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					                                   Solar Thermal
What is Solar Thermal?
A solar thermal system does not generate electricity like solar photovoltaic panels do;
solar thermal collectors actually generate heat that is used for hot water, radiant heating,
and HVAC heating needs. Residential solar thermal systems are economically a greater
investment. Solar Thermal systems are cheaper than a residential Solar PV system which
will yield greater savings and a quicker return on investment. For commercial or large
solar thermal systems, the scope and cost of the project as well as any available
incentives and tax credits will determine the length of payback & savings. One great
advantage to a large solar thermal system for large applications is the potential to utilize
the sun’s radiation for several significant heating requirements. Heating, cooling, and hot
water are the top three energy consuming items of an electric bill. A great feature of Solar
Thermal systems is the fact that these systems are expandable. You can add onto the
system in the future for solar to provide heating and cooling needs in addition to solar
providing your hot water needs.

Types of Solar Collectors
Evacuated Tubes
Evacuated Tubes are the most efficient thermal collector on the market, and the glass
tubes absorb solar radiation for energy use in water and space heating. The evacuated
tubes are glass tubes manufactured from strengthened borosilicate glass. The tubes have a
double outer layer, and the outer layer is fully transparent to allow solar energy to pass
through unimpeded. The area between the inner and outer layers of the wall is evacuated
and acts as a vacuum. This acts as a thermo-insulator to keep heat from escaping into the
atmosphere. Evacuated heat pipe tubes are designed such that convection and heat loss
are eliminated. In addition, evacuated heat pipe systems are lightweight, easy to install
and require minimal maintenance. Each evacuated tube will produce 1,000 BTU/day on a
bright sunny day. Collectors come with tubes of 10, 20, & 30.

               The 2 images are the Evacuated Tube solar collector design.




esisco@solarwindtek.com                 Eric Sisco                     Cell: 740-837-0649
Flat-Plate
Flat-Plate solar collectors are durable weatherproof boxes which contain a dark absorber
plate located under a transparent cover, and are still the most common type of collector
used for water heating in many countries despite being inferior to evacuated tube
collectors in many ways. Flat plate collectors are the most widely used kind of collector
in the world for domestic solar water heating and solar space heating applications. These
collectors have an operating range from well below 0ºF to around 180ºF, which is
precisely the operating range required for these applications. A heat conducting fluid
(Glycol) passes through pipes located below the absorber plate. As the fluid flows
through the pipes it is heated. Flat plate collectors have a distinct advantage over other
types in that they shed snow and frost very well when installed in climates that
experience cold wintry weather conditions.

There are only a couple differences in efficiency between the two main styles of solar
collectors for hot water and space heating needs. Evacuated tubes are more efficient
regarding the amount of heat loss, especially during the winter when outside temperatures
are colder. Flat-plate collectors can shed snow & ice quicker than the evacuated tube
design. They are equally efficient during the summer months; however, a heat dissipater
is necessary to avoid overheating issues. Basically, it boils down to the type and size of
the system, and what applications (hot water, space heat, heated sidewalks, or a
combination) will be implemented. A decision on which solar collector to use could also
be based on aesthetics and where the solar collectors will be installed at the site.

                  The 2 images are the Flat-Plate solar collector design.




Types of Solar Water Heating Systems
Active Systems
Active systems use electric pumps, valves, and controllers to circulate water or other
heat-transfer fluids through the collectors. They are usually more expensive than passive
systems but generally more efficient. Active systems are often easier to retrofit than
passive systems because their storage tanks do not need to be installed above or close to




esisco@solarwindtek.com                 Eric Sisco                     Cell: 740-837-0649
the collectors. If installed using a PV panel to operate the pump, an active system can
operate even during a power outage.

Closed-Loop Active Systems
Since we are in a region that is prone to freeze conditions, a closed-loop (indirect flow)
design will be implemented. These systems pump heat-transfer fluids (a glycol water
antifreeze mixture) through the solar water heater. Heat exchangers transfer the heat from
the fluid to the water that is stored in tanks. Double-walled heat exchangers or twin coil
solar tanks prevent contamination of household water. Some standards require double
walls when the heat-transfer fluid is anything other than household water. Closed-loop
glycol systems are popular in areas subject to extended subzero temperatures because
they offer good freeze protection. However, glycol antifreeze systems are more expensive
to purchase and install, and the glycol must be checked each year and changed every few
years, depending on glycol quality and system temperatures.

Drainback Systems
Drainback systems use water as the heat-transfer fluid in the collector loop. A pump
circulates the water through the solar water heater. When the pump is turned off, the solar
water heater drains the water, which ensures freeze protection and also allows the system
to turn off, if the water in the storage tank becomes too hot. A problem with drainback
systems is that the solar water heater installation and plumbing must be carefully
positioned to allow complete drainage. The pump must also have sufficient head pressure
to pump the water up to the collector each time the pump starts. Electricity usage is
therefore slightly higher than a sealed closed or open loop, but still a very efficient and
zero maintenance system.

Passive Systems
Passive systems move household water or a heat-transfer fluid through the system
without pumps. Passive systems have the advantage that electricity outage and electric
pump breakdown are not issues. This makes passive systems generally more reliable,
easier to maintain, and possibly longer lasting than active systems. Passive systems are
often less expensive than active systems, but are also generally less efficient due to
slower water flow rates through the system because there is no pump present.

Thermo-Siphon Systems
A thermo-siphon system (Passive design) relies on warm water rising, a phenomenon
known as natural convection, to circulate water through the solar absorber and to the
tank. In this type of installation, the tank must be located above the solar collector. As
water in the collector heats, it becomes lighter and naturally rises into the tank above.
Meanwhile, cooler water in the tank flows downwards into the collector, thus causing
circulation throughout the system. This system is widely used with both flat plate and
evacuated tube collectors. The disadvantages of this design are the poor aesthetics of
having a large tank on the roof and the issues with structural integrity of the roof. Often
the roof must be reinforced to cope with the weight of the tank. This design is also
intended for small hot water applications.




esisco@solarwindtek.com                  Eric Sisco                      Cell: 740-837-0649
In summary, a closed-loop active system will be the best choice and most efficient
system design to meet your large demands for hot water.


Solar Space Heating
The solar collectors that generate heat to provide hot water can also provide heat for
building and home heating needs. In effect, our limited supply of fossil fuel consumption
will be reduced, clean energy will be used to heat the water and buildings, and you will
reduce your electric bills and ultimately save money. A solar space-heating system can
consist of a passive system, an active system, or a combination of both. Passive systems
are typically less costly and less complex than active systems. However, when retrofitting
a building, active systems might be the only option for obtaining solar energy.

Passive Solar Space Heating Systems
Passive solar space heating takes advantage of warmth from the sun through design
features, such as large south-facing windows, and materials in the floors or walls that
absorb warmth during the day and release that warmth at night when it is needed most. A
sunspace or greenhouse is a good example of a passive system for solar space heating.

Active Solar Space Heating Systems
Active solar space-heating systems consist of collectors that collect and absorb solar
radiation combined with electric fans or pumps to transfer and distribute the solar heat.
Active systems also have an energy-storage system to provide heat when the sun is not
shining. The two basic types of active solar space-heating systems use either liquid or air
as the heat-transfer medium in the solar energy collectors.

Radiant Heating
There are two types of radiant heating which all can be supplied by solar radiation.
Electric radiant floors and hydronic radiant systems are the two types of radiant heat.

Electric Radiant Floors
Electric radiant floors typically consist of electric cables built into the floor. Systems that
feature mats of electrically conductive plastic are also available, and are mounted onto
the sub-floor below a floor covering such as tile. Electric radiant floors are usually only
cost-effective if they include a significant thermal mass, such as a thick concrete floor,
and your electric utility company offers time-of-use rates. Time-of-use rates allow you to
"charge" the concrete floor with heat during off-peak hours (approximately 9 p.m. to 6
a.m.). If the floor's thermal mass is large enough, the heat stored in it will keep the house
comfortable for eight to ten hours, without any further electrical input (particularly when
daytime temperatures are significantly warmer than nighttime temperatures). This saves a
considerable number of energy dollars compared to heating at peak electric rates during
the day.

Hydronic Radiant Systems
Hydronic (liquid) systems are the most popular and cost-effective radiant heating systems
for heating-dominated climates. Hydronic radiant floor systems pump heated water from


esisco@solarwindtek.com                   Eric Sisco                      Cell: 740-837-0649
a boiler through tubing laid in a pattern underneath the floor. In some systems, the
temperature in each room is controlled by regulating the flow of hot water through each
tubing loop. This is done by a system of zoning valves or pumps and thermostats. The
cost of installing a hydronic radiant floor varies by location and also depends on the size
of the home, the type of installation, the floor covering, remoteness of the site, and the
cost of labor.

Installation Options
Solar collectors for solar hot water systems can be mounted on the roof at a 45-60 degree
angle. Collectors can also be mounted on the side of a house on the wall or mounted on
the ground. Ideally, solar collectors need to be installed close to the hot water tank to
reduce the length of pipe necessary to run from collector to storage tank.

        Here is an image of a solar collector mounted on the side wall of a home.




During the summer, the solar collectors will produce more heat than is necessary to
provide hot water. A heat dissipater is installed so the heat will be dissipated and that is
included in the cost. However, the excess heat can be transferred to a spa or swimming
pool to reduce the electric necessary to heat the water.




esisco@solarwindtek.com                  Eric Sisco                       Cell: 740-837-0649
                Here is a diagram of a typical solar hot water system.




esisco@solarwindtek.com              Eric Sisco                     Cell: 740-837-0649

				
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