My solar panels and batteries work as per spec and warranty. But it requires doing tons of homework ahead of time to know what you can get in your situation (peak solar hours per day in your area, avg sunny days, angle of roof facing south, avg power consumed per day per month, etc.). Know enough to almost do it yourself, then hire a solar installer and you'll be able to tell which installers are offering you a pipe dream.
I guess it's like anything else expensive.