A South American fleet-telematics equipment maker came to us for a 20 W panel that no catalogue part covered: rectangular, sized to the mounting area of a vehicle tracking terminal, with a junction box, spare lead at both ends and a vehicle connector in place of MC4. Like most custom flexible solar panels projects, the hard part was never the cells. We drew the part, selected the cells and ran the build at the partner factory we work with, and the first 500-unit batch was handed over in early 2024.
| Project | Detail |
|---|---|
| Application | Panel powering a satellite vehicle-tracking terminal on freight trucks |
| Part | 20 W semi-flexible PET laminate, 36 monocrystalline cells, about 691 x 278 mm |
| Custom points | Rectangular format, junction box, extra lead length at both ends, non-MC4 vehicle connector |
| Volume | Quoted at 100 / 300 / 500 units, ordered at 500 |
| Timeline | First contact 2015, order placed August 2023, delivered early 2024 |
Four things worth taking from it:
- The connector set the schedule, not the laminate: the original supplier would not tool for a batch this size.
- 36 cells in series put the maximum power point near 18 V, which is what charging a 12 V vehicle battery needs.
- Feedback from the customer's own assembly work, including antenna clearance, went back into the drawing before the run.
- A finished pallet at 1.62 m missed a 1.60 m aircraft belly-hold limit and had to be rebuilt as two.
Why a tracking terminal on a truck needs its own panel spec
On a truck roof the panel is part of the terminal's housing, so the vehicle and the device decide the footprint, the cable exit and the connector. This customer started from a standard round magnetic-mount panel, fine for a demonstration unit and awkward for a product assembled the same way several hundred times. The round format did not match the terminal's rectangular mounting area, and MC4 was the wrong connector for a vehicle harness.
The replacement spec was rectangular, with a junction box and deliberate slack in the cable at both ends so the installer can reach the terminal without a splice. That moved the panel from a bought-in accessory to a part with a drawing, a revision and a mating connector that has to match the harness on the other side. Stock sizes like the ones in our flexible solar panel collection are where these projects usually start, before a drawing exists.
Electrically the panel is conventional. Thirty-six monocrystalline cells in series put the maximum power point near 18 V, which leaves enough headroom above a 12 V battery for a charge controller to do its job. Nameplate watts assume standard test conditions, and a horizontal roof under dock shade and road film collects a good deal less, as the DOE primer on solar radiation sets out.
Semi-flexible suited the weight limit and a roof surface that is not perfectly flat. The trade-off is set out in our comparison of flexible vs rigid solar panels: a PET front sheet is light and follows a curve, and it ages faster than glass. On a terminal replaced at fleet refresh that trade is acceptable; on a twenty-year rooftop asset it is not.
The connector problem: when the supplier will not tool for 500 units
The connector, not the laminate, is what stretched this project across years. MC4 is made for fixed arrays: it is bulky, and it does not mate with a vehicle harness without a cut-and-crimp step on every unit. The customer specified a vehicle-type connector that mates directly with their own harness, which turned a catalogue item into a tooled part.
The connector supplier they had in mind would not open a mould for a batch of this size, so we went looking for a second source willing to run a non-standard automotive connector in small volume. Finding one and getting a firm price back added months to the quotation in 2021. The panel was never the bottleneck.
Once the connector was settled the rest of the spec froze quickly: about 691 x 278 mm to match the terminal's mounting area, a PET semi-flexible laminate, 36 cells in series, a junction box and the agreed lead length at each end. Moving any line of that drawing reopens the price. Most custom solar panels enquiries arrive with the watt figure decided and everything else open, which is the reverse of the order that sets cost.
Two pieces of feedback from the customer's own assembly work fed back into the spec: the antenna fouled the terminal's protective cover in some builds, and their engineers asked what the surface coating was made of. Both are cheaper to answer in a drawing review than on a bench with a batch already built.
We stay direct about the PET trade-off. Why flexible panels delaminate comes down to heat, moisture and edge sealing, and a vehicle roof supplies the first two in quantity. It is also why we ask buyers to read what a flexible panel warranty covers while the spec is still open rather than after the first field return.
The 500-unit run and the 2 cm that stopped a flight
The order was placed in August 2023 and the panels were produced and handed over in January and February 2024. There was no separate prototype at that stage, because the configuration had already been through several rounds of quoting and sampling, so the line built straight against the frozen drawing. The part of the job that actually went wrong was the packaging.
Palletised, the finished batch stood 1.62 m tall. The belly hold of the passenger aircraft on the planned routing takes 1.60 m. Two centimetres of carton and pallet deck meant the shipment could not fly as booked.
The fix was mechanical. The forwarder's warehouse broke the pallet down and rebuilt the batch as two shorter pallets, which cleared the limit and opened up flights that had been unavailable. Height and handling rules of this kind sit with the carrier and the IATA cargo programmes behind air freight, not with the factory, which is why we now ask for pallet and door limits at quotation instead of at pickup.
The repack mattered because of the calendar. Chinese New Year closes production and freight for weeks, and this batch was collected before the cut-off. Missing it would have pushed delivery deep into the following quarter.
Import clearance stayed on the customer's side: their customs broker handled the importing country's conformity certification and import licence, which is the correct split, since the licence belongs with the importer of record. The customer had also told us that an earlier purchase took about six months from order to goods in hand. On a custom part the production window is rarely the long pole.
Nine years of iterations, and what we now settle before quoting
The outcome is a customer who kept coming back across nine years, from a trade-show conversation in 2015 to a delivered batch in 2024. There is no testimonial to quote here; the repeat ordering is the signal. What changed on our side is the list of questions we settle before a price goes out.
| When | What happened |
|---|---|
| 2015 | First contact at a trade show |
| 2019-2022 | Repeated quoting and sampling rounds, including the connector search |
| 2022 | 500-unit batch price confirmed |
| August 2023 | Order placed |
| January-February 2024 | Production and delivery |
Eight items now go into the first reply on a vehicle-terminal enquiry:
| What we ask for | Why it moves cost or schedule |
|---|---|
| Mounting surface and curvature | Decides semi-flexible against rigid, and how the panel is held down |
| Footprint and keep-out areas | Antenna, cover and fixings get placed before the laminate is drawn |
| Watts and system voltage | 36 cells in series suit a 12 V battery; another voltage changes the cell count |
| Connector part and mating side | The item most likely to need tooling and a second source |
| Lead exit position and length | Sets junction box placement and whether the installer has to splice |
| Front sheet material | PET service life weighed against the device replacement cycle |
| Carton, pallet and height limits | Decides whether the finished batch can fly as booked |
| Who holds the import certification | The licence belongs with the importer, not the supplier |
Sampling is the line buyers argue with most. This batch went into production without a fresh prototype because the configuration was already proven, and that is the exception: the case for samples before a bulk order holds the moment any line on the drawing moves.
The checklist generalises past trucks. It runs the same way for custom solar panels for IoT manufacturers fitting a laminate to a sensor housing, and the electrical half is identical whether the load is a tracking terminal or any other piece of solar power for IoT devices. Cells in series set the voltage; the enclosure sets everything else.
Standards, testing and the next step
The honest position on standards: IEC 61215-1 is a design-qualification standard for complete modules, written around mainstream module construction. A custom laminate built to one customer's drawing is tested against that customer's specification, not against a module type-approval programme, so we do not present it as a certified module.
What we can stand behind are the house rules: RoHS-compliant materials, ISO 9001 partner factories, and sealed connectors, IP67-rated where the part exists, because a roof-mounted joint sees vibration and water. Charge control stays a device-side decision: whether MPPT or PWM is the better match depends on the gap between panel voltage and battery voltage.
Can you fit a connector other than MC4?
Yes, and on vehicle work it is usually the right call. The constraint sits with the connector supplier: tooling and minimum order quantity decide whether a part is available at your volume. Send the part number and say which side mates with your harness.
Flexible or rigid for a vehicle roof?
Semi-flexible where the surface curves, where weight matters or where a low profile is required; rigid where the surface is flat and the installation outlives the device on it. A PET front sheet buys conformability and gives up service life against glass.
What is the minimum batch?
This project was quoted at 100, 300 and 500 units and ordered at 500. On a custom part the floor is normally set by the connector or the tooling supplier rather than by the laminate, which is why the connector question gets answered first.
If you have a device that needs its own panel, send the enclosure dimensions or drawing, the connector part number, the battery voltage and the quantity you expect to build, then request a quote. With those four items a quotation takes far fewer rounds.
