For the last fifteen years or more, I have been making my own electricity with the use of a home-sized renewable energy system. This system is based around photovoltaic panels, but also includes a wind generator, batteries, inverter and power control circuitry. The following is a description of the system, with photos where appropriate.

PHOTOVOLTAIC PANELS

4 Carrizo Solar, 36 cell recycled "quadlam" panels connected in series to provide 12 volt, 4 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 in parallel with the 12 volt quadlam panels above.

18 Siemens SP75, 36 cell panels, connected in series-parallel to produce 36 volt output.

The nominal power output of these panels on a clear, sunny day is approximately 1000 watts. The 12 volt array provides battery charging to run a small inverter system to provide a few lights and run office equipment. The 36 volt array is dedicated to a grid intertied inverter.

The output of the 18 Siemens SP75 solar panels is wired through a combiner which splits the panels into three arrays of six panels each. The individual panels are connected in series strings of three to provide 36 volts, then two series strings of panels are paralleled. The three series/parallel arrays are then sent to the Maximum Power Point charge controller for conversion to 24 volts to charge the battery bank.

BATTERIES

Storage of the power produced by the 12 volt solar panel array falls to a pair of Trojan T-105 deep discharge, flooded lead acid batteries. These batteries are six volts each and series connected for 12 volts nominal. Storage capacity is 180 Ampere-hours

The 24 volt system uses two 100 ampere-hour, 12 volt gel cell batteries connected in series. Since this system doesn't need to supply power to loads when the sun is not shining, the 100 ampere-hour capacity is more than adequate.

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 in the 12 volt system 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. A commercial 50mV shunt is also installed in the system, connected to the E-Meter. The homebrew shunts measure 12 volt PV current, wind plant current, charge current total, and total charge/discharge current of the batteries.

The 24 volt system uses standard 50mv shunts, a 500 ampere shunt on the main battery supply connected to the E-Meter and a 50 ampere shunt on the photovoltaic supply connected to a dedicated 0-50 ampere analog meter.

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 12 volt batteries is 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.

The 24 volt system uses 2-0 welding wire for the batteries and inverter feed, and the PV panels are connected to the combiner with 8 gauge. 4 gauge welding wire is used to connect the PV combiner breakers to the batteries.

DISCONNECT: A 250 amp disconnect is provided to remove power from the 24 volt system for maintenance or fuse replacement.

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 on the 12 volt system. 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).

A 150 ampere DC rated fuse protects the 24 volt inverter from overloads, and three 20 ampere DC rated circuit breakers plus one spare are used for PV panel disconnects. A rack panel of 24 "grasshopper" fuses provides low-current disconnect and overcurrent protection for small loads on this system.

METERING

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

CHARGE SOURCES: On the 12 volt system, 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.

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: On both the 12 volt and 24 volt systems, 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 output of the 24 volt system's Outback inverter to measure total kilowatt hours produced/delivered to loads.

INVERTERS

Two inverters convert the 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.

OUTBACK GTFX2524 : 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. Programming and control of this inverter are accomplished by use of the Outback "Mate" display panel and control surface.

HEART 1200: While not actually installed in my system, I have a salvaged Heart Interface 1200 watt modified sine-wave inverter hanging around in case I need portable power on the tractor or on a job. This inverter was 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, two separate controls are used on the individual systems. On the 12 volt system, a Trace C-30 charge controller limits the terminal voltage to the batteries in three steps, bulk, absorption and float. In the 24 volt system, the battery charge is regulated by the Outback GTFX2524 inverter.

The 24 volt system was recently outfitted with an Outback power Systems MX-60 charge controller which utilizes maximum power point tracking (MPPT) to optimize the amount of power generated by the photovoltaic panels. This charge controller is capable of taking a voltage higher than the battery bank's nominal terminal voltage of 24 volts and stepping the voltage down while increasing the available charging current. The MPPT system integrates the voltage and current being delivered to the battery, calculating the power in watts. The controller then adjusts the operating voltage of the PV arrays to provide the maximum charging current, while continuing to deliver the proper 24 volt nominal charge voltage to the batteries. This is a truly remarkable technology, wringing the maximum available amount of power out of the PV array under all conditions of temperature and light.

POWER CABINET

The 24 volt inverter, metering and batteries are installed inside a waterproof NEMA style enclosure located underneath the PV array. In the old system, very long runs of undersized wire carried the power from the panels to the "power trailer", with a lot of resulting loss of system efficiency due to voltage drop in the wiring. When I rebuilt the new system, I decided that I wanted the inverter and batteries as close to the panels as possible. Finding a surplus cabinet that was big enough to hold all of the gear, and completely water tight made it possible to put the important parts of the system right where the power was being generated.

The cabinet has 19" rack rails, which made mounting the various components easy, and allows the system to be changed without having to tear things too far apart, new rack panels can be fabricated and mounted in place of those in the photo if and when the existing equipment is replaced or updated.

The top panel contains the E-Meter, Outback "Mate" keypad and display, and a 0-50 amp meter for reading PV output current.

Below that is the AC power panel, with a killowatt-hour meter to accumulate power production totals, circuit breakers for AC power input and output to the inverter, and a pair of convenience receptacles, one on the utility side and one connected to the inverter's output.

The thin panel with the many slots is the "grasshopper" fuse panel, which has only a few fuses installed for the E-Meter and cabinet fans, and a set of binding posts.

The bottom rack panel is dedicated to DC power. Four 20 amp circuit breakers for PV input and a 175 amp breaker for inverter DC input/disconnect.

The inverter and charge controller are bolted to the rear of the cabinet, and the batteries are situated in the bottom of the cabinet, surrounded by rigid foam insulation.

WIND GENERATOR

A Southwest Wind Power AIR 403 wind generator is installed in the system, and sits atop a small 25' 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 110 volt ac 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 !

In summer of 2005, the home-built flat plate collector was replaced with a commercially manufactured flat plate collector with an area of 4 by 8 feet. This collector is equipped with all of the proper accessories, low-iron glass, anodized aluminum collector plates, and an extruded, gasketed, sealed enclosure. The difference in heating efficiency between the home built collector and the manufactured one is astounding! I have a total of three of these 4x8 collectors. Once the other two are online and operating, I should have more than enough hot water to run the washing machine, showers and all of my domestic hot water needs from solar.

SOLAR POWER IN THE DAYS OF YESTER

In summer of 2005, nearly the entire system was rebuilt and re-outfitted with new equipment. Some of the solar power equipment I had used up until this time was borrowed seasonally from the Oregon Country Fair. My association with this group ended formally in 2005, and I returned the equipment for the last time in June of that year. This allowed me to make choices of newer, more appropriate equipment to better serve my needs. The old solar power system was detailed on this page, and is now archived here for your reading.

Last Update: May 6, 2006