If you do finance be extra careful of liens or a UCC (fixture filing usually) against either the panels themselves or your home with a secured loan.
@ArizonaJon's suggestion is good but I've seen stupid/bad/etc loan programs that don't allow you to pay off panels early which can really put you in a bind as you look to sell as encumbered properties are extremely challenging to purchase. Lease programs sometimes have these issues as well, especially with early termination clauses which makes assuming the lease something the buyer would have to take on, decreasing the selling price.
@wjgjr's advice about the HELOC or cash-out refi on a primary mortgage is much cleaner in this sense but can be more expensive up front with both fees and hassle, especially on a primary refi.
If you ask me personally? Go cash and avoid all of the headache entirely.