Solar Hot Water Basics

Posted by admin | | Sunday 15 February 2009 8:47 pm

Solar Thermal Hot Water

The Basics:
Solar Hot Water Heating uses basic principles and components to capture incoming solar radiation (sunlight) and transfer that heat to water – providing the hot water needed for domestic, commercial, industrial, and other uses.  Solar Hot Water Heating Systems have been around decades, and over the years, a number of different, upgraded products have come along for the needs of an industry that is ever-growing and evolving.

This section is intended for you to review the basic principles, systems, and components that go into making Solar Hot Water Heating a viable alternative of the future – and the present.


Solar Hot Water Systems Types:
Closed-Loop – Glycol System
Closed Loop Solar Hot Water Systems use a heat-transfer fluid (typically a water and glycol (anti-freeze) mixture to capture heat and a heat exchanger to transfer the heat thermally to household water.  Active Closed Loop Systems use electric pumps, valves, and controllers to circulate the heat-transfer fluid through the collectors.  The water-glycol mixture makes these systems particularly useful in areas that are prone to freezing conditions throughout the year – such as middle and northern states.

Closed Loop – Drainback System
Drainback Systems use water (and only water) as the heat transfer fluid within the collector loop.  A pump forces the water through the collectors, and then, as they are nearing the end of the loop, gravity is used to drain the water to the storage tank and heat exchanger below.  There are no valves in a Drainback System, and when the pumps are shut off, the collectors are emptied of all water/mix, which eliminates any potential freezing problem, and allows for auto-shut off if the storage tank becomes too hot.

Open Loop- Thermosyphon
Open Loop systems use no heat transfer fluid within the lines  – the potable water is run directly through the collectors heat exchanger on its way to the inside of the house for use.  There is a glycol water mix within the panels and on one side of the heat exchanger.


There are a few important, large components of any Solar Hot Water Heating System.  These components include:  Collectors, Storage Tanks, Piping, Controls, and Pumps (not necessary).  Active Systems use pumps to circulate the water, or heat-transfer liquid, through the collector loop, while a Passive System relies on gravity or natural convection, not pumps, to move the fluid.                                                                                                                           solar_collector_detail

There are a couple of different types of Solar Collectors for hot water heating available commercially today.  There are Flat Plate Collectors (the most common type) and Evacuated Tube Solar Collectors (quickly becoming more and more popular – especially in colder climates).  Flat plate collectors are made of an insulated, weather-proof box which holds a black absorber plate, and metal (copper) tubing which carries transfer fluid through the box in an S-Pattern, heating it along the way.  Evacuated tubes use vacuum sealed tubes to heat a copper heat pipe, which is used to heat the transfer fluid as it travels through a manifold at the top of the solar collector.

Like most hot water systems, many Solar Hot Water Heating Systems require a well-insulated storage tank.  Many in use today have a converted electric storage tank, or have a new, solar-designed tank in series with the traditional electric storage tank.  Additionally, many of today’s storage tanks come with internal heat exchangers built right into the tank, eliminating the need for an external heat exchanger with the system.

Controls and Circulator
Solar Hot Water Heating Systems are generally controlled and monitored by a differential temperature controller.  The temperature is generally measured at the solar collector outlet, and at the storage tank.  When the collectors are warmer than the tank, the controller will turn on the circulator and cycles the heat-transfer fluid though the collectors and the heat exchanger in, or next to, the storage tank.

Heat Exchangers
The heat exchanger is a Solar Hot Water Heating System that is used to transfer the heat from the heat-transfer fluid to the potable water that is used within the home water supply.  The Heat Exchanger is no more than a coil of copper pipes submerged in the storage tank, or in an adjacent compartment externally.

If you have any additional questions about the basics of Solar Hot Water Heating Systems, or about where to begin purchasing and installing a new Solar System, please feel to Contact Us any time.