How to evaluate proposals from solar panel installers

I have too many demands on my time to be able to review this proposal unless you are willing to hire me for which I charge $250 an hour. 

In general though, look for:

  1. Panels made by companies you recognize (like Panasonic, LG, Sunpower, and I just bought Solaria) so they have the staying power to honor the 25 year warranty. Don’t go with cheap panels from no-name companies many of which are Chinese. 
  2. A 25-year panel power production warranty that allows you to make a claim based on the data in the app – avoid the warranties that require you to get the panel inspected. 
  3. A 10-year “total energy per year from the entire array” warranty from the installer
  4. A 10-year roof penetration warranty if there are roof penetrations. If you have a flat roof get a quote for a ballasted system. If you have a standing-seam metal roof, great, the panels clamp onto the seams, if you have slate or shingles forget a roof mount and look at either ground mount or suppliers like NexAmp or community source aggregation in your town. 
  5. Get the NPV, IRR and payback periods for the investment. Be wary of inflation calculations higher than 3% as they inflate the returns. Electricity prices (which determine your avoided cost or cost savings) are currently astronomical (almost 50c/kWh) because of the war in Ukraine and are likely to come down. I am currently using 25c/kWh plus 3% annual inflation in my projections. 
  6. Barring these numbers (which are not easy to do properly) look for the cost per kWh over the guaranteed life of the panels. Calculate this by taking the net cost of the array (after tax breaks and subsidies) and dividing it by the guaranteed kWh produced per year, multiplied by 25 years. This should come out somewhere between 8-12c per kWh. The lower the better.  Even the high end is a 50% discount to my 25c/kWh long term estimate for electricity prices and is by far the cheapest way to get electricity. 
  7. If the cost differences and warranty differences are small, trust your gut and go with the installer you feel most comfortable with. 

I hope this helps!

David Green – the “Green Guru”

Heat pumps insulation triple glazed windows and solar panels Zero Carbon Home author David Green
Cut your carbon emissions and utility bills to zero, I have done it
Book energy efficiency Zero Carbon Home 2020 edition front cove. Profitable ways to cut your home's carbon emissions and bills. How to get a net-zero-carbon house. By Green Guru David Green.
Zero Carbon Home paperback book front cover

The highly-acclaimed book “Zero Carbon Home”

How David Green, the "Green Guru" cut his home's utility bills to zero by adding heat pumps, insulation, triple-pane windows and solar panels to make a 15% return on investment. David Green is the author of the books Zero Carbon Home and Zero Carbon Pool. He is also the author and presenter of the webinar Zero Carbon, Zero Bills. He is recognized as the "Green Guru" for his expertise in energy efficiency, profitable ways to cut carbon emissions and save money, and the design of houses for net-zero living.
Cutting carbon footprint

How we cut our home’s carbon emissions to zero

How David Green, the "Green Guru" cut his home's carbon emissions and utility bills to zero by adding heat pumps, insulation, triple-pane windows and solar panels to make a 15% return on investment.
How David Green, the “Green Guru” cut his home’s carbon emissions and utility bills to zero by adding heat pumps, insulation, triple-pane windows and solar panels to make a 15% return on investment.

Useful links:

The Easiest Way to Calculate Your Home’s Carbon Footprint:

Written Answers to over 300 Questions about Zero Carbon Homes:

Finance and Net Zero Energy Terms explained:

Zero Carbon Home Website Home Page:      

Database of State Incentive for Renewable Energy (DSIRE)

Published articles on Zero Carbon and Net Zero Energy:

Department of Energy, EnergySage, “Zero Carbon Home”

Zero Energy Project, “My Zero Energy Retrofit beats my 401k”

Cool Effect, “Mr. Green’s Zero Carbon Home”

Green Energy Times, “My Zero Energy Pool is a Great Investment!”

Published Presentations on Zero Carbon Zero Bills:

To see a 3-minute interview of David Green by NBC Boston anchor Joy Lim Nakrin, please click here:TV interview

To see a 20-minute TED talk at Harvard Business School, please click here: TED Talk

You can watch a recorded version of my Zero Carbon, Zero Bills webinar here: Zero Carbon, Zero Bills Webinar

Reviews of my “Zero Carbon, Zero Bills” webinar included, “Minute-for-minute, point-for-point, one of the best webinars I have ever attended. Thank you!”, “David is a true inspiration and asset to our community. He inspired us to get solar panels and a new front door”, “This is like a masterclass in ZeroCarbon”, “Thank you soooo much for the sensible advice and your fabulous resources!!” and, although this next comment is a little flowery, it does express the sentiment of many other comments, “Your contribution to Greening America is great and will probably help our survival as a species a bit longer than expected”.