Now that the panels are producing and we have been off grid for four days now, I thought I would go back over the project.
From our experience, there are three top-level considerations that need a bit of thought before spending a cent. These are shown in a circle because getting this right requires iterative thinking. I tip my cap to anyone who can make only one pass around this loop and achieve success. I’m sure I made a few dozen loops before the trade space was narrowed to my satisfaction.
Solar arrays have the potential to be quite ugly. They can seriously ugly-up an otherwise pleasing boat. Solar panels are generally about hard corners and right angles, while boats, generally, are not.
Support frames have to be substantial enough to be secure, and that generally means substantial enough to be seen. Support frames need to provide breathing room for the panels as heat is an issue, and that means the panels are prominent.
Wiring has to be substantial enough to carry significant current with minimal voltage drop… and that generally involves a visual impact.
Clearly the size of the array is the central issue. The aesthetic challenge increases roughly with the area of the panels. Certainly there are boats of a size and configuration that moot these points, but for most modestly sized cruising boats aesthetics require some serious thought.
For us, we wanted panels with a frame color close to that of our bimini (Dark Blue). We wanted a stainless, rail-based frame that visually integrated with the rest of our rail/frame works.. And we wanted the two #4 gauge wires (in wire loom) visible for the shortest distance possible. These choices significantly affected the physical layout of the array.
I spent quite a few hours with bimini photos and graphics software digitally mocking up the arrangement until we had something we could live with. When we moved to the next phase, this work paid off in terms of telling us what wouldn’t be satisfactory, but it didn’t produce the final design…at all.
Solar arrays (panels, frame, and wire) aren’t particularly heavy. Our weight penalty for 405 watts is 98# total. However, they tend to go well above the boat’s meta-center (adding to tenderness) and well aft increasing the potential for weather helm. After looking at the weight of arch style davit/solar/wind/radar frames, less the weight of our current davits, (our radar is on the mast and we don’t do wind power*), we decided to integrate the solar frame into the bimini frame, This included strengthening the bimini frame against lateral sway and longitudinal rocking resulting from the mass of the array being placed nearly five feet above the bimini frame pivots.
When I sought price quotes on the design we thought we could live with, we choked on the prices offered. It was clear the people involved did not need the work. They offered 100 to 200% markups on materials and labor rates were at the diesel mechanic level. So we began to think laterally. What could we build ourselves from [somewhat] readily available components? This resulted in a design far more aesthetically suitable than our original that provided a more elegant solution to our desire for the panels to be tiltable.
However, we still had to make sure the panels would tilt within the double back-stays without metal-to-metal chafe underway or when tilting the panels. I’m sure even a simple CAD-CAM software package would have helped, but ultimately we built a wooden mock-up of a panel with its mounting features (clamps etc). We used this to arrange the stainless frame in the proper fashion.
To get the ventilation stand-off distance and to facilitate tilting, we discovered the transom grab handles on our boat bolted vertically to the top of the bimini bows fore and aft made perfect anchor points for the one inch stainless pivot tubes (hand rail material).
There was more physical thinking associated with this project than electrical or aesthetic. From design, through materials selection, through identifying source of supply, to fabrication, fitting, and error correction, two-thirds of the time spent had nothing to do with generating watts.
I can run a genset (fie) or the engine (fie-fie) or tie up to a dock with 30 amps (fie-fie-fie) any time. I can only get solar watts during the day and on a wobbly curve shaped by date, latitude, boat heading, panel tilt angle (I assumed a heel angle of 0) and cloud cover. The area under the curve is the effective “Insolance” or “Insolation.”
I decided to model a year of cruising. It was a crude model, but it showed what an “energy budget” (total out, total in, net) wouldn’t have. There were places we planned to go where we had better keep some diesel handy for the genset, and there were others where we would end up with “excess watts” on a lot of days. The net of our “budget” was we could satisfy our needs/desires with a roughly 300 watt array. The net of our “model” was 375-380 was more like it. The nearest multiple we could come up with was 3 x 135 watts = 405 watts.
The Kyocera panels that fit this bill would fit perfectly were not quite the perfect fit for the boat. While they would clear the backstays just fine, clearing the swing arc of the boom required them extend a bit (nine inches) aft of the bimini. We decided this was a suitable trade.
Having decided on 405 watts max output (from “nominal” 12 volt panels), we sized the controller accordingly and settled on the Blue Sky Power Boost 3024 MPPT charge controller with remote control. The distance from the panels to the batteries is such two #4 AWG wires (13/32 inch dia each) were needed to ensure a voltage drop of less than 3%. The controller had to be mounted in a splash free zone with good ventilation, so we located it near but not right next to the charger/inverter. Because the remote control also provides lots of systems performance information, a current shunt was required (to collect the data). Fortunately, the shunt already installed for the charger and for the alternator regulator was the correct size, and we could just connect to it. With well configured positive and negative bus bars, it was possible to connect the controller output cables in appropriate positions.
Of course the day we connected all, the overcast and full battery charge delayed our assessment of the panel output, but the controller worked as it was supposed to. Two days later, a beam of bright (for October) late morning sunshine graced us for a few minutes and the output current shot up to nearly 28 amps…
That had an aesthetic value all its own.
* Why no wind power? Noise.