Solar is simple. In many businesses solar water heaters will work much like a residential system, just bigger on most occasions.
In California most businesses will benefit from an "Active" or "Open Loop" solar water heating system. This means that cold water is pulled out of your tank and passed through your solar panel on your roof and is heated and pushed back into your tank.
In commercial solar water heating systems the pump is typically operated on a thermostatic differential control. The distances and heights are normally larger than on residential systems, so AC powered pumps are more suitable for these applications.
Solar heated water can reach scalding temperatures many businesses will require mixing valves in order to send the correct code temperature water for domestic usage like washing hands in sinks and much higher temperatures for laundry rooms and dish washing machines. This makes it feasible for commercial buildings to have a single solar heating system with multiple uses for the water. Just like with regular fossil fuel.