This conversation will soon change
Firstly, a number of companies are now offering a simple lease of the equipment (no up-front cost, no maintenance). The only thing one needs to consider is the lease cost in comparison to one's dollar savings for a particular area (which is still an undertaking, but makes the entire solution and decision less problematic). I understand that when the home is sold the new owner can choose to retain the system, replace it or have it removed as the solar installation is the property of the lessor and they will take it.
Secondly, we all know its coming, well most of us. In perhaps as little as 1 year or 2 years we will be seeing fuel prices skyrocketing as many countries now, including China and India and the US are all in an up-cycle. As liquid and gas petroleum skyrockets, so will the cost of coal, although perhaps somewhat slower. Coal is our primary electricity generator, in most of the world. Gas electric plants may be converted to coal to reduce costs. A new generation of coal home furnaces could even make a reappearance (gasp!)
However, out of this energy frenzy, the solar equation will no longer be looked at in present terms but rather as a hedge against a very uncertain energy pricing future which will be scaring the crap out of everyone.
Just as the stock market trades on the rumor and future events anticipated and even uncertainty, when faced with the next wave of skyrocketing fuel prices, there will be for the first time, a massive exodus to solar and other alternative energy simply due to UNCERTAINTY- regardless of whether it makes sense financially or not, since people at this time will finally have lost their trust in future energy prices.
Appraisers will be confronting this issue soon.
What is the VALUE given a particular property by the market to "HEDGE AGAINST UNCERTAINTY"! That may be the primary component of the value, although a clear financial incentive in terms of then present day savings shouldn't be far behind, if at all. We will need to look at pair sales, certainly.
The one thing that disturbs me about the Solar Equation is that it is just like any other piece of technology in our home. While homeowners as of the effective date may value the solar panels in a particular market in a particular way, it would only take a significant advancement or breakthrough in efficiency or appeal, etc., to wipe out that value the next day. So it will be a very dynamic and changing problem to solve. Maybe homeowner's insurance and even lenders will require the purchase of a rider to insure against obsolescence of the solar installation due to such advances to replace the system in such event to preserve its contributory value.
We will likely be getting our panels and most other alternative energy from China, since they can invest in technology without there being a financial incentive that is immediate. They are forward thinking and they plan for the future. Capitalism plans for the present - it is our weakness and it should be recognized. Governments should take this role and look to the greater good, but making unpopular or non-financial investments are not popular here. We have made some investments, but they pale in comparison.