The typical American household uses 10,000 to 15,000 BTUs of hot water per person per day. A 20 vacuum tube solar collector can produce 30,000 BTUs on a summer day with a footprint on a roof of only 36 square feet. The system can provide 100% of summer hot water needs and depending upon regional weather 30% of winter needs.
Larger parallel arrays can be used for hydronic in floor heating and hot tube spas.
You can pay the utility or pay yourself first with direct solar gain hot water heating. And walk a lot more softly on your Earth.
The average American household CO2 emission output is 26,028 lbs / year.
A nominal 1 kW solar DHW system in Detroit, Michigan, can readily produce +2,000 kW / hr /yr. This is a Offset of ~1,500 lbs of carbon.
Solar domestic water heating can greatly reduce carbon dioxide emissions--the cause of global climate change. See this BBC web site for graphic illustrations: