Solar Charging on Home Free

February 28, 2023

This post is intended to add to a discussion on the Nordhavn Owner’s Group. Other readers may find it useful and/or interesting, but without access to the prior discussion, it may seem disjointed.

Home Free has a two types of solar panels, used for testing, however the current implementation (put in around January 31, 2023) will likely be the basis for future changes.

First off, Home Free is primarily a 24v boat (although it has 12v, 110v (just the refrigerator) and 230v (all large loads)). Since most panels are 12v, it quickly became clear that stringing 12v panels was probably not the best solution. Instead, I found 24v panels that would be easier to manage. Worth noting is that most panels already generate voltages in the 20-40v range, so taking advantage of these voltages seemed to make the most sense.

The next step is to pair them with MPPT controller(s). These controllers have a maximum voltage and a maximum current. I have chosen 100v/50A as my maximums. It is possible to use multiple controllers or get larger/smaller controllers. To be clear, the two panels I have will generate a maximum of 37.6v each and 5.32A of current, so with two panels, the maximum is 75.2v and 10.6a.

This controller(s) is then wired to the batteries (in my case, the bus bar at the lazarette control panel) so that any power generated is used to charge the batteries.

The boat already had a Victron Skylla-i charger (24v/100A/1+1 Outputs, accepts 180-265Vin and 45-65Hz which is important for use on different continents) as well as two MultiPlus stacked inverters (each with 24v/3000W/70A charging).

One of the benefits of the solar system is that these components can be integrated into the components already present with various Victron system monitoring components In many respects I have a bare bones system because I know what information I am looking for. For the casual user or the user who perhaps wants the convenience of simplified information, other components can be added, in particular, the GX Touch Screen and the BMV-712 battery monitor.

The most important of all of these, in my view is the Cerbo GX which allows for the monitoring of all of the components listed above as well as many others. It allows for triggering events (such as alarms or generator start for example) and most importantly for me, has a web interface (VRM) which allows users to view data about the system from anywhere in the world.

On Home Free, currently the system is just being used for two primary purposes. (1) to turn some sunlight into battery power and reduce generator usage and (2) to allow me to monitor my battery charge level remotely.

I have two additional 100W – 12V flexible solar panels (supplied by Renogy) which I sometimes place on the deck (2 in series to get 24V) when at anchor to add some charge capability to the system. I won’t discuss these in detail because they have performed poorly and will not be a direction I take this (or any) system in the future. It is worth noting that when these flexible panels are added to the system the total system voltage gets close to the 100v maximum that can be handled by the MMPT controller, but still well below the current maximum at about 15 amps total.

For those that are new at solar implementations, it is relatively easy to connect and disconnect panels with MC4 connectors, splitters and joiners. You can find out more about them on WikiPedia or just search on Amazon or similar vendor sites for these products.

Here are some photos of the components:

Solar Panels

Our solar panels are Rich Solar 200W 24V and are a bit small, but easy to manage. While larger panels would be better if permanently mounted, my intention was to mount them on the starboard side rail of the boat deck, put them on rotating mounts and then they can be deployed horizontally (with few shade/blocks) and turned vertically while lifting/deploying the dinghy. At first I was intent on building the mounts myself. In the end I went to pre-made mounts from Hamilton Ferris (see here) which still required me to drill holes, but were easy to install. If you have your own workshop, you can build these yourself for half the price I paid. In the end I installed them in about two hours or so.

Note that the cable was already run through the stack to the engine room and back to the lazarette, so I just had to drill holes in the mounting bars, bolt the pieces together and mount them on the rail. I did this without any extra hands, which is another reason to use the small panels. If there is a problem, you can move them around single handedly.

It is also worth noting that my cable routing could be considered dangerous as the cables are not buried, not even tied down, but I still consider this a work in progress. You can also see the MC4 combiner (Y cables) that allow me to simply plug in the flexible solar panels, or any others and lay them on deck when the dinghy is not on deck. Here are photos:

These panels rotate without effort. The mount is a seadog rail clamps. They come with the pre-made mounts, but they are only $30 a pair in some places (here is Go2Marine’s website). The point is that they have a little rubber strip to give it grip, but still be able to rotate. They have been rock solid underway in some pretty rough conditions.

The MMPT controller is as follows:

Charge Controller (MPPT 100/50). Note the disconnection switch which is a safety MUST.

And the Cerbo GX installed (note I am holding up/out of the way, a wifi booster which helps the Cerbo wifi signal get to my Starlink router from in the lazarette)

Cerbo GX

These components on their own provide some nice information. In fact the charts that others have been putting on the NOG, are from the wifi connection to just the MPPT charge controller (or the BMV-712 battery monitor). But you have to be close to one of those devices to get that data.

Here is a look at the data for the current day, taken just before mid-day with the sun shining brightly overhead. Note that the nominal capacity is 400W at 24v, therefore the momentary efficiency is about 75%. I have seen efficiency closer to 85%, but it often much lower. In the graph below, the ‘best’ day was achieved with the 100W flexible solar panels plugged in for part of the time.

Home Free solar charging data (11:30 am on a sunny day in Turks & Caicos)

Also noteworthy, the panels were plugged in for a long time prior to January 31, but just laid upon the deck. That means there were a lot of shadows, and the production was horrible. The lesson from that would be to get your panels as much clear sky as possible.

All of the days before the ‘Today’ bar, the panels were laying on the deck, with lots of shadows from the dinghy, stack and davit.

The Cerbo GX allows all of the components of a Victron system to be interconnected and monitored, as well as some other components as well. Over the past week, I have connected the inverters and charger to the Cerbo GX which provides a dramatically better view of my overall system.

Here is an image of the overview data for the System. Note that I don’t have an appropriate voltage monitor connected to the Cerbo on Home Free.

The Cerbo GX data is viewed on a web portal (VRM) and the combinations of data can be overwhelming. Here is a view of my consumption and generation since the integration was done last week.

Home Free’s demand/production information

As can be seen from this graph, our consumption is about 6x the production of the solar system. As well, the battery percentage information is ‘calculated’ and not representative because I don’t have a BMV-712 installed. We are currently tied to a dock and the AC gets used, the oven, the hot water heater, etc.

Here is a graph the comes from the VRM when the charger/inverters are connected to the Cerbo GX. Note that the chart is for the past month, but the wires were just installed in the past 10 days, so the chart is lopsided. Significant loads can clearly be distinguished and if the time frame is shorter the data clearly becomes more discrete (3 hours is the minimum I think, and I believe 90 days the maximum, at least of the preset ranges).

Home Free – A representative graph covering the past 12 days or so (since I connected the system)

I have another system installed at home (not Home Free), and it does nothing other than collect sun, run some heating from time to time and look kinda pretty.

Overview data for the house. Note that this is built to be an off-grid, 12v lithium system and currently has almost zero loads.

Here is a 30 day chart for this implementation. (This is a 12v system with lithium batteries, four large panels (385W) and no significant loads in the middle of Canadian nowheresville, so the parameters are a bit different.)

The screen shot below shows a few bits of interesting data.

  • System – Battery Voltage and Current – note the rhythmic voltage rise and fall. The empty part was when my internet connection went down for a few days. The lower bumps are snow storms and my panels were covered.
  • Note that the Lithium batteries have been taken to completely empty at least twice last winter (2021-2022) and everything is still awesome. Lithium is pretty awesome.
  • This system has a CerboGX, a colour touch screen and a BMV-712 battery monitor, so note my state of charge info. It is accurate.
  • There are a LOT of graphs that can be shown when the Cerbo is connected to the charger and/or inverter as well as the MPPT and battery monitor. It’s too much data to discuss.
  • This system also has two triggers for heaters. One is a small heater in the battery box to keep the batteries warm, the second is to a 110v outlet which heats the garage when temperatures drop (currently inactive, so the load isn’t showing on the graph).
A wide range of data can be seen here

Solar production in Southern Ontario, Canada.

I hope this helps those who may be interested in installing solar to understand what is available. The primary questions relate to your expectations for the system. On a larger boat like many Nordhavns, a substantial amount of solar would be required to eliminate generator use. At the same time generator use can be dramatically reduced with some solar capacity.

Finally, I realize that I didn’t discuss our power needs. Home Free typically requires about 400W of power for ‘normal’ daily loads (fridge, freezer, standby device power, charging handheld devices etc.). This data is available from the Cerbo GX when tied to the inverters.

To cover our needs with solar we would need substantially more than this to recharge during daylight and have sufficient energy overnight. I estimate that our ‘typical’ loads would require 800W of generation. We are currently generating about 300W with 400W of panel capacity. So six of these, currently installed, panels would likely cover our typical needs. That would require a hard top, or cover our rails with panels, which is not aesthetically pleasing.

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