TriStar® VS variable speed pool pumps are the most energy efficient on the market, according to EPA ENERGY STAR 3rd party testing data. Saving pool owners up to 90% on energy costs, they are specifically designed to replace most single speed pool pumps.
www.hayward-pool.com
You can get a 1.85 hp model or a 2.7 hp model.
The 1.85 hp model is good for lower flow applications. For higher flow applications, the 2.7 hp is preferable.
Even if the 1.85 hp model could meet the flow requirements at full speed, I recommend the 2.7 hp model if you would ever need to run the 1.85 hp model at more than 2,700 rpm due to the noise.
There are multiple models in both sizes. You will need to check the individual details to see what works best for you.
In my opinion, manufacturers make choosing a product unnecessarily complicated and confusing when they create too many models that are not really different.
Based on your second story solar system, I would probably go with the 2.7 hp model to reduce the noise because the 1.85 hp model would need to run at higher speeds and generate more noise.
Do you have any trouble balancing the flow between the lower and upper panels?
I would think that the lower panels would get most of the flow unless you used a valve to adjust the flow to make it even.
It looks like Hayward has rebates available. Many utilities also have rebates available for switching to a variable speed pump. So, check for any available rebates.