Here's an archived copy of the page describing my previous version of the solar power system. For the current configuration, go to the (New) Solar System.

PHOTOVOLTAIC PANELS

8 Carrizo Solar, 36 cell recycled "quadlam" panels connected in parallel/series to provide 12 volt, 10 ampere output. These panels were salvaged from a commercial solar power utility project, then re-sold to the public. (Here's an interesting link to a description and photos of the now defunct Carrizo Solar electric power plant from which these panels were recycled)

1 Siemens M75 48 watt, 33 cell panel, connected to a relay which switches it either in parallel with the above Carrizo panels for additional battery charging current, or series, to produce 24 volts to run the circulating pump for my solar-heated hot tub.

2 Siemens SP75, 36 cell panels, connected in parallel with the rest of the 12 volt string of PV's. These modules are on loan from a friend, and will eventually replace the quadlam panels, which take up a lot of rack real estate.

16 Siemens SP75, 36 cell panels, connected in series-parallel to produce 130 volt, 8 ampere output (the photo above shows only 8 of these modules). The power produced by these panels is wired back to the house as high voltage, then run through the Todd 75 amp "Power Source" to provide 12 volt, 65 amperes. They are also used to charge my electric vehicle during sunny weather.

The nominal power output of these panels on a clear, sunny day is approximately 1600 watts. The panels are properly grounded and have metal-oxide varistors installed for lightning and surge protection. The negative leg of the 12 volt array, and the positive leg of the 125 volt array share a common conductor on the way back to the power trailer. This produces a semi-balanced circuit, further reducing voltage drop and associated power losses.

POWER PROCESSING

The output of the 16 Siemens SP75 solar panels is wired back to the power trailer as 130 volts, at 8 amperes to minimize the losses associated with long runs of small gauge wire. At the power trailer is a Todd Engineering 75 amp "Power Source" battery charger. This piece equipment is a switching power supply capable of converting 125 volts, AC or DC into 12 volts, at an efficiency of 80%. This power supply has been slightly modified, bypassing the original input rectifier to increase output by about 2 amps. I estimate the power losses in the wiring using this configuration at approximately 3%, as opposed to over 50% using the same undersized wiring at 12 volts directly to the batteries.

One reason for using the high voltage array is that the output of the series connected modules is a perfect match for charging my electric car. A double-throw disconnect is installed to allow me to interrupt the current going into the renewable power system, and instead, shunt the power produced directly into the EV's 108-volt battery pack. The mismatch in voltages works out to my advantage, as the fully-charged terminal voltage of the car is about 130 volts, approximately the nominal output of the PV's under a moderate load. No charge controller is installed on the car's feed, so I have to pay close attention to the state of charge in the car, and manually disconnect it when it is fully charged.

BATTERIES 

Storage of the power produced by the solar panel array falls to a set of 24 recycled C&D 450 ampere-hour lead-calcium batteries. These cells are connected in series/parallel to produce 12 volts at 1800 ampere-hours. The practical ampere-hour rating of these batteries is reduced to approximately 900 ampere-hours or less to minimize the stress placed on this type of cell during deep-discharge conditions. These batteries were originally the back-up power source for the Bonneville Power Administration's head office telephone system, and as such, never saw much use, having been float-charged for most of their life. The batteries are housed in a separate insulated enclosure to isolate them from sensitive electronic equipment. As a bank, these cells weigh almost 2,000 pounds. (That's a standard desk telephone atop the batteries in the graphic, to show relative size.)

SHUNTS/WIRING/FUSES

SHUNTS: A variety of current measuring shunts are employed throughout the system. As some of the recycled meter movements that I chose to use did not comply with the default 50mV specification, I manufactured my own homebrew shunts out of various sizes of threaded brass rod, 6-32 rod for 15 amp shunts, 10-32 rod for 30 amp shunts, and 1/4" rod for a 100 amp shunt. Two commercial 50mV shunts are also installed in the system, connected to the E-Meter  and Todd charger outputs. The homebrew shunts measure 12 volt PV current, wind plant current, charge current total, and total charge/discharge current of the batteries.

WIRING: As much as possible, wiring for the system was oversized to allow a comfortable margin for expected currents that would provide the least voltage drop. Wiring to the batteries is four runs of fine-strand 0 gauge, while most small 12 volt loads is 10 gauge. The exception to this is the wiring to the photovoltaic panels, which is eight runs of 10 gauge, 150 feet long, pitifully undersized for the job it is expected to accomplish. My next investment in the system will be for heavier gauge wiring to the panels.

DISCONNECT: A 400 amp two-pole disconnect is provided to remove power from the system for maintenance or fuse replacement. This device was custom built using an ITE three-phase, 200 amp disconnect cabinet which was salvaged after one of the three legs burned out. The interior of the cabinet was modified to include DC circuit breakers, small load fuses and two 50mV shunts.

FUSES: A variety of overcurrent devices are installed in the system. A 110 ampere Class T fuse is installed in series with a 100 amp DC circuit breaker to protect the Trace 812 inverter. A 350 amp class T fuse protects the Trace SW2512 inverter. Eight Airpax low voltage circuit breakers protect the charge sources, loads, and second battery charging branch circuit. Dozens of automotive-type 3AG fuses protect the metering circuits, which are connected to the shunts in the positive leg of the system (there is a reason for this, but don't make me explain it).

METERING

A variety of meters allow constant supervision of the condition of the solar electric system:

CHARGE SOURCES: Several shunts and associated meters measure incoming charge current from the photovoltaic panels, wind generator, and grid-connected charger on 0-15, 0-30, and 0-50 ampere analog meter movements. A master charge current meter of 0-100 amp scale is connected in the circuit between the PV's and the batteries. On the high voltage side of the PV's array, a 0-150 volt meter measures potential, and a 0-10 amp meter keeps tabs on current going into the Todd DC-to-DC converter.

ANALOG EXPANDED-SCALE VOLTMETER: A homebrew 11-15 volt DC analog voltmeter (constructed from plans found in Home Power Magazine) provides a continuous indication of the battery terminal voltage.

E-METER: A Cruising Equipment Company digital E-Meter provides continuous information about battery voltage, charge/discharge current, total ampere-hours plus or minus, and total hours until discharged.

WIND GENERATOR VOLTAGE:  An analog 0-15 volt meter movement provides an indication of relative wind activity from the wind generator.

ANEMOMETER: While not strictly an instrument connected with the solar electric power system, a Trade Winds Instruments anemometer provides direct measurement of the wind velocity on two analog scales, 0-30 and 0-120 MPH.

AC VOLT METER: For the few times I wish to check the output voltage of the inverters, an antique, copper-cased, iron-vane voltmeter provides the indication on a 0-150 volt scale.

KILOWATT HOUR METER: A standard utility-type AC kilowatt hour meter is connected in the AC line with the Trace SW2512 to measure total kilowatt hours produced/delivered to loads.

INVERTERS

Two inverters convert the 12 volt direct current from the batteries to 120 volt alternating current:

TRACE 812: The workhorse inverter in this system is a little Trace Engineering 812, 600 watt modified sine-wave inverter. This power conversion device runs all of my AC lighting (compact fluorescents and low-wattage incandescent), kitchen appliances, stereo equipment and more. In the early days of the system, it even ran the hair dryer, Skil saw, belt sander and various shop tools. This inverter will surge to 1200 watts for a short period, and so far, it has been indestructible.

TRACE SW 2512: This is a 2500 watt sine wave inverter, and is used primarily to run the computer and to power loads for charge controlling. As the low-power efficiency (<100watts) of this inverter is less than the Trace 812, I "save" it for larger loads like the vacuum cleaner and loads which require sine-wave power to operate properly (no scrolling interference lines on the computer monitor). This inverter will sync up to the power line to allow load diversion and battery charging simultaneously. Multiple digital metering and programming features make this inverter very flexible.

HEART 1200: While not actually installed in my system, I have a few salvaged Heart Interface 1200 watt modified sine-wave inverters hanging around in case I need portable power on the tractor or on a job. These inverters were purchased from a local RV manufacturer as scrap and refurbished to operating condition.

POWERSTAR POCKET SOCKET: Also not part of the solar system proper, I keep this 100 watt inverter in the pickup in case I need to solder something, or run the compact fluorescent trouble light. It has on one occasion, kept a FM radio station translator on the air during a power failure.

CHARGE CONTROL

If left unregulated, the current flow from the solar array would overcharge the batteries. To prevent this, a homebrew charge controller senses the battery terminal voltage and switches on a relay when the voltage reaches 14.6 volts. This relay is connected to the AC power input of the Trace SW2512 inverter, which is programmed for utility intertie, allowing the excess current from the panels to be used to run AC loads, primarily the refrigerator. When the battery terminal voltage goes down to 13.1 volts, the relay is de-energized, disconnecting the inverter from the AC supply, and again allowing the solar panel current to flow into the batteries. To be fair, the Trace SW2512 contains a voltage sensing circuit nearly identical to the homebrew controller I use, but since mine was already in use with the Trace 812, I used it instead. A manual over-ride switch allows the inverter to be powered up from the AC line continuously for battery charging from the grid. A second relay is also connected to the solar panel charging circuit to allow charging of a second, smaller back-up battery bank.

WIND GENERATOR 

A Southwest Wind Power AIR 403 wind generator is installed in the system, and sits atop a small 20' stub tower in the yard. Wind conditions here are minimal, and with the tower being so short, this machine is used as kinetic sculpture more than anything. One day, I would like to put it atop the 80 feet of Rohn 25G tower I have stacked in the yard, but I fear the zoning and permit people down at the city offices would have a fit! One day...

FLAT PLATE SOLAR WATER HEATER 

As I do not live on property which has geothermal possibilities, I had to come up with a renewable energy solution to heating water for the hot tub. Some recycled copper strap from a demolished radio station, used plate glass, scraps of wood and rigid insulation and some cut-off ends of reflective Mylar from the plastic supply house, and presto! the cheap-o solar water heater is born. I did have to buy some new copper tubing and fittings, but the cost was minimal. I have one piece of advice for anyone who thinks they would like to construct their own flat plate collector, DON'T! I ended up putting about 100 hours of my time into this monster. It would have been cheaper and easier to purchase a ready-made panel and just install it. Otherwise, it works great! A 24 volt permanent magnet motor runs a centrifugal pump to circulate the water, a filter to catch the big stuff and some garden hoses complete the water circuit. I did weld up an adjustable azimuth and elevation mount so that I can manually track the sun during the day. This set up provides 100% of my hot water needs for bathing for 4 months out of the year, with some assistance from wood-fired backup for another two months. During the summer, the water sometimes goes above 122 degrees F !

SOLAR POWER GOES ON THE ROAD  Go to the Power Trailer Page

For six weeks out of the year, the various components of this solar electric system are used to power Main Camp at the Oregon Country Fair. The batteries, SW2512 inverter, some of the metering, and photovoltaic array are assembled as a system on a tandem-axle horse trailer and hauled out to the woods to power lights, kitchen appliances, power tools and electronic communications equipment. During this time, I am left with only the Siemens M75 48 watt PV panel to keep the home power flowing. Fortunately, I use the utility grid as a back-up power source during this time (Oh, how I hate to see that electric meter spin the "wrong" direction!).

Last Update: Feb 12, 2005