In exchange for a reasonable discount of course. 

But this is precisely the reason I wanted to post this question--to get insights from people who with different experience and perspective.

It sounds like they have money, and it sounds like in exchange for that money you're setting them up with an income stream.

Regarding a 1031 exchange, it is important to have a conversation with your accountant prior to getting it done.

For context, 4 adults and all our tech living here, we were running about $250/mo on average per month for electricity anyway... outside of summer a/c useage. so all in all, its saved me about $2k a year if i had to guesstimate for you (it stays hot here through October usually).i still owe about $23k on mine, have no intentions of selling the house. but if i decide to move out and rent the whole house out, our market would support higher rent in exchange for no electricity bill. i think you just need to decide what YOUR main benefit of having the panels are. for me it was for the house-hack, and consistent billing, despite the usage. if its strictly for property value increase, i'm not sure it would be worth it, pending your specific market. 

You may also see a discount fee which means you are buying down your mortgage interest rate in exchange for higher upfront cost.

Do that for a year or two and then help that owner buy another and you take a cut in the deal maybe in exchange for management. 

e.g. is it possible for someone to lend $100k on a deal in exchange for, say 6% interest rate plus 10% share of profits?

Paying cash is fine, but plan on using that equity to scale up with a cash out refi or 1031 exchange.

If you're not exactly excited about jumping back into the market, there Are passive investments that are eligible for 1031 exchange as well.