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Tuesday, August 18, 2015

Solar Panels

Solar panels are installed and making electricity. The past few weeks has been a crash course in solar power technology. We ended up with six Kyocera panels for a total of 840 watts. We went with Blue Sky MPPT controllers for their compact size and excellent efficiency. With solar panels, shading is the enemy as it will reduce the output of other panels that are in the same circuit. To provide some isolation (which minimizes shading on one panel from affecting the rest of the array) we wired the panels in parallel, with home runs from each panel down to the controllers. We put three panels on each controller to further isolate the effects of shading on the overall output and to provide some redundancy. Each panel is fused before the controllers and the output of each controller is fused where it meets the positive bus of the house battery bank. This was a lot of wiring and took most of a three day weekend to finish. With everything online, we have been able to pull 50 amps out of the array at 14.2 volts during the day with clear skies. It could probably go a little higher if the house batteries a little less charged up. We had to turn on a lot of electrical stuff to get the controllers to see enough demand to get the output up to 50 amps. Our target for the rooftop array was 50-60 amps max output so we are pretty close to our expectations. We have been "off the grid" for three days now, with daytime solar charging seeming to keep up with our 24 hour demands. Each afternoon, our "state of charge" for the house batteries is back up to 100%. The nice summer weather and long days have helped. We are still using the shore power for the electric element in the water heater but when cruising, our domestic hot water can be heated on demand with the diesel burner that provides our hydronic heating circuit or via the heat exchanger with the engine coolant when we are underway. Everything else is running off the 12 volt house bank (refrigeration, lights, pumps, etc.) or using the AC output of the inverter (misc appliances, home depot freezer, and some electronics) which is fed by the same house battery bank. I think that a couple of more panels (maybe on top of the aft dinghy davits when we get those built) will give us a very solid solar power set-up to meet most of our demands most of the year. A wind generator would be a nice add-on too. Of course the beauty of solar is no moving parts and little to no maintenance.

Stud Welder

In order to mount the solar panels, we decided to rent a CD (Capacitive Discharge) stud welder to create the attachment points for the solar panel brackets on the wheelhouse roof. It consists of a welding unit and a gun that holds the threaded studs and is spring loaded to "fire" the studs into the molten metal that is formed when an arc is created by the machine in the base metal. It all happens in a few milliseconds, and creates a very strong threaded attachment point on the steel deck plate. The beauty of this machine is that it welds so quickly that there is little to no heat transfer to the back of the plate that you are welding to. This means no paint burn, and no need to remove the interior panelling and insulation on the backside of the weld (we tested this first just to make sure). This saved us at least a days worth of labor removing and re-installing the interior overheads and painting the burn through, which would be required with conventional welding. The whole job (including some extra studs on the foredeck for the kayak cradle brackets) took just a few hours. We used 316 stainless and painted the weld area well with epoxy primer and top coat.