Continuing in my series on solar
power basics, in this article we'll take a look at solar hot water - the
benefits of heating water via the sun, how it works and the costs involved.
Solar hot water benefits
One of the most energy intensive (and therefore costly) processes in any
house is the heating of water. Heating water accounts for more than 20% of
residential energy use in the USA and around 40% of energy used in Australian
homes.
This represents not only a massive chunk of your power bill, but also a
substantial proportion of carbon dioxide emissions. A solar hot water system,
over a period of time, will save you money and lessen your environmental impact.
Solar hot water equipment types
There's two main types of solar hot water systems
Passive: A passive system consists of a tank for
hot water storage, a solar collector, piping and frame. The entire system is
mounted on the roof. Water heated by the panel flows upward naturally and then
is gravity fed into the house.
Active: An electric pump is used to circulate the
fluid through the panel collector, meaning that the tank does not need to be on
the roof. The advantages of an active system include:
a) can be easier to get local government approval
b) less weight and strain on the roof
c) doesn't require major roof modifications
d) more aesthetically pleasing design
Solar collectors
The solar collector is the business end of a system, heating the water and
many advancements have been made in solar collector technology in recent years
to improve performance. The most common types of solar collectors:
Flat plate
A flat plate collector is the traditional type and consists of an insulated box
containing a black sheet of metal with embedded pipes. The heat is absorbed by
the sheet and transferred to the water in the pipes.
Evacuated Tube
An evacuated (or vacuum) tube collector consists of glass tubes with a layer of
heat absorbent coating through which water pipes run. As the tubes encasing the
water pipes are a vacuum, this reduces heat loss; making them more efficient
than flat plate collectors; so these are particularly suited to colder climates.
While evacuated tube systems are a little more expensive than flat plate, their
increased efficiency (up to 97% thermal energy retention) more than makes up for
the added cost.
Heat pumps
Heat pumps are a form of solar hot water technology that don't use any sort
of collector. Heat pumps use heat in the air to raise water temperature - even
in freezing conditions down to -10 Celsius (14F). A heat pump is like a
refrigerator, but in reverse. I've spoken to a few people who have these units,
and even in the depths of winter they've had no problems with a steady supply of
hot water.
Evacuated tube solar hot water system
Image courtesy Energy Matters Australia - solar
hot water specialists
What about when it's cloudy?
While a solar hot water system can still warm water on cloudy days; if the
cloud is too heavy for too long, the effectiveness of a flat plat system and to
a lesser degree, evacuated tubes, is greatly reduced. For this reason, many
solar hot water systems also come with an electricity or gas assisted system
whereby if the temperature falls below certain point, the backup system
automatically kicks in to maintain the desired temperature.
What about the equipment's environmental footprint?
Renewable energy naysayers are quick to point out that the production of
renewable energy equipment is an energy intensive process. This is quite true,
however, given the equipment is designed to last a very long time, the amount of
energy required to create the components is more than offset by the amount of
energy it saves.
While it varies with the type of system and location where it is used, a flat
plate passive system energy payback time can be as little as 18 months. A solar
hot water system can also save up to 4.5 tons of greenhouse gas emissions
annually!
How much does solar hot water cost?
Again, it depends on the type of system, but for a family of 4, expect to pay
anywhere from $3,500 for an evacuated tube system to $4,000 for an evacuated
tube system with electricity assist. In addition, you're looking at between
$1200 - $1600 to have it professionally installed. It's a lot to outlay, but
there's ways to cut costs substantially.
You can buy retrofit kits that can decrease the price by around a thousand
dollars. The cost can also be dramatically decreased by taking advantage of renewable
energy rebates that many governments offer. In some cases, rebates can be so
generous they'll reduce the price of a solar hot water system to make it
comparable with traditional hot water services.
Solar hot water payback time
To calculate an approximate payback time, deduct any applicable rebates and
then take a look at your current electricity or gas bill. If you're in the USA,
calculate 20% of the bill as being attributable to hot water, or if you're in
Australia, take 40%, then divide the residual cost of the system by that figure.
This will give you an approximation of how many months or quarters it will take
to reach a stage that the system has paid for itself - after that, it's
basically free hot water heating up to around 25 years, when the system will
likely need to be replaced.
A viable, green alternative
Solar hot water systems have been around for many years and are certainly not
just a gimmick for hippies. The copious amounts of energy consumed in heating
water has seen some governments make their installation compulsory. For example,
Hawaii now requires all new homes to install solar hot water systems and in
Israel, 90% of homes have solar water heaters installed.
By the way, if you want to experience solar hot water for under 10 bucks, try
a solar
shower bag - I use one when I'm roughing it :). If you're interested in
learning more about other solar and wind power energy options, check out some of
the articles listed below.
