Imaior

Chris Laughton

© 1998 Chris Laughton

Above: The Reclamator with one of its three PV arrays in place.

hile staying with friends in Scotland during the Christmas

_ _ break of 1996, I met the owner of a rather unusual piece of equipment: The Waste Reclamator. This machine is a flat-bed trailer holding a four meter (13 ft) long conveyor belt to sort out waste at fairs and festivals around the UK. Collected trash from an event is tipped into a galvanized steel chute at one end of the moving belt, allowing a line of people to pick reclaimable items. Remaining debris tumbles off the conveyor and into waiting bins.

During its first year, the belt had been powered from either the 240 VAC grid mains (the utility grid to Americans), using a long flex (a flexible round cord), or with a portable 1 KW gasoline generator. The final drive was a 370 watt (1/3 hp) star-wound motor with a 1:36 reduction gear pulling up to 1.5 amps. There was a Siemens MicroMaster NN37 drive controller in series with the supply. This rather clever item allowed a smooth motor start-up under load, but also variable conveyor speed, adjustable with a user-set knob.

Bright Idea

Despite the winter conditions of the Scottish surroundings, a bright idea came to us over the Christmas turkey—to apply some renewable energy to the Waste Reclamator. This would not only enhance its appeal as an attraction but also improve its environmentally benign credentials. I based the design on my previous stationary PV systems. I wanted to provide an on-board inverter to eliminate a generator on remote sites, and to charge the batteries during storage, traveling, and whilst operating.

First we had to decide where to mount the PVs. My first preference was to create a new framework over the trailer to make a horizontal PV roof which would happily charge no matter which way the trailer was parked. However, the clearance required for people to work underneath on the conveyor would have meant a very high structure which would not fit in the Reclamator's garage. Also, the thin trailer sides were not strong enough to hold the PVs while traveling. This left us no option besides a removable array.

BP Solar Donation

At this stage BP Solar generously donated twelve BP160 65 watt framed modules, which seemed like the maximum number for a movable array. To ease the constant re-making of the array at each site, sets of four modules were bolted to 50 mm (2 in) aluminum U-channel. We had three sections in all, each weighing 35 kg (77 lb)—just light enough for one person to lift. The weight of arrays was taken by the trailer bed, using galvanized 40 mm (1.6 in) steel tube. The removable subarrays pivot to allow angle adjustment at each site.

Heavy Problems

The challenges of designing a mobile PV system were now becoming clearer. Not only did the array need to be easy to dismantle and store on the trailer, but the trailer offered no natural protection for the equipment. This was quite an issue considering the inevitable road salt spray behind a towing vehicle. But the biggest hurdle was the accumulating weight of gear. The location of the conveyor on the trailer bed meant that the weight distribution was already badly skewed to one side, and the battery location had not yet been chosen. Our first tasks were to upgrade the suspension, add close-coupled tyres, and a hitch with up to 3500 kg (7,716 lb) capacity.

A Tight Fit for the Batteries

The 300 kg (661 lb) of lead-acid batteries had to be slung under the trailer bed well away from the proposed inverter location, and all of the weight had to be balanced. Flooded cells were out of the question because of ground clearance and maintenance issues, so we chose sealed-gel batteries. We purchased used 6 volt DC cells from a Telecomm project, with a capacity of 100 amp-hours at a 10 hour rate. They are entirely cased in hard yellow plastic with threaded M6 posts. We laid two rows of four on their sides, so that all interconnects would be accessible.

Below: The Reclamator power panel showing inverter, charge controller, AC breaker and MCB, and shunt. The back of the E-Meter can be seen in the folded down door. At right are the three plugs for the PVs.

Above: The feed end of the conveyor belt. Local solar techie Phil Evans shows the power panel.

A battery case was constructed from welded angle steel and 25 mm (1 in) exterior plywood. One side was cased in Perspex (trade name for a type of clear acrylic sheet) to allow the public to see the wiring. We bolted a 160 amp fuse to the positive terminal to protect against a short between the inverter and the battery bank. We terminated all cables with crimped terminal ends, with wing nuts on the battery posts. Two long bolts came through the plywood of the box, one for positive and one for negative, to allow easy removal of the main connections. Then the battery case could be lifted on a hydraulic jack and bolted to the trailer chassis as one unit, without any cables attached.

System Components

This battery layout worked well for the 24 volt system, resulting in a total 100 AH capacity to 50% discharge. It also suited the PVs and the choice of a Trace 624 SB/E for the inverter/charger. A Trace C40 served as the PV charge regulator and an E-Meter was used for monitoring the system. The harsh environment dictated a high-integrity lockable IP65 steel cabinet for this equipment. We bolted two pull-out Class-T fuses (50 and 100 amp respectively for the PV array and battery) to the sides of the cabinet as emergency disconnects. We bolted three yellow 32 amp CE22 sockets to plug in the arrays and a blue 16 amp CE22 socket for mains battery charging to the other side. Finally, we mounted another blue socket externally as the 230 VAC inverter output, via internal 5 amp RCDs.

We ran the battery cables into the bottom of the cabinet through steel bushings penetrating both the cabinet and trailer chassis. We were concerned about the possible heat build-up in the sealed cabinet, but the large metal

Photovoltaics j-j.

The clamator's Power System

Utility grid 230 volt AC

Twelve BP 160 photovoltaic modules 65 watts each, totaling 780 watts at 24 volts

Utility grid 230 volt AC

Twelve BP 160 photovoltaic modules 65 watts each, totaling 780 watts at 24 volts

Yellow 32 amp CE22 plugs & sockets

Eight 6 volt lead-acid gel-cel batteries wired for 120 amp-hours at 24 volts

Cruising Equipment E-Meter

Yellow 32 amp CE22 plugs & sockets

Eight 6 volt lead-acid gel-cel batteries wired for 120 amp-hours at 24 volts

Cruising Equipment E-Meter

20 amp fuse

Blue 16 amp CE22 plugs & sockets

Trace 624 SB/E inverter/charger 600 watts continuous

Three-pin 13 amp plug

Blue 16 amp CE22 plugs & sockets

Trace 624 SB/E inverter/charger 600 watts continuous

20 amp fuse

To Reclaimator motor and controls

Blue 16 amp CE22 plugs & sockets surfaces were likely to dissipate the heat. The Trace inverter was given extra lower supports to protect it from road vibration. It may be worth noting that here in Europe, a gradual harmonization of voltages is taking place such that the UK 240 VAC is being lowered to 230 VAC, so this E version of the Trace is set at the lower voltage.

Grounded

The principal hardware we used is undoubtedly familiar to Home Power readers. But spare a thought for how this system could be grounded. In particular, should the

DPST charging switch inverter neutral be tied to the chassis/battery negative and the PV negative and frame? Bear in mind that the grid mains might also be connected at times. At first, the neutral was linked to the earth ("ground" to Americans) terminal in the 240 VAC distribution/disconnect box, which is common practice in portable generators in the UK. This earth terminal is linked to the chassis and to both negatives. However, this would trip the obligatory RCD earth protector when charging the batteries via the grid mains. So the link was removed and the neutral only becomes linked to earth by the utility at its sub-station. A future solution for this may be a triple pole changeover switch on the charging circuit. The UK regulations covering low voltage systems are not as well defined as they are in the USA NEC code, especially for portable PV generators. Strictly speaking, a copper grounding rod should be used at each site and all extraneous metal parts in the system linked to this point, which is a problem on pavement.

Cable Notes

The round trip distance from the furthest PV module to the C40 regulator was measured as 16 meters (52 ft). We used 10 mm square (between 6 and 8 AWG) stranded conductors. All three flexes were cut to equal lengths to balance the arrays. However, this was a tight fit into the gland (a rubber seal) cut into the box at the back of the BP160. The final drive motor was theoretically rated to draw a maximum of 1.5 amps at 240 VAC which meant a possible 15 amps on the DC side over the 10 meter (33 ft) round trip to the inverter. This meant that two lengths of 35 mm square (2 AWG) for each polarity should be ample. Imagine my horror when I connected the clamp-meter of my Fluke 123 oscilloscope and saw peak currents of 10 amps on the AC side!

Further analysis revealed the reason for this. The clever Siemens drive controller was in fact causing problems with the volt-current phase relationship. This was not surprising, as it is principally a large set of capacitors powering an inductive load. Amazingly, the AC side was happily at 1 RMS amps (full conveyor speed), 287 peak volts, and 228 RMS volts. This compared to 326 peak volts and 235 RMS volts when using the grid mains, indicating the flat top characteristic of modified sine wave voltage curve. Measuring the DC side indicated that the Trace inverter was coping admirably with this strange load, with peak current at 18 amps within each 10 millisecond cycle (equivalent to 50 Hz on the AC side), and 10 RMS amps.

Reclamator PV Upgrade Costs

Description of Materials

Cost in £

Twelve BP160 PV modules (retail & freight)

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