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Solar power system

After much research and supplier costings we took the plunge for a solar system. Early days to feedback performance but here is my design. We already have two Victron combi 3000/24/70s providing 6kW with 840Ah batteries @ 24V. Plus a 15kVA generator connected as an alternative shore power input.

esme solar_panels
After several discussions with Victron and reading of their solar data sheets, because our ship is almost entirely 230VAC (24V for instruments only) I have taken Victron advice which is that the highest efficiency is to NOT charge batteries with solar output or invert from the 24VDC side but to have a high voltage solar array driving a new inverter and paralleled into the OUTPUT of the Multis to the ship AC distribution board. Along with some software changes to the Multis (that Victron have provided) the solar 230VAC output automatically becomes primary provider, excess current is reversed back through the Victrons to charge batteries if required or supplemented by them in the normal way in 'assist' mode if demand is higher than the solar output.

In order to maximise low light output, ezpecially in winter, I have chosen 250W panels (x10 = 2.5kW max) with higher than average 50VDC outputs arranged as per houses in a series string to give potential 500VDC into a Sunny Boy 2500 inverter that has a DC range 175-560V (max 700). This means that even at low light levels invertion will still take place at down to 35% of max performance.

As with most household stuff, this approach is standard for roof top on-grid system and very well priced. In our case the grid is the Victrons which provide a permanent 230VAC supply. If there is little or no AC demand, the Sunny boy will reduce the output accordingly and so will the Multis. We are fortunate to have a large wheelhouse roof that will just take two rows of five 1600x1060 mono panels. I paid about GBP130 for 250W panels. With the addition of AC and DC isolators and cables the total cost was about GBP 2,300.

Like many, I started out looking at DC MPPT charge controllers and 30V panels but concluded that these would not be well optimised or prioritised with the Victrons or any other Inverter for that matter. The Victrons have a huge advantage that they can be reverse AC fed and have power assist which I don't think Mastervolt (or at least when I last checked their specs) can do.

When all is up and running and proven, I will write up a full report for the Knowledge base with links to the various docs used in the design.

I'm now working on a power diverter using the open source Arduino digital controller at openenergymonitor.org . This controller uses small current transformers placed around the 230VAC cables to monitor power usage from solar, to house (ship) and to/from grid (shore power). When there is excess not being used or in house cases being sold back to the grid, it sends this surplus to a water heater. I'm modifying the software and hardware to enable it to operate 'off grid' and when connected to shore power to avoid exporting spare solar power which is illegal without a certified installation and probably frowned upon by harbour masters seeing their meter going backwards. My other improvement will be to sense battery condition so that priority can be given to battery charging and then water heating. The system is very cunning and calculates usage and any excess every single cycle, if spare, diverting it to the water heater via a burst fire triac. This ensures that ONLY the watts available are diverted for that cycle. The size of the immersion heater is not important as long as below 3kW, the max the triac will handle. Finally, daily totals kWh for ship use, shore power, generator and solar with trends are logged on to an SD card. My final touch will be to write an Android App which will connect to the data via bluetooth and display trends and live sharing of power. Anyone interested, particularly if familiar with C or Android programming contact me here

We have an Adverc on the main engine charger that just optimises the battery charging and / or feeds the Victron 24V input which as well as keeping the AC going (up to 70A alterator Victron DC input) charges the engine start battery via the second Victron charger output.
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