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Power And Upgrading Our Solar & Batteries

Like water, food, and pretty much every consumable item, electricity is a limited resource for cruisers. We use it to power everything from a coffee in the morning, to our bilge and water pumps, our navigation, and of course to charge our phones. But how much can we generate and how much can we store? We have several sources of power on the boat, which is probably reasonably common for cruisers:


  • Hooking up to the 'mains' power at a dockside pedestal

  • Alternator/s when the engines are running

  • Diesel generator

  • Solar power (I'm going to talk about this one today)


I personally am a big fan of solar power. I think it's amazing that we can take something that nature gives us for free and turn it into useful energy. From a cruiser perspective, it's a relatively low initial cost, and it's quiet to run (silent in fact!).


When we first got the boat, it had 4x 100W panels on top of the bimini, and 4x 100Ah AGM batteries. Whilst I did not know a lot about solar, I knew that that wasn't going to be enough for what we wanted. But how much would we need?


The first thing to do is to be able to measure it accurately. Whilst our MPPT solar charger controller does have a voltmeter (which I find unreliable at best) it doesn't give a good read on the amount of power we are using at any one time. For that, you have to install a battery monitor. I highly recommend this one by Balmar (review here)- it's a high-quality piece of kit, and I also have the BlueTooth adaptor so I can view all the readings on my phone. Its unique selling point is the 'State Of Health' (in addition to 'State Of Charge' - how full the batteries are) which shows you the 'healthiness' of your batteries and indicates how well they are performing.

The Balmar SG-200 battery monitor

The easiest way to work this out is simply to test it. Turn off the incoming supply, and see what your 'default' usage is. I would define 'default' as the lowest which you can go but not give up any major systems. For us, at night, with only the anchor lights on and a couple of phones charging, we use around 12A max (ranges 7-12A). This will happen when our fridge and freezer come on at the same time. Water pumps and the occasional bilge will draw more, but it happens rarely and for a short amount of time so as not to impact the overall need.


Since we were getting a new bimini cover, we decided to reposition the 4 solar panels we already had further forward, and add 2 more up there with them. This would give us a 600W on the bimini, plus 4 additional panels which we can move around the boat as needed. So far so good. You can find the 100W flexible solar panels here. Their working voltage is around 20V and I have them connected in series pairs to create 40V x 5A max.


6 panels on our bimini top

To increase the batteries, I added another 2x 100Ah. I would have used larger batteries but it's important to match the type and capacity of the existing ones, and they were already 100Ah. We still have space for more in the future. The batteries can be found here (don't forget your cables)


3 of the batteries with the battery monitor shunt on the right

All in all that's a 50% upgrade on our bimini solar panels and 50% increase in batteries. We think that's a pretty good start, and as we learn more about our power needs I expect we'll be adding more.









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