Solar e-Clips - What's new in 2002 for Solar Water Heating?

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What's new in 2002 for Solar Water Heating?
source: William T. Guiney Solar Access 2002.2.5

Americans who are choosing to reduce energy use in their homes and
businesses or do their part in reducing emissions and improving air quality
in their communities. And now people are seeing solar water heating as an
element in assuring energy security for themselves and the country.

I'd like to ask you to take a look at solar energy honestly and objectively. It is clear
that solar water heating applications contribute more to reducing emissions
and saving energy than any other solar technology. When the costs of solar water
heating are compared to photovoltaics (PV), it doesn't take a rocket scientist to
conclude that solar water heating at $1.50-$2.50 per watt is a far better investment than PV at $6.00- $10.00 per
watt. Even when you consider the subsidies and buy-downs offered for PV
systems, more then 9 times out of 10, solar water heating will still be more
cost-effective and contribute more to reducing energy consumption and
improving air quality.

What's changed? Well, for the most part, a lot has changed in the solar
water heating industry starting with the development of better systems,
certified installers, lower prices and proven performance. Many new system
sales today are to repeat customers installing systems on their new
homes. After 15 to 20 years of field experience by those lucky enough to
have had solar water heating systems installed during the heydays of the
80's, they know the value and performance They know that solar works!

For many years, we have heard that the biggest problem facing the solar water
heating industry was the high up-front cost for solar water heaters. But when you
consider the real economics when compared to conventional gas or electric
water heaters and the associated paybacks of PV, solar thermal water
heating should be a real bargain. I think
the biggest problem for the solar water heating industry is still transparency
of the industry. To most homebuyers, those interested in solar technologies
and folks replacing old or leaking conventional gas and electric water
heaters, solar thermal is just not presented as an option. Water heating is
not the first thing folks think about when they hear the words "solar energy."
Most think solar energy is limited to photovoltaics. They really just don't
know the difference between the technologies. It is generally the same for
pool heating, water heating and photovoltaics. All of them get the solar label,
but with very little explanation. This is also the biggest problem with the
electric utility companies, the regulatory agencies and Congress. They just
don't know the difference.

You've heard this before: Solar is solar. It costs too much and takes a roof
full of equipment to do the job and it is not reliable. But I'm sure you agree
that every one of these ideas is false.

The problem is more flash than cash. As I have heard many times, "PV is
cool" and we all know Americans buy cool. Consumers are asking for PV so
many homebuilders around the country are now offering PV systems as
options or standard features in new homes that still have energy guzzling
conventional gas and electric water heaters.

There are only four terms you need to understand: direct, indirect, passive,
and active. I'll take each of these terms and make it real simple for you. The
easiest terms to understand are active and passive.

If a solar water heating system has a circulation pump to transfer heat from
the collector to the solar storage tank, it is an active system. If the system
has no pump or control system to transfer the heat to the storage tank, it is a
passive system.

Passive systems use natural forces like thermosyphon (cold water is dense
and heavier then hot water) or batch/bulk storage. Thermosyphon action is
where the cold water forces the hot water out of the collector into a storage
tank located above the collector. The tank can be located on the roof or in
the attic, maintaining the low profile of the solar water heating systems
appearance on the roof. Thermosyphon systems are the most popular
system design used outside of the United States. Travel anywhere in the
Caribbean, Middle East, Mediterranean, Australia or Asia and you'll see the
common thermosyphon system. These are all areas where solar water
heating has been long considered the only option for heating domestic hot
water in homes and small businesses like restaurants and hotels.
Americans have a problem seeing the tank on the roof so the solar water
heating industry has developed and is working on systems that install the
storage tanks into the attics or located on areas of the roof not visible from
the front of the house.

The simplest solar water heater is the batch or bulk storage system that
combines the solar collector and the storage into one unit. These systems
have integrated collector storage (ICS) and have a higher profile on the roof
or are set down into the roof to conceal the size of the system. These
systems should only be used in the warmest climates due to their
associated heat loses at night, heat losses are especially high in areas
with cool clear nights like the desert that will allow heat stored in the system
to reradiate back to the sky. The hot water generated by ICS systems should
be used during the afternoon and evenings so the stored hot water is
consumed or transferred into a separate storage tank in the house before
dark.

Direct solar systems heat the water that is consumed or stored in the water
heater. If the water from the storage tank or water-heater is heated in the
solar collector, it is a direct system. Active and passive systems including all
of the ICS systems are or can be direct solar water heaters. Direct systems
should be limited to warm climates or those areas that experience only a
couple of freezing days per year. They are intended to be located in areas
that have occasional freezes in the winter, not sustained days or long, clear
nights below 40 degrees Fahrenheit.

The choice of a solar water heating system is quite simple. The most
important factor is the climate where the system is to be installed. If you live
anywhere that experiences regular seasonal freezing weather, you need to
have an indirect system. Most of the U.S., except parts of Florida and
California, need indirect systems. Indirect solar water heating systems have
a heat exchanger in them to transfer the heat energy from the collector to the
water heater. Heat transfer fluid if left in the solar collectors during freezing
conditions will damage the collector unless it is protected with anti-freeze.
That is not to say all indirect systems use antifreeze. Some systems have a
drain-back design that allows all the heat exchange fluid to drain out of the
solar collector into a reservoir when the pump stops circulating. Pumps
should not run at night, only during the day when there is heat in the solar
collector.

What about days when it's overcast or there isn't enough seasonal sun to
heat the water up to the desired temperature? This is something very
important you need to think about. What is the typical water heating option in
the area? Electricity, natural gas, LPG or propane -- all of the conventional
water heating systems -- can be used as the back-up heating fuel. Electricity
is the easiest; most solar storage tanks have an electric element that heats
only a portion of the storage tank when necessary to increase the
temperature for delivery into the house.

If you use gas, other then a demand heater, you must use a two-tank
system. One tank for the solar heated water and the other a standard gas
water heater. Because a typical gas water-heater has the burner located at
the bottom of the tank, whenever hot water is used in the house, cold water
entering the tank turns the burner on and it heat the whole tank. To use a
solar system with gas as a back up, you must have a separate solar
storage tank that has the connection for cold water entering the system. The
solar storage tank will supply preheated water to the typical gas back-up
heater. This way the gas burner will only run when necessary to boost the
temperature of the preheated water for delivery into the house.

Many active solar water-heating systems use a photovoltaic module to
generate the electricity to run the pump. This is one of the better uses for PV;
the current generated by the PV panel controls the speed of the pump that
has a direct relationship to the amount of heat energy being generated by
the solar thermal collector. Consumers can have PV, along with a solar
water heater. Now that is really "cool." Water Pumping is one of the most
cost-effective PV applications.

The development of home energy ratings programs, the EPA EnergyStar
Homes TM
Program and some hard-working folks in Washington state energy offices
including Florida, Illinois, California and North Carolina to name a few, are
helping to transform the way homebuilders look at water heating options
and energy improvements in new homes. City of Chicago and their partners
to develop a solar industry and create job opportunities in solar energy;
other renewables and the environment are developing the latest
opportunities.

The 35% tax credit for solar water heating in North Carolina, the SunBuilt TM
Program in Florida and isolated utility programs are giving the solar water
heating industry an opening into what has been considered a closed
market. Homebuilders are now learning the advantages of incorporating
solar water heating systems into new homes. The renewable portfolio
standards in some states will allow solar water heating to demonstrate the
reliability and performance of today's systems and offer real savings to
buyers and lower risks for contractors and financers.

Consumers have shown that if given the opportunity, they will choose a
solar water heating system. Granted, not all homes are ideally solar-ready,
just as many homes don't have golf course frontage, many homes in the
development only have golf views. Working with a solar contractor to identify
the subdivision lots with good orientation and the models that are
aesthetically pleasing with the new skylight-styled solar water heating
systems can simplify the sales process and narrow the options for the
builder and consumer.

When Congress gets back to work, they may pass a national energy bill
sometime in the first couple of months of the 2002. Most of those in the
know expect there will be new opportunities for solar water heating and
energy efficiency. Combining tax credits for the builders of energy-efficient
homes and credits for the purchase of solar water heating systems could
increase demand nationally. I would imagine a few firms have a couple of
new designs waiting for the right market opportunities. A solar water heating
system may cost $2,000-$4,000 or more now, but maybe that
long-awaited$1,000- $1,500 system is out there on the drawing boards of a
couple of engineers. Maybe someone is even building it right now. Have you
checked it out lately?

Author Access
Bill Guiney is the Manager of the Water Heating Division at Duke Solar
Energy LLC in Raleigh, North Carolina