Tuesday, July 29, 2014

Solar developments

We are back aboard in the Whitsundays, with the simple project of enjoying a relaxing cruise to Townsville, and ensuring that all is in order for the big adventure to the Louisiades starting on September 12th.

I thought I would discuss developments in solar power on boats, for those interested. No doubt some readers of this blog are already ahead of me.

After the lightning strike, and the electrical refit that followed, I asked for consideration to be made for a future increase in solar panels. As part of that, our solar regulator was changed from a Steca Solarix PRS 2020, which used the PWM system and was good for 20 amps, to a Morningstar Tristar TS-MPPT-60 solar controller, which uses the MPPT system, and can handle 60 amps.

The difference between PWM and MPPT is important.

In simple terms, the task of the controller is to reduce the voltage coming from the panel to a level that is safe for the battery. This is particularly important with the lithium batteries that we have. The older systems of solar regulator basically throw away any voltage that is too high.
But the MPPT (Maximum Power Point Tracking) solar regulators manage to convert excessive volts into more amps at 12 volts (safe for the batteries), thus increasing the effective yield from the panels.

Another bonus from this is that one can attach more than one panel in series, and boost the harvest from the beginning and end of the day when the sun is weaker. The Tristar TS-MPPT-60 can accept up to 150 volts maximum. 

The second development of interest is the arrival of Solbian thin flexi-panels that can be zipped into canvas shades. Previously I had imagined that we would need to build some solid fibreglass panels and mount conventional solid glass panels on them. Because they will lie under the boom, and dangling ropes such as reefing lines sometimes sweep across the cockpit roof at speed when we gybe, I had imagined our expensive solar contraptions landing with a splash somewhere downwind.

But the recent arrival of 2mm thick flexi-panels means that we can zip them into our existing canvas sunshades with minimal weight and expense. 

They are connected as two sub-arrays, port and starboard, with the pair on each side connected in series, and the two subarrays connected in parallel to the MPPT controller.

Each sub-array can put out a maximum of 48.5 volts. The MPPT controller massages that down to a safe level and boosts the amps.

On a sunny day I have seen it registering 25 amps. Loverly! My Dad would have been very impressed!

I can unzip the panels and remove them and roll away the sunshades if we are leaving the boat over the cyclone season, or are exposed to high winds.

All good!

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