24h/day and can tap them back to live when they stall. so i bought the grundfos pumps and haven't look back since. they also use less electricity and circulate to a higher distance vertically at start up. plus they can be pmw controlled, whilst my chinese pumps sounded like a small jackhammer when in low speed.
i would certainly expect the quality pump to last 10 years in daily usage.