How well do solar panels work in the Pacific NW

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Skipper_Vic

Member
Joined
Dec 31, 2016
Messages
9
Location
USA
Vessel Name
Resolute
Vessel Make
Pondarosa 42 Sundeck
I am looking to install a good MPPT type solar charge controller and 300 to 600? watts of solar panels on my Pondarosa 42 "Resolute". My cruising area is Puget Sound and North into BC and hopefully SE Alaska. My cruising months are May to September.

The battery loads are primarily a 3.2 Cu.Ft. freezer and a refrigerator. Resolute gulps about 200 AH every 24 hours so I currently need about 2 hours of Gen-Set running time with 150 amps of battery chargers to keep up. My goal is to perhaps cut the Gen-Set run time to an hour a day (more or less).

My question is to anyone in my area that has logged at least a year of experience in the PNW with a similar solar system and can tell me what I can realistically expect out of solar panels. In theory, each 100 watt panel should should provide about 8 amperes of charge to my 12 vdc house banks but this is not exactly Florida so I'm sure the results are significantly less. The hard question is how much less ... 25 watts, 50 watts, or? If I "guess wrong" I might over or undershoot my goal by a NM.

By the way, I have room for panels aft on top of the Sundeck and in front of the main windows up forward. These would be relatively un-shaded areas and flat facing upwards.
 
Will work great in late spring summer and early fall. Not so good in rainy and winter weather 10 months in PNW.
 
Regardless of the loss in efficiency due to sun angle your boats batteries will be much happier connected to panels. We will be building a home in the south sound designed to be DC powered predominantly from panels augmented by wind and grid if needed.

The problem with solar power on boats is some act as if it doesn't replace your generator entirely it doesn't give any benefit which is straight hogwash.
 
Well, you can get a few points of anecdotal data from members, or you can look at real, hard data. The following gives a solar insolation map for the US in July, the middle of your cruising season- http://www.nrel.gov/gis/images/map_pv_us_july_dec2008.jpg

The far PNW gets about 5 KWh/M2 each day in July. That is for a flat plate tilted south. Your panels will probably be fixed horizontally so maybe you will get only 3.5 KWh/M2. A typical 100 watt panel has 1,000 sq inches of area or about .65 M2 and converts about 20% of its solar insolation to power. You also have about 10% losses in the controller and wiring.

So, multiplying through, 3.5*.65*.20*.9= .40 Kw or 400 watts or about 30 amp hours at 13.5 V (the average battery charging voltage) each day.

FWIW, that 30 Ah from a 100 watt panel figure jives pretty well with my own experience on the east coast and other responsible reports I have seen on this forum.

YMMV, David
 
David:
I'll have read reports that solar panels can be severely impacted by shadows. Claims that 5% shadows can reduce outputs in excess of 50%. This seems odd and I'm not at all convinced that an antenna's shadow could render a whole panel nearly useless. Have you heard this or got any hard facts on this reported phenomena. BTW I like your math approach. Its how I always attack a design issue. Vic
 
Here are some numbers

Al Thomason, who writes a very interesting and well informed blog about living aboard and boating in the PNW, provides some actual data here:

mv.VikingStar: Solar

Detailed graphs are in there, but the executive summary is that output is, of course, highly seasonal, but in the summer months, May-August, he was pulling 150 A/H per day from two 245 watt panels.

There is lots of good stuff in there, as well, about installation and equipment selection.
 
Yes, a small shadow can have a big effect on a solar panel's output. There are two ways to partially deal with this problem:

1. Some solar panels divide up the panel into 4 or more elements and isolate them with blocking diodes in the junction box. That way if 1/4 is in a shadow the other 3/4 will continue to put out. But of course this depends on where the shadow is.

2. There is always the argument whether to wire 2, 12V panels in series or parallel. Series (if the MPPT controller is designed for it) reduces wiring size and voltage drop. But if one panel is shaded that causes an internal resistance that blocks both panels. If you wire in parallel then if one panel is shaded, the other will continue to put out full. So the choice is whether shade is a possiblity or not.

Another question is 12V (17V mp) or 24V (34V mp) panels. The 24V panels are usually cheaper per watt, but because they can't be shipped UPS like 100 watt panels, if you just buy one or two they can be more expensive due to MF shipping costs.

12V, 100 watt panels are pretty darn cheap now anyway. Amazon has them for about $100 each, shipped free with Prime membership.

And if you are only going to use 100-200 watts, consider a cheaper PWM controller. You will lose 15% of the potential power with that controller compared to a MPPT but it will be half the cost.

David
 
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Skipper_Vic said:
this is not exactly Florida
Click to expand...

Actually the average horizontal plate insolation in July in the PNW is about the same as Florida. (The irradiation angle isn't as favorable, but the days are longer.)

For example, Ganges (Saltspring Island) average for a day in July is 6.26 kilowatt-hours per square meter, according to Photovoltaic and solar resource maps | Natural Resources Canada.

So I would say djmarchand's calculations are a bit pessimistic about average insolation but perhaps optimistic on conversion efficiency, so they end up being about right :).

But I would also say that if you are burning 200 Ah per day on refrigeration, you could do well looking at inefficiencies in that system...
 
SteveD said:
Al Thomason, who writes a very interesting and well informed blog about living aboard and boating in the PNW, provides some actual data here:

mv.VikingStar: Solar

Detailed graphs are in there, but the executive summary is that output is, of course, highly seasonal, but in the summer months, May-August, he was pulling 150 A/H per day from two 245 watt panels.

There is lots of good stuff in there, as well, about installation and equipment selection.
Click to expand...
SteveD ... I have spent some time reading over the data posted by the skipper of the Viking Star. It is about as much data on the subject as anyone could ever need to make choices and feel comfortable with the expected results of a Pacific NW solar panel system. My job now is only to study the surface areas I have available verses the available panel dimensions ... and the all important budget (actually this is likely no place to do it on the cheap though). Thanks to you and everyone else who has shared their thoughts. Vic
 
I installed 3 x 250w panels on Content a couple of years ago. They're on the doghouse roof, horizontally mounted, and are barely affected by shadow at all. I have an Outback MPPT controller. When its sunny, the panels pump out up to 42Ah at peak. Last summer (2016), I averaged 220Ah per day.

I have switched all lights to LED, reducing my load by about 45%, which is just a no-brainer easy gain. The solar pretty well covers my daily requirements, and I have accordingly disposed of my generator. Smiley faces all round!
 
MV Content ... Your results of 220 AH from 750 watts of panels is spot-on consistent with what I am hearing from several others on the forum. It seems 30 AH per 100 watts of panel capacity is a good gauge for sizing panels. That being an average per day, in the summer, in the Pacific NW USA/Canada/SE Alaska.
This was my first posting of a question on Trawler Forum and I am impressed with the quick responses and great information. Thanks again to you and all. Vic
 
One More Thing...

If you are considering buying full-size panels in the PNW and wish to avoid shipping, Platt Electric, which has stores all over, will sell you one or two panels. You just call up, and they will drop ship them to the store.

https://www.platt.com/platt-electri...&GroupID=204&CatID=863&vendors=SolarWorld_209

Also, solar panels for small installations, like those we do, are exempt from Washington State sales tax. You just need hand them a copy of the exemption form when you pick up the panels. (Check 6a. on this form:
http://dor.wa.gov/Docs/Forms/ExcsTx/ExmptFrm/BuyersRetailTxExmptCert_E.pdf)
 
Thanks for that link Steve. I have a commercial account with Platt and it surprises me how capable I am in overlooking the obvious.
 
djmarchand said:
Yes, a small shadow can have a big effect on a solar panel's output. There are two ways to partially deal with this problem:

1. Some solar panels divide up the panel into 4 or more elements and isolate them with blocking diodes in the junction box. That way if 1/4 is in a shadow the other 3/4 will continue to put out. But of course this depends on where the shadow is.

2. There is always the argument whether to wire 2, 12V panels in series or parallel. Series (if the MPPT controller is designed for it) reduces wiring size and voltage drop. But if one panel is shaded that causes an internal resistance that blocks both panels. If you wire in parallel then if one panel is shaded, the other will continue to put out full. So the choice is whether shade is a possiblity or not.

Another question is 12V (17V mp) or 24V (34V mp) panels. The 24V panels are usually cheaper per watt, but because they can't be shipped UPS like 100 watt panels, if you just buy one or two they can be more expensive due to MF shipping costs.

12V, 100 watt panels are pretty darn cheap now anyway. Amazon has them for about $100 each, shipped free with Prime membership.

And if you are only going to use 100-200 watts, consider a cheaper PWM controller. You will lose 15% of the potential power with that controller compared to a MPPT but it will be half the cost.

David
Click to expand...

Passagemaker Magazine had a lengthy article a while back on boat electrical, not discussing solar but rather ideas on reducing the cost electrical power derived from running engines, either propulsion or genset. Bigger alternators and only running the genset when house voltage dropped below a certain threshold were discussed, as well as bigger and/or more efficient house batteries. It seems like the marginal cost of a watt of energy could be compared between solar and other sources. I was curious if David has run these numbers.
 
Ken:

Well, I am a retired engineer and therefore a data/numbers kind of guy, but there is no single answer to your question for everyone.

Once you have a genset onboard, burning a little diesel to make power is pretty cheap. My NextGen 3.5 KW unit probably averages 2KW load and burns a quart an hour of diesel producing it. That is about 30 cents per KWh.

Similarly if you have several hundred watts of solar installed, then the cost of power output is essentially free. But you need a place to put it, ie. enough battery capacity.

Batteries are just there to reduce the time between recharging whether it comes from solar, genset, propulsion alternator or shore power charger.

So, I don't think you can "run the numbers" without a specific set of facts to base them on.

But I would offer one generality. If you don't need A/C on your boat at anchor, then if you have room for them, solar panels are a really good way of providing power at anchor- relatively cheap, quiet, no maintenance or operating costs. You can install a thousand watts of solar panels for a fraction of the cost of a genset- if you have the room for them. You will need about 400 Ahs of battery capacity to absorb that much power.

David
 
djmarchand said:
Ken:

Well, I am a retired engineer and therefore a data/numbers kind of guy, but there is no single answer to your question for everyone.

Once you have a genset onboard, burning a little diesel to make power is pretty cheap. My NextGen 3.5 KW unit probably averages 2KW load and burns a quart an hour of diesel producing it. That is about 30 cents per KWh.

Similarly if you have several hundred watts of solar installed, then the cost of power output is essentially free. But you need a place to put it, ie. enough battery capacity.

Batteries are just there to reduce the time between recharging whether it comes from solar, genset, propulsion alternator or shore power charger.

So, I don't think you can "run the numbers" without a specific set of facts to base them on.

But I would offer one generality. If you don't need A/C on your boat at anchor, then if you have room for them, solar panels are a really good way of providing power at anchor- relatively cheap, quiet, no maintenance or operating costs. You can install a thousand watts of solar panels for a fraction of the cost of a genset- if you have the room for them. You will need about 400 Ahs of battery capacity to absorb that much power.

David
Click to expand...

Good answer and point well taken on the need for specifics in order to make meaningful comparisons. In my case, I have flirted with the idea of adding a couple solar panels on my hardtop. But before even addressing their output and their cost, I'm asking myself if they're needed at all. To wit, I have 160 amp alternators that keep my 1000AH house bank up when we're traveling. I'd be running the genset anyway when the galley stove is in use, thus charging the batteries concurrently. No A/C installed and diesel heat is used since we're in PNW and Alaska. Never on the hook for more than a couple days. I think I have enough electrons (?) Is there still a case for solar panels?
 
No Ken, you do not "need" solar panels. You have plenty of charging sources without solar.

Your boat and usage patterns is similar to mine. I run the genset at anchor for 30 minutes to an hour each night to heat hot water for showers and power the stove burner if we are using it for dinner. I also run it for 30 minutes in the morning to make coffee and top off the batteries. I can go forever on the hook with this pattern. I do have a 100 amp charger powered by the genset and with an hour or so of running I replace the 75 amphours I use daily.

You will probably use more than 75 AHs daily if you run your diesel furnace. So it may take you another half hour or so of genset running time. Pretty cheap at 30 cents per KW though. But you do need a large capacity charger, typically an inverter/charger and sufficient battery capacity to absorb that power.

So, I don't need solar and neither do you.

David
 
Ken:
I too am a retired engineer and a numbers guy.

Much as I love the "freedom" my gen-set and 1000 AH batteries now give me, the desire for ice cream and steaks = 2 hours of noise per day. If solar panels cut this in half then ....

ROI = $1,500 / 200 cruising days of 1 hour less time listening to the gen-set = $7.50 per hour not listening to the noise. .... darn .... you just had to make me run them numbers. Vic
 
Skipper_Vic said:
Ken:
I too am a retired engineer and a numbers guy.

Much as I love the "freedom" my gen-set and 1000 AH batteries now give me, the desire for ice cream and steaks = 2 hours of noise per day. If solar panels cut this in half then ....

ROI = $1,500 / 200 cruising days of 1 hour less time listening to the gen-set = $7.50 per hour not listening to the noise. .... darn .... you just had to make me run them numbers. Vic
Click to expand...

Ha! That puts things in perspective!
 
Thank you! This thread has answered by questions about expected output per 100W for PNW summer. I will be adding two 300W panels to my Selene 47, with tilt up rail mounts on the boat deck. Should I be looking at mono or poly cells?
 
Last edited:
When I installed 1kW of solar panels I also switched my electric stove and oven to propane.

Now I seldom need to run the generator. :)

Heating domestic water has not being a problem but I only cruise in the summer and usually change anchorages every couple of days and, thus, heat the domestic water with the engine coolant.
 
To my mind, in the PNW and coastal BC and southern AK, Efoy is a better way to go and you aren't as sun dependent. If you already have solar panels and add the middle Efoy, you'll be good to go even into long cloudy extended periods, whether spring, summer, fall and winter.
 
nwboater said:
Thank you! This thread has answered by questions about expected output per 100W for PNW summer. I will be adding two 300W panels to my Selene 47, with tilt up rail mounts on the boat deck. Should I be looking at mono or poly cells?
Click to expand...


One is a little more efficient than the other but can't remember which. But the efficiency difference gets lost in the noise. Also 100 watts is 100 watts irrespective of efficiency as long as you have the room as the lower efficiency one will be a little bigger.



David
 
Solar is great.
Now we are heading towards summer the genset rarely gets used and we run 240v for almost everything.
House bank and Hot water system at 100% by lunchtime.
We have 2.2kW of panels.
 
I have had 2 mono cell panels on the roof of my pilothouse here in BC for the last 2 summers. We have 6 golf cart batteries for the house bank and a total of about 550 watts of solar with a good quality MPPT controller.
For the past 2 years, on most days, the house bank reaches 100% charge by early afternoon (using solar alone) unless we have heavy low cloud or fog for most of the day. On sunny days, no problem achieving inputs of over 30 amps when the batteries are down a bit.
I have only "had to run" the generator on about 5-10 days total in the 2 years of experience to charge up (out on the boat for at least 3 months each summer). I have chosen to run the gen set for hot water on more occasions, as often we will sit in one anchorage for several days. Even on the poor weather days, running the gen set early for about 1 hour to "top up" the batteries has allowed the solar to mostly complete the charge.

This is real world first hand experience mostly in northern BC (this year Broughtons and last year as far as Prince Rupert). I am very happy with the performance of (in the summer) of my panels here in BC waters.
PS: My main loads are an 8 cubic foot fridge and a 35 litre freezer, and normal "other items" like lights, etc.
 
As a follow-up to my 2017 comments, about 18 months ago I installed 2x350 watt panels on my hardtop, with a mppt contoller. I've made one trip to SE AK with the panels and many PNW outings. On sunny days, I'm charging at about 30 amps; on cloudy days, 10-15 amps. I consider the panels to be an always-on float charger during daylight hours with no noise or fuel required. I'm sure there are lower-cost alternatives on a cost per watt basis, but the simplicity, quiet and no fuel means a lot. I wish I would have installed them years ago.

I added the panels in conjunction with converting my 11 cu ft galley refer and 6 cu ft freezer to DC only which was a big reduction in my electrical requirements. I now run the genset very little, where I used to run it 4 hours/day. My house bank is 8 flooded golf cart batteries, about 900 ah.
 
Last edited:
Skipper_Vic said:
Ken:
I too am a retired engineer and a numbers guy.

Much as I love the "freedom" my gen-set and 1000 AH batteries now give me, the desire for ice cream and steaks = 2 hours of noise per day. If solar panels cut this in half then ....

ROI = $1,500 / 200 cruising days of 1 hour less time listening to the gen-set = $7.50 per hour not listening to the noise. .... darn .... you just had to make me run them numbers. Vic
Click to expand...

You may also want to consider upgrading your alternator charging system. I am adding solar for next season, but did the alternator upgrades this season. July - Oct, I ran the genset a total of about 4 hours. All the other charging done by the alternator while underway, or at the dock (3/4 of the nights at anchor). The combination of solar and a good alternator obviates the need for a genset in the PNW.
 
poly vs mono

Nwboater

If you will have any shadows on you panels you will get better performance from panels where the cells are wired in parallel. Or, at least shorter chains of cells in series. With cells wired in series, as soon as one of the cells is shadowed, the rest in that string will produce very little power. Something to research anyway.
 
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