Choosing pump to match existing panels

How high is the new storage tank going to be ? Hight = work, and more work means more power or time needed. 60w is not a lot of power. so it may take a long time.

Figuring out the "head" needed, will drive the choice of pump.

Thanks for your reply Mike.
I think I need a total head of 4 meters (2m pool depth + 1m height of the water tank + 1m stack of pallets to keep it raised from the ground)

Similar to what Mike writes, but I'd add: If you have grid power available, use that. Seems a lot of hassle for one application, especially when time may be a factor due to fouling of the water when the attendant problems of sight, smells and health considerations of open, standing water are take into account. After a few days you'll have a lot of green water. After 4 months, you'll have a swamp.

To your pump choices: Figure out how long you want to take to drain the pool. Then, look at the pump curves for various submersible pumps that will pump the water out at ~ 4m head in the required time. Or pick a pump that fits your budget and read the discharge rate for that pump from its pump curve and est. drainage time from: drain time ~ = total vol. of H2O in the pool/pump discharge rate at 4m head.

If you choose a D.C. pump/use the panels, look out for startup surges and check the power factor of the pump motor and take those into account when matching to your panel characteristics. Also, don't expect the panels to produce their rated power except under ideal conditions, and usually much less than their nameplate power rating.

Unless you are completely off grid, I'd get a small A.C. pump that will deliver ~ 3-5 l/min. or so at 4 m of head, fit it with an accessible filter on the inlet, throw it in bottom of the pool ,and keep an eye on it. I've drained many a pool that way.

Not a plug, and FWIW only because it has worked for me many times in very similar/identical applications to what you describe: I've had a Lil' Giant pump similar to their current 5-MSP for going on 50 yrs. I drained pools I've owned with it many times. Fit for purpose. It's A.C., draws maybe ~ 500 running W. or less, although I've never put a Kill-A-Watt meter on it. Current spec sheet/pump curve shows it pumps ~ 3,000l/hr. ~ 4m of head. That figure seems about right to my observations. Costs ~ $100 U.S. Plug & use. See Google.

If you don't have/don't want to use grid power for this application, find a D.C submersible pump that will run on, say, 40W or so. but be careful of the starting current and power factor of the pump.

So, now you look for a pump that will give you a flow of ___ at 4M head.