Don't wait for cheap solar cells - there are effective ways to use solar energy today.
by Skip Fralick, P.E.
et us pay due respect for the en- ergy benefits provided
by the sun. Electromagnetic energy from the sun provides the life force
for our earth. Without it, our planet would quickly assume room temperature
that is, the cold "room temperature" of outer space! Amory Lovins,
energy guru and founder of the Rocky Mountain Institute (www.rmi.org), said
the best energy source is a nuclear power plant located 93 million miles
away. How true!
Solar energy comes in many forms. The forms
most commonly thought of as "solar" are thermal, thermal electric,
photovoltaic, wind, hydro, and biomass. In all of these, solar energy plays
an important function.
This article will discuss solar thermal energy,
for which Southern California is the best location in the nation. Indirect
solar energy sources wind, hydro, and biomass are not as available here,
except that modern wind generators can be cost effective at sites with less
wind than previously thought (most wind generator designs need an average
wind speed of at least 12mph to be cost effective).
The most common application of solar technology
in San Diego is heating water for domestic use, as part of a two-stage hot
water system.
The first stage consists of a solar collector
panel, a storage tank and a circulating pump. During collection hours when
the water in the solar collector is hotter than the water in the storage
tank the pump circulates the water from the storage tank through the collector
and back to the tank. The water in the tank provides a large heat reservoir,
for hours when the sun is not shining and for times of high demand.
The water from this first "pre-heat"
stage may not always be able to provide the 120 - 140 degrees required for
domestic use. Therefore, water from the storage tank is fed to the second
stage: a "backup" water heater that takes it up to the required
temperature. In 85 percent of San Diego homes, the backup heater is fired
by natural gas. Because the water has been pre-heated by the sun, the second
phase uses a lot less energy than a conventional, non-solar system.
The installation of a solar water heater typically
costs $2,000 to $3,000. This is more expensive than the solar heaters typically
used for swimming pools, because the hotter temperatures require more expensive
collectors with glass covers and an insulated metal enclosure (to create
a greenhouse effect). Compared to the cost of a conventional natural gas
heater, energy savings will usually pay for the system in seven to 15 years.
If you currently have an electric water heater,
you should rush down to your local solar companies and get quotes, because
heating water with electricity costs about 4 times as much as with gas!
Get two or three quotes, ask a lot of questions, and follow-up with references.
If the salesperson says no maintenance is required go elsewhere. I know
many of the solar contractors who survived the lunacy of the early 80's
solar tax credit boom/bust cycle, and for the most part, they are very professional.
Sizing a solar water heating system is fairly
straightforward if your family is normal and uses the average 20 gallons
per person per day. But if you have a teenager, throw away the sizing book.
They either don't wash (a badge of honor), or you can't get them out of
the shower.
There's another category that uses a lot of
hot water. I was monitoring hot water consumption of 35 apartment buildings
when I noticed one building's consumption being way off-scale: over 100
gallons per person per day! Not believing my instrumentation, I drove to
the building. Once I stepped into the courtyard, the reason for the high
consumption was readily apparent - I was in Hooker Heaven! Beautiful, friendly
women leaning over the railings, GI's coming and going... I got out of there,
fast. I had discovered a new category for the hot water statisticians.
The most simple use of solar energy is for
heating swimming pools. If you can afford the luxury of heating a pool,
you should seriously consider buying a pool cover, then a solar pool heating
system (in order of cost effectiveness), rather than burning fossil fuel.
When I had a pool in Tierrasanta, I experimented
with both a pool cover and solar panels that I'd installed. With neither
solar nor cover, the pool temperature was above 80 degrees for only about
5 months. With a cover, the 80 degree season was extended by about 3 months.
Solar had the same effect, but cost much more. With both the cover and solar,
the 80 degree temperature was good for 9 or 10 months.
A typical pool solar system consists of metal
or plastic solar panels on a south-facing roof with an area of 50 to 100
percent of the pool surface area. Pool water is pumped through the collectors
when energy is needed and available for collection. Risk of freeze damage
to the collectors is minimized by automatic draining after use. Cost effectiveness
depends on many factors. Most simulations I've run show a payback of 3 to
6 years, compared to heating with gas year round.
Space conditioning means heating and/or cooling,
and can include ventilation. Space conditioning can be done actively (with
solar collectors and pumps or fans), or passively (using simple building
design techniques). Because of San Diego's mild weather, active solar heating
or air-conditioning is generally not cost-effective. The collection and
storage components are too expensive for the relatively short heating or
cooling seasons.
Efficient building design coupled with good
solar orientation makes economic sense, and can cost little more than a
standard Title 24 building (Title 24 is the code that sets the allowable
annual energy consumption budget for new California buildings). Work with
an architect or engineer familiar with passive solar design.
In passive solar systems, it is important to
pay heed to proper collection, storage and distribution. Typically, solar
radiation passing through south-facing windows warms up a thermal mass (slab,
stucco, brick, etc.). The heat is reradiated, blown or conducted into the
space to be heated. A greenhouse on a southern exposure is an example of
a simple passive heating system.
But remember to put in appropriate ventilation
or cooling controls. Months after I'd held an open house at SDG&E's
Pala Passive Solar Test Facility, I got a call from a desperate woman (no,
not my ex-wife). This lady had liked the greenhouse so much that she had
a contractor install one on the south wall of her home. However, they forgot
to include a masonry wall between the greenhouse room and the living room.
As a consequence, she said the living room temperature was approaching 120
degrees! A thermal wall would have intercepted the solar radiation, storing
it for reradiation into the living room at night, when needed.
In a future article, I'll show how we plan
to integrate many of the above features, along with strawbale walls and
photovoltaic electricity, into a cost-effective demonstration "green
building" at U.S. International University.
You are invited to our free monthly program
on sustainable development and the green building demo project, held on
the first Thursday of each month at 6:30 pm at Green Hall on the U.S. International
University campus in Scripps Ranch. Call me evenings at (619) 565-2603 for
more information.
Skip Fralick is an energy engineer at San Diego
Gas &Electric and a volunteer for Habitat for Humanity
