Central Solar System
Jack Knowles - Pamela Jung
Five years ago hunter black was taking a course in construction management
when he happened on the book "form and function" by paul jacques
grillo. Hunter black had what he calls "an awakening." "gone," he
said, "was my interest in the standard construction mode that i was
being taught. I wanted to discover inspiring, practical, and, above
all, natural methods of design and construction. I wanted to build
'real' houses, in other words, that combined a harmony of
spirit and nature."
about that time hunter learned about an intentional community that
was based on principles of meditation and cooperative living. It
was located in the foothills of the sierra nevada in california,
about 80 miles northwest of sacramento. He visited the 800-acre community--
named ananda--with his wife and four children. they liked what they
saw and decided to move there. hunter brought along with him a design
he had done for a school project for a solar adobe house. Well,
four years later in 1990 the concept of a single adobe house had
enlarged a bit. it had turned into a 5,000 square foot rammed earth
home that was part of a cluster of four homes--all of them sharing
one central solar power system. This system includes a central solar
array of 288 modules and a central power building filled with batteries
and power equipment. It is designed to service a total of 9,000
square feet of housing that accommodates eight adults and 7 children.
the cluster took its name of almora from a sacred spot in india with
a long spiritual history.
System design
ananda electric, an electrical contracting company in nevada city,
california, which has a division that specializes in photovoltaic
installations, designed most of the system and installed it. Sam
vanderhoof and john berdner of photocomm inc. of grass valley, california
assisted in the design and provided most of the major components.
The home owners in almora, especially hunter black
who was the originator of the idea of a central system, assisted
by providing the solar array mounting structures, constructing the
power building, and installing the underground conduits.
Well before construction started the home owners calculated how much
power each home would use. ananda electric
arrived at an average daily power usage. Using a computer program , we were able to come up with figures on the average
amount of sun hours available for every month of the year. This is
based on the weather patterns in our particular area. From this information
we sized the array and the battery banks, allowing for 5-7 days of
reserve power in the winter.
The homes are 100' to 250' from the central
power building, and the solar array is 200'--a substantial distance
that required large wires that greatly added to the cost. This was
done because of personal preference and not because of technical
considerations; The home owners simply wanted a certain layout--one
that took advantage of configurations of the land, allowed
for views, preserved trees, and generally just "felt good," as they
put it. If the distances were cut in half, the
savings on these wires and feeds would be more than 50% because you
could use smaller wire and less of it.
The array
The solar array is made up of m-51 style 4-volt laminates (which
are commonly used to make what is known as "tri-lams" or "quad- lams").
these came from an arco power plant. Sixteen laminates, or modules, were
mounted into one solid metal frame with copper bussing tying them
together. this configuration of these huge units, which we nicknamed
"monster modules", made them very easy to mount as we only needed
to support and bolt down the main frame. Each "monster module" is
supported by four pressure treated 8" poles set in concrete. We
bolted two pieces of slotted galvanized angle iron to the poles,
then bolted the modules to the angle iron. By doing some minor rewiring
we got the 24-volt output we needed. we drove a 5/8" x 8' ground
rod for each set of three "monster modules", making a total of six
ground rods at the array.
The number of laminates/modules presently installed is 240, and these
adequately serve the needs of homes totaling 8,000 square feet. another
48 will be added when the 4th house of 1,000 square feet is built
by a couple with a baby.
The system is designed to give a total continuous output of 6,600
watts with about 40,000 watts generated in the winter and 60,000
in the summer. That is total daily output on an average clear day.
The power control panels
at the heart of the system are the power control panels. Ananda power
technologies custom manufactures these in their shop.
they are the same company that makes the "ultra power center" that
is marketed by photocomm. inc.
One enclosure is 24 inches x 24 inches and the other is 36 inches
x 30 inches. Housed inside are three heliotrope cc120b charge controllers,
two 800 amp shunts for the cruising equipment co. amperehour meters,
three double shunts for the spm 2000 meters, and an assortment of
lugs, fusing, bussing and wires. A generous amount of ventilation
and additional heat sinking is built in to dissipate the very high
heat given off by the fets in the charge controllers. Mounted in
the front doors are 60 ampere 2 pole square d breakers. These provide
overcurrent protection and disconnecting means for the incoming array
and outgoing dc lighting and small appliance loads. The array breakers
interrupt the power before and after the charge controllers so that
they are completely isolated from the system for ease of maintenance
and proper protection.
We drove one 5/8 inches in diameter x 8 foot ground rod at the control
panel. This rod is bonded to the negative termination lugs for the
battery, array, and load wires with a #2 copper conductor. We bonded
a #6 wire to the metal housings of the inverters, control panels,
and the 5 foot x 10 inch x 10 inch raceway.
The power building
This building consists of a 10 foot x 15 foot rammed earth walled
section for the battery room and a shed type portion with a cabinet
to enclose the control panels, inverters, and battery charger. Rammed
earth construction is a great way to go because it provides stable
temperatures for the batteries. A small kohler 3 kw low rpm generator
and a ibe 60 ampere, 24 volt battery charger provide the backup charging.
with the size of the solar array, we predict the generator will seldom,
if ever be needed, but it's nice added insurance.
The batteries
We wired six trojan 175j15, 1493 ampere-hour, 24 volt steel cased
batteries in parallel for a total storage capacity of 8,958 ampere-hours
or 215,000 watt-hours. each battery has a 400 ampere fused 1 pole
disconnect switch for protection and ease of maintenance. these switches
are another product made by apt, inc. A separate run of 4/0 welding
cable attaches each battery to the disconnect switch, and from the
switch on to the lugs in the control panels.
These batteries are heavy, very heavy. they weigh in at 2,500
pounds each. We used a forklift to get them to the building. then
with lots of sweat and muscle, we rolled them over 2 foot sections
of 2 inch pipe and pry barred them into position.
By the way, we prefer these batteries that are composed of factory
installed cells and cell interconnects as opposed to batteries that
require you to install the loose cells. even though it might be easier
to move the components around in the latter, the factory installed
versions greatly reduce any chance of battery terminal corrosion.
The inverters
Each home has its own inverters which consist of: one 4,800 watt continuous 120/240 volt inverter, one 3600 watt continuous 120/240 volt inverter, and two trace 2524s for the homes with lower power needs. all inverters have performed flawlessly. the only unpleasant incident happened when a carpenter
plugged his bosch cordless battery charger into a trace 2524 and
the charger melted down, case and all. Makita chargers seem to work
fine. just be careful and check to see if your charger gets very
hot right away. if so, you'd better unplug it immediately.
Meters and controls
We installed a spm 2000 that gives a digital readout
of battery voltage, array and each house's load current and keeps
a running total in watt-hours and amp-hours for array input and load
draw. We also installed a cruising equipment company ampere-hour
meter to monitor how full the batteries are. this meter monitors
the actual amperes in and out of the battery with compensation for
inherent losses. a regular volt meter, on the other hand, can only
give you valid readings on the amount of charge when the batteries
are in state-of-rest condition with no charging or discharging occurring.
Ampere-hour meter.
a handy control feature of the photocomm inverter is its remote switch
(which we installed in the houses) to control "always on", "off",
or "sleep" mode. this allows you to keep a low wattage draw device
such as a vcr operating to record a show while you are gone. or by
shutting the inverter down as you leave you can be sure no power
is used by something you may have forgotten to turn off.
The house wiring systems
The houses have a combination of ac and dc wiring in them. most of
the lighting is 24 volt dc with a mixture of incandescent, quartz,
compact fluorescent, and large fluorescent lamps. The homes have
wiring for dc refrigerators with sun frost units installed in two
of them and propane in the other two.
The 120 volt ac is used for table and floor lamps that plug in and
a few hard wired fixtures, compact fluorescent lamps are used in
these. The ac power also runs the clothes washer, dryer, kitchen
small appliances, coolers, vacuum cleaner, entertainment equipment
and miscellaneous items.
We installed three conductor stranded #12, #10, and #8 gauge
romex for the 24-volt dc, and we ran some #2/0 feeders in the 5,000
square foot home due to the long runs and voltage drop problems.
We used the three conductor cable so that one wire could be a
ground for the fixtures. thus, we not only met the national electrical
code standards that say any metal parts of fixtures or electrical
equipment need to be grounded. W also made it possible for the entire
house to be switched over to 120-volt ac in the future if it should
ever be needed.
An important ingredient in the dc lighting system is the use of dc
rated switches. we use leviton #1330-i for the single pole and #1331-i
for the three ways. these may need to be specially ordered from your
local electrical supply house.
Square d size 12/24 load centers with qo style breakers were used
to distribute the 24-volt load because they have a dc rating and
high reliability.
We did the ac wiring with normal romex in the standard fashion. the
120/240-volt ac power is distributed with ite/siemans standard residential
load centers and breakers.
conduits and wires
At each home we installed a 3-inch conduit for the dc, a 2-inch conduit
for the ac and a 1-inch conduit for the metering and control wires.
for the dc house loads the wires range in size from 4/0 up to 500
mcm aluminum, depending on the amount of load and the distance. The
runs are from 150' to 250' long, which requires large wire sizes.
The ac feed wires ranged from #2 on up to 2/0 in size. because the
average run to the array was 200' we installed a 2" conduit with
two 400 mcm aluminum wires on each set of 48 modules. We used splicer/reducers
on each end of the array and dc load wires to reduce the size down
to a #6 copper thhn at the control panels and a #2 copper xlp at
the array. this helped us manage and terminate them easily. For the
metering and control wires we installed fifteen #14 thhn stranded
wires, color coded the same as the wires on the meters.
We used aluminum wires for the large main feeds because the cost
was one half - of copper in the same amp carrying capacity. aluminum
wires must be terminated properly to keep resistance to a minimum.
heavy-duty compression or set-screws type lugs must be used with
aluminum anti-oxidant compound applied to the thoroughly cleaned
cable end.
We sized wires carefully to keep voltage drop to a maximum of 5%
throughout the system. We use a computer software program called
"basic voltage drop calculations" (orloff computer services, santa
ana, california) to make this task easy and accurate.
At the power building we brought all of the incoming array and outgoing
ac and dc load wires into a large 10 inch x 10 inch x 5 foot metal
raceway (that is nippled to both power control panels). Then we installed
the splicer/reducers on the wires inside this raceway, with the smaller
wires continuing down into the control panels. We used a special
wire pulling winch to pull the large wires through the 200 feet+
long conduits. It would have been extremely difficult--if not impossible--to
pull them in by hand.
power consumption
As it worked out in the almora cluster, two of the home owners did
not have the money to both build their homes and finance a quarter
of the cost of the solar power system, while the other two did. so
they all struck a deal. The two home owners with the extra resources
financed the system up front. the others buy their power from them.
All the houses have a dc watt-hour meter on them to calculate the
amount of power they've consumed in a month. this may well be a perfect
solution for any group that wants to be together but has unequal
money resources.
These meters will also be giving us useful information for future
design purposes. It will be most interesting to anyone interested
in cluster living to see how the different numbers of people, square
footage variation, and lifestyle habits affect the actual amount
of power consumed. It will probably be of great interest to the individual
families to see if the power they end up consuming over time matches
the estimate they had in the beginning--a reality check that might
help reestablish priorities.
The homes are basically very conventional as far as appliances and
usage go. Washing machines and gas dryers, small kitchen appliances,
entertainment equipment and a normal dispersion of light fixtures.
some homes even have dishwashers and air-conditioning. The only
variations in these homes as opposed to a typical utility connected
home are for the refrigerator (they used sunfrosts and propane),
energy efficient lamps and the absence of electric space heating.
Even though it's a little early to get some realistic average usage
readings we thought to tell you what we know now. tom oesterle, one
of the homeowners, reports that they are using about 200 amps, or
4800 watts a day in their home. This is during the early summer months.
he admits that he isn't making any effort to conserve power since
they have quite a bit more than they need at this time of year.
They run their clothes washer and dryer, dishwasher, small appliances
and lots of lighting regularly. they also have a few phantom loads
that they just leave on all of the time. why build such a system
together
The reasons for building this type of group configuration, at least
for the residents in almora, are numerous. contrary to what one might
think, the primary reason was not cost savings. In fact, it might
even be a wash between the cost of bringing standard utility electric
power in and the cost of designing, installing, and maintaining this
system. nope, the residents' motivation
was more complex.
On the down-to-earth level they wanted to achieve the self-sufficiency
of a mini-village, shared maintenance, and the efficient use of a
renewable resource. on another level they wanted to experience a
level of interaction among the residents that went beyond the casual
neighborliness that is common today and, all too often, unsatisfying.
Yet on another level there was even a spiritual aspect to it,
a strong desire to live in harmony with nature. As Hunter Black put
it, "i think it was more from a spiritual yearning to reflect the
divine than a practical understanding of what we were getting into
that led to the creation of this solar system. There aren't any statistics
we can use regarding this. we don't even know how much power we truly
need to keep
people happy...(but) living in closer harmony with nature should
be a goal of all living environments. A closer connection to nature
is a closer connection to spirit.
author/installer-copyright Jack Knowles
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