Solar collector performance help please.

Greetings folks.
Thanks for having me on here.
I'm trying to design my own solar collector panels (flat plate) and I'm trying to decide if I need to go to the expense of double glazing them. I live in africa in the tropics (17⁰ south latitude at 5000ft altitude) so plenty of sunshine and we don't get freezing conditions in the winter. The panels I want to make are just the normal copper tubes in a box with glass front. I would like the water to get up to about 70 degrees C or 160F are these types of panels capable of producing that kind of temperature if designed, built and insulated properly? Second question...does anyone have an idea of how many square feet / meters I need to heat 600 litres / about 160 us gallons of water please?
Thanks in advance...

Dave

 

what is the water used for at that temp Dave ?
@DaveinZim
Sloth , Im doing the math now also


These are my own solar collector panels, I removed them due to the work involved around freezing in Canada.

 

Welcome to the site. Lots of members have experience with solar collectors. Do you have any preliminary construction plans? Do you have enough severe weather to justify double glazing your collectors? Will you run your (water?) through tubing or allow it to run freely between the class and back panel? If water can you control the deposition of minerals?

 

Hi Sloth. Thanks for the reply. Mainly domestic hot water. But I also want hot water in home workshop for washing greasy parts and such. Which is why i would like it a bit hotter. 150F or 65C should be fine and really anything hotter than that is getting dangerous. But as i said, it's my workshop really that has me wanting a bit of a higher temp. We don't have central heating in this part of the world. On a normal cold winters day temp drops to about 12⁰C and our absolute minimum at 04.30 or so in the middle of winter might get down to -1⁰C for a couple of hours till the sun comes up. Thanks

 

Hi Marvin.
I used to own a vehicle radiator shop and I have a lot of 1" flat brass tubing left over from that. I intend to use that for the collectors as it means I don't have to buy copper. I'll just use what I have. I don't have any specific plans at the moment. I've just been doing a bunch of reading and you tube videos. I don't think I need to double glaze. But I wanted to check first. I live out of town and we have baboons come in the garden pretty much daily so whatever I build has to be pretty robust otherwise they will destroy it when they run on the roof. Evacuated tubes are out of the question.
And expensive. We also get quote serious hail here every few years. Up to sort of golf ball size so whatever glass I use has to be tough. (And expensive) apart from that we don't really get extreme weather here. Yes, I'll be using water (no glycol) and running it through brass pipes. Water will be from borehole so lime scale is an issue. I will have a descaler installed on the water input to the system. Thanks.

 

Good info , not going to happen , but only some days , -1c is squat / nothing .. 140 F is the limit SIR !!!!! On DHW for kids , do not fudge ,, use better soap ..

I will PM you on LAT & Long of area , and get the better info ,,
Sir / Ms it takes TIME to be true and pointing in the right direction ,,
No worries , if I make a mistake , many will say here , and I'll learn more .
Sloth

 

My lat and long are: 17.8° S, 31.0° E That's close enough for any calculations

 

Have posted thanks

 

I'd paint the tanks black and make sure there in the sunlight,Even our grass here will get up to 141 degrees

 

What kind of pump will you be using to circulate the water ? The temperatures you're looking at are no problem, especially if you run a DC pump and can vary the flow rate. Be sure you install a temperature and pressure relief valve near your panel outlet in case things get away from you. Single glazing should do fine, but if hail is an issue, you may want to go tempered glass.

 

Thats some good sunshine from your numbers Dave.
Ill post in Imperial sizes , for all to follow .
Im saying 8X8 feet square should collect enough and a way to tip it to follow the sun arc
would improve it as well. pipe size id use to collect is 3/4 " or 1" round ridged copper to feed
the input with 1/2" and restrict the outflow down to 3/8 " . that way the water is there longer and the flow is slower , picking up more heat. On mine i used 2 10 watt PV panels on the same plane as the collectors , so when the sun hit the panels the pump started .

If you mount the copper pipe to 1/8 "thick strips of 2.5" flat bar of aluminum painted black and then strap the copper down with copper straps to the painted AL then paint both black , stopping electrolysis between the two. 4 pipes per foot 32 pipes and support the runs on the top and bottom of the two 90* elbows making the U .

That way heat expansion can happen . Use adell clamps to support the metal off of the plywood. Copper pipe here N49,124W Canada we have thin wall L and M thick wall and K that is soft & $$ , go with thin wall for best heat transfer . isolate the flat bar from each other since the further along the water will be getting hotter .

Sloth

 

Hi Andy,
Yeah, with the hail and the baboons I think tempered is the only way to go. I've been advised to go with 5mm / 0.2" Glass.
I've also read that non reflective glass is better than normal clear. Is this true?

I have these little pumps (See attached pics) They are great. They have three speed settings, on slowest they use 55watts and pump 1000ltr / 260 gallons an hour. If the tank is 600ltr/160gallons that means the tank contents will pass through the collectors about every 36 minutes. Might be a bit fast. Any comments?
My whole house runs off solar PV and inverter so it doesn't matter that the pumps are 220volt. I'll just wire them up as normal. The only time I ever switch off my inverter is for battery maintenance or lightning storms. Another thing we get a lot of here.

 

Thanks Sloth, really great info.

 

Yes I hear you. I was thinking of running the collector circuit and it's heat exchanger with distilled water. I also like the idea of having a self draining collector circuit back in to a reservoir with vent to atmosphere. It's a very simple way of making sure the system doesn't overheat. When it reaches temperature, the pump switches off and the collectors drain.
There's a lot to think about, the more I research this, the more I realize it's not just a case of slapping some tubing in a box.

 

This has got me thinking now. I have most of the materials to make the system lying around already.
If I'm going to have a copper coil heat exchanger, why not reverse the system and instead of having the heat exchanger on the collector side. Have it on the water supply/house side. It eliminates the need for pressure vessels. I could make my own hot water reservoir out of much thinner material which would be a huge saving on getting someone to build a pressure tank?

 

That is how I built my first collector (mine was smaller ,for testing in the 80's) but it worked.
You did see my pictures of my bought collectors ? 4 of them in total !! All on the ground and behind the house now ..

You know why , to much BS and trouble ,, now im PV panels to immersion 24Vdc heaters and never going that route again ,, your into a make work project Dave
Sloth