I’m very much new to Solar but already I’m finding it a game changer for charging the batteries on my narrowboat.
My boat has a 20 year old Victron Phoenix inverter. This year I added two Perlite Delta 175w panels mounted flat to the roof coupled to a Victron MPPT 100/30 Smartsolar charge controller.
On my initial setup I wired everything in parallel and it seemed fine but three weeks ago I thought I’d give series a try and that’s where my query comes in.
On first connection I expected to see voltage from the solar panels double as they were now mounted in series but it didn’t. I thought this was odd but being a novice I decided to leave it a few days. I thought the performance was disappointing so investigated and immediately found a hot spot on one of the panels, I could hardly touch it without burning my hand. I decided to check everything at this point and broke and remade all of the connections to the panels. Hey presto everything came back correctly - hot spot gone. Solar panel voltage up to around 35-40 which is what I expected to happen in the first place. I assume it had been a poor connection but I’m still puzzled why that could result in a hot spot on one of the panels?
It’s been fine for the last couple of weeks until last night. We were forced to moor up under trees. It was still strong sunshine at this point but the sun was dropping in the sky by then. I was expecting some effect from the shading but not as pronounced as I saw. The voltage and current readings in the app were fluctuating wildly. Sometimes the Solar voltage would drop below 20 then would climb back to normal levels only to drop again a few minutes later. One panel was partially shaded at this point while the other was in full strong sun. I’ve heard that shading can cause strange behaviour but hadn’t expected it to be quite so pronounced. My question is simply - is this normal behaviour in partial shade? Can I relax!
Panels in series are more prone to shading effects. Panels have bypass diodes in the to allow the power to bypass a shaded panel or section of panel. If the shadow is tree leaves that are moving and the shade is varying you can get cycling as part of the panel produces and is then bypassed. Parallel is usually better for narrow boats that have variable shade.
My main reason for switching to series was to up the voltage. I’d read that the controller needed to detect a voltage from the panels in excess of 5v above the batteries in order to start charging. I was concerned that on dull days the charging process might not start soon enough. What do you think? Should I switch back to parallel?
A generic curve is shown below. The start up +5V requirement is against the Voc of the panels because they will not be producing power. This does drop with light levels so if your panels were rated for Voc of 20V then at low light they could get marginal as they would dip towards the 18.5V so I understand your concern. The only way to find out would be try it, it is a compromise between start up and shading. Modern panels are better at handling shading in series than older one so see how you go in series and if OK over the summer then leaving it will be better for autumn and winter.
Thanks for this. The Voc of my panels is 19.64v so you are very close.
This morning things are more stable with the panel voltage steadier at around the 35v mark. Although there is still some shading it’s from trees on the other side of the canal so it’s ‘softer’ whereas last night it was from the trees immediately above the boat and there was quite a breeze moving the leaves which fits your original explanation. We’re going to move shortly so I’ll see how things are tonight, I’ll try to find a more open mooring.
It’s all starting to make sense now. Thanks for your help.
Totally concur with @pwfarnell , the installation of choice for a cruising canal boat in my opinion is also parallel for the reasons stated (be mindful of the +5v startup differential).
My installation summary
On my boat I have 3 arrays (600w, 600w, 820w), each on their own controller (think redundancy, shading mitigation, although there is an increased equipment cost in return, but personally I value convenience of power availability over cost), and mounted flat…
Why flat on a canal boat?; You might find some googling useful and it will grow your knowledge too.
Solar installation considerations on a cruising canal boat
1.) Requires no real mounting complexity.
2.) Does not require raising (E rection is not allowed…Lol) of panels or levelling when mooring / moving (think wet, icy gunnels or high winds, overhanging vegetation, air-draft etc) panels are always deployed and working with zero effort from you.
3.) Over a day I generate fractionally more than inclined panels (think early morning / late evening (see 5)). There are a number of youtube channels that discuss inclined / flat / vertical mounting. make sure you view the ones most applicable to your use case (mobile / boat)
4.) Thermal effects of panel efficiency (see 5).
5.) Angle of incidence.
That said, for a boat in a pre-dominantly marina setting, fixed location, no shading, preferential orientation to sun, I’d choose inclined series (there are some minimal equipment cost reduction benefits in this regard too, but not really any solar harvesting benefits, between parallel and series)
For parallel installations, I’d install panels with a higher Voc (>31v). Try to get physical separation of the panels (along the length of the craft) to mitigate any possible shading. If possible I’d have 2 panels or arrays, with 2 controllers (redundancy and shading mitigation, there is of course a cost implication here along with controller installation location space).
My reason for mounting the panels flat was purely aesthetic. I’m not keen on the appearance of the tilt mounts plus they can be problematic with low bridges and have a sail effect in windy conditions. I realised at the outset I’d lose optimum efficiency but made the decision to live with that.
In terms of the VOC I really didn’t factor this in when I bought the panels. My mistake, I realise now and probably too late to change the setup without more expense. Never mind I’ll have to live with it for now.
Anyway, tonight I’m moored in a shade free location and everything is working well. So clearly @pwfarnell gave me the correct advice. I’ll see how I get on with serial connection but I can always swap back later to parallel if the shade issue causes problems again.
Optimum efficiency over a year, summer and winter in my data from 3 years, shows flat is optimum, across multiple boat installs.
Flat mounting does not achieve the highest peak input for a given point in a day, inclined does this. However our boating goal is to harvest the maximum possible across a day, to finish the day with the highest SoC we can get, we have no grid to fall back on.
Mounting flat has a flatter charging input curve, but a broader one, we start charging earlier and finish charging later. Over a year we’ve achieved slightly better results than inclined.
I use Shelly switches, with the Cerbo to monitor system state via a custom script I wrote for the Shelly and switch loads as required so nothing is lost. E.g turning on / off an immersion / washing machine when SoC is above 80% and time parameters is met (this changes based on battery bank size / array) but for me this is ideal.
Mine are flat on a predominantly cruising boat, you do not get peak power but it does not matter what orientation you moor. However, tilted are better in winter if you are moored with the panels facing roughly south without trees.
I specifically addressed the advantages of flat mounting and parallel setup in my original reply…?
The only caveat was marina moored boats:
Blockquote
That said, for a boat in a pre-dominantly marina setting, fixed location, no shading, preferential orientation to sun, I’d choose inclined series (there are some minimal equipment cost reduction benefits in this regard too, but not really any solar harvesting benefits, between parallel and series)
My boat is a leisure boat rather than live aboard so it’s used a lot in spring summer and early autumn but laid up for the winter months on shore power. So flat is certainly best for my needs.
Everything is good again this morning btw so it was definitely that overhanging tree causing the erratic behaviour from the panels the other night.
I’ve so far been pleased with my modest Solar setup. It’s been a game changer. We can now moor up for a day or two without having to run the engine for ages. It’s fine for our needs.
Slightly at odds with your original reply but glad you’re now saying flat has its advantages. 