Buildings are valued based on a Cap rate calculation, which essentially says something like this: If a building’s operating income is $50k, you apply a cap rate of 16-20X to that, which brings the value of the building to $800k-$1M.
If you improve the operating income of that building by say $5k per year by installing a solar system that costs you $20-25k (a 4-5 year payback is very common in many areas in the US today) then the value of the building is going to increase by $80-100k.
That is how a $20k investment in solar will instantly create a $100k value for a building owner.
Of course, this above example will not work out in areas that have super cheap electricity rates or where where cap rates are higher (or where the multiples are lower). In areas where the electricity rate is above 20 cents per kwh, it is very likely to reach this level of a return.