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mr-canada · 14-09-2017, 21:14

Hi there electrical junkies.

I am planning on buying a 150W 8A solar panel and a controller (good for up to 30A) for the boat as I am waiting on a waitlist for a marina and so I am moored off grid.

I have traditionally ran a dehumidifier and ceramic space heater on very low over the winter when connected to shore power. Obviously the dehumidifier is completely out (it's big enough to dry out a huge house) and the space heater I currently have is going to be useless (120V AC, 750/1500W).

The goal is not to make the boat nice and toasty, but rather to have the heater kick in when it reaches near freezing. It doesn't usually get brutally cold here in the PNW but in the dead of winter it usually reaches about -5'C for a little while. In the odd winter (like last winter) it can drop to -15'C but that is pretty abnormal, if it got cold like that I might just wait for a calm day and plug er into shore power and run the AC unit.

It is a Columbia 26 MkII, the cabin is roomy but it's not a huge boat. I am mostly just wanting to make sure my fresh water system doesn't freeze up and burst.

The 150W solar w/controller at 8A should not have a problem charging the battery and keeping it solid, but as we all know when it gets cold you're usually not getting the best sunshine for very long even on a good day. Mostly overcast happens here and rain. Rain is good because it's not freezing, but it does reduce the output of the panel.

I've been digging around for 12V small space heaters and I keep turning up reviews where people are calling the things junk that are blowing their fuses. Maybe they're expecting too much from a 75-150W 12V space heater, maybe the things just dont put out enough heat to do anything, I don't know.

Drilling exhaust ports for a diesel heater, running the propane stove to heat the inside, the upside down flower pot hack are all things I'm not really too comfortable with. Oftentimes in the winter I check on the boat, pump the bilge (manually... :-( ) and stay the night on board before going back home as I'm not moored that close to my home. I mostly use the boat for summer sailing but hell if it's nice out I would gladly go and drop crab pots and fish and make use of it if I'm there. Obviously I'd be dressed warm.

Anyone have any ideas? I was thinking that a low power space heater on 12V below the solar panel's rated wattage would be able to at least keep the boat from freezing up if it dips below freezing in there, with some battery drain if the light source isn't optimal but that the panel would recharge over time because it would always be on with a controller.

**Paul Elliott** · 14-09-2017, 22:40

Quote:

Originally Posted by mr-canada

was thinking that a low power space heater on 12V below the solar panel's rated wattage would be able to at least keep the boat from freezing up if it dips below freezing in there, with some battery drain if the light source isn't optimal but that the panel would recharge over time because it would always be on with a controller.

The problem with this is that the solar panel only puts out its wattage when the sun is shining. We typically assume that you will get five hours worth of rated output, and this includes the lower power generated in the morning and late afternoon hours.

So, your 150W panel would only deliver 750 watt-hours of power per 24-hour day. This is enough to continuously power a 25W lightbulb (or 25W heater), with a few watts left over to keep the battery charged.

But, in the PNW the winter sun is low on the horizon, and as you point out there is often cloud cover. I don't see that you mentioned the size of your house battery, but even with a large battery that 25W heater will probably kill the battery after a day or two of cloudy skies. And due to the sun angle, your panel won't be putting out 150W either.

And a 25W heater isn't going to help very much anyway. You will have to install a *lot* of solar panels to reliably power an electric heater that will make a difference.

You might consider chemical dehumidifier crystals. Air circulation helps, too, and small fans don't suck up too much power.

mr-canada · 14-09-2017, 22:59

Quote:

Originally Posted by Paul Elliott

But, in the PNW the winter sun is low on the horizon, and as you point out there is often cloud cover. ... And due to the sun angle, your panel won't be putting out 150W either.

And a 25W heater isn't going to help very much anyway. You will have to install a *lot* of solar panels to reliably power an electric heater that will make a difference.

You might consider chemical dehumidifier crystals. Air circulation helps, too, and small fans don't suck up too much power.

Yeah I'm mostly just trying to keep from freezing conditions; rather than actually heat the boat to a comfortable temperature for dwelling. I'm not sure if anyone has any experience in what wattage a 26ft boat with an 8ft beam will require when it gets cold.

On the plus side, when it's not freezing or near freezing, the heater will not be activated and the diffuse energy will trickle charge the battery over many days. On the negative side, when it gets cold it will stay cold, and this will strain the battery capacity.

I'm using a 770 F150 pickup truck battery. Its usually enough capacity for my needs, but running a heater is a completely different equation. Normally I'm a weekender with shore power. This solar thing is entirely new to me. An 80W rated solar at 3.6 A seems to be enough to charge the battery over a weekend, and I am meticulous about conserving power if the sun isn't shining. I keep most of the breakers off, only vampire draw is the GPS because I don't want it to lose my waypoint programming but it's a handheld converted to run off 12V battery so it can't have much draw when off.

I've contemplated buying another battery and banking them in parallel, but for the weight and the actual amount of power I use it seems like six of one, half dozen of another. If the solar can't recharge it or provide enough power I could have 8 batteries and it could still drain them to damaging levels.

Any experience with a small space heater on 12V? I've seen its enough for one of the car units to defrost the windows, all I'm looking to do is prevent hard freezing of the fresh water system and maybe keep the boat a bit drier during the swing season.

Maybe alternative ideas? As I said if it's dangerous cold I'd probably hit transient or seasonal moorage and just go with 120V shore power. It's the nights and the humidity I'm trying to combat while I'm not on the water for sometimes a month or month and a half at the time.

**Dockhead** · 15-09-2017, 00:02

Just do the math and you'll see that you can't get useful heat from a 150 watt (or even 500 watt) solar panel. You'll need to burn something when you don't have shore power. I'm not aware of any good way to protect an unwinterized boat from freezing when you are neither on board, nor connected to shore power.

Pizzazz · 15-09-2017, 00:55

Your best bet is a thermal blanket. These typically run at 12V, 6A or about 70W. They cycle on and off (there is a temp setting knob), so you could expect a 30% duty cycle or about 20 AHrs total draw at night.

Another option is an oil lamp, candles or a propane heater with the relevant safety devices. Do look at diesel heaters again. They are not that difficult to install and provide plenty of heat.

CatNewBee · 15-09-2017, 01:03

Lay out a black canvas on your deck and you will get more heat into the boat than using the solar panel. May be a wind generator can be more useful in winter time with low solar radiation.

rabbi · 15-09-2017, 02:48

Your 150w panel may produce enough energy to feed
a webasto / eberspächer diesel heater for a few hours per day.
But if you wire an electric heater directly to the panel it will not give you a 1deg rise in temperature throughout the boat.

mr-canada · 15-09-2017, 06:44

Quote:

Originally Posted by Pizzazz

Your best bet is a thermal blanket. These typically run at 12V, 6A or about 70W. They cycle on and off (there is a temp setting knob), so you could expect a 30% duty cycle or about 20 AHrs total draw at night.

Another option is an oil lamp, candles or a propane heater with the relevant safety devices. Do look at diesel heaters again. They are not that difficult to install and provide plenty of heat.

I've never heard of a thermal blanket- would this be like an electric blanket, only running on 12V?

An oil lamp or candles won't work at all, seeing as I will be leaving the boat tied up to the dock and won't be aboard; I would end up getting heat when I don't need it and when the fuel/candle runs out in a day or two then I'm back in exactly the same boat.

Not sure how automated diesel or propane heaters are for this purpose I honestly don't know much about them. However I would imagine having a reliable way to expel exhaust for them would be very important.

My goal is to just mitigate the lows of the lows. Dips to about -5'C happen here in the Dec/Jan, and here in the PNW often if it gets that cold for any length of time or colder, it's because the skies are clear with no cloud cover.

Winter sunshine here can be bright but it's certainly no equatorial grade sun and the days are shorter.

I do have a battery and could potentially buy another one to run in parallel, but current draw is current draw and if the 150W 8A solar can't keep the main house battery charged with electric heat running then it's just delaying the inevitable.

john61ct · 15-09-2017, 07:13

Producing any significant heat from stored off-grid power is a non-starter except for very large systems, especially if solar-only.

Add an auto-starting generator to the mix and anything is possible, just a question of runtimes and how big a bank to allow timeshifting.

Otherwise, a diesel heater is best, then propane a distant second everything else even more dangerous.

But IMO these only for while you're on board, just saw you're talking long term unattended.

The passive options are interesting, water as thermal mass. Too bad heat goes up, would need a small circulating pump to get it below.

Or lots more panels, straight to an insulated barrel of water with a heating element in it.

**Dockhead** · 15-09-2017, 07:34

Quote:

Originally Posted by mr-canada

. . . Not sure how automated diesel or propane heaters are for this purpose I honestly don't know much about them. However I would imagine having a reliable way to expel exhaust for them would be very important.. . .

Look up Webasto and Espar. You can run these even if you're not on board. They are available with remote control devices which you can activate with a text message, or you can set a timer.

But even one of these requires more electrical power for a few hours of operation, than you can produce per day in the winter time from a 150 watt solar panel.

And as others have said -- forget about electrical resistance heat powered by solar.

But don't believe us -- roll your sleeves up and do the math. You can find data on how much practical yield per day you will get out of a given amount of solar, in a given location and time of year. Then discount that for charging inefficiencies. Then keep in mind that some days will be worse than others -- heavily overcast days a LOT worse. Then you will get a feel for how many amp/hours or watt/hours of power you can realistically spend.

Then you can figure how many hours you need how many watts of heat, or how many watts does a Webasto take, and you will see clearly enough what you can and can't do.

For keeping the boat thawed when you're not on board, it's pretty hard to beat shore power and tube heaters. If you add a bunch of solar (maybe 500 or 600 watts) and a bunch of battery capacity, then MAYBE you can get a couple hours a day out of a Webasto heater, but it sure will be simpler just to bite the bullet and take a marina berth during the cold months.

**Dockhead** · 15-09-2017, 07:50

Quote:

Originally Posted by mr-canada

I'm not sure if anyone has any experience in what wattage a 26ft boat with an 8ft beam will require when it gets cold..
. .

We use tube heaters to keep boats from freezing in the mild winters on the South Coast of England. The smallest ones are about 120 watts, I think, and you need multiple ones. Fiberglass boats are as a rule very poorly insulated, and will require a fair amount of watts of heat, to raise the temperature by much.

mr-canada · 15-09-2017, 07:52

mmm

not looking good for this solution.

I am definitely going for the solar, as the vast majority of the year i'm a weekender on the boat and during heavy summer use the sunshine is great and the 150W panel will augment the battery charge. For reference sake I have a 1.1A smart charger/conditioner I've left attached to the battery when on shore power and I've always come back to a full battery; which if you put all this heating issue aside means a 150W 8A solar should definitely do the trick for keeping the battery good and charged under normal conditions.

Back to the heating issue in the dead of winter I guess I'm down to a limited number of options:

1) Buck up for a marina on seasonal with shore power and just use the space heater I already have (pros: no need to buy anything, cons: seasonal is expensive compared to annual and I'm already on the wait list for annual)

2) Buy a sh*t ton of high capacity batteries and some 12V low wattage heater, let the whole bank charge off the panel while it's warm, hope for the best when freezing weather hits and hope the winter isn't too cold (pros: no marina charges, I'll have practically unlimited house battery power, cons: batteries are expensive and heavy)

3) Self starting 12V or 110V generator with some sort of rapid charger and a decent heater (pros: lots of power when running and has other uses, cons: money, weight and fuel usage)

Looking at the money equation it's looking like hoping for the best on the winter and moving to shore power in the bottom of winter might be the best bet. Batteries are around a hundred bucks a pop, lord only knows what a self-starting generator would cost and I'd need to get a rapid charger to add to it, plus I'm buying the solar for my needs the other 10 months of the year anyway.

I guess there's always potable antifreeze, hell of a lot cheaper if I don't want to pay the marina. I figured there would be a low wattage option the panel could handle.

**Dockhead** · 15-09-2017, 08:08

Quote:

Originally Posted by mr-canada

mmm

not looking good for this solution.

I am definitely going for the solar, as the vast majority of the year i'm a weekender on the boat and during heavy summer use the sunshine is great and the 150W panel will augment the battery charge. For reference sake I have a 1.1A smart charger/conditioner I've left attached to the battery when on shore power and I've always come back to a full battery; which if you put all this heating issue aside means a 150W 8A solar should definitely do the trick for keeping the battery good and charged under normal conditions.

Back to the heating issue in the dead of winter I guess I'm down to a limited number of options:

1) Buck up for a marina on seasonal with shore power and just use the space heater I already have (pros: no need to buy anything, cons: seasonal is expensive compared to annual and I'm already on the wait list for annual)

2) Buy a sh*t ton of high capacity batteries and some 12V low wattage heater, let the whole bank charge off the panel while it's warm, hope for the best when freezing weather hits and hope the winter isn't too cold (pros: no marina charges, I'll have practically unlimited house battery power, cons: batteries are expensive and heavy)

3) Self starting 12V or 110V generator with some sort of rapid charger and a decent heater (pros: lots of power when running and has other uses, cons: money, weight and fuel usage)

Looking at the money equation it's looking like hoping for the best on the winter and moving to shore power in the bottom of winter might be the best bet. Batteries are around a hundred bucks a pop, lord only knows what a self-starting generator would cost and I'd need to get a rapid charger to add to it, plus I'm buying the solar for my needs the other 10 months of the year anyway.

I guess there's always potable antifreeze, hell of a lot cheaper if I don't want to pay the marina. I figured there would be a low wattage option the panel could handle.

Sounds like you're on the right track.

Solar is the ideal power source if you have room for it. So even forgetting about heating with it, it's great to have.

For heating -- I think you really need to do the math if you want to keep thinking about this. Without the calculations, none of this is worth much.

Winterizing the boat could be a fine option -- but keep in mind that it is a fair amount of work and expense every time you do it. Will you be using the boat in the winter time? If you're just storing it for the winter, then winterizing it is good. Query whether you might be better off on the hard, though, if you won't be using the boat at all.

john61ct · 15-09-2017, 08:14

I would NOT recommend DC low-volt direct space heating, really is a non starter, cross it right off unless you're talking 1000w solar.

Unattended auto-start genset, or the diesel "parking heaters" mentioned above. The latter really don't use **that** much 12V power, commonly run off cranking batts.

Even then IMO wow risky unattended.

The thermal mass of a heated water container will cut runtimes enormously.