Not sure. They don't use a ton of electricity, but some. That would be easy enough to determine once you know the brand and the size of SWG needed (based on pool size). But SWGs also require pump runtime, at a minimum RPM. It's not a lot of watts. Mine works fine at about 1500 RPM, but I run mine for 8 hours a day. Vacuums and solar heaters require much higher RPMs (if either are in your future, mine run at about 2400RPM). And solar heaters need a lot of runtime.
And I'm not discouraging your efforts to plan for the pool's energy consumption. You have to, of course. Only pointing out there are a lot of variables. I had a similar situation, in that I was reconfiguring all my pool gear at the same time my PV was going in. So how to calc the # of panels? But I did have a pool prior to PV, so the previous year's PG&E bills provided at least some basis.
I had these types of discussions with my solar installer, and concluded the same as I shared. Get close, add panels if need be. There's room on my roof for several more panels, so I can always expand a fair bit. So far, my true-up bills have indicated I have a perfectly matched system to my usage ($0 to PG&E!). As the panels degrade, and I have to start paying PG&E, I'll add another panel or two. Maybe I'll need a few more for the electric car we'll all be driving. Maybe by then they'll be the size of a roof tile and provide twice the juice!
But I did plan ahead. I mounted my pool solar heater on the north side of the roof, to save the south side for the PV. Something to consider if you think you might ever get a solar heater: you'll need space for the current PV system, any expansion of that, and another spot for the pool heater panels.
