A few questions about a solar pool heating system

[Leicesterboy]

I'm about to install a solar pool heater on my house in Mexico. Eight 10' X4' panels, about 35' above the ground.
I'll only use the system for a few weeks in the winter/spring, so am intending to use a variable speed pump.

This will enable much lower cost pumping than my current 2.5kw pump, because , for the vast majority of the time, it'll be running at low speed, saving money (@40c/kwhr it is not cheap there)
My problem is pump selection. I need something that will have sufficient power to overcome the very significant static and dynamic head. I'm thinking about a Pentair Intelliflo VS or a Hayward SP3400VSP.

I believe that, once primed, I can still reduce the speed to give me the necessary flow rate of approximately 32 GPM (4GPM per panel), which will still be cheaper (per hour) than my current pump (although running more hours). It'll be more expensive when it is running (for a limited number of weeks), but, overall, it'll be cheaper, with less stress on the system and, hopefully, a cleaner pool. (By the way, if I look at the pump curves, I can see the speed required for a particular head. Once the pump is primed and water is flowing, does the downward flowing water compensate for the upward static head and reduce the speed required?

Does anyone have an opinion if this is a good idea? Would a booster pump be better? Would a two speed pump be better? I am tempted toward a variable speed pump because I do not know the details of the plumbing and panels, and, therefore, cannot know exactly what fixed speed pumps will work, nor have the flexibility to adjust and control like I can with variable speed pumps.

Also, I read that the Intellflo VF doesn't work with solar systems because its automatic priming system shuts off before it can lift the water to the roof. Can anyone confirm that variable speed systems don't have this problem?

Final questions are related to drainage and the effects of a vacuum relief valve. What is the best way to drain? I have read some stuff about "specialized" three port valves which auto drain. Also, wonder what the exact plumbing method is, especially the need for isolation valves. Any help gratefully appreciated.

[Naptown]

Ok
Once the system is filled the head becomes just the static head.
You put the vacuum breaker at the opposite end of the outlet from the collectors at the top

Lastly there is an automatic three way valve that goes into the outlet of the filter to either return the water directly or divert it to the solar. This valve and controller are thermostatically controlled
And lastly and most importantly you need to place a check valve at the outlet of the filter before the diverter valve or your system will backwash into the pool if the pump shuts down while the solar is filled.

[Leicesterboy]

Thanks

Rich

Appreciate the feedback. Couple of thoughts:

When you said that after the solar system is filled with water you are just left with static head, did you mean dynamic head.....that would make more sense to me.

I have already bought a three way, thermostatically controlled solar/bypass system (Goldline), although I'll need to get a Cat 5 extension cable to get to the roof.

When I was talking about a special three way valve, it was in relation to the drainage. When the system is not in use ( i.e the solar input 3 way valve is diverting the water straight to the pool via the bypass, or it is manually set to bypass, the output from the solar panels should simply drain into the pool. Is that right? Presumably, there is a check-valve above the solar output to make sure the bypassed water mentioned earlier doesn't go backwards up the "solar output" pipe.

What confuses me is what happens if it is a sunny/cloudy day. When the thermostatic controller automatically diverts the water through the bypass, does that mean the water drains out of the panels every time it gets cloudy? It doesn't feel right to me to have this happen several times a day, because it would mean having to re-prime the system every time the sun comes out. I doubt that I could program the pump to do that. I was wondering how that problem is solved.

I had the impression from something I read that there was some specialized three way valve that helped in this situation......although I didn't understand how.

As you can see, I've got some of this figured out....but there are still a couple of things that confuse me.

[Naptown]

On the partly cloudy day the valve will turn to return to the pool without going through the collectors.
However there is usually a small hole in the diverter that will allow the collectors to drain albeit very slowly.
You do not need a cat5 cable to run to the roof. A standard 18/2 thermostat wire is more than sufficient.

[Naptown]

Only the one check valve after the filter and before the diverter is needed.
I have never had a pool system lose prime on the pump at any time unless there is a leak in the suction side.
The pump sits before the filter so the one check valve will prevent the system from back washing and losing prime.