Solar numbers–Nerdy post!


I have not done a lot of blog posts about this stuff as I’m worried most readers will find it boring. However, as boring as it is, its our life on a daily basis. There is not a day that goes by where were are not living by the power numbers. Our lives and the devices we operate are literally controlled by the power we generate on a daily basis. I know there are readers that don’t realize we live %100 off the grid! Our boat has not actually plugged into “shore power” for over 2 years (its almost 3). All the power on our boat is generated by either solar or by running our Honda 2000 generator. Its the bane of my existence to run the Honda for just power and we have only done it a handful of times (less than 5) in the last 9 months.

While we will delve deep into the actual data in this post, this is something we only do every quarter or so. On a daily basis I have set the boat up with multiple gauges that tell everyone aboard what they need to know at a glance. Even the kids can decipher our power situation at any moment (and don’t bother asking to plug stuff in if we are low). However, looking at the data every quarter helps us spot potential issues (maybe a bad wire connection, failing solar panel, or other issues).


So first, lets start out with some background. Our boat is setup with 3 completely independent solar arrays (redundancy is good on a boat dontchaknow). We have 2 300W arrays and one 200W array. One 300W array is original to the boat when it was manufactured (Shell Canada solar panels). The other 2 arrays were installed by me and my brother Ryan in Key West. This is important to make sense of the graphs that I’m about to present. Each graph will have 2 bars for each array. One bar from Feb and one bar from June (yup 6 in total). Alright… onward to the pretty graphs… Ok, not so pretty as I’m cheap and this is the best Open Office could generate!


Average Watt-Hours generated each day (averaged over 30 days).


I suspect this graph is the data that people will find of most interest. This is essentially a picture of the average power we generate each day, you just need to add the numbers up. We averaged 3.195Kwh/day in February. We should have easily beat those numbers in June as the sun is at a better angle. Unfortunately it was cloudy for most of June and we actually did slightly worse. What I find very interesting is our 15 year old Shell solar array only generated %2.5 less power than our new modern Renogy panels. We see people replacing old panels al the time. Many times its because they believe the panels have lost capacity with age. I wonder how many of those people actually measured the capacity to verify that fact. Anyway, I’m excited to see what these numbers will be for September as its the hottest month down here. I’m expecting close to 5Kwh/day.


Max Watts Generated (averaged over 30 days)


This graph is a good gauge of how healthy our panels actually are. It shows how close the array is getting to its rated output on a regular basis. Its pretty clear that one of our arrays is not performing as well as it should be (the 200W array). This was expected as that particular array had a panel fail and I was not able to find an exact replacement. Mixing panels with different specs in an array is never a good idea, but sometimes you have no other options. Now looking at this data it dawns on me that I could probably get %10-15 more out of that array if I change the configuration from series to parallel (sigh another boat job).


Its important to understand that the numbers above are an average of the highest watts each array did. The actual peak numbers (the highest watts we saw at any point over 30 days) are below.

300WShell-Feb 311W
300WShell-June 314W
300WRen-Feb 330W
300WRen-June 349W
200W-Feb 178W
200W-June 177W


That right, 2 of our solar arrays are actually capable of producing more power than their ratings. The new Renogy array produced a full %16 more than its max rating on one day. Of course, the conditions had to be exactly perfect, the boat had to swing the exact right way, and it probably only produced that number for a short period (under 1m). More shocking is the 15 year old panels can still produce more power than rated. Of course the 200W array is also showing its weakness here. The 2 mismatched panels didn’t even come close to their 200W rated maximum.


Time In Float (averaged over 30 days)

Time in Float


Float is the phase where our solar controllers have detected the battery is full and they stop charging. This is an important metric for Lithium batteries as the goal is to keep you controllers NOT in this phase as much as you can. Once the controllers switch to float you are essentially throwing away potential power. On top of that, lithium batteries are happiest when they are NOT at %100 charged state. As you can see, I haven’t done a great job at keeping out of this phase. I would like to see this number under 20 min. I’m not sure I will ever be able to get it there though. When we leave the boat for land based excursions, I power down everything non essential so the boat draws very little. Call me crazy, but I just don’t think its safe to leave inverters on, laptops charging or electronics plugged in without supervision. The fridge, freezer and bilge pumps are the only things I’m comfortable leaving powered when we are away.


This graph also clearly shows a potential problem. In a perfect world, all three bars from the same month should match or be very close. The fact that the 200W bars are much higher shows that there is a problem somewhere (most likely a corroded connection causing high resistance). In fact, I actually found this problem around mid-June and fixed it. This is why the 200W June bar is closer to the other June bars (unlike February which is WAY high). However, even correcting that problem will not get the graphs in perfect sync as the voltage detection on the Victron gear is much less than perfect.


So there you have it, a nerdy post about power and solar arrays. It may be boring, but I’m hoping it may be interesting to some. I know that someday when I’m back on land life and have forgotten most of this stuff, I will love reading it. Actually while writing this post I searched our website for some of my old posts. I actually posted our solar generation in February of 2018. We generated about 2.5Kw/day that month. This February we generated almost %25 more power than that February. Of course environmental conditions play a role in some of that difference, but our new batteries are also a large part. Its said that installing LiFePO4 batteries is like getting %20 more solar for free. Based on my numbers, I would agree %100.

  2 comments for “Solar numbers–Nerdy post!

  1. Sara
    July 17, 2019 at 6:52 pm

    Long time reader, first time commenter. Thanks for all the nerdy info! As a future cruiser, these kinds of posts are very helpful. Thanks!

    • travis
      July 18, 2019 at 5:30 am

      Thanks for reading.. One thing to keep in mind with our power stuff, is watermaking is not included. We have a 110V watermaker that is run from a Honda 2000. If we had a 12V watermaker (like a Spectra) we would need significantly more power (or have to change our habits).

      We have had a couple people comment that they are using WAY more power than us and didn’t realize we don’t have a 12V watermaker.

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