Assuming you are in the United States… Look at your roof on google earth.
- Does it face south?
- If not, is it facing southeast or southwest?
- Is it obstructed by trees, other buildings, pipes, or chimneys (i.e. is it often shaded)? To find this out, look at your roof throughout the day yourself (if possible).
- If it is shaded, are you able and/or willing to cut down trees or branches to ensure it’s a lot less shaded?
Plenty of (if not all) solar PV companies will provide free financial analyses, including tax credits/deductions, utility or government incentives, and a payback period. Analyze that thoughtfully or hire someone like me to do so. Look into the assumptions they are making – electricity rate currently, projected electricity rate, depreciation, impacts of producing more than you’re using (i.e. net metering), etc.
Personally, I think any payback period that is less than (or even equal to) the life of the system makes sense if you want to do the right thing – i.e. reduce your contribution to climate change, etc. Everyone varies in their level of comfort, but a payback period of 5-10 years means that after that, you will be cost positive. They are incentivized to sell more systems and more panels, so be on the lookout for whether each panel makes sense. Look at the layout the company proposes: are they taking into consideration all of the potential shading that will occur at all parts of the year?
Evaluate the proposals you get from PV contractors for all of the aforementioned, but also get a sense of the company – who you will be working with, how communicative and trustworthy do they seem (speak to prior customers), what do the panels look like, what’s the maintenance policy if any, do they come out to remove snow from the roof (unlikely – so that’s on you if you want your system to be running!), who’s the manufacturer / will they be around if you need replacement parts, etc.
Solar PV makes a ton of sense when done properly, though one should definitely also look at improving the efficiency of their home first or in addition. There are likely many other, lower cost items that have shorter payback periods that may not be as “sexy” as solar, but are great for the pocketbook.