So, let's run some calculations
Assume you're breaking even with your utility costs versus solar
Start with $1000, a reasonable first investment, or a reasonable minimum up front cost for solar
Put $275/month into a 1% Money Market, or into solar
This is pretty simplistic and compares a basic lease-only solar.
Lets do a really rough guesstimate and some basic math assuming that electric will be an average of 25% more expensive in 10 years. Let's assume that electric costs bumped by 25% the day after your system was installed (best case imaginable for solar, but highly unlikely)
Year 1 MM: +$4328 In your pocket
Year 1 Solar: $825 In your Pocket in theory (Fixed solar cost, versus increasing electric, which just went up 25%)
10 Years of Electric Costs Avoided: $8160
Year 10 MM: $35,817 In your pocket
Year 10 Solar: +$8160 In your Pocket in theory (Fixed solar cost, versus increasing electric)
Let's assume another 25% increase at 10 years + 1 day
Another 10 Years of Electric Costs Avoided: $10,290
Year 20 MM: $74,276
Year 20 Solar Totals, First 10 years plus last 10 years = +$18,450 in your pocket in theory (Fixed solar cost, versus increasing electric)
This is super basic math with super basic assumptions, but you get the picture.
Your basic 1% Money Market is the clear winner here. And this is assuming an incredible best case for solar: two massive, 25% rate increases during the 20 year install. And 1% is a bare minimum for a "good" investment, ideally you'll find at least 5%, and a good overall is 8-10% return if you're into max growth. Your 20 year return on a cash investment (or even real estate) is looking A LOT better than solar. Even if the total 20 year money in your pocket savings for solar DOUBLED to $36,900, your basic 1% market investment is STILL a clear winner.