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Types of Solar Water
Heaters
This page involves types of
Domestic Solar Hot Water Systems.
For other systems, see:
Solar Electricity: Photovoltaic PV Systems
Solar Space Heating basics
Solar Space Heating in
radiators, radiant floor and air forced systems
Solar Cooling
Passive and active solar water
heaters
Solar water heating systems may have circulation pumps or not.
If the system uses a pump to transfer the heat to the storage
tank then it is called a active system.
If the water (or the anti-freeze liquid) in these systems
circulates without the aid of pumps or controls, the system is
called a passive system.

Image Credit:
EERE
Thermosyphon systems
Passive systems – those without pumps - use
thermodynamic forces as the thermosyphon, based
in cold water heavier nature and higher density (relatively to
cold water).
Thermosyphon systems are very popular in hot and
sunny temperate climates, but they are rarely used in countries as the United States,
except in sunnier states as California or Florida.
Direct Solar water heating
systems
Direct solar water heating systems (also known as “open loop”
system) do not use antifreeze solutions: the hot water is directly heated into the collector. The system
circulates pure, potable water (which is commonly stored in a
hot water tank)
Due to the fact that they do not use anti-freeze, these system
shouldn’t be used in cold climates, namely in its simplest
configuration
Batch or bulk storage system
These solar water heater systems are a good example of direct (they do not use
anti-freezing solutions) and also passive systems (they do not
use pumps).
They are very simple systems combining the solar
panel and the storage into one single unit (hence its
technical designation: ICS – Integrated Collector Storage
system).
Since this type of system do not use anti-freeze solutions and
is very simple in its essence, it should only be used in hot
or temperate-hot climates. To avoid strong heat loses during the night, the hot
water generated at the collectors level should be consumed
quickly or transferred into a storage tank before evening.

Image Credit:
EERE
Indirect solar water
heaters
Indirect (or ‘closed loop’) solar water heaters use an
antifreeze solution and a pump to move it through the solar
collector and out of it. After being heated, the antifreeze
solution is driven into a heat-transfer unit where it warms the
water… (the antifreeze solution is continually flowing into and
out of the solar collector without ever mixing with the house’s
water).
This system is the most appropriate in climates with extended
periods of below-zero temperatures. Most of the U.S., except
parts of southern states, need indirect systems.
Which system to choose?
If you need freeze protection or if the water in your region is
an hard type one, choose an active closed loop system with antifreeze
and, obviously, a heat exchanger.
In other climates, you may choose either a simple system (as the
thermosyphon one) or, in case of larger needs, a open loop
direct system with an heat pump and a storage tank.
Solar water heater and non sunny
days
What about the days or periods when there isn’t enough solar
energy to heat the water up to the needed temperatures?
The solution in this case is in an auxiliary heating system to
solve the solar water heater insufficiencies during worst
weather-days. Auxiliary electricity system are easy to
implement, while standard gas water heater may be more
difficult: they will demand a second solar storage tank:
Note:
For a full environmental solution, you may want to implement an auxiliary PV (photovoltaic
solar electric) system. It would be a simple
and cost-effective application of
solar electric
energy.
See also:
Basics of
solar power systems
Domestic Solar Hot Water Systems
Solar Systems Orientation and
Location
Pros and Cons of Solar
Energy Panels
Costs and payback of
Solar Energy
Solar Panels Technology
Quotes and the
buying process
Market and Prices of Solar Hot
Water Systems
Market and Prices of Solar PV
Electricity
Manufacturers of Solar
Power Systems
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