Solar Ready means chase runs for installation of wiring and plumbing between the solar panels (hot water and/or PV) and related equipment (inverter and/or hot water tank). Often this is a chase between the attic and the basement, making to easy installation of solar equipment. An optional step could be to add permanant roof anchors pre-installed or even pre-installed roof stand offs for racking. The cost to the builder is very minimal, but the benefits are potentially huge. Solar equipment (SDHW, PV or both) can be installed in the new construction, because it is designed in and can be included in the mortgage financing. If installation comes in later years, it is simplified because the chase makes it easy to run wiring and plumbing needed.
Here is a link to more Solar Ready Home information for builders.