The market appeal of this type of real estate development is two-fold. The first is aiming for people who pride themselves on being eco-conscious; the second is a bet on rising energy prices. The thought is that the premium for getting a solar home, when the materials are purchased for an entire solar community, is much lower due to economies of scale, and the promised reductions in energy usage (including reverse metering, where photovoltaic systems sell electricity back to the grid) will more than offset the premium within a given period of time. Given the price of oil (used for fuel oil consumption) and gradually increasing prices for coal, this isn't a far-fetched gamble.
From your perspective, as an investor in a real estate development, the appeal of a solar community is ease of construction. Where solar panels on the rooftops of homes used to be a very "do it yourself" sort of project for an individual home owner, most solar communities are build from modular pre-fabricated assemblies, including all their special energy saving features, like the aforementioned rooftop solar panels and the shared solar thermal systems. In addition to these features, high R-rating insulation is common, as are optically coated windows that block IR light coming in without reducing (much) of the visible spectrum light, and energy star appliances.
When they're being built, the pre-fabricated nature of the modules used in building solar communities increases the cost a small amount (since you're shipping completed subsystems to the site, rather than raw materials), but most of that cost is offset in reduced waste disposal fees, and reduced construction time. (Indeed, in California, where labor prices for construction work are traditionally high, these offsets are more than the surcharge for the prefabricated modules). The secondary benefit is economy of scale; by purchasing solar panels and the requisite insulation and coated windows on a "per community" level, you're getting large enough orders to drive prices down. This drops the surcharge for a solar-friendly/green friendly solar home to under $20,000 for an 1800 square foot home, and to less than $30,000 for a 3,000 square foot home, and translates into a home that's easier to sell in this market.
There are several types plans for solar communities, ranging from single-family homes as part of two or three streets in a real estate development, to units sharing centralized resources. One real estate development with units sharing centralized resources is a 20 home subdivision in Okotoks, Alberta, which routes all the passive solar heating into a central energy station, where it's redistributed to homes in the subdivision. The solar-thermal system is complemented by rooftop solar panels, and several improvements to keep the 52 homes in the community energy efficient; it's estimated that over 90% of the energy needed to heat the homes in Calgary will come from the joint solar venture.
In contrast to this, is the real estate development of a solar community at Clear Lake, California. Unlike Calgary, where the dominant energy expense is heating in the wintertime, Clear Lake's development modus is built around reducing day-to-day electrical usage. Average solar home prices in Clear Lake run under $220,000, as compared to the non-solar models in adjacent developments at $200,000. The community of over 80 homes includes three models, with floor plans ranging from 1800 square feet to 3150 square feet. As with all of the green housing efforts, the aim is to cut back on energy usage, and a premium is set on good insulation and coated windows. Because the main driver in electrical usage in California is daytime cooling, Clear Lake homes can reduce total utility bills by up to 70%, with negative utility bills (where the utility provides a credit against future bills) happening in the height of the summer. It's estimated that an average home owner will save over $120 per month; or $1500 per year, meaning that the premium for a solar home will pay for itself in just under 15 years of reduced utility bills.
Making your investment in solar communities is an interesting gamble in real estate developments. Before committing to this, you should take a look at the development tract you're buying, and look for details like altitude (higher altitude is better) and sight lines to the southern horizon (good for passive solar thermal systems.) You should also do research in systems providers for the components, like solar panel providers, and whether or not you want to go into pre-fabricated construction homes, which offer a trade off in limited floor plan availability.
As homes in solar communities are, ultimately, a premium upsell in a down market, they're worth considering as an investment. Your solar systems can give you an edge in finding buyers for your homes when compared to more conventional competing properties.