Ever wondered if you can power a floating home entirely with the sun? In this post and our latest video episode, we’re taking you aboard our wide beam canal boat for a full walkthrough of our solar panel installation — from layout to wiring to those tricky tech decisions. Whether you’re baffled by series vs. parallel, unsure what Nominal Module Operating Temperature means, or questioning if 3kW of panels is genius or madness on a boat — we’ll show you exactly how (and why) we made it work.
If you remember, I installed our 940w solar panel solution on our sail boat by myself. It wasn’t difficult and the system ran flawlessly for years.
However, here at Staniland Marina, we have the comfort of having Gary of GS Boat Controls based right next to our berth. Gary has already helped us with a few projects on board Happidaze so we invited him along to spearhead our latest solar panel project. He’s a qualified electrician with a lot of experience installing panels and the various Victron peripherals that go with them.
We’re Big Power Consumers
Compared to our power usage aboard our sail boat, it’s no exaggeration to say that our consumption has seen a step-change since moving onto our wide beam canal boat. Gone are the days of traveling with an ice box and reading a book in the evening by gaslight. We don’t want to be taking our washing to the local launderette, we want our home comforts like a washing machine, fridge and freezer, internet. We make no apology for not being traditionalists, but all of these consumables come at a cost: power. And on Happidaze we consume 144 watt hours of energy. That’s 144 watts per hour, every hour, over a 24 hour period. How do we know this figure? Because when planning for a power generation solution, in order to match the panels with our power consumption, we need to know how much we consume over a 24 hour period.
On Happidaze we have many things running. There’s the obvious consumables like fridges and freezers, but also the router, ethernet switch and security camera are always on. Jamie likes to leave his computer on to act as a media server and I will power up my laptop for up to five hours a day.
And then we might watch two hours of TV in the evening. Lights, charging the phones, water pump – these all add up. All of these are a mix of 12volt and 240 volt systems, so the first thing we need to do is to look at the wattage of all these devices and work out what our average consumption is over a 24 hour period, measured as watt-hours.
Estimating our power consumption over 24 hours
A caveat before we continue. The figures I’m about to present to you are rough estimates only. How much does a fridge consume, for example? That depends entirely on its design, how big it is, how often you open it, ambient temperature, to name just a few factors, but to get the ball rolling here are a few figures to throw into the mix.
Now that we know how much power we consume over 24 hours, let’s look at matching that with our panels.
Standard Test Conditions and Nominal Module Operating Temperature
Panel specs are divided into two categories – Standard Test Conditions and Nominal Module Operating Temperature. STC figures are the ones you’ll see advertised. They’re theoretical figures, absolute maximums possible under laboratory conditions, and they’re mainly used to help standardise different panel models across the industry. These figures are useful for configuring wire size, MPPT type, fuses and so on, but for real-world numbers we need to be looking at NMOT, which give a much more realistic picture of your panel’s potential output.
We’ll come back to those figures in a moment, but first a note on series vs parallel. You’ll notice we’ve opted for a parallel configuration, not series, which we’ll go into in a moment, but first a quick reminder:
Series vs Parallel and why we went parallel
In series wiring, you connect the positive of one panel to the negative of the next.
1. Identify the positive (+) and negative (–) terminals of both panels.
2. Connect the positive (+) terminal of Panel 1 to the negative (–) terminal of Panel 2.
3. The free negative (–) of Panel 1 and free positive (+) of Panel 2 go to the charge controller (or MPPT).When wiring solar panels in series, the voltage of each panel adds together while the current remains the same. For example, Voltage = Sum of both panels (e.g., 40V + 40V = 80V), while the Current = Same as one panel (e.g., 10A)
This is useful for systems that require higher voltage, especially when using MPPT charge controllers that operate most efficiently at elevated voltage levels. One advantage is that thinner cables can be used, reducing wiring costs and voltage loss over long distances.
However, there’s a major downside—shade on just one panel can significantly reduce the output of the entire series string, because the current is limited by the weakest panel. That makes proper sunlight exposure crucial for all panels in the string.
In parallel wiring, you connect positive to positive, and negative to negative.
1. Identify the positive (+) and negative (–) terminals of both panels.
2. Connect both positive (+) terminals together using a branch connector or combiner.
3. Connect both negative (–) terminals together the same way.
4. Run the combined positive and negative wires to the MPPT input.In contrast, wiring solar panels in parallel means the current from each panel adds up, while the voltage stays the same. For example, Voltage = Same as one panel (e.g., 40V), while the Current = Sum of both panels (e.g., 5A + 5A = 10A)
This configuration is better suited for situations where shading is unavoidable or panel orientation varies. If one panel is shaded, it won’t drag down the performance of the others, because each panel works independently.
However, the downside is that higher current requires thicker cables to avoid power loss, and MPPT units need to handle more current at a lower voltage, which can reduce their efficiency unless specifically designed for that range.
Ultimately, the choice between series and parallel depends on your site conditions and your MPPT charge controller. If you have consistent, full sun and a controller that can take higher voltage input, series wiring is often more efficient. But on a boat there is one factor that overrides everything else: shade. If you have two panels wired in series, and one gets covered in shade, it will affect the output of both. In parallel, however, only the panel covered in shade is affected.
What is the daily energy output from our panels?
Looking at each MPPT:
• 2 panels in parallel → Voltage stays the same, current adds
• So:
◦ Vmp per MPPT ≈ 34.44 V (unchanged)
◦ Imp per MPPT ≈ 10.95 A × 2 = 21.9 A
◦ Pmax per MPPT = 34.44 V × 21.9 A ≈ 754.236 WTotal for three arrays:
3 × 754.236 W = 2262.7 W (2.263 kW) under NMOTThe potential daily output, based on real-world figures, is now 2.3kW, not the 3kw of potential power we thought we were installing. We’ve lost lost 700-odd watts! Anyway, taking that figure let’s try and work out our average daily output because this depends on the number of effective full-sun equivalent hours per day, often called Peak Sun Hours (PSH).
Peak Sun Hours
Peak Sun Hours (PSH) is a standard measurement used in solar energy to quantify the amount of solar energy received in one day, expressed as the equivalent number of hours per day during which solar irradiance is at its peak value of 1,000 watts per square meter (W/m²).
Daily Energy Output based on five peak sun hours
Our daily energy output from our panels over five peak hours:
2.263kW × 5 hours = 11.315kWh/dayHow does this compare to our daily requirements?
• Daily need: 3.45 kWh
• Daily generation potential: ~11.315 kWh
• Result:
we are well covered — 3× more solar generation than daily needsThis is great! This gives ample room for inefficiencies, which we’ll mention in a moment, but before we break out the champagne there is one crucial factor I can hear you screaming at me: in what world does the UK get an average of five peak sun hours a day? The short answer? None! Because in this part of the world that average peak sun hours spread over 12 months is actually only 3 hours a day! Yes, you heard that right. Disappointing, isn’t it?
Daily energy output based on three peak sun hours:
Energy per day = 2.256kW × 3hours = 6.768kWh/dayDespite this, our numbers are still looking good. Our daily requirements are around 3.45 kWh, while our yield across the year per day is 6.8kwh. But there are yet more inefficiencies we need to discuss, the most obvious being panel angle.
Mounting solar panels at an angle
When installing solar panels on a canal boat in the northern hemisphere, the ideal setup is to tilt them towards the south at an angle close to your latitude. This maximizes exposure to the sun, especially during winter when the sun sits lower in the sky. Angled mounts can dramatically improve efficiency, particularly when daylight hours are limited…
… but for a boat that’s always moving, getting the angle just right becomes a bit of a juggling act—each mooring spot is different, and shadows from nearby trees or buildings can throw off your plans. Still, for anyone trying to get the most from every watt, angled panels are the textbook solution.
The reality for us, however, is that we have more than enough solar so we don’t need to be chasing every last bit of efficiency. And to be honest, I’m not a fan of the mounts themselves; they’re bulky, visually intrusive, and take away from the clean lines of the boat. Plus, with the boat shifting position regularly, we’d be climbing up and down constantly to reorient them. That’s not the kind of relationship we want with our energy system. So, despite the theoretical benefits, I’ve opted for simplicity: flat-mounted panels, plenty of them, and peace of mind. That said, we have decided to glue our panels down with silicone rather than bolt them, so if in future we decide to angle the panels, it’ll be less destruction to the roof.
We could delve even deeper into the rabbit hole of power inefficiency. Shading, incorrect panel angle and wiring losses all contribute to further inefficiencies. Flat mounting could remove 15% of the panels’ potential, while you could lose around 10% through wiring. When you factor these into short winter days and overcast periods over a year, we’re far removed from that 3kw of potential power we thought we were installing.
Despite all this, there is one rule that over-rides everything we’ve discussed so far, and it takes us back to the question we avoided earlier when we asked how many panels we need. Furlong’s Law states:
FIT THE MAXIMUM AMOUNT OF PANELS YOU CAN EITHER FIT OR AFFORD!
The truth is we are investing in peace of mind and maximising our solar power potential to cover those short days. We won’t know in real terms what the winter months are going to be like but with panels being so cheap now it made sense to buy as many as possible. We’re under no illusion that we’ll still be dependent upon the generator, engine or shore power at certain times. We know from experience: on our sail boat it only took two days of cloud cover for us to haul out the generator.
How we installed our panels
The main issue was working out how to run the wires. It was unavoidable to have cables running across the roof because it wasn’t an option to drill into the roof and run cables internally without taking everything apart, so we’ve ended up with six cables back at the cockpit. Although we haven’t done it yet, the plan is to use cable mounts epoxied to the underside of the top of the gutter to keep the cables clear. This is something we’ve already done for our cat5 network cable and has worked out successfully.
We then removed the old coax cable box mounted behind the companionway door. We never planned to use this coax anyway so it made sense to remove it and use that space for our cables. We had to make sure we had a clear run into the control panel cupboard before Gary then drilled through the steel plate. Cables were run through this hole into the main control panel cupboard where we installed three 100/50 MPPTs.
These charge controllers are smart, meaning we can access their data via Bluetooth on the Victron app. In future we hope to mount a Cerbo GX unit to allow us remote access to the whole system, meaning we can control the panels when away from the boat (e.g. turning them off when there is excess sun).
How have the first 24 hours been off-grid?
Being at the height of summer the panels are performing brilliantly. In fact it’s almost becoming a problem as the batteries are at a constant 100% state of charge. With lithum batteries we don’t want that, so we’ve taken to turning the MPPTs off, which we can do via the Victron app.
We’ve switched from a gas to an electric kettle. We had an old 2500-3000W kettle knocking around and it boils water in about two minutes! Actually, that kettle is a little over-rated and the inverter warning light comes on when in use, so we’re looking to buy a 2kW kettle to replace it. Either way, this is saving a lot of gas.
The other thing we did is re-wire the calorifier (immersion water heater). Previously it had been wired up to the generator, but it makes sense to use the excess energy from the panels when available. It’s rated at 1kW and, on our first test, we still had an extra 500W charging the batteries.
In the near future we hope to install Victron’s Cerbo GX, which is a mini-computer that will allow us access to all peripherals, and the ability to monitor and control them remotely.
What equipment did we install?
Our friend Curtis put us onto these panels, which are available from City Plumbing in the UK at a ridiculously cheap price. City Plumbing throw in free next-day delivery too. They’re the DMEGC 500W bi-facial all-black model, and when you compare these to branded panels, they’re a steal. No, I hadn’t heard of DMEGC either, but the company has been around since 1980 and, from what I can see from the website, they’re flying off the shelves… for good reason!
The MPPT charge controllers were the Victron 100/50 model. This means they are rated at 100V and 50A.
Cabling, fuses and other peripherals were supplied by Gary.
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