- How does a solar
water heater work?
- What are the components
of a solar domestic water heating system?
- What is the difference
between a passive solar heater and an active one?
- What type of backup
system do I need?
- By what amount
does solar water heating reduce emissions?
- What is the energy
efficiency of a solar water heating system?
- What can I expect
to spend on a solar water heating system?
- What is the annual
operating cost of a solar water heating system?
How
does a solar water heater work?
Water circulates between the solar storage tank and
solar collectors. When a household hot tap is opened, the solar storage
tank releases pre-heated water into the conventional gas, electric
or oil water heater, which only fires its burner or heating element
if the desired temperature cannot be maintained by the solar heater.
What
are the components of a solar domestic water heating system?
A water system is composed of a well-insulated storage
tank, solar collectors, and inlet and outlet systems. In two-tank
systems, the solar water heater preheats water before it enters the
existing gas, electric or oil water heater.
The number and size of the solar panels for your roof
depends on your water usage, as well as collector orientation and
geographic location.
What
is the difference between a passive solar heater and an active one?
Passive Solar Water Heaters
Passive heating systems have no moving parts and use
the sun as the sole external energy source. In a passive solar water
heating system, the storage tank is installed on the roof, often
with structural bracing. A passive solar heater relies on thermosyphon
action instead of a pump. They are a cost-effective and reliable
solar water heating option.
Integral Collector Storage
Systems
Ideal for areas in which temperatures rarely fall
below freezing. The system consists of one or more black 40 gallon
water tanks placed in a well-insulated box that acts as Integral
Collector Storage, or a batch heater. Cold water flows in from the
bottom where glass or plastic helps the tanks capture solar energy.
Using local water pressure, hot water flows out of the top and into
the conventional water heater where your thermostat determines if
the water is already hot enough for use or if additional heat is
necessary.
Thermosyphon systems
Water flows through the system when warm water rises
as cooler water sinks. The collector must be installed below the
storage tank so that warm water will rise into the tank.
What
type of backup system do I need?
A backup system helps compensate for cloudy days and
increased hot water demand. Rooftop tanks with thermosyphon systems
serve as a back-up heating source.
By
what amount does solar water heating reduce emissions?
By reducing natural gas consumption, solar water heating
reduces carbon dioxide emissions by approximately 2,000 lbs per water
heater every year. The system also reduces nitrous oxide emissions
by approximately 1 pound per water heater each year.
What
is the energy efficiency of a solar water heating system?
To calculate the energy efficiency of a solar water
heater, you need the solar energy factor (SEF) and solar fraction
(SF).
The solar energy factor is the system’s energy
output divided by the electrical or gas energy input. The higher the
resulting number, the greater the energy efficiency. Solar energy
factors range from 1.0 to 11, with a common result of 2 or 3.
The solar fraction is the portion of the total conventional
hot water heating load (delivered energy and tank standby losses).
The higher the solar fraction, the greater the solar heating source,
which reduces the energy demand from the backup water heater. The
solar fraction varies from 0 to 1.0 with typical solar factors running
0.5–0.75.
What
can I expect to spend on a solar water heating system?
Solar water heating systems usually cost more to purchase
and install than conventional water heating systems. However, a solar
water heater can usually save you money in the long run.
A typical residential solar water heater with home installation costs
$4,000 and provides over two decades of service. Solar water heaters
can cost as little as $2,500 when installed during new home construction.
During construction or refinancing, you can insert a solar water heater
in a 30-year mortgage for between $13 and $20 per month.
The federal income tax deduction for mortgage interest
attributable to the solar system knocks that down by another $3 to
$5 a month. So if your fuel savings are more than $15 per month, the
solar investment is profitable immediately. On a monthly basis, you're
saving more than you're paying.
Solar water heaters operate with a fixed cost following installation.
Free solar energy exempts you from fuel shortages or price hikes.
Solar water heater installation typically results in
a 50 to 80% reduction in water heating bills.
Factors in solar hot
water pricing
• hot water usage
• geographic location, sun exposure
• conventional fuel cost (natural gas, oil, and electricity)
• cost of fuel for backup water heating system
What
is the annual operating cost of a solar water heating system?
To calculate the operating costs, determine the system’s
solar energy factor (SEF), the fuel type of your auxiliary tank (gas,
electric, oil) and local utility costs.
With a gas auxiliary tank
system:
You need to know the unit cost of fuel by Btu (British
thermal unit) or therm. (1 therm = 100,000 Btu)
365 × 41,045/SEF × Fuel Cost (Btu) = estimated
annual cost of operation
OR
365 × 0.4105/SEF × Fuel Cost (therm) = estimated annual
operating cost
Example: If the SEF is 1.1 and the gas costs $1.10/therm
365 × 0.4105/1.1 × $1.10 = $149.83
With an electric auxiliary
tank system:
Convert the unit cost of electricity by kilowatt-hour
(kWh).
