I have a section of deck behind my mainsheet track that, when single or short-handing never gets walked on. It's plenty big enough for a solar panel.

I'd like to have a single panel like one of these: www.outbackmarine.com.au/victron-solar-panel-185w-12v-mono-1485x668x30mm-se

The main goal would be to extend the length of time I can run the autopilot and nav systems without running the motor or flattening the house battery, which is a nice big AGM. I'm not running a fridge... Yet..... Most of the time the boat is in a marina with access to shore power and always 20 minutes of motoring to get in and out.

What's the minimum I need to make this happen? Links to actual products appreciated.

Edit, is this a stupid idea on an open transom boat? Is any "marine" solar panel going to tolerate potentially having waves breaking over it?

Do you need more charging capacity or storage capacity?

Great question. Are you suggesting just adding a battery? It's not out of the question because if I had to add 30KG there's a spot in the bottom of the boat where i could do it without it being in the way just behind the motor and existing batteries. It's a light boat though so 30KG is not "nothing".

The real problem is I have no idea how long the pilot will run before I run out, and it's hard to know because sea-state and point of sail will dictate how much juice it uses.

So i guess I need "Power Management" whether I put a third battery in or a panel or both, and I have no idea what to get.

20 minutes of motoring in and out of the marina - sounds like Westernport Bay. Been there, done that.

A simple volt meter (permanently wired in, or one using a cigarette socket)
An example from Ebay:

will tell you what's the state of charge of the battery/ies. Anything below 12.2ish and you need to recharge:

Depending on your sailing habits/duration, then you can think of how to recharge. Motoring will be the simplest method, and you could always add a solar panel (and regulator or MPPT) for longer trips.

The solar panel you linked to is quite large. A tillerpilot/autopilot (Simrad or Raymarine "arm" type) will use about one amp, i.e. 12 volts, one amp, which equates to 24 amp hours over a day obviously. Your large AGM I'd guess is a minimum 100 A/hr.
I use a 40 (now 60) watt panels, via an MPPT, to a 100A/hr battery. The fridge was the killer last time, but nav/lights/radio, and a/pilot are fine with that set-up.

RE; extend the length of time I can run the autopilot and nav systems without running the motor
Your battery will have "x" amount of amp hours. You haven't mentioned what that is.

RE ever gets walked on. It's plenty big enough for a solar panel.
I take this means yourare thinking of mounting it flat.

The solar panel will charge at its most efficient in the middle of the day in summer.
Also for max efficient the angle to the sun should be pretty close.
If your panel is mounted astern, it will be good when traveling to the west, pretty useless when traveling east and marginal on other courses.
And of course when the sun is low or the weather is cloudy, you will not add the current that is taken out on the battery by the autolpilot.
1485x668x30mm is a large panel to make adjustable.

RE: I'm not running a fridge... Yet.....
Now we are talking about a real 24 hour drain.

RE The real problem is I have no idea how long the pilot will run before I run out, and it's hard to know because sea-state and point of sail will dictate how much juice it uses.
Your manual will give you info on current draw. (This is Raymarine ST information)
I would take the max as the working standard.

Phill what panels and MPPT are you running?

My 10c

. As Gary indicated an autopilot doesn't use loads of power.
. I have 200 w solar but most charging still comes from alternator.
. Don't put the panel under the boom.
. A lifpo4 battery will double your capacity (use a suitable charging system)

Not if guys, how? what? What bits make up a system? What kind of MPPT? What panels are you running?

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JonE said..
Phill what panels and MPPT are you running?

OK. I do keep bookmarks of products I've bought and shops.

Solar panels: Mostly I like branded models, not unknown models on Ebay. I think I've got from Whitworths, this 40W panel www.whitworths.com.au/sunyo-portable-solar-charging-kit-40w but I cut off the alligator clips. I did buy their 20W panel, and for a year now I've been running the 40W and the 20W in parallel. The 40W panel is underneath my boom, so it is not the best place for generating electricity. The 20W is on the transom rail and can tilt by about 20 degrees if needed. I have one or 2 x 10W panels with alligator clips (or they're in the shed) that can be employed if I were on summer sailing holidays again.

Then you need a regulator to shut off the electricity when the batteries are full, or better is to buy a MPPT. I bought this now-discontinued model in Clayton: www.altronics.com.au/p/n2026-gsl-12a-mppt-solar-charger/ but they'd probably have a similar model. Otherwise in Preston (or mail order) Preston Off-Grid (formerly Low Energy Developments) have some here prestonoffgrid.com.au/product/victron-mppt-75-15-smartsolar-charge-controller/ this smaller model will do 10 amps, or you could go the next model. Link: prestonoffgrid.com.au/product-category/solar-power/solar-charge-controllers/mppt/?orderby=price
PrestonOffGrid do solar panels also.
Perhaps Jaycar will also have similar products.
I have a lead-acid AGM, so it is these MPPTs. Different devices are used for lithium batteries, which I don't have.

Have I forgotten anything? My 28 foot yacht has an outboard with a pitiful charging coil thing, which made just enough electricity running overnight with an almost-dead lead-acid battery. Otherwise I would have hand steered for a few hours overnight (until the solar would kick-in in the day time). I don't have the luxury of an alternator, but have a camping generator in the shed (it makes 100 W of 12V, and about 700 watts of 240 volt electricity), and I have a battery charger (car type) if I ever spend time again past Wilson's Prom

Select to expand quote

Madmouse said..
My 10c
. Don't put the panel under the boom.

D'oh )))

Also be aware that partial shading of solar panels, even from a backstay/rigging will reduce the output by about 50%,. This is why panels are usually mounted above the cockpit: to avoid shading, to shade the people, and to be out of the way.

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FabulousPhill said..

Madmouse said..
My 10c
. Don't put the panel under the boom.

D'oh )))

Also be aware that partial shading of solar panels, even from a backstay/rigging will reduce the output by about 50%,. This is why panels are usually mounted above the cockpit: to avoid shading, to shade the people, and to be out of the way.

Agree. Mine is on a dedicated frame out the back. Even then the sail can cast a shadow if heading against the sun etc.

The panel l used does work around shadows thru it's circuit design when coupled with the mppt regulator.

But under the boom on the roof of the coachhouse will mean the panel is in partial shade virtually all the time.

I'm surprised to see that the auto pilots mentioned only draw 1.5 amps, so in theory 15amp hours draw in a 10 hour work session. As to solar panels obviously the more watts the better, multiple panels have a better chance of at least one being in optimal position. Now the charge controller, I can't recommend the red arc dc to dc charger highly enough it has a mppt solar controller ( only the most basic set up would use the older pwm type units) and when the engines running the battery charging is much better than the alternator alone, there's many other advantages. I've seen evidence that a controller per gang of panels ie port or starboard gang, is a worthwhile investment. Batteries, big is best but only if you can charge it, at the marina so easy but at sea not so easy. The usual mo is to calculate all the amp draw fridge, pilot, radio etc, size the battery to suit then develop a charging system to suit the battery

Select to expand quote

woko said..
I can't recommend the red arc dc to dc charger highly enough it has a mppt solar controller

The Redarc BCDC1250D is probably one of the best investments I have made for my boat!!!

It was a game changer & that was 6 years ago & still loving it!!

Select to expand quote

JonE said..
I have a section of deck behind my mainsheet track that, when single or short-handing never gets walked on. It's plenty big enough for a solar panel.

I'd like to have a single panel like one of these: www.outbackmarine.com.au/victron-solar-panel-185w-12v-mono-1485x668x30mm-se

The main goal would be to extend the length of time I can run the autopilot and nav systems without running the motor or flattening the house battery, which is a nice big AGM. I'm not running a fridge... Yet..... Most of the time the boat is in a marina with access to shore power and always 20 minutes of motoring to get in and out.

What's the minimum I need to make this happen? Links to actual products appreciated.

Edit, is this a stupid idea on an open transom boat? Is any "marine" solar panel going to tolerate potentially having waves breaking over it?

Have you thought about installing a wind generator.

Select to expand quote

FabulousPhill said..

JonE said..
Phill what panels and MPPT are you running?

OK. I do keep bookmarks of products I've bought and shops.

Solar panels: Mostly I like branded models, not unknown models on Ebay. I think I've got from Whitworths, this 40W panel www.whitworths.com.au/sunyo-portable-solar-charging-kit-40w but I cut off the alligator clips. I did buy their 20W panel, and for a year now I've been running the 40W and the 20W in parallel. The 40W panel is underneath my boom, so it is not the best place for generating electricity. The 20W is on the transom rail and can tilt by about 20 degrees if needed. I have one or 2 x 10W panels with alligator clips (or they're in the shed) that can be employed if I were on summer sailing holidays again.

Then you need a regulator to shut off the electricity when the batteries are full, or better is to buy a MPPT. I bought this now-discontinued model in Clayton: www.altronics.com.au/p/n2026-gsl-12a-mppt-solar-charger/ but they'd probably have a similar model. Otherwise in Preston (or mail order) Preston Off-Grid (formerly Low Energy Developments) have some here prestonoffgrid.com.au/product/victron-mppt-75-15-smartsolar-charge-controller/ this smaller model will do 10 amps, or you could go the next model. Link: prestonoffgrid.com.au/product-category/solar-power/solar-charge-controllers/mppt/?orderby=price
PrestonOffGrid do solar panels also.
Perhaps Jaycar will also have similar products.
I have a lead-acid AGM, so it is these MPPTs. Different devices are used for lithium batteries, which I don't have.

Have I forgotten anything? My 28 foot yacht has an outboard with a pitiful charging coil thing, which made just enough electricity running overnight with an almost-dead lead-acid battery. Otherwise I would have hand steered for a few hours overnight (until the solar would kick-in in the day time). I don't have the luxury of an alternator, but have a camping generator in the shed (it makes 100 W of 12V, and about 700 watts of 240 volt electricity), and I have a battery charger (car type) if I ever spend time again past Wilson's Prom

Another fan of Preston off grid here, they are helpful and cooperative, happy to discuss options and will send a quote promptly, unlike a number of other traders up and down the east coast.

I would also consider looking at Solar4rvs. Ive bought quite a lot of gear from them. Victron MPPT's, smart battery monitors with a shunt, Enerdrive Lithium 100 Ah batteries etc. They are not the cheapest but they do know their stuff. Based in Rowville.