Backwoods Solar Electric Systems

For an Earth Restored and a World at Peace... Independent Electric Power Systems for the

Remote Home—Solar Electric, Wind, Hydro

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Steve & Elizabeth Willey • 8530-HP Rapid Lightning Creek Road • Sandpoint, Idaho

Lincoln J. Frost, Sr.

Lincoln J. Frost, Sr.

So you are thinking of going solar. You are wondering, "Can I do it? What will it cost?" First question, if you know or can learn what a volt, ampere, ohm, direct current, and alternating current are, if you can add, subtract, multiply, and divide; you've got a start. If you can recognize black, white, green, and red colors, and differentiate between + and -, you've got a good leg up. Having a modicum of skill with hammers, screwdrivers, various pliers, and a few small wrenches, saws, etc. should about do it. Power tools are a big help but you can do it all by hand.

The second question depends on how far you want to go. A good midpoint figure might well be $20,000. A modest setup might be $10,000, whereas a fairly plush one might be $30,000. That's if you do all or most of the work yourself and shop around a bit. My firsthand experience has been with the $20,000 setup, coupled with utility backup and what all it took to get there.

A PV system needs four main things: solar modules, batteries, voltage regulator, and an inverter. There are, of course, miscellaneous fittings and hardware. I selected the Trace SW4024 inverter because it would do just about anything I would want, now and in the foreseeable future, plus I could add on for 240 volts should I want that feature at a later date. Next, I wanted batteries that would have the capacity to keep the installation running for four consecutive cloudy days. I chose twelve L16, 6 Volt, 350 Amp-hr Trojan batteries.

The more or less unknown factor was the solar modules. There are many to choose from. I wanted enough to get started yet to which I could easily add on to fit actual requirements. Ten Siemens PC4JF PV modules were chosen. Finally I found that a Heliotrope PWM CC120E was required for my voltage regulating job. With these four basic components I started to accumulate the "miscellaneous hardware" and build it into the system.

My house had already been built for some years and fortunately had a utility-powered distribution box in a fairly handy place to allow jumping circuits to the new solar distribution box from the old box. Now don't get the idea that I am an electrical whiz or guru, I'm not. I'm just an 84 year old former chemical engineer. The miscellaneous hardware can usually be found at Home Depot, Scotty's, Wal-Mart, K-Mart, True Value, Grainger, Graybar, your local hardware store, or electrical supply house. I live in Everglades City, Florida, pop. 350, 35 miles south of Naples. The four main items you will probably have to get through a dealer. Look in Home Power or inquire around locally.

The Installation

A local welder made aluminum frames out of 2 inch angle stock that held five modules each. This was later found to be a poor choice because you can more easily wire six modules in a set, in parallel and in series, than wire the two sets of five in parallel and then in series. #8 wire was used, feeding into 1/0 AWG for the 50 ft. run to the controller. The frames were carefully fitted to the module dimensions so as to be a "kiss fit" all around and were fastened together with small stainless steel bolts, nuts, and washers. They had three hinges along the bottom and three adjustable stays at the top so they can readily be raised and lowered to achieve an optimum angle for the sun, twice a year. Stainless steel bolts have been used wherever possible due to our proximity to the Gulf and salt spray. All the copper wire is oversized since I had a friend who gave it to me. Lucky!

The 12 batteries were wired in parallel and series, four in a set, with 4/0 AWG cable and suitable connectors. 24 VDC comes in on 1/0 AWG cable via the PWM controller to the two opposite end corners and exits to the inverter at the opposite alternate corners of the battery bank via 4/0 AWG cable. Two 50 Amp fuses protect the batteries at the incoming side and two 250 amp fuses protect the batteries to the inverter.

The Trace inverter was hooked up to the batteries and the outgoing 110 vac fed to a Square D 60 amp breaker into the solar distribution box. Since this box was adjacent to the utility box we jumped one house circuit at a time over to the solar box. There are four house circuits on solar and they feed all lighting, the audiovideo center, two computers, a printer, copy machine, ham radio shack, one or two Hunter ceiling fans, and two (as I later discovered) refrigerators. We also run an electric tea kettle, toaster, fry pan, roaster, crock pot, bread maker, etc. as occasion warrants.

What will this setup do out in the real world with utility backup? First of all everything worked! We initially needed the utility for back up once a week to bring our batteries up, a 12 hour charge at 20 Amps. That was when we had only ten modules in place. We were delighted that everything worked but now asked, "How well did it work and what could be done to make it work better?" Copious readings were taken of Volts and Amps, coming in at 24 VDC and going out at 110 vac,

Above: Siemens PV modules shown at both summer and winter tilt angles.

time of day, condition of sun, what appliances we were using, etc. An analysis of this data showed that everything was working well, but to be more self-sufficient additional solar modules would be needed. We would need to add 14 for a total of 24.

The 14 additional PV modules were ordered. We concluded that they should be in four sets of six to simplify wiring the 12 V modules for 24 V. While shifting the modules around, we availed ourselves of the opportunity for obtaining more data by not shutting the system down completely, but running tests on one of the original sets of five modules while it was still functioning. Then we ran tests on the six new modules when they were ready. Data on the ten modules (original two sets of five) had been obtained previously so we measured 12, then 18, and finally the full 24. While gathering the data we blew the fuse in the original C-30 controller so ordered the PWM 60 Amp Heliotrope. Before it arrived we found we would need the 120 Amp model. Yes, we were taking on electricity in sunny Florida at 67 Amps or more!

With all 24 modules in place and the new 120 Amp controller, we settled down to see just what this setup would do. It was along about here we found that we had been running two regular 20 cubic foot GE refrigerators all along! The solar modules had been set at about 40° degrees elevation (Fall equinox) so now at Spring equinox we set them at about 10°. These will be our two yearly settings at equinox time, because the sun altitudes here are roughly 43° December 21 and 87° June 21. Daylight saving time came in and the days got longer. We've been on 100% solar power since January 1, 1996. Keep in mind this is a utility backup system.

Above: Finished Battery enclosure, Trace SW-4024 inverter, Heliotrope CC-120E charge controller.

We do not run any 240 volt on it. No stove, water heater, washer, dryer, air conditioner, nor my shop.

What is the bottom line? Solar is producing 49% of our total electrical requirement! Just about as planned!

Discussion

Let me tell you how we found out that we had two refrigerators on the system. The second and much older fridge stopped freezing caused by a worn out and stuck circulating fan. While the fridge was out of service, we noticed that the PWM controller occasionally indicated "battery charged". This indicated that more watts were being taken in than were being used. What to do with this "excess" electricity? The answer was readily apparent, use it in the second fridge! So after the fan repair job the other fridge was put back in service and thus used up the "excess" electricity.

The next obvious question was just how close were we to a good balance between input and output? We filled the fridge's freezer compartment with gallon jugs of water and let it freeze. Then we put a timer on this fridge and ended up cycling it at 11 AM to 2 PM, the "sunniest" time of the day, and 11 PM to 2 AM when the least electricity was being consumed. The water in the jugs acted as an energy reservoir, freezing and thawing as the fridge was cycled. The PWM does not now show "charged" and we still do not need utility back-up except to offset sudden energy demands and then only for the time of the relatively short requirement!

When using the Cannon PC310 copier, we found that, occasionally when the battery voltage is a little on the low side, the copier will "stick". This can probably be corrected by setting the Trace's Min. Bat . Voltage 0.50 volts higher.

When using the TenTec Delta II short wave radio I thought that there was some RF interference between receive & transmit. Changing the ham radio to a Yaesu FT676GX seems to have eliminated this problem. Further investigation will better pinpoint the cause of this radio frequency interference (RFI) problem.

The Bottom Line

It would be of interest to compare this year's performance to last year's, using past electric bills (before solar) as the best reference available. Taking the 34 month average (January '93 to October '95) as 35.6 kWh and the 8 month average (November '95 to June '96) as 18.1 kWh, it is found that the present system is providing about 50% of our total electric requirements and about 100% of our engineered goal.

Below: Twelve Trojan l-16 Batteries, 1050 Ampere-hours at 24 Volt.

Frost System Costs

Above: Solar modules, juncture boxes, and adjustable stays.

PV Modules

The Siemens PC4JF photovoltaic modules were readily installed and mounted in the custom made, hinged, aluminum frames. Wiring was made a little easier by using auxiliary connectors to attach the #8 wire to the terminal boxes. They were wired in sets of three in parallel then the two sets per frame are paralleled for 24 Volts. The owner's manual and installation guide were somewhat helpful and should be read and reread to insure a correct installation.

Battery Charge Controller

The Heliotrope General CC120E controller was easily installed after very carefully reading the manual. It came equipped with a fan and battery temperature sensor. The table and diagram in the manual about state of charge required some study. Several trial settings were needed to zero in on the correct setting that ended up being 30.6 volts. The door, or the front plate, of this controller should be hinged so that the adjustments can be more readily accessed.

Batteries

The twelve Trojan L16 batteries were checked on receipt for voltage and were found to read 6.27 Volts in February '95. After being in the system during it's many trials and adjustments the specific gravity read 1.280 on March 29, '96 just after an equalization charge. A second complete check was made and the specific gravity was 1.200 on all cells.

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