After starting this solar power on sailboats-series with part 1, where I showed a pretty standard solar array installation on an Oceanis 41.1 and diving deeper into the topic with part 2, where we got to know a way of “spicing it all up” by taking on a notch and installing an custom made “tailormade” solar array on a sailboat I decided to as well upgrade my new boat with such a custom made solar power installation: Planning the array with the Austrian company making these awesome products by the name of Solbian, I was able to increase the power generation capacity from 50 Watt-peak to some 140 Watt-peak, which is awesome.

This is where we start: A theoretical idea

Making contact with Solbian was a no-brainer. The company was quick to deliver a first draft for the power generating solar panels for GEKKO which is described in part 3 of this series. Now, the boat has been finished in the yard and brought to Germany two weeks ago where it now awaits further installations and – the solar-upgrade. In this fourth part of the series, before the real installation and activation of the custom made Seascape 27 / First 27 SE solar array is finished, I want to go back a step and dive deeper into the basics: How can you calculate and plan your own solar-upgrade? This time I talked to Michael Koerner, CEO of Solbian Austria & Germany, who helped me revive seventh grade physics-knowledge …

Calculating the power consumption of a boat

First thing you do when planning your solar power installation is to calculate the overall demand for current in your boat. Modern sailboats do have a very little overall power consumption as mostly the main current-consumers like lights are made of LED-lights which have a very low demand for electricity. The biggest consumers might be the fridge (mostly the freezer) and of course the electronics, like chart plotter. When underway the autopilot will draw constantly from your batteries. Now, how to calculate the power demand of your boat? As my new Beneteau First 27 SE arrived and we pulled her into the yard, I re-calculated some of the properties.

GEKKO has arrived: Let´s start!

Michael Koerner says, that a spot-on calculation of current demand of a yacht is a simple summation. Checking the current intake of a specific part of the equipment and multiplying this with the amount of hours which this part is on the grid daily. The sum of all of these numbers would be the daily current demand of the boat. Michael says: “Generally speaking, after doing this math, it is absolutely reasonable to add some 10 or even 20 per cent to the demand just to have some safe reserves.” Another way would be the other way round to check how much current the built-in battery is providing and how long this amount of energy lasts during normal utilization. “For example, if your a lead-battery with 100 Ah lasts roughly one day before re-charging, that means, that you can use 50 Ah – half of it – for current consuming.” Well, let´s take a look at GEKKOs battery then.

A massive Lithium-Ion-battery as main powerhouse of the First 27 SE

I went for Torqeedo´s WH 48-5000 Litium-Ion battery which is a huge beast for sure! It is roughly ten times bigger in size than the First 27 SE standard AGM-battery and weighs in at 36 kilograms. The usable energy is 5.000 Wh – meaning Watt-hours. “That means that for example an engine or any other current consumer with a power rating of 5 kW can run one hour before the battery is drained. Or a smaller engine with 1 kW can un five hours. Normally, a battery like this won´t be discharged any lower than 20 per cent, which is much, much more than a lead-battery with 50 per cent by the way.” Now that I know how much capacity this gib battery has, let´s check for the main current consumers of my boat. In the meantime the boat arrives at the showroom and I climb on her deck. I can see the yard-installed standard solar-array delivering 50 Wp of power. That´s the one to replace.

Standard 50 Wp solar module on GEKKO

I am sailing in the Baltic Sea which is a fairly small sailing area but nevertheless there are long legs to be sailed. For reaching Denmark for example that’s a rough 8 to 10 hour sailing trip from my home port. Going to Sweden requires some 40 hours of sailing. Knowing that I can say that the most important electric equipment on board is the autopilot. So let´s check it. “I don´t think that the autopilot on the First 27 SE will eat away much current”, says Michael Koerner of Solbian. “This is a very well balanced boat and if sails are trimmed accordingly I´d reckon that the autopilot wouldn´t need more than 50 Watts. With your battery that is roughly a four day potential to have the autopilot running before battery needs recharging. And saying that we´d have some more current demand of other equipment of 100 Watts there is even more safe-margin of two days.”

Planning a custom solar array for Boris Herrmann´s MALIZIA Imoca

My aim with GEKKO is that the solar array is upgraded to a degree that re-charging of the battery is done quicker and thus more efficient than the standard array can do. The past weeks Michael has checked the deck-layout of my boat and planned a new custom array with a CAD program: “We have done this, by the way, for the Imoca 60 of Boris Herrmann for the Vendeé Globe as well and it worked just fine!”, says Michael. The outcome was a 1:1 cardboard print-out which Michael sent to me to check if everything fits just fine. That´s the next step on the boat itself. Next chapter in my calculations was a quick math on my engine. For the boat I went for the Torqeedo Cruise 4.0 electric engine. The power rating of that engine is 4.000 Watts. I ask Michael: “4000 Watts means that after running this engine one hour on full throttle your battery will arrive at about 20 per cent capacity. As there are some more current eaters on your boat, let´s say chart plotter, VHF and so on, the battery will be drained a bit quicker.” I learn: With a fully charged battery I can drive my boat one hour at full speed.”

Cardboard models of the new power array for the First 27 SE

That is a figure to bear in mind: Some day a foul weather front could be a surprise or a thunderstorm approaching pose a risk – now I know that I can push her to her max speed for one hour safely. “For checking her power consumption going at cruise speed we´d have to see her in the water”, says Michael. Back in the shed I cut out the cardboard gauges of my new solar power array with a scissors and go to the boat´s deck. My new array should have a capacity of 144 Wpeak. What is a “Watt-peak” though?

Things to know about solar power on sailboats

As I put the cardboard-panels onto the boat and fix them with some tape, Michael explains: “A Watt-peak is the output of a solar panel at standardized conditions. This standard is solar radiation of 1.000 Watts per square metre and a temperature of the solar-cells of 25 degrees Celsius. Every solar cell on the world is measured this way so that a normative possibility of comparison is given. This figure also makes it possible to calculate a daily power output of a solar array.” Michael explains that in reality it is a bit more complicated, as also different temperature coefficients, different properties in dusk and dawn, mechanical differences and so on have a certain impact. “Most important for us when planning an array are shadows. Of course, any shadow should be avoided, but on a sailboat that is virtually impossible.” Why is that so important? “Solar cells on a module are series-connected. That means, the one solar cell with the lowest power output determines the output of the whole series.” One cell determines the output of the while panel? “That is correct. We can counter this shadow-effect by incorporating bypass-diodes. These measures the current and can bypass areas in the shadows, maximizing current and power output. Together with the right charge controller we can achieve a pretty good shadow-resilience.”

Fitting the paper modules

I apply the cardboard-panels as accurate as I can and check for the perfect fit. Michael told me to be as just as I can because the panels will be produced on demand and exclusively for my boat: Any mistake would later cause many trouble. Shadow won´t be a big issue on my boat as in the foredeck area – either the jib is in the way or not. Nevertheless, even my comparatively small array will have some bypass-diodes. “On your First 27 we have five of these bypasses installed. Compared to Boris Herrmann´s MALIZIA where sources of shadow are extreme, that´s peanuts. On his boat we have a 1.2 kWp-array with no less than 33 bypass diodes and 15 special Step-Up MPPT-modulators installed. A pretty fascinating and complex system.” Looking at my solar array I am happy: The area is utilized to the maximum and the panels, except for a small 5 mm margin, fit just perfectly. The better any layout graphics or construction plans of the boats are, the more accurate Solbian and Michael can plan the panels. I mark the overcut areas and as a next step I will send these panels back to Michael to work on the project. In the meantime I´ve ordered a solar-charger at Torqeedo to fit most perfectly the big Lithium-battery. Now, how fast will my new 144 Wp-array be charging up the battery?

Marking the offcut

Michael explains: “Well, this of course depends on the Sun and the duration of the panels receiving her energy. In the Mediterranean for example you can easily take the Watt-peak-number of your array and multiply it with factor 4 to 6. That means that a 100 Wp-module will have a daily power output of 400 to 600 Wh – we normally take the more conservative approach just to add safety margin, which is factor 4. Meaning that your array with 144 Wp will be able to produce some 550 to 850 Wh daily.” Doing some math that figure means that my Torqeedo battery, discharged to let´s say 20 per cent capacity, would be fully re-charged within five to seven days. That is not as impressive as one would hope, admittedly, but usually a solar power array is not used to re-charge drained batteries but rather constantly add consumed power, conserving the state of charge. My aim with GEKKO is exactly this.

GEKKO is ready for the next steps

For now I am flashed by the outcome and the developments. GEKKO is treated for her underwater hull and will receive her antifouling soon, the electric engine is ordered and will be delivered and installed soon. Regarding the solar power array, Michael Koerner will now re-work the changes and then the panels will be produced. I hope to have it installed in April when my new boat arrives at the Sea. Still, so many things to learn …


You may also be interested to read these articles:

Solar power on sailboats, parts 1, 2 and 3

LED-lights wiring on my old boat

Eco-friendly boat building – is this possible?