Understanding cash vs loan vs lease ROI
Why cash purchase typically wins on pure ROI
Paying cash upfront avoids interest costs entirely, so every dollar of savings goes directly toward recovering the initial investment rather than partially offsetting a loan's interest expense. This structural advantage means cash purchase almost always shows the highest ROI of the three paths, assuming the buyer has the capital available and isn't giving up a higher-return use of that same cash elsewhere.
Why loans still make sense despite a lower ROI number
A loan-financed system still typically shows positive ROI, just reduced by the interest cost, checked in detail by the total interest paid calculator, baked into the monthly payment, and it allows someone without the full cash amount available to still capture most of the financial benefit. The tradeoff is a lower percentage return in exchange for a much smaller upfront cash requirement, which is often the deciding factor for many households regardless of the ROI comparison itself.
Why leases often show negative ROI in this framing
A solar lease is typically structured so the leasing company retains system ownership, the tax credit benefit, and guarantees itself a profit margin through the payment structure, regardless of how the underlying system actually performs. This means a direct ROI comparison usually favors ownership paths, though leases can still appeal to people who specifically want no upfront cost, no maintenance responsibility, and no ownership risk, priorities this calculator doesn't capture in a pure ROI number.
What degradation does to the numbers over time
Solar panels lose a small amount of output capacity each year, typically 0.3 to 0.7% for modern panels per NREL field research, which means annual savings gradually decline rather than staying perfectly flat across the comparison horizon. This calculator applies that degradation consistently across all three financing paths, so it doesn't change which option wins, but it does make the numbers more realistic than assuming flat savings forever.
Building on this result
If cash purchase isn't feasible, compare the loan option against the financing calculator's monthly cash flow view for a more detailed month-by-month picture, or check the 10-year savings projection for a longer time horizon than shown here. To round this out, the ROI percentage calculator covers the remaining piece.