Yes Carl, I'll agree to that bad wording on my part.
Like to know more on your system, how about re plumbing to 3 banks of 10, rather than 2 of fifteen may reduce the problem you are having when running up fast? The pressure issue is due to dynamic head pressure as the flow can't get through easily enough. On my system I get loads of flow but very little pressure (0.25 PSI). That would cause me a problem with Richard's setup as there wouldn't be enough grunt in the pump to gain much flow so I would have to up the size of my pump. but yours as you say is hugely different being closer to the ground, variable speed pump allows you to tailor to specific needs. have you any flow, pressure temp data you can pass on? What panels do you have?