PHAT ENERGY approaches solar sizing from a cash-flow perspective first.  We leave you to consider other subjective factors (environmental, personal, etc) to reach the decision of how much larger a system you would want than the one that will pay back the fastest.

Each utility has different rates and rebate programs. So system sizing on a cost per kiloWatt (1kW=1000Watts) varies radically in Southern California - what makes sense in Woodland Hills may make none in Sherman Oaks, and vice versa.