For several years we ran one 2x20 panel on an 18'x48" deep pool averaging in the mid 80s for temps except when we had to bypass end of July/start of August because it was too hot - always WITH a solar blanket to keep the heat in. We are in the FAR northwest Minnesota, as cold a summer as you can get. We had ours on a 45 degree ground rack facing south - this year we have 18x33' x 52" and obviously more panels on an elevated rack facing south - not operating yet this year due to construction.