Some days even a fairly large system (15-25kW) will output just 1-3 kW; the extra cost from 10KW to 15 kW is not 50%, but maybe 20%, so sizing a system, smaller

Some days even a fairly large system (15-25kW) will output just 1-3 kW; the extra cost from 10KW to 15 kW is not 50%, but maybe 20%, so sizing a system, smaller or bigger, is a calculation that gives different results to different people based on the cost structure, consumption and electricity cost in the area.