Equipment and design advice

with the heating panels above the tank, you need a way to halt nightime thermalsiphon

If no freezing, I'd consider putting the tank above the panels and making the system a thermosiphon type, and thus eliminate the pump altogether.

See builditsolar.com for lots of ideas and info on some plumbing requirements like an expansion tank, relief valves for press. & temp., valving, etc.

Think safety first !! and always.

The first consideration should be how to control the temperature of your water for safety reasons. Hooking up those 3 panels will easily boil water in the summer creating dangerous pressure on your system.
One panel should be good for 60 gallons of water at 130+ degrees. For safety reasons I recommend drain back systems because when the max water temperature is reached the main pump turn off and all water drains out of the panels preventing overheating and dangerous pressures and temps. There are additional costs associated with this type of system but it should be safe.
Take a look at the SRCC web site and search out your panels to determine how many gallons of water they will safely heat in your climate area.

N0t going to put tank above the panels due to weight on roof.

I will to start with one panel and a 80 gallon tank to prevent getting to hot, thx for the advice!

I was advised to use something like this check valve above the pump to prevent thermosiphoning at night. The valve is teflon coated to prevent fouling.
Will one check valve above the pump line be enough?

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Any advice on the brand of pump? The el sid is 320$ out here. The topsflo is 60$ on amazon!

Anyone convert a used elec. tank to use with the panels?

Aloha,
Michael

I posted the wrong link. This is the lead free version.

Pump needs to be stainless or bronze and capable of overcoming system head pressure, some calculations are needed to select the pump.

As LucMan writes on pump (and other materials).

Usually, systems are sized (that is area/panel X # of panels) and oriented (azimuth and tilt) as application available if a roof mount to meet the hot water load or as much of it as the design requires or can be done in the space and orientations available. Then, the flow rate is calced' for best trade off between pumping cost, including initial costs and (usually) much lower pumping costs, thermal efficiency, and system design for best/longest trouble free design/maint. Then, the pump is sized/selected based on pump curves and the estimated pressure drop through the system collectors, piping and valves, etc. It's a bit of an iterative process.

Others will probably think this way too high for a flow rate, but for many sound fluid mechanical and thermal reasons probably boring to most, I pump a minimum of ~ 1.7 GPM through 2 ea. 4 X 8 collectors plumbed in series. In San Diego, on a sunny day in spring/fall, I can raise the temp. of 80 gal. of H2O by 110 F. or so, if I don't cover at least 1/2 of one of the collectors.

With that in mind, in HI, 3 ea. 4 X 10 collectors (or close to 2X my size) will probably boil 80 gal. of water most of the year on a sunny day. Not safe and a waste. After load sizing, including considerations for use patterns, I'd consider either using 2 panels and know 1 of them will be intentionally covered a good portion of the time, or use 2 ea. 80 gal. tanks, or one 120 gal. tank, or, 3 collectors tilted ~ 45 deg. or thereabouts and a 120 gal. tank.

Or.... ?? Lots of other possibilities.

I'd suggest you learn something of piping design and solar thermal engineering. There are lots of ways to construct designs that look good on paper but will be dangerous, not to mention inefficient and probably failure prone.

Also, don't forget wind, seismic and other important structural requirements.

There are a lot of details important details necessary for a safe design you sound unaware of that cannot be covered in the limited space available here.

Take what you want of the above. Scrap the rest. Just think safety. What you don't know can and will hurt you. It'll also cost you money and time.