Solar hot water systems without pumps and controls could really make installing and using the sun to heat water much more simple. Sunnovations has developed a new product using a passive geyser pump that generates pumping action using just the heat of the sun. This is a closed pressurized system to regulates its own flow rate and automatically shuts down when temperatures get too hot. Would love to try this system out here in Montana when it becomes available and hope that their real world testing goes well. Check them out and I will let you know when the product becomes available.