Solar, off grid and heat problem

[Paul Elliott]

Originally Posted by john61ct

A minimal solar setup will keep the diesel heater going 24x7 unattended until it runs out of fuel, about a gallon per day.

Here's my math on that:

Espar Airtronic D4 runs low-power at 0.6A, burns 0.02 gallons/hour.
This = 14.4 Ah/day at 100% duty cycle.

Location? Vancouver WA? Latitude = 50 degrees N.
Earth tilt = 23 degrees.
Sun angle at winter solstice = 17 degrees, or 73 degrees from vertical.
Assume solar panel is pointing straight up.
Cosine of 73 degrees = 0.292
150W (solar panel) * 0.292 = 44W
Assume five hours average effective sun.
44W * 5 hrs = 219 Wh / day (assuming zero shading)
At 12V this = 18.3 Ah / day.
Assume 80% battery charge / discharge efficiency, deliverable Ah = 14.6 Ah/day

So the panel should be able to power the heater in low-power mode. Just barely. At 50% duty cycle for the heater there will be a decent margin.

[GILow]

Running the heater all day is crazy. Partly because the temperature does not need to be that high and partly because the rate of heat loss is directly proportional to the difference in temperature between inside and outside.

Since all that is needed for the OP is a few degrees of extra warmth, a diesel heater than can act on a decent thermal mass over a short period of time will be fine.

Heck, make it really efficient and set a low range on the thermostat so that the heater only operates on the thermal mass when needed. Couple this with a minimum run time to prevent coking.

[Paul Elliott]

Agreed on the low heater run-time. Probably an hour or two total run-time would be sufficient, and a thermostat set appropriately low would do the trick. So, figure a 10% duty-cycle, for a current consumption of 1.5 Ah/day.

I'm just trying to run the numbers to make sure that the OP doesn't kill his battery. I should have allowed for cloud cover as well, but fortunately in the PNW the truly cold days and nights are the clear-sky ones. But the solution has to be able to handle a few days of heavy cloud cover. If he has a 50Ah battery that would ride through a month of darkness (at 1.5 Ah/day load), so the battery isn't a problem as long as the average charge-rate is good.

I think the 150W panel would work.

[john61ct]

Yes I was not talking about "running" all day.

Heating a thermal mass, would enable the water thermostatic control based on very low air temps near the critical location.

Even in arctic conditions I would think 3-5 runs of less than a half-hour would be tops, likely much less if the main tank is insulated.

The "standby mode" and sensors are miniscule draws.

[Paul Elliott]

Originally Posted by Paul Elliott

If he has a 50Ah battery that would ride through a month of darkness (at 1.5 Ah/day load), so the battery isn't a problem as long as the average charge-rate is good.

I think the 150W panel would work.

Oops, I meant to use a 50% battery discharge limit, but forgot to divide by two. We only get two weeks of total darkness holdover. This should still be fine, and even in heavy cloud cover we do get *some* charging.

[mr-canada]

Originally Posted by taxwizz

Sorry...I have never wanted to sail with someone hanging over the bow breaking ice with an ice pick. Or having to first shovel the decks clear of snow. LOL

Question...Propane explosions from propane heaters or stoves? I think that many of us have propane stoves.

Hahaha. I have had to shovel the decks clear of snow before. Not that fun sleeping in there.

[mr-canada]

Originally Posted by Paul Elliott

Here's my math on that:

Espar Airtronic D4 runs low-power at 0.6A, burns 0.02 gallons/hour.
This = 14.4 Ah/day at 100% duty cycle.

Location? Vancouver WA? Latitude = 50 degrees N.
Earth tilt = 23 degrees.
Sun angle at winter solstice = 17 degrees, or 73 degrees from vertical.
Assume solar panel is pointing straight up.
Cosine of 73 degrees = 0.292
150W (solar panel) * 0.292 = 44W
Assume five hours average effective sun.
44W * 5 hrs = 219 Wh / day (assuming zero shading)
At 12V this = 18.3 Ah / day.
Assume 80% battery charge / discharge efficiency, deliverable Ah = 14.6 Ah/day

So the panel should be able to power the heater in low-power mode. Just barely. At 50% duty cycle for the heater there will be a decent margin.

Wow. You know your electrical man!

Yes as another poster posted, the truly cold days in the PNW it's clear skies. Cloud cover tends to warm it up due to the greenhouse effect. When it's cold and sunny is when the rivers start to freeze up (very rare, maybe once every 5-7 years) and icy conditions persist for weeks. Solar energy capture would be reduced due to atmosphere but its better than diffusion with the clouds.

What is the product you guys are talking about? I missed it somewhere in the thread. Normally in winter I keep the thermostat on very very low, only to mitigate freezing, not for heating the boat to comfy warm. Honestly if I wanted to sleep on the boat comfy warm I'd just hit a transient slip somewhere and get shore power and crank up a 1500W space heater on max - and engage the 1500W dehumidifier while I'm at it to dry the boat out and kill two birds with one stone.

Regardless of the heating issue, I'm getting the 150W 8A solar panel and controller, mostly just to maintain battery charge while my boat is homeless and off grid. It will do double duty during the summer when cruising, will let me blare the stereo and run the sounder/fish finder and VHF full bore without worrying about overdrawing the battery.

Correct on the assumption there is no hot water system. It is just a fresh water tank with a hand pump on the sink for washing dishes and making coffee.

I am not planning on living aboard over winter. Summertime, maybe, never know, but I have a place to live and cats and a fiancee and a bunch of nice home electronics so downsizing to a 26.7 ft boat would be a quite the crunch. There's lots of work here no need to downgrade that bad unless I wanted to cut civilization loose for some reason.

I was looking up solar panel types, this one I'm buying is a mono-crystalline rigid which seems to take partial shading well as the shaded cells do not vampire the power from the lit cells. The controller is absolutely amazing for $22 bucks; digital display and programmable.

[Paul Elliott]

I would be interested in the details for that shade-tolerant panel. I suspect that it has the typical bypass diode arrangement, which with a single panel won't make much difference in the shading effects. Where these diodes do help is when you have multiple panes in series and a "MPPT" controller that can handle the resulting wide voltage range.

I also suspect that your $22 controller is a series-pass or PWM type. Please share the details on this as well. This won't extract the most possible power from your panel, but it's probably adequate for your needs. An MPPT controller will usually extract more power, but typically only 10% - 20% more, and you probably need to spend around $100 for a good one.

[john61ct]

Yes, have yet to see a controller I'd choose other than Victron for under $100.

And old-school Specialty Concepts ASC, excellent for weather exposure, but the AF or AEF options are hard to find anymore.

[john61ct]

Originally Posted by mr-canada

I'm getting the 150W 8A solar panel

Link please, ideally to detailed specs like Voc, Isc etc

[john61ct]

Originally Posted by mr-canada

What is the product you guys are talking about?

Best if you quote the post to clarify

[mr-canada]

12V/24V 30A Solar Charger
https://solarsystemdepot.com/collect...roller-charger

Digital voltmeter, programmable and adjustable. Up to 30A, will disconnect power and reconnect it automatically based on battery charge to prevent damaging deep discharge.

Panel is being bought second hand. 150W 8A. Yes comes with a built in diode, mono-crystalline, rigid glass with aluminum frame, separated cells. From my reading, panels of this type do not fight to feed current to shaded cells as each cell is independent and run directly to the diode. I might be wrong on how they wire it, but that's how I read the literature on mono-crystalline panels.

---

Upon re-read I think perhaps it was mentioned that the unit could handle powering a diesel heater, but I am not sure if it was an actual heating unit running directly off the solar or if it was an autostart diesel.

[GILow]

The heaters being discussed are fuelled by diesel but use the 12 volt battery supply to start the burner and to run the associated fans and/or pumps to distribute heat from the diesel burner.


FURTHER EDIT: That controller you linked does not specify VOC or other critical figures. There is a slim chance your panel is higher voltage than the controller can handle. You need to gather a bit more data before you make a purchase.

[Paul Elliott]

Originally Posted by mr-canada

Panel is being bought second hand. 150W 8A. Yes comes with a built in diode, mono-crystalline, rigid glass with aluminum frame, separated cells. From my reading, panels of this type do not fight to feed current to shaded cells as each cell is independent and run directly to the diode. I might be wrong on how they wire it, but that's how I read the literature on mono-crystalline panels.

You are almost certainly reading that wrong.

I wouldn't worry about that though. An appropriate monocrystalline panel will deliver all the power that the available sunlight will generate, unless there is shading. Shading can cause anything from a slight reduction in power, to a complete loss -- it depends on the shadow size, percentage, orientation, and panel specifics. In your case with a single panel and a simple controller, the diodes will not make any difference.

What is critical is the voltage of the panel. I used an identical controller as the one you are planning (for a simple portable power source) and it worked fine. But it needs a panel designed for a 12V battery -- usually a 36-cell panel. Such a panel will put out around 20V with no load. If your panel is designed for a higher voltage system (perhaps a 72-cell panel), you might fry the controller and you will certainly throw away half of the available power.

So find out more about the panel!

[mr-canada]

Panel is 3.5x5 ft. All isolated cells, single mono-crystalline, rigid, glass and aluminum frame.

As for efficiency, I'm reading from:
Which Solar Panel Type is Best? Mono-, Polycrystalline or Thin Film?

Unless my basic electronics knowledge is completely out of whack, I can't imagine a 30A controller not being able to take a 150W panel that can push a maximum of 8A in perfect conditions; in theory it should be complete overkill, which is fine by me, better to be overpowered and less heat on the controller because it's capable of far more power than to short out on the controller and have it screw up because its overloaded.

Panel puts out up to 30V at 8A of 150W, but that is perfect conditions. It is designed as a 12V charging system, it is coming off of an RV on a 12 volt system.