Cheap and dirty: Figure out the savings from one system to the other as (the diff. in annual generation) * (ave. electricity cost you currently pay per kWh). Divide that number into $1,500. Then decide if waiting that long in years for that simple payback is worth it to you.
You can, if you choose, get fancy with process economics, life cycle costing and time value of money methods if the numbers are close or some other reasons, but my guess is unless the annual diff. is > ~ 150 bucks, it ain't worth it. Take part of the $1,500 and get your roof inspected/repaired before install. You'll sleep better when it rains. Honest.
I'd still spend a lot more effort on evaluating vendor quality as a better long term ROI gamble. A roof leak will cost you a lot more than $1,500.
You can, if you choose, get fancy with process economics, life cycle costing and time value of money methods if the numbers are close or some other reasons, but my guess is unless the annual diff. is > ~ 150 bucks, it ain't worth it. Take part of the $1,500 and get your roof inspected/repaired before install. You'll sleep better when it rains. Honest.
I'd still spend a lot more effort on evaluating vendor quality as a better long term ROI gamble. A roof leak will cost you a lot more than $1,500.
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