There are published studies (I was involved with one) that shows a net-positive impact on value for owned PV systems & energy-efficient homes. However, that positive impact is significantly dependent on the particular market as well as a number of other factors. And, it isn't as big as many would think (2-5%, and 5% is at the very top of the range; 2-3% is more around the middle). I wouldn't rely on those studies of general market data to conclude what impact on value, if any, might apply to your property.
Most of the studies show that to reasonably value such systems/performance, it takes more work than what a standard mortgage-appraisal is usually expected to do. One advantage you have is if this is for PMI removal, presumably, the appraiser is not under a tight deadline (and, therefore, has enough time to adequately analyze the component).
The preferred method for valuing these systems is direct comparables (sales of homes with other systems). All appraisers are familiar with that process.
Another acceptable, but less employed, method is to analyze the savings of the system over a reasonable holding period. The analysis is too complicated to go into detail here, but when I do it*, it effectively considers:
A. How much money you are saving on your utility bills due to the system.
B. How old/how efficient the system is.
C. A reasonable holding period (even though you don't intend on selling the house now, that doesn't matter to me).
D. Maintenance costs. Some appraisers, depending on the age of the system, might include a removal/demolition cost.
E. How much the system is expected to degrade (become more inefficient) over the holding time; this impacts how much money you will save going forward.
F. Discount the above by a reasonable rate.
The result is a net present value based on the savings on the occupancy costs of the home. In theory, if it costs less to occupy a home, then it is worth more than the one next door where it costs more.
*(there are some variations of the above, and some analyses forecast out to the useful life of the system which may be longer than the typical holding period)
What isn't considered in the above is:
1. How much the system cost (that doesn't matter; a rational buyer will only consider what they can anticipate saving going forward).
2. Any rebate/net income you may receive due to selling the energy back to the utility company. That simply is too uncertain, and can change at any time.
If a 2-3% difference in value is the tipping point for your PMI removal, then what I would recommend is that you ensure the appraiser who appraises the home for PMI removal have some experience in appraising homes with such systems.
Just be prepared to see that, based on the analysis, there is little or no impact on value.
Good luck!
