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from east to west and north to south, all at [he same time. At dusk, the "trackers" automatically reset hack to the east, awaiting the sun's return the next morning. Each tracker is driven by two small electric motors,

A small baLicrv operates the motors ai night so the array is pointing toward the east.

Controlling the Power

Under a bright, clear sky the three arrays will produce over 118 amps continuously Peak current has been noted at over 125 amps, A Heliotrope General CC-120E was used lo control the current to protect Lhe batteries.

This controller is state-of-the art in power MOSFET design. Using PWM (pulse width modulation), the power MOSi-ETs keep the baUer> bank from being damaged by overcharging. Although the CC-120E is specified lor 120 amps, the first unit did noi survive. After consulting with Heliotrope General we decided to add additional heal sinking to the controller This heat sink consists of a half-inch thick aluminum plate about Four feet square. In addition to the aluminum plate, several sections of a large extruded heat sink were also attached to the plate.

The CC-120E has an internal cooling fan controlled by the temperature of the blocking diodes. The fan will run when the case temperature reaches 100°F. Al no time has the automatic thermal shutdown stopped lhe CC- 120E.

Battery Storage

We used good of lead-acid batteries, wired in a 24-volt system, The bank consists of 24 6V golf-cart batteries. Each battery has a capacity of 220 amp/hrs. so the battery storage bank has the capacity of 1320 amp/hrs al a 20-hour rate of discharge.

Loads

A Trace 2420 sine wave inverter supplies AC lo all of the loads. So far, there has not been any load that the Trace ha:s not been able to handle. This includes a deep well pump and various refrigeration units. The Trace has an internal DC charger, but this feature is noi being used. With automatic shutdown from everything from a low battery to an over-temp condition, the Trace has been working without a glitch since day one.

It has also managed to survive several very close lightning strikes, when it would shut down, wait a lew minutes and then restart.

The Trace inverter, at the time the system was being designed, was available only for 24 volts. It is now available for 4tt volts. Had that unit been on the market, 1 would have chosen il, which would have reduced the cost of the welding cable used to bring in the power from the arrays.

System performance

The system has been online for over a year ant! has produced over 4 million kW hours.

Two of the dual-axis trackers failed, hut they were replaced by the manufacturer. Since the replacements were installed we ha\en*t noted any problems with the trackers.

With the dual-axis trackers, in the summer months the array-to-load ratio is over 10:1. This means there is slightly more than twice the arra} capacity than load demand. The battery bank can be depleted to 50 percent at night and he fully recharged by lhe middle of the next day.

During the winter months, the array-to-load ratio is a break-even 1:1. The battery storage is sized a bit uh> small to operate alt the loads during the winter. Increasing the battery size would provide greater running time, but it would also increase the time required to fully recharge. In Lhe summer. Ohio averages over seven hours of sun per day when using the dual-axis trackers. However, in Januarv we average only three hours.

Things I Would Change

My original design did not specif) the dual-axis trackers. 1 had specified a seasonal adjustable top-of-pole mount. In this location of Ohio, the trackers will nut produce much additional power during the worst part of the year.

In January, the sun sits too low in the south for the trackers to do much good, but Chuck had to have them.

I had original iy specified Trojan L- i 6 batteries for the battery bank. Chuck decided against them from two reasons. First, new 6-volt lead/acid golf-cart batteries were available for S38 each from a local source. The L-I6s. on the other Iwid. were S190 each The !16 is also 6 vulLs.

The golf-cart battery weighs about 70 pounds. The L-I6 is 120 pounds. Since the batteries are in the basement, each battery would have had to be carried down hy hand. Of course, when a battery went bad, it would have to be carried up as well.

Wh\ not use a different batier> ? Well, ideally, a forklift batter) would have been my first choice. The problem is, you need a forklift to move tine! We considered NiCd batteries, bui their cost pul them out of the question. When the current batteries need replacing, we ma> use large 2-volt sealed lead-acid batteries.

The Bottom Line

What is the payback period? Well, the whole system cost about S35,000. Had Chuck gone with the top-of-pole mount instead of the dual trackers, he would have saved S7.500. And using I -16s instead of lhe golf-cart batteries would have cost him about $2,000 more.

As for the payback period? Well, Chuck will mure than likely never see the system pay for itself. However, several months after the first array went online. Chuck's electric bill dropped so much Ohio Edison sent out a troubleshooting crew.

Still, not counting any maintenance of battery replacements. Chuck is looking at around 15 years before he breaks even.

Caveats

Electrical spacc healing and refrigeration are two loads that should be run on a source of energy besides PV In this case. Chuck is running both air

Continued on fmge H3

Photo B, Tiw array is supported by an S pipe which is seated in five feet of concrete.

Number 35 on your Feedback card

GEM Electronics, Inc.

Need a Data Sheet 011 □ particular relay, or some general information on relays'? GEM Electronies can help you with their line of Meder Electronic Relays. Circle Reader Sen ice No. 203.

CK»n Urtciilirj

Active Filter Cookbook

CK»n Urtciilirj

Active Filter Cookbook

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Active Filter Cookbook

Microcomputer guru Don Lancaster has been at it again with tins E 7Lh edition. So whafs ;in active filter? It's a combo of op-amps, resistors, and capacitors which replace traditional bandpass and highpass filters with something smaller, less expensive, easier tuning, and simple in design. The book runs 240 pages and is packed with enough application circuits to keep a nuifder happy for months. Ils S2N.50 via beuer book stores or from Synergetics Pre>s. Box S09G, Thatcher AZ 85552, Circle Reader Service No. 20K.

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Cubex Antenna Company

The CUBEX Antenna Company has produced the

"BUMBLEBEE" 6m element quad antenna. It is all fiberglass with .i heavy duly aluminum mast to boom coupler The antenna is ted directly with 52-ohm coax and features the exclusive CUBEX tuning block thai allow s the antenna resonance point to he adjusted so that the entire 6m band can he used without completely changing the wire elements, The antenna comes with the driven element pre-marked for a resonant frequency of 50*4 MH/. giving the antenna a bandwidth ot 1.5 MH? at an SWR of less than 1.7 to 1 > The antenna can he rotated for horizontal or venical polarization, and has a boom length of 27 inches. The best feature ¡s the price of $69.95 FO B. BREA CA. PLUS S12 S & H. Circle Reader Service No, 202.

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