Excellent question, and a growing concern in the real estate sales community.
The building and retrofitting of energy efficient features are well ahead of the sales community -- meaning anyone who's thinking of selling their green home with energy efficient improvements should not expect to reap great financial rewards at this time.
Many solar installers reference old Wells Fargo data stating that $1 saved in electricity usage equals $30+ in appraised value. Not true! Value is determined by what a buyer is willing to pay and there's not sufficient data to support that.
As a real estate agent myself, I had to work with my local Realtor association to make many needed changes to our Multi Listing Service (MLS). My MLS, SoCal MLS, has been consolidated and is now owned by six different Realtor associations throughout Southern California. Each association needed to approve the changes so the process is extremely laborious.
Even if these features are added to the MLS, most buyers are using sites like Realtor.com, Zillow.com and Redfin.com to find their homes, and these sites do not list solar and related green features.
It takes great creativity and an established network within the "green" community to reach potential buyers of homes like yours. So your only real chance of potential buyers who are interested in your home's green features is to make sure your Realtor has listed these features in the description copy.
Some unorthodox marketing techniques I use include specific Google AdWords campaigns, creating a web page for each green home listing with details of what's included along with the proper meta tags and descriptions so search engines find it.
You can also try reaching out to any local green building and solar groups to see if they'd like to take a tour of the home. I organize a solar tour through the American Solar Energy Society (ASES) and have had homes on the tour that were for sale.
I also call the listing and selling agent of any home with a solar system to see if having the system played a positive or negative role in the sale. Out of the five or six I've spoken to, only one had a reaction to the solar system and it was negative. The solar held up the insurance policy, which held up the financing for an additional week or so.
Lesson to learn is that you must hire a green real estate agent who is both experienced and has expressed an interest your home's green features. Seek real estate agents who have been certified by EcoBroker, Green (by NAR), or even the USGBC's LEED Green Associate or LEED AP.
Soon we'll have a "miles per gallon" type of efficiency rating for our homes (like the UK already has!), so home buyers are able to make educated decisions when shopping for their next home.