Portland PV Power

Mark Whitaker

©1995 Mark Whitaker have been interested in solar electricity since I was a teenager. I remember dreaming of a cabin in the woods with solar panels on the roof and a woodstove for heat. This was in the late seventies and early eighties, when Mother Earth News was a big fat publication crammed full of do-it-yourself articles and classified ads for cheap land. It wasn't until the nineties that my dream started to become real, at least in part.

I picked up my first issue of Home Power - #22 - at the Oregon Country Fair in 1991, and at the same time I got a catalog from Alternative Energy Engineering of Garberville, California. I was amazed to see how many people were already living this dream of mine, and how easy it seemed. In 1993, I visited some friends in Humboldt County and saw their off-grid home, and also visited Arcata's Renewable Energy Fair and AEE's store in Garberville. I finally realized that a small photovoltaic system was within my reach.

In January 1994, I took a week-long class in solar design taught by Johnny Weiss of Solar Energy International. The class culminated in the installation of a 225 Watt photovoltaic system at the shop of Mr. Sun, a Portland solar water and pool heating dealer. After this, I decided that I was ready, and, in February, when AEE had a sale on some 53 Watt Solec PV panels, I took the plunge and bought two. These are 36 cell panels that make 3.1 peak amps each at 17.1 peak volts

The Loads

My intent was to put together a small system that could power my computer, a couple of lights and possibly my stereo. Since I live in the city presently, and am grid connected, this would give me a chance to live with the system for awhile and get to know its limitations (and my own!) before having to rely on such a system for all my electrical needs.

My computer is a Toshiba laptop that uses only about 50 watts, and I bought a Canon BJ-200 printer specifically because of its small size and low power draw: only about 15 watts or so. I have one 50 watt, 120 vac halogen light and one 13 watt, 120 vac compact fluorescent in my office. My stereo draws about 25 to 75 watts at 120 vac. Also plugged into the system is an old Zenith shortwave receiver.

Other Equipment

Now that I had almost $600 invested in PV panels, the pressure was on! Next came the inverter, and I chose a Statpower PROwatt 250. It had plenty of room to run the computer, a light and the stereo all at once, it was small and portable, and it was cheap.

The other major components of the system were, of course, batteries and a charge controller. The batteries are two Trojan T-105 deep cycle, six Volt batteries wired in series, for 220 AH at a nominal 12 Volts. I also purchased a heavy duty, corrosion resistant box for them. Originally I had planned to make one of plywood, but this plastic box seemed to be superior to anything that I really had in mind. The charge controller is a Steca Midi 8 Amp unit that has a function that allows the controller to charge the batteries to a lower voltage (13.7 V) when the battery was not used heavily the night before. When the battery was used heavily (down to 12.4 V), then the controller charges to a higher voltage (14.5 V). The manufacturer calls this "gassing regulation" and AEE recommends them highly. The Steca Midi also has a low-voltage disconnect.

Other necessary ingredients included a set of analog meters for system voltage, array amps and load amps; a 12 Volt fuse box; a 30 Amp, 2 pole fused

Above: two PV modules make 100 Watts of power.

disconnect; and lots of copper wire. I used #10 AWG type TC outdoor wire to connect the panels together and to a junction box near the roof. From the junction box to the disconnect inside, I used #4 AWG uSe wire. All the rest was wired with #10 AWG primary wire, except to connect the batteries, which was done with #4 AWG cable.

The Process

Now I had to install this pile of expensive equipment so that it worked. I mounted the disconnect, the fuse box, the meters and the charge controller together on a 1 X 10 board. I connected everything according to a combination of the diagrams that came with the charge controller and the general purpose diagrams in the AEE catalog. All connections were soldered and taped. The cigarette lighter plug on the inverter was removed and a normal household socket and plug were specially wired for the inverter to plug into. The neutral was used for positive and the ground was used for negative. This way, if the inverter is accidentally plugged into a 120 vac outlet, it won't be damaged (Assuming, of course, that the 120 vac socket is wired properly. So far as I know, this is not a code-approved way to do this. Editor's note: Mark is right. This inverter's installation does not conform to the NEC.) The cigarette plug was kept and adapted to take a regular household plug, so I can still use the inverter in a car if need be.

The system was ready in time to go to Portland's 2nd Annual IN-POWER Energy Fair in July and powered the Oregon Conservancy Foundation's sponsor booth. We ran a notebook computer which was used to add names and addresses to the OCF mailing list. Oddly enough, besides the system for the music and the stage, mine was the only complete, working PV system there.

Problems

But alas, things were not perfect. Since the loads are handled through the LVD on the charge controller rather than directly from the battery, I couldn't put the array meter between the controller and the battery. It went instead between the controller and the array. This meant that when the batteries were full and the controller short-circuited the panels, the meter would read as if amps were still flowing from the array to the battery. Not true!

Mark Whitaker's System Cost

This was easily remedied however, by bypassing the LVD and taking the loads straight from the battery. The array meter was then moved to the other "side" of the charge controller where it only registers the amps that are actually going to the battery. Since the "control center" for the system is right next to my desk, I can keep an eye on things and I don't need the LVD.

Also, I discovered that my stereo amp doesn't really like modified-sine wave power, as it persisted in producing an annoying hum whenever powered by the inverter. The digital tuner was apparently not fond of the inverter either and promptly mixed up or lost all the pre-set stations. Fortunately, these problems went away with a return to sine wave, grid power.

The third problem really had nothing to do with the system itself. Before I could mount the panels on the roof of my house, I had to replace the roof. During the summer, I had been dragging everything outside during the day to charge, then bringing it in to use in the evening. Obviously this couldn't go on for long, and in September I finally re-roofed the house. It was October, however, before I mustered up the courage to drive screws through my beautiful new roof and mount the panels. On November 13, the whole thing was finally hooked up and running, and I moved one step closer to the dream of my teenage years.

Next Time

As could be expected, I have a few ideas about things I would do differently if I were starting a project like this again. Mainly, I would buy a bigger charge controller and bigger ammeters. The 8 Ampere controller leaves no room for expansion. In fact, I have a Siemens 35 Watt PV panel for my boat that I would like to use at home right now, but the controller won't handle it. I should have bought a controller big enough to handle at least two to three times as many panels as I initially bought. Also, I don't see the need for a low voltage disconnect in this sytem. Since I will someday need to

Mark Whitaker's System Cost

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  • aayan burns
    How to hook power from the meter to the fuse box?
    8 years ago

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