SOLAR
How to Estimate a Solar System Expansion
Contractor method for estimating adding capacity to an existing solar system.
Solar expansion bids fail on the cost per watt and the inverter. The added capacity is easy math; the real cost per watt and the inverter compatibility determine the quote.
THE SHORT ANSWER
How do you estimate a solar expansion?
Confirm the current capacity, set the added kW, then multiply by the cost per watt. Adding 3 kW to an 8 kW system at $3.50/W runs about $10,500.
Confirm the current capacity
Note the current system size in kW and the inverter rating. The inverter must accept the new total capacity or it needs replacing.
- Note the current kW
- Check the inverter rating
- Confirm roof space
- Check interconnection rules
Set the added capacity
Decide how many kW to add. The added capacity converts to watts (kW × 1000) for the cost calculation.
Apply the cost per watt
Adding panels runs ~$2.50-$3.50/W in the US. Use the Solar System Expansion Cost Calculator to price the added capacity, then add inverter or racking work.
Check the total
Your total should land within 10% of the calculator output before markup. Confirm the utility interconnection approval.