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