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Copyright 1998, 2003 by Leonard G. Barton.

Solar power adventures

Commentary of March 20, 2003

The system described below was first online on March 5, 1998.

Our five year anniversary passed in March 2003. As the French say, the more 
things change, the more they stay the same. The big change in the electric power 
industry was the deregulation of generation and distribution in California and
the subsequent expolitation of the marketplace by energy producers and traders.
The constant is that the liars, thieves, and incompetants are still in charge
and busily picking our pockets. In fact, our Governor (Gray Davis) recently
appointed a term limited  politician to be the Director of California's Department
of Finance (an important position as our state has a deficit of 22 to 35  billion
dollars).  The new director? Ex State Senator Steve Peace, the architect 
of California's failed electricity degregulation scheme!

Back in 1998 some of us were concerned about the popularity of SUVs and now we 
have General Motor's Hummer 2 - which is now being marketed to young women who 
are being told that they should "put on something a little more metal" (despite
the fact that they are far more likely to die in a single vehicle rollover than
in a sedan - this since these high and tippy SUVs have notoriously weak roof 
structures despite a carefully crafted and illusional solid appearance).

In 1998 we were concerned that dependence of foreign oil would drain resources 
from health and education into the military and industry. Now, contrary to
international law and the norms of civilized nations our president George W. Bush
has "reluctantly" chosen to spend hundreds of billions of dollars to crush (and then
rebuild with contracts to contributors and cronies) an oil rich country (Iraq) and to
control its region while a nearby city (Oakland, California) must choose to either
close seven of its 14 libraries or keep them locked four days a week. Another (Berkeley)
has sent layoff notices to 25 percent of its teachers, including 13 of 19 at a
"magnet" school targeted for minority students.

And now, the Californa Public Utilities commision is proposing to impose a
"departing load" charge upon solar and wind instalations under the rational
that the revenue bonds written to support the expensive long term electricity 
purchases by the Department of Water Resources must be paid for by all ratepayers.
This is not based on the load displaced but on the power provided, even if it is 
for new load and the power provide is peak power and the load is off peak. How 
stupid can they get? Undoubtedly they will top even this!

As Lilly Tomlin said: "No matter how cynical I get it's never enough."

But if you are reading this, you probably already are aware. 

"If you aren't outraged you're not paying attention!"

[Roof_View] Here is some documentation on an photovoltaic, on-grid, tracker mounted solar power installation. This residential installation is the third on-grid photovoltaic system in Contra Costa County, California, U. S. A. and is the first in this county to use trackers.

Right: Easterly view of trackers from roof of house with Mount Diablo in the distance.

Below: Westerly view toward back of house from court. [Back_Court_View]



Photovoltaic ("PV") systems produce electrical energy directly from sunlight. Full sun at sea level has a power of about one kilowatt (1000 watts) per square meter (10.6 sq. ft), or 94 watts per square foot. A domestic polycrystalene PV panel will produce about 300 watts per 24 square feet, (12.5 watts per square foot) which works out to an Direct Current (DC) efficiency of about 13 percent. Conversion of DC to Alternating Current has an efficiency of 80 to 95 percent, varying with the percentage of maximum inverter capacity.

Current developments in higher efficiency panels include thin-film devices at 15 percent (with low production cost but limited lifetime at present), laser remelt of polycrystalene cells to obtain 20 to 25 percent efficiency, and rumored laboratory microlithographic devices using dipole antennas of lightwave scale with 70 percent efficiency. While the presently available 20 to 25 percent efficiency devices would be very desirable for an upgrade to this installation, the high cost currently makes them suitable only for space satellites and planetary probes, where the high cost can be readily justified by lower launch weights.

March 2003 - Here we are 5 years out and there has been no real 
progress in efficiency. My plans were to replace the low efficiency  panels
on the trackers about now. Predictions are that it is 15 years out before
we will see higher efficiency. So rather then upgrading the trackers we are
having additional capacity added to the house roof. This will have the additional
benefit of shading the most solar exposed portion of the roof, an aid to comfort
on those hot summer days.

There has been one substantial improvement in the technology. With the use of a 
new type of inverter (the Sunny Boy), panels may now be connected in high voltage 
series strings that greatly simplify and reduce the cost of connecting the panels
to the inverter. This enables the use of easily worked 3/4 inch conduit and
number 10 wires and is ideal where the panels are distributed over several locations
on the roof (provided the panels have the same orientation and shade timing or are
organized into similar parallel groups). Because of its sophisticated internal
protection software it is practical to build an "overloaded" system that gets both
morning and afternoon light through separate panel systems. This is suitable for a 
piched roof house aligned on a north-south axis. With time of use net metering it
can be advantageous to align fixed solar powers to the west, rather than the south
which will produce the most total power. The western orientation produces more power
during the peak afternoon cooling time.


An "on-grid" system puts excess power into the supply grid, driving the meter backwards. California is by law a "net metering" state, which makes such systems practical without batteries, since this power is credited against power used. This is considered to be an exchange of power between producers, commonly performed between large utilities. Without this law, the supplier would offer only a few cents per kilowatt hour for this balancing power (as is paid for any monthly surplus). A further advantage to the home producer in California is that the "costs" of utility deregulation (paying off the "stranded investments" of the utilities in uneconomic nuclear power and pumped storage) are born by a KWH rate surcharge, rather than a regressive monthly connection fee. The state of California also offers solar rebates for on-grid systems, presently estimated to be $2.75 to $3.00 per AC (inverter output) watt. These rebates are paid from the same rate surcharges used to bail out our utilities, so the non-solar ratepayers are funding the solar rebates. The only remaining fixed cost is a minimum electrical use charge to cover meter reading of about $6.00 per month.
March 2003 - Increased subsidies for 2002 and 2003. are now $4 to $4.50 per
AC watt. At the five year anniversary of the legislation it was about to expire
without additional approval by the California Assembly and Senate. Believe it
or not, the utilities lobbied against this renewal, claiming that the poor
ratepayers were cross subsidizing solar (not that I consider that a bad thing).
Analysis showed this subsidy to be about one penny a year per ratepayer. The 
limitation on installed base is still a meager 1/10 of one percent of total 
system capacity. I really don't understand the utilities motivation for being
against end-user distributed solar and wind except that perhaps they might feel 
a loss of control (of their hand in my pocket).

New for 1999 - Annual Net Metering.

1998 regulations in California allowed only for monthly net metering, which made it impractical to produce excess electricity during the long days of Spring and Summer, since the excess was boughtback by the utility at an extremely low rate. With annual net metering it is now practical to have enough capacity to cover all electricty use year-round. This is a win-win situation for the both the household and the utility, since the summer surplus is produced near peak utility demand times.

The new regulations also allow wind power and combined photovoltaic and wind power systems to qualify for net metering.

Annual Net Metering - 
it works for the homeowner and for the utility.


A tracker orients the panels toward the sun. This is especially effective in the months near the summer solstice, since the tracker can find the morning and evening sun positions, as well as maintain an effective presentation of the panel to the incoming solar rays throughout the day any time of the year. Trackers add little additional production near the winter solstice at higher latitudes. Single axis trackers (such as those used in this installation) may be left in a fixed position, or the second axis may be adjusted manually throughout the year.

Economic Rationalizations

Is it economically feasible? On a conventional balance sheet it is not. However, the PV system does not add to nuclear waste, global warming, sulfur, heavy metal, and particulate pollution, "defense" costs for imported oil, etc. If the money spent on this installation was put in the bank at one half percent per month (six percent per year, what an uninsured certificate of deposit with some small risk might bring), the interest alone would pay for about 1000 kilowatt hours each month at current California second stage residential rates of 13 cents per kilowatt hour. The late Spring and Summer monthly output for this system is estimated to be over 700 kilowatt hours and annual average of 400 KWH per month. This does not consider the depreciation of the equipment or the non liquidity of the investment.

March 2003 - With the sink in interest rates, combined with the 
results of depredations of Enron, El Paso Gas, Williams, etc., etc., 
and  the response of our government (our Governor signed long term 
contracts  when prices where highest) home solar power is now even 
more attractive. Some computations show that an investment in solar
power is equivalent to 3.25 percent taxable interest on a Certificate
of Deposit.
On the other hand, the current electric rates do not include costs that are "externalized" by the power producers, such as the medical costs associated with pollution related disease, government handling and storage of nuclear wastes, damage to crops from acid rain, global consequences of climate changes due to carbon dioxide, or destruction of rural and wilderness environments from strip mining and impoundment flooding. If these and other costs were reflected in the price of electricity, then solar electric would likely look like a bargain by comparison and wind power would be a "no brainer".

March 2003 - Looks like the powers in charge have "No Brains", 
when you look at their DECLINING support for alternative energy 
research and development and their continued (and even increasing)
subsidizing of conventional energy production methods. Of course,
our representives deny that the flood of money to their campaigns
and parties has even the slightest influence on the appropriations,
taxes, and regulations they vote for - does anyone believe that?
Also, the price of electricity is expected (by the conventional wisdom promoted by the deregulation interests) to fall in five to ten years with the ratepayer payoff of the "stranded costs" of uneconomic nuclear power and pumped storage. Given expected economies in the extraction and transport of coal and the willingness of our elected officials to fold under the lobbying pressure and financial muscle of powerful and rapacious extractive companies (such as Peabody Western Coal and its related companies) it looks like we will be dealing with coal power for some time.
March 2003 - Well, well, well - look what happened to energy prices!
Since second tier rates in California are now over $0.15 per KWH and
interest rates are now the lowest in years, SOLAR POWER IS AN EVEN BETTER 
DEAL! (Even partial replacement of household energy replaces the highest
cost electricity first.)

Load shifting is the moving of energy demand from high cost time of use
to low cost. For air conditioning, this would involve chilling water during
the late night and early morning (12 midnight to 6 A.M.). This not only uses
lower cost electricity, it is also much more efficient as the heat is being
rejected into a lower temperature atmosphere. This cold water is then used to
chill air (or the interior structure of the building) when it is needed during
the heat of the day. At this time, the solar panels help shade the roof from
the sun and produce electricity that is bought back at up to seven times the
cost of using it at night. The recharging of an electric vehicle is an easily
shifted load, although this works much better with batteries other than the
low cost lead-acid type.

By combining time of use net metering with load shifting, it should be
be practical to satisfy a household's needs with a system of modest size.

Note that the economic foundations of the people making claims of lower future rates are the same ones that said our cable TV rates would fall under the pressures of competition (they are going up at twice the rate of inflation).

March 2003 - Now cable TV rates are going up at MORE THAN THREE TIMES
the rate of inflation! (Ours went up over FIVE times the rate in 2002.)
For this we can thank the regulators which allowed AT&T to buy our cable
provider (TCI). AT&T then scrapped its plans to deliver cable like services
through fixed location microwave. (Studies have shown that cable rates are
17 percent lower where there is competition.)

Now AT&T has sold out to Comcast. So what can we expect? What has happened
in the past is that the new owners first say they will "invest" to "improve"
the system (actually so they can deliver more extra cost services such as
pay per view and extra cost "digital" cable) and then raise the basic rates
to pay for this so called investment.
Large wind turbines are presently almost as cost effective as coal, have the advantages enumerated above for solar, provide a great amount of employment per watt installed, and could be the preferred national power source but for the political clout of these entrenched interests and the narrow and short term views of members of our government, fostered by our absurd campaign financing methods and unwillingness to make the broadcast industry pay back for its spectrum usage with free time for candidates.

March 2003 - In the U. S., wind is now competitive with coal at the site of
production, but we lack the strong national infrastructure needed to support
our superior wind sites. In the late 1970s the U.S. dropped its energy crisis
inspired subsidies and research for wind power. The government of Denmark
continued to encourage these developments with a goal to generate fifty percent 
of their power with windby 2020. Danish manufactures now are the leaders in large
wind turbines (10 to 30 Megawatt and larger) and are now exporting large turbines 
to the USA. This could have been an American industry.

As far as the politics - more of the same and its getting worse!

By the way - did you know that the profession from which members of the
U. S. House and Senate come is mostly the law, while in Europe the largest 
parlementary representation is by teachers? Which would you rather have 
representing your family's interests as citizens? Which would you rather 
have representing your corporation's interests if you were a corporate 

If on-grid solar isn't economically practical right now, why do it? Probably for the same reason some people buy four wheel drive Chevrolet Surburbans that never see mud or snow and seldom carry more than the driver alone to the convenience store two blocks away to buy one pack of cigarettes - it looks to the buyer like a worthwhile thing to do, however impractical. Unlike the more expensive Suburban, however, PV power is on the correct side of any "green" ledger, costs almost nothing to operate, has an expected useful life of 30 or more years, and is incapable of crushing small cars.

March 2003 - I now drive an electric vehicle (a 1998 Ford Ranger EV
obtained in January 1999 at very favorable lease rates) - but I don't
see  many on the road.  Both GM and Ford have terminated their electric
vehicle development programs, despite the fact that they had people on 
waiting lists for lease and purchase.  Not only that, but the Suburban 
has been outweighed by the Ford Expedition (which was unsucessful in 
the market and will not be continued) and now the ultimate in SUV excess,
General Motor's Hummer 2.  This is so successful that they have waiting 
lists and is so heavy that they do not have to publish milelage (said to
be 11 miles per gallon).  Our government in its tax wisdom will subsidize 
most of the costs of this monster for the self employed.  This is an 
unintended  consequence of legislation to encourage investment in medium 
weight work vehicles by tradesmen to boost the economy.  Apparently the 
pols did not expect that anybody would buy a 6000 pound GVW truck for 
personal use - but we know that the manufacturers did as they plan years 
in advance, and they are often invited to assist the pols in writing the 
laws.  So what is the Bush administration's latest?  They intend to  
increase and accelerate the tax subisidies that can be applied to 
this vehicle!
Installing this kind of solar power can also be compared to making tax-free investments, even though the net return may be less than a taxable investment, simply because one doesn't want "them" to have the money. Not practical, but very satisfying for some.

Another way to look at the expense is that a substantial portion (40 to 50 percent) is paid off in avoided electricity costs within a reasonable period (15 to 30 years), and the remainder is strictly a personal subsidy to pay for its "toy" value or "bragging rights" (like that gas guzzler in your driveway).

January 2003 - Solar is an even better deal now!

A Specific System

Installation Site

The trackers are installed in the back yard of a suburban ranch style home near Walnut Creek, California. (38 degrees north latitude).

A quarter acre (10,000 square feet) lot allows room for the trackers without crowding the house or yard.

Purpose of System

Provide sufficient power for whole house air conditioning and general household use during ` summer. Provide all household power at other times except near winter solstice. Note that this is contrary to conventional wisdom, which states that Photovoltaics won't economically support household air conditioning, but this is usually said of fixed panel off grid systems using lead-acid batteries. This PV system is being specifically installed to support whole house A/C in a "green" manner.

March 2003 - We have not got the whole house AC yet, but can chill one room 
while not drawing power from the grid. With  the addition of the new rooftop
system (2.4 KWDC) the system now produces 20 to 25 KWH per day in March 2003)
When paid of we expect to install several reversable heat pumps, freeing us
from the high cost of natural gas heating in the cool season, increasing summer
comfort, and powering our electric transportation. Not only that, we may obtain
a zero net carbon usage.

Weather and sunlight conditions at this site.

Winters are cool with mix of rainy/cloudy, some ground fog, and cool, bright sunny days. Late Spring has a few warm days which do not heat the house if it is ventilated in the cool morning and closed against the heat of the day. Summer and early Fall have warm days(85 to 90 deg. F), sunny and dry with cooler nights, with one to three day hot spells of 95 to 100 deg. F. (In 1996 the daily high temperature was over 95 degrees F for ten days in a row.) It is at these times of sequential hot days that the house gets "heat soaked" and can be quite uncomfortable.

We have occasional early morning and late evening coastal fog during the Summers, with correspondingly cooler weather, in some years for weeks at a time.

The trackers used in this installation are sensitive to easterly or westerly winds of over 25 miles per hour. Wind is not expected to be a significant factor in tracker operation. During summer, the site is sheltered from prevailing westerly winds by an adjacent hill. The only significant winds are from the South during winter storms. Smog and haze are usually significant only during the Fall season, when prevailing westerly winds are replaced with a slow north-east flow and particulate pollution from primitive fireplaces and agricultural rice straw burning becomes significant.

Local terrain and vegetation cause late afternoon shading but only an hour or two before sunset, a time when the solar insolation is reduced by the long path through the atmosphere.

These are favorable conditions for this installation, since during hot spells we have plenty of sunlight to generate power for air conditioning, lacking the hot, humid, and overcast conditions of Eastern states.

Predicted System Performance

Estimated peak equivalent solar hours in this location: 9 to 10 (theoretical maximum is 11 to 11.5. without shading, compared to 5.5 for a non-tracking system.)

Equivalent solar hours are calculated by dividing a day's DC watt-hour production by the panel's peak watt production. If this done by measurement over several years it can account for local shading and weather conditions.

Initial results for sunny days in March through May show a typical midday AC current of 7.5 amps, producing about 1800 watts, substantially less than the design peak of (0.9*2340) = 2106 watts. Higher output is seen with certain sky conditions, such as high thin cirrus or passing fair weather cumulus. This lower production is probably due to the near sea level altitude and relatively moist coastal air.

Actual System Performance

It took a while to break even in 1998, due to an unusually cool and cloudy spring due to the strong "El Nino" effect, with March, April and May production only reducing our electrical bill.

Actual results for June and July 1998: We are producing a surplus of power, up to twenty kilowatt hours per week in late Spring and early Summer. Our weather has been relatively cool due to coastal breezes from the bay region, so we haven't needed much air conditioning. So now on a hot day we run the room air conditioner much more than we we would have in the past, since the most significant effect is to drive the meter backwards at a slower pace.

Actual results for August 1998: Hot days, but who cares? Hole up with the air conditioner! We have one of our rooms fitted with a very powerful under window unit. We run it for a couple of hours in the morning, pre cooling the walls and ceiling. Then the room is comfortable for the early afternoon without running the unit (nice and quiet). Later in the afternoon we run it as needed, still producing some surplus power.

Actual results for September and October 1998: The panels work more efficiently in cooler weather and with reduced A/C load we are still producing a small surplus despite the shorter solar days and increased use of lighting.

Actual results for November and December 1998: While no longer producing a surplus, the added solar power greatly reduces meter spinning, producing about half of the power we use.

Long term performance - 1999: Usage history through May 1999 was recently provided by PG&E. Of particular interest is the balance under the new annual net metering tarrif. In these late Spring months we are accumulating a credit of close to 200 KWH per month, owing to the sunny days this spring with the departure of "El Nino" weather. The weather has also been pleasantly and unusually cool, averaging about ten degrees below normal. This cool weather is expected to continue through August, so we should have a substantial energy surplus to use for both our usual hot weather between mid August and mid October, with enough surplus remaining to cover our our winter use. This indicates that the system as installed is the correct size for our present power useage.

January 2003 - Without the electric vehicle we would break even over 
the year. The vehicle represents about an addtional 50% annual load 
increase. This is not an especially efficient vehicle - about 0.5KWH 
per mile. With time of use net metering we would probably do better 
than break even as the EV can be charged at low off peak rates - but 
is that just gaming the system?

Special Contract Required

The electrical utility here requires execution of a specific contract covering operation and billing. This contract was designed for large co-generation plants.

This contract prohibits resale of electricity to other customers, requires the keeping of a system log, and restricts the production capacity of the system to 10,000 AC peak watts. It also prohibits the use of time-sensitive metering, which is unfortunate since the production almost coincides with peak demand times. (Note: this may change under the new annual net metering when appropriate meters are developed.)

Liability Insurance Required

The electrical utility requires modest ($100,000) liability coverage (of course, they asked the regulators for $millions in coverage which would have effectively killed the market, but for some reason didn't get what they wanted). This more reasonable coverage is included in the usual fire, casualty, and liability coverage for a household.

Utility Cooperative

To my delight, the utility (Pacific Gas and Electric) cooperated in getting the system online, and did not impose any unusual requirements.

System Vendor

The system was designed and installed by Light Energy Systems of Concord, California (formerly Solar Self-Help). All work was done to the highest commercial/industrial standards, with no surprise costs.

System Cost

About $23,000. This may seem to be a lot, but consider that our previous low use of air conditioning was not based on economic factors but rather upon the burden to the environment and consideration of the hidden costs imposed upon our fellow citizens. Now, we use all the air conditioning we please with a clear conscience and may soon be adding an electric vehicle to our transportation mix.



4KW Trace model 4048. This inverter is designed specifically for on-grid use and will disconnect from the grid if the grid power fails. This is so that line workers are protected and so that the inverter does not attempt to provide power to the immediate neighborhood. There is an additional lockable disconnect switch proved for use by the utility company should they need to work on unenergized wires with absolute security.

Output is 240 volts nominal, two wire, single phase. If converted to an uninteruptable power supply (UPS) at some future time this will require the use of an additional 240V to 120V transformer.


4 DG-300, 4 DG-285. (totaling 2340 watts) manufactured by ASE Americas, Inc.. These panels are characterized by a large unit size and consequent low installed cost per watt. They are also unique in that they have tempered glass on both sides, affording added environmental and mechanical protection. Each panel delivers its power through blocking diodes that prevent a shaded panel from absorbing electrical power from its mates.


ZomeWorks passive trackers have distinct advantages over active trackers. These trackers operate by transfer of a working fluid from one side to the other by gas phase pressure developed by differential heating. As seen in the illustration, the sunlight falling on the chambers on each side is modulated by shaders. These shaders also act as reflectors to cause the tracker to "flip" from an extreme position, "waking up" the tracker in the morning. The tracker is finely balance on low drag bearings. The shock absorbers act as dampers to prevent overshoot and excessive response to wind gusts.

Competitive trackers require that the gearing be strong enough to transfer wind gust loads from the panels to the supporting structure.

Efficiency and Performance Test

On June 11, 1999, a consultant employed by the California Energy Commision inspected and tested the system. Results were:
     Time: 0940 Local Daylight Savings Time
     Panel Temperature: 61 degrees Farenheight.
     Sky condition: thin scattered cirrus.
     Panel position: Tracking within 5 degrees.
     Solar Radiation: 894 Watts per square meter on panel axis.
     DC Watts:        1828
     AC VoltAmperes   1711
     Power factor     not measured, assumed 1.0
     From this we can calculate:
     AC Watts = VA*PF = 1711*1.0 = 1711
     Panel actual performance:
        (panel rated wattage of 2340 is at 1000 Watts per square meter).
        1828 /  (2340 * (894 / 1000)) = .873 (probably due to 61 deg temperature)
         Panel performance is thus 87% of design maximum.
     Inverter efficiency:
        Inverter operating point 1828/4000 = .427
        Inverter efficiency = ACW/DCW = 1711/1828 = .936
     System efficiency:
        Collection area     17.86 sq meters
        Net system efficiency 1711 / (17.86 * 894) = .107
     Consultant observations: The use of trackers keeps the panels much
     cooler than when closly fitted to a roof. Performance of non tracking
     systems at this time of day would be typically thirty percent of maximum.
     Owner observations: panels had not been washed recently, but were not
     significantly dirty, either. Net system efficiency of .107 is somewhat lower than
     the expected .12, but close enough for our purposes. Low inverter loading of .427
     is only a bit above the peak inverter efficiency point. Operating at the optimal
     loading would give an expected inverter efficiency of .96.

Tracker Mounting

The main poles are 16 foot lengths of 8 inch diameter pipe with 1/4 inch wall thickness. Additional hight is provided by a reducer to a one foot length of 6 inch diameter pipe. While the pivot height of 11.5 ft above ground was intended to allow safe walk-under and elevation above fruit trees, the rack configuration delivered resulted in a 14 by 9 foot unit, rather than an expected 10 by 10. The pipe extends downward 5.5 feet into the ground with a substantial concrete footing to distribute the load into the adobe clay soil. The mast and footing have been designed to withstand 90 MPH winds, with only 70 MPH being required to satisfy local requirements. (Wind design requirements are reduced in urban areas, where the trees and buildings slow the wind flow near the ground.)

Space under the trackers may be used for gazeebo or lathhouse. Check back in Summer of 2000 for further developments.

Expansion Capacity

Future expansion is planned to cover the electrical energy requirements of an electric vehicle. Portions of the house roof are suitable for placement of fixed or seasonably adjustable (non-tracking) panels. A 1600 AC watt reserve inverter capacity remains available for future use. Conduit stubs have been provided for a third tracker unit, should an additional tracker be installed. Addition of a third tracker would require either additional DC wiring or the relocation of the inverter and conversion of a long DC run to AC, or acceptance of some additional wattage loss due to wire heating. Since the bulk of additional power will probably only be required during the months of low sun, this need may be addressed with the addition of roof mounted fixed panels, with pitch angle optimized for October through March.

A limited uninteruptable power supply (UPS) capabilility may be installed at a future date to support a sump pump and refrigeration. This will require some site specific electrical engineering owing to unique requirements. This will probably require the use of an AC charging system for normal standby (battery float charge), with manual or automatic switching of panel output to a DC charge controller for emergency use. Current systems are designed for either "on grid", with no backup, or primarily "off grid", and so lack the sophistication desired for this installation.

Tracker Justification

In our lattitude, trackers offer 130% of the power of fixed units on an annual basis, and 140% during the peak sun months in spring and summer. Operating the units over a longer period will drive the inverter at a more efficient operating point than would the equivalent capacity in fixed panels (which would generate more current over a shorter period) and will leave more reserve inverter capacity for future expansion. Also, trackers are cool to watch, like giant sunflowers. The current units do have a rather industrial appearance. Unfortunately, the solar power rebate offered by California offers no bonus for trackers at this time.

Tracker Locations

Position of poles was restricted for several reasons. Too far south and a large oak on the adjacent lot would shade the units near the winter solstice. Too far west and a large Italian Stone Pine would shade the units in afternoons near the summer solstice. In any site, early morning and late afternoon summer shading is more likely with trackers than would be true for fixed roof mounted units, which would be inefficient at this sun angle, while winter shading of the trackers is more likely due to the lower elevation of the panels. Further considerations were a desire to not position the units into scenic view lines, and the location of a standard sized apricot tree and another neighbor's tree.

Sun Path Instrument

Trackers were located with the aid of a sun path instrument. This device contains a magnetic compass (adjusted to compensate for local magnetic variation) and bubble level. At a location to be examined, the instrument is oriented using the compass and level. A sun path card has arcing lines representing daily sun paths during the year for the site's lattitude. This card is covered by a plastic bubble. The operator positions the device so that the reflected image of the operator's eye aligns with the center of the card (where the bubble is located). The reflection of the surrounding environment can now be examined for intersections with the sun path lines. With a little practice this is much easier that it sounds.

[Pathfinder_In_Use] BELOW: View of sun path instrument with reflective dome removed. A specific card is installed for the lattitude, oriented for compass variation. The compass is used to orient the device and a bubble level can be seen at the center.


RIGHT: View of sun path instrument in use. The environment is reflected from a dark transparent dome covering the instrument. The sun path lines on the card under the dome are inspected for intersections with the reflected image to determine shading at various times of year and day.

BELOW RIGHT: Image of sun path card. Curved lines represent sun path for different months of the year. Card is adjusted for compass variation by aligning the number at top with a mark on the instrument.


Site Wiring

The inverter is mounted a few feet from the service box. 107 feet of 4 conductors of AWG 4 wire runs to a box on the base of the first pole and an additional XX feet connects this to the top of the second pole (2 AWG 4).

What about Aesthetics?

As they say, beauty is in the eye of the beholder. However, I was surprised when the first unit went up. What I was expecting was a (nominal) ten foot square, but what Zomeworks delivered was, with panels, more like nine by fourteen feet. I ran my ten by ten design by Zomeworks, and they said it was practical, but did not have enough demand at this time for trackers mounting this panel to justify the engineering costs.

So now I had four choices on a second tracker unit:

1.) Match the unit I have - this will both stick up in my neighbor's sight line and intrude on walk-under head room (the original motivation for the poles was to avoid intruding on usable yard space).

2.) Find an available tracker and panel combination that will give me a ten by ten unit. Unfortunately, this is limited to 900 watts.

3.) Go to a smaller zomeworks tracker mounting two DG-300 panels and put the additional panels on the roof. Roof panels in 1998 would require extensive and expensive ground fault protection (see 4 below).

4.) Put 5 DG-300 panels on my roof and build my own tracker for subsequent panels (the original game plan was for two tracker units with subsequent roof panels). This is impractical since Trace does not provide an upgrade to a unit suitable for use with roof units under current building code, so the unit would have to be returned with a subsequent restocking fee. This restrictive code will be relaxed in the new code which will be effective in 1999.

We decided to purchase a second zomeworks tracker, but painted white to reduce its visual noise level to the nearest neighbor. Unexpectedly, the dampers provided were gloss black (Zomeworks just doesn't get the picture), so these were spray-can repainted with Rustoleum gloss white over white primer, after sanding the gloss black.

We do expect to modify the industrial appearance of the units. Use of the poles to support a vine trellis, potting house, pergola, or gazebo is being investigated. The visually severe edges of the panels may be softened with decorative elements and so transforming the devices into large kinetic sculptures (check back in 2000).

Household Electrical Load Reduction

Almost all incandescent bulbs have been replaced with electronic fluorescent replacements with a substantial reduction (15%) in electrical usage noted. A new refrigerator is much more efficient than the 15 year old unit it replaced. Some thought is being given to replacing an ancient chest type freezer (est. 50 yrs old, runs frequently during the summer) with Sunfrost units. Air conditioning is presently two window units, used very conservatively (our August 1997 electrical usage was 485KWH, quite low for our area considering that we have an all electric kitchen). Future household A/C is expected to use ground heat rejection, which should offer much higher efficiency than conventional units, and which will be highly zoned. Heat pumps are also being investigated, as are a new development, direct-indirect two stage evaporative cooling. This latter appears suitable for our climate and would use little power in exchange for some additional water use.

View into yard from back porch showing tracker units.


View of pole. Pole is 16 feet of 8 inch diameter, 1/4 inch wall steel pipe, terminated with a reducer and one foot of 6 inch diameter pipe. Top of pole is 11.5 feet above grade.

View of a single photovoltaic panel. Panel frames are 50.5 inches by 74.5 inches.

Closeup of photovoltaic panel showing polycrystalline silicon. This is where the sunlight is converted to electricity, which is collected by the metal traces on each side.

View of one of the two tracker boilers.

View of boiler cross connector shield on the low side of the tracker. A tube connects the boilers.

View of tracker shader/reflectors.

When tracker is not pointing at the sun, shading function will expose one side boiler, causing transfer of fluid in the liquid state to the opposite side, where it condenses, the additional weight causing tracker motion. The reflector function enables a grossly misoriented tracker to flip over (typically in the morning) to start the tracking process.

Overall back view of tracker.

Closeup of tracker pivot.

Closeup of damper. The damper stabilizes the panel against response to wind gusts and prevents overshooting during the morning flip.

Closeup of pitch arm. The pitch arm may be seasonally adjusted for better performance. Adjustment is by positioning the arm to a different bolt hole. This may be replaced with a homemade screw type device for adjustment from ground level.

Closeup of wire drops from panels to upper box.

Closeup of lower box on west pole. Large 1.25 inch conduit proceeds underground to house, routed around fruit trees and sanitary drain. Gray plastic conduits are stubs for future instrumentation or telephone.

Exit of conduit from ground at house.

Run of conduit along house to inverter.

Picture of trace inverter all weather enclosure.

[Inverter_Left] Left: Interior of weather enclosure from the Direct Current (DC)side. DC feed is on the right side. Cylindrical object at top is a large capacitor, required when no directly connected batteries are used. Smaller tubular devices on rear wall of enclosure are fuses.

[Inverter_Left] Right: View of Alternating Current (AC) side. Additional connections are provided for generator input and essential AC output when used as off-grid or emergency system. Conduit over top of unit carries AC wires to the disconnect switch.

Safety disconnect switch for use by electric company.

Additional 30 amp breaker supplies power to the buss bars in the service box.

Construction Details

Truck mounted auger is used to drill the foundation pits. This truck was maneuvered and operated from a station at the rear of the truck after disconnecting the driver's steering. [Auger_TRuck]

Soft adobe soil in this location dictates use of a large diameter concrete footing.

Drilling a pit.


Pits were completely flooded by rainstorms and the water softened the walls. After pumping out the water a worker had to scoop out the muck at the bottom of the pits.


Bottom of pits are filled with chip stone for drainage.

Reinforcing cages.


Through rods prevent punch-through and pole rotation within foundation.

Five workmen erecting the pole.


Concrete pumper.

Pumper hose

Ready mix truck. 2.5 yards were delivered. Due to muck removal, additional concrete was required and was mixed on site to complete the pour. Interior of poles were filed up to the top of the base, where a weep hole allows condensate drainage and airflow to dry the interior of the pole.

BELOW: Technician securing conduit to pole


Electrician wiring panels to collector box.