Solar Water Heating Energy Self Assessment
The solar water heating calculator estimates the equipment requirements to meet
50 percent of your hot water energy usage. Reducing your hot water needs before
you consider a solar water heating system will reduce the size and cost of the system
needed. Installing high efficiency water
heaters, insulating hot water pipes whenever possible, repair leaking pipes
and taps, and turning down the temperature on hot water heaters will reduce energy
needs for heating water.
High efficiency water heaters have 90% or greater thermal efficiency and less than
a 1% per hour standby loss resulting in an overall energy factor or efficiency of
73% or higher. High efficiency water heaters are insulated much better than standard
(older) water heaters, keeping the water warmer for longer during periods of non-use.
A typical gas or oil water heater has a thermal efficiency of 80% but a standby
loss of 2.5% per hour resulting in an energy factor of 50 to 55%. Tankless or instantaneous
water heaters, which heat water as its needed, have thermal efficiencies of 80%
or higher and no standby losses because they don’t store any water resulting in
an energy factor of 80% or higher. Electric water heaters have thermal efficiencies
of 100% and, if well insulated, can have a standby loss of 0.75 per hour for an
energy factor of 84%. Note: a water heater’s efficiency or energy factor is one
variable to consider when choosing a water heater. The decision to use gas, oil
or electric, tank or tankless should be based not only on the efficiency, but also
the application, maximum flow rates and energy costs.
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The most economical way to use solar thermal energy is for preheating water before
it enters a water heater rather than 100% replacement. Preheating results in less
energy used by the current water heater. The calculator estimates the surface area
of solar thermal panels required to preheat the water to replace 50% of your water
heating energy use. The calculator evaluates thermal energy use based on user input.
This tool does not provide a site-specific renewable energy assessment. If after
using this tool, you want to take the next step, contact a certified solar site
assessor to do an evaluation of your specific location. Trees, buildings and terrain
can affect the amount of solar energy that can be collected.
Frequently Asked Questions:
How does a solar water heating system work?
Solar energy from the sun is collected by solar collection panels and transferred
to a heat transfer fluid circulating through tubes in the panels. The fluid, typically
an antifreeze, transfers the heat to water in a heat exchanger. The warmed water
is stored in a water tank and is used as preheated supply water for a water heater.
The level of preheating will depend on the type of collection system used, climate
conditions (temperature, solar radiation) and the exposure of the solar collection
panels to direct sunlight. Solar collection panels used for water heating are different
from those used to produce solar electricity.
What sites are suitable for solar collection?
When choosing a site for solar collection, consider sites with minimal tree coverage,
and sites free from shadowing by buildings, hills, or other structures. Solar collection
panels should be kept clear of snow, bird droppings, or other obstructions. Most
dirt is typically removed by rain and melting snow. A knowledgeable solar water
heating contractor can help locate the best site on your property and will provide
information on cleaning the panels or other simple maintenance requirements.
What types of applications are solar water heating systems used for?
Solar water heating can be used wherever there is ample sunlight and a daily demand
for hot water. Typically, the greater the hot water demand, the faster a solar hot
water system will pay for itself. Suitable applications may be residential water
heating, milk house or on-farm dairy water heating, supplying hot water for a retail
farm stand or commercial kitchen area, heating rinse water used to clean harvested
vegetables, or heating water in fish propagation tanks in aquaculture.
What are the components of a solar water heating system?
Solar collectors collect the sun’s energy which is transferred
to a fluid, typically a glycol solution, which runs through a piping system in the
collector. In areas where freezing temperatures seldom occur, water can be heated
directly which eliminates a heat exchanger. If freezing weather is forecasted the
water is drained out of the collectors hence the name “Drain Down System”.
Flat-plate collectors are the most common but
evacuated tube solar collectors are the best option for high temperature
or high volume applications such as a car wash.
Glazed flat-plate collectors are made of an absorber plate set underneath glass
glazing. These panels are insulated along the back, and framed so they can be mounted
at an angle. Heat collected by the absorber plate is trapped below the glass glazing
and retained with insulation along the back panel. These panels can be used in colder
climates and for year-round applications. Unglazed solar panels or collectors are
often used in very warm climates or for seasonal heating such as swimming pools
during the summer.
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Evacuated tube solar collection is done via a solar absorber plate located inside
a sealed glass vacuum tube. A liquid (usually alcohol) inside the heat pipe vaporizes
as heat is transferred from the absorber plate to the heat pipe. The vapor rises
to the top of the evacuated tube where water condenses the liquid as heat is transferred
from the heat pipe to the circulating heat transfer fluid, usually a glycol solution.
As the heat pipe fluid is condensed it flows back down the pipe to repeat the cycled.
Heat transfer fluid is pumped from the collector to a heat exchanger at the storage
tank where the heat is transferred into the water for future use. Evacuated tube
solar collectors have minimal heat loss to the environment, and are recommended
for high heat applications and cold climates.
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Heated fluid circulates between the storage tank and the collector(s)
by natural convection (thermo siphon) or mechanically pumped systems. In an indirect
circulation system, a glycol antifreeze solution is circulated between the solar
panels and a heat exchanger where the heat from the antifreeze is transferred to
water. These systems are used in cold climates with long periods of freezing weather.
In a direct heated system, water is used as the heat transfer fluid and circulated
directly to the solar panels from a storage tank.
Pre-heated water from the storage tank flows into the water heating
unit as hot water exits the water heater for use. A solar water heating system requires
a conventional water heater to heat water that didn’t reach the desired set point
due to lack of solar energy.
A controller manages water temperature
and actuates the circulating pump when solar energy is heating water in the solar
panels.
How much does a solar water heating system cost?
The cost of a solar water heating system will vary according to the application
and size of the system. A typical two-panel (with fifty square feet of collection
area) solar water heating system costs between $5,000 and $6,000. Solar water heating
systems have very good paybacks relative to other small-scale renewable energy systems.
The simple payback on a typical residential system in the Midwest is 5 to 8 years
when replacing propane. Shorter paybacks can be expected for the southern and southwestern
US. Energy cost savings with solar water heating will depend on your hot water demand
and current energy source, but typically range from 50% to 80% depending on location.
An additional system cost is an insulated storage tank for preheated water which
is often sized at the same volume as the water heater. A rule of thumb used for
active solar water heaters is that 1.5 gallons of storage are required for each
square foot of solar collector.
Are there any incentives or tax credits available for solar water heating systems?
The Energy Policy Act of 2008 made tax credits available for solar energy systems
until December 31, 2016.
|
Federal tax incentive (% of installed cost)
|
Residential use
|
30%
|
Business
|
30%
|
Non-profit / Government owned
|
Not eligible
|
Visit www.energystar.gov
to find more information about the federal tax credit currently available for solar
systems. The federal tax credit amount is automatically calculated in the assessment
tool.
Many state and utility programs are available to fund solar energy projects. Contact
your utility company or visit www.dsireusa.org
for possible state incentives available for your solar water heating project.
I am interested in using solar water heating. How do I get started?
Step 1. Determine if there are opportunities for conserving hot water use and turning
down your water heater’s thermostat. This can reduce the size of the solar system
needed and usually has a faster payback than the investment in a solar system.
Step 2. Educate yourself. It is important to understand how a solar water heating
system operates, and how to manage the system.
Step 3. Investigate the type of permitting required in your local area. Your site
may be located in an area with a homeowners association or township laws which govern
solar panel installation. Be aware of any building permits that may be required
for installation.
Step 4. Determine the availability of tax and grant assistance programs, including
their application and payment processes. Some incentive programs may require paperwork
or other steps to take before the system is purchased or installed.
Step 5. Get a site assessment - Consult a professional solar thermal installer to
estimate the potential for solar water heating at your business, farm or residence.
A certified solar professional can be found at the
National American Board of Certified Energy Practitioners.
Step 6. Get quotations from two or three companies. Compare quotes to ensure they
are quoting similar size and type of equipment. Ask questions.
Step 7. Consult with your tax preparer to ensure that you can take advantage of
any state and federal tax credit available.
Step 8. Check with your insurance carrier to see if your proposed solar system is
insurable.
Step 9. Order the system to be installed by a professional solar thermal installer.
Step 10. Once the system is installed, complete all applicable grant or tax incentive
forms.
How can I find a reputable installer of solar water heating systems?
Solar water heating system installers are located throughout the country. You may
have to search your local yellow pages for “solar”, “energy” or “renewable energy
system installers” and the internet is also a great resource. It is recommended
to choose an installer that is North American Board of Certified Energy Practitioners
(NABCEP) certified, or in the process of becoming certified. The Find Solar website,
www.findsolar.com/index.php?page=findacontractor,
hosts a network of professional solar water heating installers. It is a good idea
to get two or three quotes from prospective installers that are based on the same
type of system.