You have a few options when it comes to solar hot water heating in this Mid-Atlantic region. One of the more common approaches is to use a flat plate collector array or and evacuated tube collector array. Both of these systems need space on your roof. Typically for a 2500 SF home it requires about 60 – 80 SF of south facing roof area. This is premium real estate especially if you have already installed a PV solar array or plan to do so in the future.
There is a new product that we have used called Sun Drum that actually mounts to the back of a solar PV panel and uses the existing housing to heat water. It is actually a very ingenious product and we look forward to seeing the results once the system we installed is live. The hot water panel is only about ¼” thick and six of the panels make up and array that will service a family of 4-5 people. Using an existing mounting system is one advantage but another more important selling point to the Sun Drum is it actually helps the PV panels perform more effectively. As a PV panel heats up thermally, the efficiency of the panel goes down, but with the addition of the Sun Drum the heat is pulled away from the panels making it work more effectively. In our specific system, we installed a Rinnai on the back side of the hot water tank so the cold water inlet is tempered water from the solar collector. On days where the sun is shining bright, the Rinnai will not even come on but on days in the winter or days where cloud cover is prevalent, the tankless hot water unit will make up the difference between the actual water temperature and the set point. Learn more about Sun Drum at www.sundrumsolar.com.