Solar water heating systems can be either active or passive, but the most common are active systems.  Active systems use pumps while passive solar systems run on gravity or thermosiphon.   Northern Lights Solar Solutions designs application based around active systems closed loop with pumps and and digital controllers designed specifically for the solar industry.

Solar water heating systems can do more than just heat your hot water.  With modern day vacuum tubes, solar thermal heating can be used in many more applications.  Home heating, space heating, solar air conditioning, and commercial solar heating are just some of the areas where solar thermal energy applications are being applied.  

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 Active Indirect-circulation (closed loop) uses a heat-transfer fluid (water or a diluted antifreeze fluid) to collect heat and a heat exchanger to transfer the heat to the potable water indirectly.  Heat exchangers transfer the heat from the heated fluid to the potable water (or other fluid). Some indirect systems have "overheat protection" by-pass which removes the heat that cannot be used.  This protects the collector and the glycol fluid from becoming super-heated when the load is low and the solar intensity of incoming solar radiation is high. The heat transfer fluid is usually a glycol-water mixture with the glycol concentration depending on the expected minimum temperature. The glycol is usually food-grade Propylene glycol because it is non-toxic. This system is typically used in hot water heating and radiator or in floor home/commercial heating.  Because the system is closed to the atmosphere, pressure can build up as the temperature rises.  Such systems will incorporate pressure relief valves and solar expansion tanks for safety purposes         

Active Direct-circulation (open loop systems) use pumps to circulate potable water through the collectors. These systems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. These systems may require a recirculation freeze protection (circulating warm tank water during freeze conditions) and this in return requires electrical power for the protection to be effective. An open loop system operates at atmospheric pressure. A pool uses this method as it is generally not operated in freezing months.  In an open loop system the usable hot water is directly circulated through the heating system.

Passive solar water heaters systems move household water or a heat-transfer fluid through the system without pumps.  They rely on gravity and the tendency for water to naturally circulate as it is heated (warm water is lighter and rises). Because they contain no electrical components, passive systems though simpler, have very minimal control for home use. Passive storage systems consist of one or more storage tanks placed in an insulated box with a glazed side facing the sun. These solar collectors are suited for areas where temperatures rarely go below freezing. They are also good in households with significant daytime and evening hot-water needs; but they do not work well in households with predominantly morning draws because they lose most of the collected energy overnight.