Solar Water Heaters required in Hawaii

Solar water heaters required in new Hawaii homes from the Houston Chronicle starting in 2010 and add $5000 to the cost. The payback period is about 3-5 years. For new houses construction, I am surprised adds that much to the cost. Hawaii is the first state to mandate solar water heating. I expect more states where it makes sense (South West US) to mandate it. Currently there is $2500 rebate for solar water heating installations in Hawaii. Some of the horse trading that went on to get it - House uses strong-arm tactics on solar mandate