Any calculation that doesn't take into account the amount of money which could be earned through other investments also doesn't paint a whole picture. If I had $20-40k in cash to invest, it wouldn't be into solar panels.
If someone is financing the unsubsidized amount of the equipment and install, they're putting even more money into someone else's bank account.
Solar does makes sense when utility level electricity isn't available at a remote site, or for things like warehouses where the roof is already dead space.
