Solar Power

Solar panels perform best when they can track the sun

There are very few cruising boats that we see these days that don’t have a solar panel fitted somewhere, and many have some pretty substantial arrays. Our experience over the last five years has been largely positive, and we’re convinced that solar has played a valuable part in our supplementary power installation, wherever we have sailed, from the far north of Scotland to the Canaries. And with prices for larger panels now falling below $1/W, solar panels are becoming a more affordable option.

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Do You Need A Generator?
  22. Efficient Generator-Based Electrical Systems For Yachts
  23. Battery Bank Size and Generator Run Time, A Case Study
  24. Battery Options, Part 1—Lithium
  25. Battery Options, Part 2—Lead Acid
  26. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Load Dumps
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Ion Batteries Explained
  31. 11 Steps To Better Lead Acid Battery Life
  32. How Hard Can We Charge Our Lead-Acid Batteries?
  33. How Lead Acid Batteries Get Wrecked and What To Do About It
  34. Equalizing Batteries, The Reality
  35. Renewable Power
  36. Wind Generators
  37. Solar Power
  38. Hydro Power
  39. Watt & Sea Hydro Generator Review
  40. Battery Monitors, Part 1—Which Type Is Right For You?
  41. Battery Monitors, Part 2—Recommended Unit
  42. Battery Monitors, Part 3—Calibration and Use
  43. Battery Containment—Part 1
  44. Q&A—Are Battery Desulphators a Good Idea?

Colin, European Correspondent here at AAC, is a deeply experienced offshore sailor who holds a Yachtmaster licence, and a gifted photographer and talented writer who has added a whole new dimension to Attainable Adventure Cruising. In addition, since Colin and Louise are from England and had their OVNI 435, Pèlerin built in France, they bring a European perspective to our site. You can read more about Colin and Louise and their business at their website.

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Chris

We carry a 405 watt array. We are an all LED boat as well and use between 30 and 150 Ah a day depending on a myriad of things. On sunny days, using MPPT, we make back our overnight deficit in three hours after the sun gets about 20 degrees above the horizon. The deficit is made up while the daytime need is being met. This is true underway and at anchor. Except for air conditioning, the large water heater, and a succession of really dreary days, we have to invent reasons to run the genset. We expected payback in 4.5 years. Given fuel and electric costs in the Bahamas we got payback in less than two years.

Colin Speedie

Hi Chris

That’s a substantial array, and it’s good to hear what can be done. Food for thought for anyone who has the space to mount such an array, and isn’t sure whether they need a genset or not.

Best wishes

Colin

Torsten Hansen

Chris, I would love to see your installation but the links you provide are now locked as private by WordPress. FYI

John Harries

Hi Torsten,

Chris has not been cruising or appearing here for some years.

Dick Stevenson

Colin, This is a really nice report. Dick

Colin Speedie

Thanks, Dick – kind comments are always very welcome!

Glad you found it useful.

Best wishes

Colin

Alain Rémi

When can we expect sails with built in solar captors ? What’s the difference between the best solar captors (The one on the International Space Station, I assume) & the best -most efficient- we can buy today ? Thanks

Colin Speedie

Hi Alain

perhaps the day that such equipment is durable enough to withstand the flogging of a soft sail – I helped an ex RAF engineer with a project many years ago to develop radar reflective sails, and it was the difficulty in making it robust enough to take the pasting we give sails that was the drawback – nothing else.

Best wishes

Colin

Matt Marsh

A very nice, thorough summary, Colin, as we’ve come to expect from you.

One small correction. MPPTs – They adjust the voltage on both sides (battery and panel) to keep the panel operating at maximum V*I (not max V), near the ‘knee’ of its performance curve. If the panel is allowed to reach maximum voltage, it will provide no current and no power.

Also worth noting re. MPPTs – You can combine several panels onto one MPPT if they are of the same type and pointing the same way. Panel banks that are under different shading conditions or held at different angles should be on separate MPPTs. (I think we used six or eight MPPTs on the last solar car I worked on; the region beside the canopy, for example, would be in quite different light than the region near the nose.)

John Harries

Hi Matt,

Thanks for the correction of the error, which was made by AAC’s morphine soaked editor, not Colin.

Colin Speedie

Hi Matt, John

Fascinating stuff on MPPT, with some new angles that I hadn’t heard of before – make sense though, so thanks for the really useful explanation.

And no blame on the editor – who was only doing his best to clarify a point that I hadn’t made as well as I should.

Best to you both

Colin

paul shard

Thanks for your report!

On our first boat we installed 2 X 55W panels (15 years ago) and they helped out in the tropics, especially when we were in the Caribbean and Med. We had a rule never to sail north of 40 Degrees so didn’t try them in Scotland. But the past 2 seasons sailing the Baltic, Norway, Shetland, Scotland I am sure it would not have made much of a contribution. Perhaps we had rainier summers than normal 🙁

We do not have solar on the new boat (Southerly 49) and are still thinking about options. Although we have all LED lights (except nav lights) we still use about 200 ah per day at sea and I think we will still need the genset until solar gets a bit more efficient.

BTW – we have just arrived in the Graciosa, Canaries from Morocco – where are you?

Chris

Paul, it must be the clouds and rain.

The generally accepted panel angle for Islay on the Summer Solstice would be 27 deg; for Georgetown, Exuma on the Winter Solstice 23 deg – not a significant difference, nor a significant boost over a flat panel.

The insolation astronomically possible on Islay on the Summer Solstice is actually 84% greater than what is possible in Georgetown on the Winter Solstice.

Between June and July, Islay has had some of the cloudiest weather since February-March. Same with precipitation.

Colin Speedie

Hi Paul

With a substantial power daily power draw, a genset still makes sense. My view is that it is still worthwhile reducing (a) demand (as you’ve done, (b) supplementing with wind and solar to reduce (at least) use of the genset.

And there’s more to come – next part will be hydro power and new tech generation – and there are some really interesting new developments in that field that might be what you are looking for.

We’re in Puerto Calero getting ready to head out – perhaps tomorrow, if the wind goes off a little……

Best wishes

Colin

paul shard

Hi Colin,

Looks like we will miss you… we are in Rubicon heading off in a few hours for Las Palmas. We are going to film the ARC for our television show “Distant Shores”! We have crossed the Atlantic 4 times but never done the ARC. Should be good fun!

Best

Psul

Colin Speedie

Hi Paul

Sorry to have missed you – and good luck on the crossing!

Best wishes

Colin

Ted

We have 4 x 95 watt mono crystalline panels mounted on an arch. They have the same footprint as 4 x 80 watt poly crystalline panels would have. They meet all of our electrical demands, except the auto helm at night, and produce as much as 25 amps when the sun is high. We use a MPPT regulator.

For passage use, we have a Dup- Gen wind/ water generator that we use in water mode. It gives us about 4 to 8 amps depending upon boat speed.

We have not used the engine for charging batteries since installing the above.

Colin Speedie

Hi Ted

Another good, positive story. And as you point out, one of the good points with mono crystalline is that you can potentially gain extra output from the same footprint as a poly panel.

Night is the big question – we’ve just installed our water generator, and expect around the same output as yours – we’ll see over the next week or so. If it works as we hope, we’ll be in the same position as you – which is what we’ve been after since the outset.

Best wishes

Colin

Dick Stevenson

Colin,
You write ,” With a substantial power daily power draw, a genset still makes sense. My view is that it is still worthwhile reducing (a) demand (as you’ve done, (b) supplementing with wind and solar to reduce (at least) use of the genset.”
On an ecological sense that is good advice. But those of us living aboard are already many many times more carbon friendly than our shore-side brethren. Redundancy is another plus. So is the quiet that comes with solar.
But I would want to consider system’s and boat complexity. All systems are a challenge to some degree. If you have a genset, run it an extra period of time to make up for what the alternative systems might contribute. You have already determined you need to run it anyway and more use is likely good for the genset. This cuts down on the systems that need figuring out, installing, maintaining etc.
By all means if you choose to function without a genset, use solar and wind etc. but if you choose a genset, they are usually enough of a headache that you might just want to concentrate on one system.
My best to all, Dick Stevenson, s/v Alchemy

Colin Speedie

Hi Dick

All fair comments, and I fully understand what you’re driving at – and my view is that there is a tipping point where you have to commit to one approach or another. For us, we’ve set out to do it ‘our way’ – kept our power demand down, and opted for a simple boat, where others opt for another.

As I’m sure you’re aware, it’s not about one being better than the other, just what is right for you. But if the mid-point is just a phenomenally complex system – well that’s no kind of win at all.

Best wishes

Colin

David

Hi Colin,

Great post.

We have 600 watts of semi-flexible mono-crystaline panels by Aurinco with two Blue Sky charge controllers and have been very happy with both. The Aurinco panels are only 1/8″ thick and can be walked on. We have them glued and screwed to the deck. No issues so far. The Blue Sky MPPT controllers seem very robust and can be hooked up to function separately or together as one unit.

For reliability it’s a good idea to size charge controllers so that their capacity is well above your panel array size so the controller isn’t maxed out. Splitting the panels into multiple arrays with separate controllers provides nice redundancy and maximizes charge efficiency (we did 2x300w arrays). The biggest downside is the install hassle and weight of the extra wiring runs.

One thing to consider, the efficiency gains of tilt-able panels aren’t as high in middle and lower latitudes especially if you forget to move the panels often. I’ve read of tests showing 10% or less difference in real-world conditions. Temperate and tropical sailors can probably get away with fixed installations and save the cost and complexity of the moveable panels.

The new semi-flexible mono-crystalline panels are worth a look if they fit on your boat. They have more installation options than rigid panels. Taking the curve of the boat, they can be bolted or glued right to the cabin, deck, or rigid bimini top and walked on, eliminating the complexity, cost, and windage of hard-panel mounting racks. And to my eye, panels that follow the curves of the boat look better. But they still have the maximum efficiency and smallest size per watt like the rigid mono-crystalline panels.

Like Chris wrote, on Tigress the nighttime deficit is made up while daytime needs are supplied, but with some exceptions. The electric waterheater or the watermaker can throw the daily energy balance off, as can the autopilot. Then we need the genset or motor. But all-in-all the free silent power with no maintenance needs is hard to beat. It’s great to go days on end at anchor without worrying about power.

And with a reasonable chance at a 15-25 year lifespan, most of the rest of the gear onboard will have been replace 2-3 times by the time they expire! (fingers crossed…knocking on wood…)

Cheers,
David, sv Tigress

Colin Speedie

Hi David

so many good points, but I’d like to highlight a couple – selecting a charge controller to match your potential future needs is a very good idea, something we neglected to do ourselves, to our cost.

The new generation of semi-flexible panels look promising for all the reasons you outline, and if they perform as well as you suggest, then there are many obvious advantages to them, not least from an ergonomic and aesthetic point of view.

You’re right about the extra benefit from being able to angle your panels being diminished in lower latitudes – but even on lower latitudes winter still comes, and we’re still seeing the benefits here at the ends of the days. And one of my main points throughout this series is what will work for you even in higher latitudes – and the benefits of being able to angle your panels are even more marked as you sail towards the poles.

Best wishes

Colin

Best wishes

Colin

John Harries

Hi David,

Interesting on the semi-flexible panels. However there is one thing that bothers me big-time about them. The temptation to install them in places where they can be walked on. When wet, these panels will have the non-skid properties of a skating rink.

We at AAC firmly believe that good non-skid is a basic seamanship requirement that should never be compromised for any reason.

See Colin’s post here: http://www.morganscloud.com/2012/08/15/staying-on-your-feet/

Of course I’m a bit paranoid about falls at the moment!

Novak

Have the flexible panels come so far as to be able to be fixed to a shade awning, to be brought out at anchor?
This could be quite a large area if draped either side of the boom?
Thank You
Novak

Colin Speedie

Hi Novak

Yes, they have, and we see an increasing number of boats equipped in this way.

But they do need a large area to match solid panels, due to their lower output, and will almost certainly have a shorter lifespan.

Best wishes

Colin

Chris

When looking at solar options, one somewhat under considered item is heat. Solar Panels don’t like it. Ventilation around the panel is essential. The rigid panels generally can be mounted to enable air circulation. The flexible ones can be, but those we’ve seen generally aren’t. On an 80 deg F day at latitude 27 in May, it is possible for an unventilated panel to heat up to 110 deg F. (We measured this on a boat docked alongside.) This can knock as much as 25% off the panel output. Panels resting on anything cannot reject the heat build up adequately. Two inches of air flow space beneath them should be considered a minimum. The MPPT controller also needs to reject heat. (PWs very much more) If it has to be mounted in a hot or poorly ventilated space, a low draw fan directing air across it will use less electricity than the thermal inefficiency of an overheated controller will rob.

David

We were worried about the heat issues with semi-flexible panels, but learned that they don’t get as hot as hard panels. It’s the construction. Hard panels usually have a transparent layer in front of the solar cells but not actually attached to the cells. That can act like a greenhouse collecting heat. Semi-flexible panels have the protective barrier fused on top of the layer that has the cells. It’s a laminated construction with hard substrate (aluminum or fiberglass) then cells then plastic layer on top. So they can be mounted directly to hard surfaces without an air gap behind and have the same efficiencies as hard panels. We’ve found that they deliver the advertised output in hot conditions.

Good point about cooling the controllers. I think we’ll end up needing to add a computer fan to improve airflow.
David

Colin Speedie

Hi David

I think you’re right – the semi-flexibles we have on deck perform OK, and the construction is supposed to cope with the heat OK. And ours certainly seem to develop the power advertised, but there may be others where the construction quality is less good.

Best wishes

Colin

Jacques Landry

Good day,

I would second what Chris just pointed out about poor ventilation of flexible panels if they are glued on deck. I would also second what John says about their slippery nature. I did not fall yet, but did some aerobic exercise on these while trying to get a reef on a friend’s boat. Even my nice non-slip fancy boat shoes were as good as skates on these! Ended up barefoot to finish the job.

I would also add a note about their low efficiency. Not only is it lower than other panel type, the efficiency of a panel is that of the less efficient cell in the array. So with flexible panels installed on a curved surface there are ALWAYS cells (even just one) oriented the wrong way, so decreasing overall output. To make it worse, they are installed in places under shadows! Reminder : the current output of most solar panel is the output of the weakest cell multiplied by the number of cells. That’s why a bit of shadow (or bird crap) on part of a panel will drastically decrease its output. One more reason to regulate panels in smaller groups to avoid one panel from limiting the output of all others. Yes, there are some more expensive models that do not have cells in series, but these are on the space station, not on the average sailboat.

Chris

What Jacques says about shadowing is true. However, some rigid panel suppliers are now offering panels with blocking diodes for each cell (the panels we have installed have 18 each).* I have not been able to find poly panels with the same features. Haven’t looked real hard either.

*However these blocking diodes create an 11% voltage drop. With MPPT this does not translate to a full 11% loss in output. The trade here is a constant small inefficiency vs an unpredictable and sometimes total loss of output from shading.

Jacques Landry

Chris,

The problem with the blocking diode is not only the voltage drop overall, but also that if say 3 or 4 of your cells are shadowed, the voltage output will potentially be lower than the battery voltage, resulting in … nothing out! OK, with MPPT you alleviate some of this if you are using 24V into the MPPT for charging 12V batteries.

I believe the problem is not with rigid panels, normally mounted over the bimini area, but more so with flexible panels that people seems to put under the boom!

Chris

Jacques,
Ours are over the bimini and well away from shade sources — except for the 50 cm tall gull that decided to drop crabs on the panels to break them up and then fly down to snack on them. We could watch the impact of his presence on the ammeter.

David

A note about shading issues and panel construction. It’s a good idea to ask the panel manufacturer how many arrays each panel is wired to have. The weakest cell multiplied by cell count issue that Jacques points out is true and that’s why a small shading area = big output reduction. It pertains to the cells wired in series. So if the whole panel is wired in series and one cell is shadowed, the whole panel’s output will be reduced substantially. But if the panel is wired to have multiple arrays (with each array wired in series and then the arrays connected in parallel), then the shading effect will only reduce the output for the shaded array and the rest of the arrays will have full output. So two panels of exactly the same size and number of cells could have very different outputs with partial shading. The manufacturers don’t seem to mention this much. Panels with multiple arrays will usually have higher outputs when partially shaded. If you can keep shade off your panels then it doesn’t matter. With 4 arrays per panel, shade definitely still has a big effect on our panels, but if the shade doesn’t cross multiple cell arrays it’s not as bad as it could be.
Cheers,
David, sv Tigress

Bob Tetrault

This is the best briefing I have ever experienced on solar power options. Although “Sea Return” is still way too power hungry for any green power installation this series has me gearing up for a flexible solar array on my smaller lobster boat rigged with an electric pot hauler. Although equipped with a deep cycle batteries and an outboard alternator the consumption often trumps the charge . A semi flexible solar array with a quality and properly sized regulator may be just the ticket to supplement my power use. Topping the batteries up prior to a long day is required if you want to keep up a fast pace, I will size a system to do just that. More importantly I am now shamed into donating to the site because I’m now a consumer of the information and not just a contributor, well done .

Matt Boney

Just a few comments:

I have Solara semi-flexible panels mounted on the deck in front of the mast. They aren’t slippery when wet, they have a tiny lens over each element. (They have already been replaced under warranty after 4 years!!!) We have mounted the new ones on car window heat reflectors and that has kept them much cooler.

MPPT controllers have one other very useful feature that allows you to connect panels in series. So three identical panels each nominally 12 volts can be fed to a MPPT controller that will accept at least 60 volts. This means the wires used can be three sizes smaller than if the panels are wired in parallel. They must all be working at the same voltage all the time – i.e no shade!

One point that worries me is all those people who happily say – “my solar panels get my batteries fully charged by midday”!!!

The regulator may have dropped down to “float” mode, but your batteries will only be about 85% charged. All the potential charge current is then being wasted. It will take at least another 12 hours at a float voltage of 13.2 volts to get the batteries anywhere near 100%. That just can’t happen with solar. If you get 6 good hours of charging a day you are doing well.

So you need a regulator that you can tweak or fool to keep charging at a higher voltage. As soon as it drops to float turn it on and off to reset it, and watch the charging current climb when the voltage goes back to 14.4 volts.
Set the absorption time MUCH longer than the manufacturer default value – but determine this by the size of your service bank.
Set the “float voltage” as high as you dare depending on the temperature. 13.8 volts should be ok even at 45 Deg C.

John Harries

Hi Matt,

All good points. This is just another area where so called smart regulators are not. Until regulator manufacturers wake up to the fact that the only way to properly measure battery state and therefore control a regulator is to have a shunt on the battery that accurately measures how much charge current the battery is taking (amps), combined from all sources, net of house loads, users will need to play these kinds of games to fool the regulators. A very poor situation since all of this results in most yacht batteries failing from undercharging. And then there is the risk of overcharging, or even explosion and fire, when the user tries to overcome the fundamental weakness of the regulators.

Richard

This “solar” article was just one of a few hundred reasons why I think this website, “Attainable Adventure Cruising”, is the absolute best on planet earth..

Real World, real cruising, real life, real problems, real fixes, hands on, trail and error, this is what we found, this is what we learned, this is what worked for us.. Real knowledge, real sharing, real recommendations..

This article really “shed light” and clarified a “dark and shadowy subject” for me.. Thank you.. Thank you, thank you..

John Harries

Hi Richard,

Thanks very much for the kind comment. Makes all the work worth while!

Steve

Chris,
Shortly I will install 3 modules to my boat with a MPPT controller feeding 6x 120Ahr gel batteries. What is the preferred method to attach the +/- feed wires from the controller to the batteries? Should I be concerned about an imbalanced charge if its connected to the positive of battery 1 and negative to battery 6? This final bit of the puzzle has eluded me.
Thanks

John Harries

Hi Steve,

Very interesting question, and one that has me giving my head a good scratch.

There are more issues here than first appear. I started typing and it got so long that I think it’s going to be a post. That will also be good as more people will be able to help you answer it. And we have some really smart members.

Anyway, one question before I go any further. I’m assuming that all these batteries are 12 volt and connected in parallel? Please confirm or correct that.

Steve

John , correct, all batteries are 12V. They are wired in a parallel circuit and Im presently trying to findetermine the method of this wiring as some methods allow a balanced charging, others not.
http://www.smartgauge.co.uk/batt_con.html

John Harries

Hi Steve,

I was noodling around with a pencil and paper, and had come to the conclusion that the problem was a lot more complicated than it looked, when I read the excellent article you linked to.

This guy clearly knows what he is doing. To connect your charging source(s) simple follow his instructions for connecting the loads and then connect your charge source to the common point that the single cable from the loads are connected to. The point being that it really does not matter whether you are balancing load or charge source, the theory is exactly the same, you have to balance the resistance of the cables. The thing that makes the calculation so funky is that you also have to take into account internal resistance of the batteries and how everything reaches equilibrium, but this guy has done the calculations for you, so just follow his instructions and you will be good.

By the way, this is why it is in many ways better to connect multiple batteries in series, using two volt batteries, rather than parallel, to build a big bank. In a series bank each battery supplies the same current and receives the same charge current without any of this messing about. Also, the consequences of a battery shorting out are usually less dramatic in a series bank than a parallel one.

Drew Frye

What about mounting semi-flexible panels with Velcro? I imagine this could be handy on biminis and decks. I did have some rigid panels mounted on a Kevlar race boat that way for about 5 years, but they never got traffic (near the transom, behind the traveler and rail). While the cheap stuff would be a poor choice, I’ve been testing some under UV and in humidity chambers, and some are quite impressive, up to 15 psi after 2 years. Specifically, it would allow mounting over deck areas that require occasional access.

John Harries

Hi Drew,

I think that might work very well. We have used velcro for all kinds of things for years with great success. As you say, the key is buying the industrial stuff. We get ours from McMaster-Carr :https://www.morganscloud.com/2007/05/18/mcmaster-carr/

Drew Frye

McMaster/Carr’s range of inventory and the speed of delivery of the most unusual item is nothing short of jaw-dropping. For many years I did plant engineering for refineries, and I swear that without them we would all bicycle and read by candle light. They got me out of a lot of tight spots, within minutes with just one call.

John Harries

Hi Drew,

If McMaster Carr ever go out of business I will give up boats and take up…knitting.

Fred Vithen

Hi Colin,
After 2 years in the Med we realise that it’s time to install solar panels. A lot of free energy.
We run 24 volt on the boat.
Three sources of power regulated, charged and stored by Mastervolt ( & Whisper) products.
Whisper genset 6,5 kw, alternator 95 a + Alpha Pro II regulator, Mass 24/100 charger,
house batteries 4 x 140 Gel Mastervolt (+ 2 x 120 start & 2 x 120 sail winches).
Isolators changed to 2 x 1603IG Battery Mate.
We also purchased the new Solar Chargemaster SCM25 MPPT.
The question is what solar panel we need to run a 24volt system?
Whisper has one 285W 1650x991x40, 24v-
But I would prefer to buy a LG 315w Neon2, 1640x100x40, ca 18 kg.
The idea is to fit it at the back of the yacht between the radar pole on one side and a new pole on the other side, means I would be able to tilt it.
What I do not understand is the difference to charge a 12v system (seams easy) and our 24v?
I’m not an marine electrician as you understand but the guys in this Marina on Sicily are not able to give me any good advice.
Thank you for your help.
Regards
Fred Vithen (Swedish), S/Y Sans Peur

Eric Klem

Hi Fred,

Sorry, I have not kept tabs well enough on the development of the exact equipment to help in component selection but what you are planning concerns me from a shading standpoint. Solar efficiency falls off dramatically with any shading at all. Given this, I think you may be disappointed with the output you get if you mount it between 2 poles unless you go to the very top of them. I know that there are lots of boats out there with radars and wind generators above their solar panels but this is really not a good practice. I know of at least 1 boat who actually had their total solar and wind generation increase by removing the wind generator completely as it lessened the shading and increased solar output so much. I love having solar on our boat and our little 140W panel just covers our needs but the key for our setup and other good solar setups is that there is nothing above the panel.

Eric

Greg Silver

A question rather than a comment. Now in refit, I have acquired 2x 100 watt rigid poly panels and a 30A MPPT controller, to feed 460 Ah batteries, 12 volt system. Panels will be mounted atop the bimini. I understand that the panels can be wired in series or parallel. If they are wired to produce 24 volts (which the controller will convert to 12 v), this will diminish the loss of power gain due to shade on the panels. Can anybody clarify or confirm this? Thanks.

John Harries

Hi Greg,

Generally you have two choices with solar panels:

Series: The voltage at the controller will be the sum of the two voltages from the panels. The advantage here is that you can use lighter wire between the panels and controller because the amps will be lower. The drawback with series is that if one panel is shaded the output from both will be reduced.

Parallel: The voltage will be that of each panel and the amps higher so heavier wire required, but if one panel is shaded the other will still provide it’s full output.

In in each case when both panels are not shaded the power generated will be the same. (watts=amps x volts)

So for your application, where I’m guessing that shading will be a constant issue due to the rig, parallel is the best option.

Greg Silver

Many thanks John. I am enjoying the vaue of my new subscription already!

William Balme

There’s an interesting youtube video out there looking at solar panels wired in series and in parallel and the effect on each of shading. https://www.youtube.com/watch?v=1qD3mN8VotQ&feature=youtu.be&fbclid=IwAR26ZGX1uX9zIzKAoA7obkMmWFJlurSlhYWcJvlxLdcV_Bj_ULsxuXOVX60

White it’s a shame they don’t consider voltage in their video, the experiment they ran certainly threw out some very interesting and unexpected results. Would love to get your take on this…

John Harries

Hi Bill,

OK, I took a look. No revelation there. In a case where there will be a shaded panel, parallel will always be better since one panel will likely be fully exposed and putting out. In series any shading on either panel will cut the total power from both panels. Think of it like a plumbing circuit. Have one circuit and shut a valve somewhere in it, and no water flows. Have two circuits and shut a valve in one, and the other will continue at full flow.

The benefit of series is that the wires can be smaller since the voltage will be double so the amps are halved. Again Ohms law.

To me, that’s the trouble with these videos: lots of prancing about by cute people, but no explanation of why something happens. Or to put it another way 11 minutes of our time to NOT explain what I just did in a paragraph.

Have a read of our Ohms Law chapter and all will come clear: https://www.morganscloud.com/2016/05/24/one-simple-law-that-makes-electrical-systems-easy-to-understand/

By the way, there is more to this because different panels are wired differently internally and that too alters the effect of shading. And then the controller type is important too. That is the other problem with videos, too simplistic.

Rob Ramsey

Hi John & Colin, great discussion over the past seven years (!) …

I have been wracking my brain to calculate the amount of solar I will need. Sun angles, usage on board, dusk to dawn, season, anchoring or coastal or ocean sailing, it all plays a role and makes things quite complex. So I have built a spreadsheet that might be of use to others. It calculates power usage for ocean sailing, coastal sailing and anchoring. Then it calculates the sun angle for different lattitudes and seasons, resulting in solar performance. Next it calculates, for different scenarios and seasons, how long I can go without needing additional charging. I can play around with different lattitudes, solar wattage, battery bank size et cetera. I can now choose solar wattage based on where I will be, what I will be doing, and how often I am willing to run the engine for additional charging and it will also also tell me if I ever need to run the engine. I will need 600W of solar panels, it tells me. I think it is pretty realistic, if I may say so myself.

It won’t do panel shadowing but it will allow for an estimate of great sun vs. cloudy days.

Can I share it with y’all? And maybe get some ideas for improving it?

John Harries

Hi Bob,

Sure, send it along. That said, I can’t promise it will get published here at AAC. Also, I probably won’t be able to dig into it for some time since, due to the new membership system, we have a huge backlog of stuff to get through.

Russell Carey

Hi guys, a lot to take in here, I’m replacing and upgrading all my solar and now I have much more to consider so I wondered if anyone had some recommendations. GoPower and xantrex are offered at defender.com but ive not heard anything about them. Any information or good place to start would be most welcome….
Cheers
Russell

John Harries

Hi Russell,

I don’t have any specific information on GoPower or Xantrex panels, but, if it were me, I would buy from a specialist like Ocean Planet or Marine How To who can advise you on whatever the best option is right now for your needs:
https://oceanplanetenergy.com
https://marinehowto.com

Russell Carey

Oh thanks.. after reading the comments I think that’s exactly what’s needed.. thanks heaps

Luke Fogleman

To those who installed flexible panels back when this article was written (~8 yrs ago), what was your experience in longevity of the panels? I have rigid panels manufactured in 1999 that are doing ok, and was interested in expanding with flexible, but have been frightened off by reliability issues (that they generally dont last). Any flexible brands that have held up well?

Stephen Wardle

Hey,
As Russell said, there is a lot to take in! Especially for me at the very beginning of my sailing journey!
I am a new boat owner and we (family) tend to sail at weekends, as often as we can.
The boat is on a swinging mooring, so I was advised to use our camping solar set up (x2 100 w hard panels – there is there is a controller wired into the set up already) when we are not on the boat to keep the batteries topped up (x2 105 house batteries).
Is this acceptable and ok to simply connect the clips to one of the house batteries (I think they are in parallel)?
Our aim is to fit a permanent set up in the not too distant future – and improve the battery bank.
Many thanks.
Steve.

John Harries

Hi Stephen,

I would not do that. Solar power, particularly if left unattended, should be properly installed and fused with a good quality regulator that is properly programmed for the battery size and usage profile.

Stephen Wardle

Ok John, thanks for the advise,
Regards.
Steve.