Step 1:
Look at all your available power plan options from your utility. You are most likely want to target a Time Of Use plan or Tiered Usage plan for solar generation.
Step 2:
Look at your current kWh average monthly usage for July and Aug for about 3 years.
Step 3:
Using the highest $/kWh TOU or Tiered summer rates, see how much power you need to generate insure you only buy power at the cheapest rate.
Step 4:
Using realistic CEC-AC output numbers (these are based on panel angle and direction) size your system. You might have to do separate calculations for each sub-array if you have house roof where not all panels are aimed the same.
Step 5:
Using your calculated production, figure out what your bill will be under a TOU or Tiered plan. Compare this to your actual bills.
So what your goal is, is to get a "dirt cheap at night, expensive during day" plan or a "More you use, more you pay per kWh" plan.
Example:
Say you can buy power 24/7/365 at .12 a kWh.
But you COULD chose to buy power at .06 kWh at night and weekends, and .24 a kWh during peak day rates.
Your solar should be sized to bring the .24 kWh down to .06 kwh average during the day. This might only be 1/3 your consumption worth of panels. However, each kWh worth of power you make with your panels is worth .18 instead of .12, and your off-peak consumption is 1/2 price. Now you program your pool pump, EVs, programmable appliances to only use .06 off-peak power.
You will end up roughly doubling bang per buck on your panels, or reducing payback in 1/2. Never generate cheap power when you can buy cheap power. Generate expensive power.
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A solar salesman wants to sell you as much panels as they can. Even if it causes you to lose money.
Example: Sales wanted $120k to do a biz. Would delete the power bill of $15,000 a year. It would be just about neutral on annual utility consumption. Some months a producer, others a consumer.
By doing the math, $40k worth of system reduces the bill to $6,000 a year (saves $9,000 a year). Every month a consumer, but at a much lower $/kWh rate.
Not counting cost of money, you can see which plan makes more sense. It is future proof because I can always expand if necessary.
$120k plan after 10 years = (15000*10 - 120000 cost) Saves $30,000, which is below cost of money.
$40k worth after 10 years = (9000*10 - 40000 cost) Saves $50,000, which is a profit center.
Note: You don't pay taxes for the 'profit center' your solar becomes. Because it is not generating paycheck income. It is reducing the cost of living, which is not taxable.