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Old 10-19-2016, 05:26 PM   #1
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solar on hook

I have read this thread, which is about 3 years old, so I start a new one.
A household fridge running on solar panels

The discussion was about how do build a solar system, which can take care of the hotel needs, including the fridge.
One side was on the running the genset regularly, the other side was on an efficiently built solar.
One scenario never came up.
What if the boat is on anchor all the time (few marinas have this option here) and the owner can be on board only over the weekends?
- He cannot run the genset daily, to charge the batteries enough.
- He can buy and install a large enough solar system, but that also has limits. (find enough surface to mount the panels, find space for extra batteries, much less sunny days on the PNW).
So, what to do?
Initial investment on a larger solar set is high, but it can earn its price back later, as long it can provide all the power the boat needs.
If there is a genset already in place, running it even daily, can be affordable, if it is just for few hours and the owner is on board daily.
Obviously, if you are not on board on weekdays, the fridge runs less and not much else is in use..
Can it be that a combination of both is the ideal solution? Solar big enough to keep the batteries happy all week long and run the genset when on board?
I know boat size matters, so lets put this between 45-55' boat length. On weekdays, just a decent size fridge, portable heater/dehumidifier, position lights would run.
What size of solar would be sufficient?
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Old 10-19-2016, 05:32 PM   #2
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If you are only on the boat on the weekends, it doesn't seem to make a lot of sense to have the refer running on a mooring. Use a cooler to take your weekend cold foods out to the boat and fire up the refer when you start the engine.
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Old 10-19-2016, 06:07 PM   #3
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Use a cooler to take your weekend cold foods out to the boat and fire up the refer when you start the engine.
Good point.
What about on very cold days? Let's say, it is freezing everything?
I guess, if it is freezing outside, I don't need the fridge....lol
Some heating and lights will still be necessary, no?
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Old 10-19-2016, 06:11 PM   #4
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...
1. Can it be that a combination of both is the ideal solution? Solar big enough to keep the batteries happy all week long and run the genset when on board?
I know boat size matters, so lets put this between 45-55' boat length. On weekdays, just a decent size fridge, portable heater/dehumidifier, position lights would run.
2. What size of solar would be sufficient?
Q1. Yes, it`s possible. But, is it practical?
Q2. Begin by calculating the load, then theoretically size your panels and batteries to provide it.
It`s not good enough to identify "a decent sized fridge" and "portable heater/dehumidifier". Both are potentially hungry devices. Find the models you want and what they draw. I`m not sure what you mean by "position lights".
If you are running 110v appliances via an inverter allow for the inverter using some amps for itself.
The cost of the solar installation may be less important if your priority is convenience, and genset minimization.
In sizing panels remember that the nominal amps output(watts divided by volts = amps) is not likely to be seen in other than ideal conditions, I assume a pessimistic 50%, perhaps that`s too conservative.
If you do the calculations and find the panels and/or batteries to support the load can`t be accommodated, physically or financially, your aim may not be achievable.
Consider whether you can run the fridge or heat at reduced load levels midweek, lowering consumption, and therefore the required size of the solar and battery arrays.
You need to take into account the supply of solar energy, the presence of sun is not guaranteed. A wind generator could be a useful alternative, overcast weather can be accompanied by breeze, giving you alternative sources of power generation.
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Old 10-19-2016, 06:14 PM   #5
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Interesting exercise. Investigate auto start generators, the RV folks dabble in those.

Upgrading/adding external insulation to the refrigerator box also helps reduce the load.

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Old 10-19-2016, 06:35 PM   #6
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Seems like a lot of trouble and expense to keep it running when your absent.

One solution would be to use a portable 12 volt refrigerator and take it back and forth with you. Plug it into the boats electrical system when you get aboard.

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Old 10-19-2016, 07:00 PM   #7
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A DC driven refrigerator, even a full size one like you would find on a 45' boat won't use too much current if no one is aboard and opening and digging around for stuff every few hours. If a refrigerator uses 100 Ah with normal use, then it will use 50 Ah with no one aboard.


So, yes one approach would be to size your solar to take care of the refrigerator with no one aboard and have enough left over to recharge the batteries after they run down during cloudy days, and enough battery capacity to carry you through a decent number of cloudy days.


Using the 50 Ah above, a 250 watt panel feeding 400 Ah of batteries would meet this criteria. The 250 watt panel would make about 80 Ah on a sunny day which will give you 30 Ah to recharge the batteries once the sun comes back. The 400 Ah batteries will give you 4 days of no sun capability as you don't want to routinely discharge batteries more than 50%.


Then when you are on board you can run the genset to cover your Ah usage which will double for the refrigerator plus all sorts of other loads.


Sizing a solar system is all about Ah demand, Ah recharging supply and Ah storage capacity to carry you through cloudy days.


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Old 10-19-2016, 09:48 PM   #8
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You need to take into account the supply of solar energy, the presence of sun is not guaranteed. A wind generator could be a useful alternative, overcast weather can be accompanied by breeze, giving you alternative sources of power generation.
Yes, I think about adding wind generator, too. I do not anticipate solar efficiency in PNW, so it will require lot more default capacity, if it is installed.
I do want to figure out the optimal alternation of genset and solar input.
Lowering the weekdays consumption will be included.
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Old 10-19-2016, 09:50 PM   #9
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Interesting exercise. Investigate auto start generators, the RV folks dabble in those.

Upgrading/adding external insulation to the refrigerator box also helps reduce the load.

RB
Yes, insulation I will do.
The other thread did bring up the auto start generator solution, but many members disagreed. They think, it is just not safe in the marine environment to let a generator without supervision. Things can happen.
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Old 10-19-2016, 09:52 PM   #10
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One solution would be to use a portable 12 volt refrigerator and take it back and forth with you. Plug it into the boats electrical system when you get aboard.
Ted
My question is not just about the fridge. I can even empty it out and turn it off during weekdays and use it only when I am on board.
I feel some basic electricity has to be alive on the boat, all the time. Anchor lights, or freezing pipes in cold weather, come to mind.
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Old 10-19-2016, 09:56 PM   #11
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Originally Posted by djmarchand View Post
A DC driven refrigerator, even a full size one like you would find on a 45' boat won't use too much current if no one is aboard and opening and digging around for stuff every few hours. If a refrigerator uses 100 Ah with normal use, then it will use 50 Ah with no one aboard.
David
I like what you say. However, another thread says the an AC fridge with inverter will not use as much either. I don't know the answer.
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Old 10-19-2016, 10:00 PM   #12
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Using the 50 Ah above, a 250 watt panel feeding 400 Ah of batteries would meet this criteria. The 250 watt panel would make about 80 Ah on a sunny day which will give you 30 Ah to recharge the batteries once the sun comes back. The 400 Ah batteries will give you 4 days of no sun capability as you don't want to routinely discharge batteries more than 50%.
David
Thank you for these numbers, it is good information.
Cloudy days we have for many long months here at PNW.
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Old 10-19-2016, 10:09 PM   #13
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One solution would be to use a portable 12 volt refrigerator and take it back and forth with you. Plug it into the boats electrical system when you get aboard.
Ted
I don't mind carrying food back and forth for the weekend, but a portable fridge would be a bit complicated on a dinghy... lol
Thanks anyway.
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Old 10-20-2016, 01:04 AM   #14
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My question is not just about the fridge. I can even empty it out and turn it off during weekdays and use it only when I am on board.
I feel some basic electricity has to be alive on the boat, all the time. Anchor lights, or freezing pipes in cold weather, come to mind.
The only electricity that needs to be "alive" on the boat is the bilge pumps. But in your winter, some kind of heating may be essential too.
When I leave my boat at the marina, I do not connect shorepower. My modest solar panels keep the batteries fully charged.
Many people do connect, and keep a fridge running,I thought that was what you most wanted.I`d be marginal doing that, though on a sunny day the solar keeps the batts up nicely while the small OEM(quite old) Danfoss 12v powered fridge runs. You can set solar controllers to power appliances only down to a certain battery voltage, to not run them at certain hours, etc.
Like others, I think your objects are attainable.I suggest you not get too concerned. Once you get the boat, you`ll have something definite to work with.
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Old 10-20-2016, 04:22 AM   #15
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Boat choice is an important factor as the size of your solar panel bank will be determined by the amount of real estate you can devote to the solar panels. For example my Krogen 42 allows two to three 140 watt panels on the pilot house roof, whereas the Nordhavn 46 allows for six such panels. The panels are cheap today.

Essentially a flying bridge reduces the real estate available for solar panels. With all the tugs (American and Nordic) up in the PNW you should have no problem finding a trawler with sufficient real estate for a large solar array.

In the Caribbean many boats exist on a combination of solar and wind. This is also a factor of refrigeration efficiency.

If I were doing this I would invest in both solar and wind, and buy a smaller Engel type portable refrigerator to keep the essential items on board when I was away.
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Old 10-20-2016, 09:52 AM   #16
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One issue to consider is the short and cloudy days here in the PNW. Solar seems to be pretty effective for some here in the summer, even with the clouds, the long days seem to help. In the winter months it would be tough to get enough sunlight to do much more than keep the batteries topped up and the bilge pumps ready.

Most anything is possible however if you have the money and the space for the requisite panels and batteries.
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Old 10-20-2016, 10:22 AM   #17
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Another challenge to the exercise:

How to maximize the solar panel performance?

Easier with the boat in a fixed position, set angles, aim south and forget about it...

How to chase the sun in the mooring field?

These folks have some great videos of tests on panel performance, shading, flat vs tilted, etc and a source of supply and their free library is extensive:

altestore.com

I'm a happy customer.

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Old 10-20-2016, 10:40 AM   #18
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I don't have shore power on my boat. I rely totally on my solar array to keep the batteries up unless the boat is underway. I don't leave food in the refer when I am not aboard because it only takes 30-40 minutes to cool down - less if you put cold stuff in it. That said, my 200 watts of solar panels are enough to keep my batteries fully charged with the refer running. Since my boat is wood, I also rely on the solar array to provide the juice for the bilge pumps. When we are out on the boat the solar allows us to run systems indefinitely unless there is an entire week of cloudy weather.

The biggest problem I have had with my solar array is that since it keeps the batteries on float, they are almost always fully charged when I head out. Consequently, when I first installed the solar I found that it pulled my batteries up too high for my engines electrical system and set off the over voltage alarm. The alarm was VERY loud. I solved that by installing a disconnect switch on the panel array to effectively turn it off when I am running under power.

Solar panels are pretty cheap now. 100 watt panels can be had for around $120. So a 400 watt array would cost about $500 plus the cost of the controller (~$100) and wiring (trivial).
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Old 10-20-2016, 08:47 PM   #19
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I definitely think it can be done. This was exactly my goal with our solar system, but I haven't had the chance to see if I succeeded. And I have to confess, just given the calculations I'm pretty sure I didn't make it. I think it's close, and maybe if I found a way to shave off some more standby load it would work. But toss in a few rainy days and pretty soon you can find yourself in trouble.
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Old 11-02-2016, 07:45 PM   #20
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Solar will provide power even with clouds...just not as much. Our fridge is an apartment size unit with self defrost. When we are away from the slip, we rely on our 4 each 150 panels to replenish all consumed power expended both during the days and night. And we are power pigs running two 32" TVs, lighting, laptops and the fridge. Our genny is ran to heat water along with perk coffee for 1-2 hours in the mornings. It also charges our 24v bank.

Humping food back an forth to a boat for us with our sailboat was a BPITA.........avoid it!
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