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Old 15-06-2020, 07:01   #1
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solar vs shore

What is the preference for power at the dock when not aboard, having shore power turned on, or leave off and let the solar panels and MPPT keep the boat powered and batteries charged.


If I use shore power, does it negatively affect the solar panels or MPPT?


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Old 15-06-2020, 07:17   #2
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Re: solar vs shore

Personally, I leave my boat on shore power when at the dock. I've got no good reason not to, and it also allows me to leave one of the A/C units on during really hot / humid weather to keep the humidity in the boat down while I'm gone.
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Old 15-06-2020, 07:21   #3
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Re: solar vs shore

We leave our boat plugged in at the home dock to keep a dehumidifier running.

Shore power has no impact in solar panels, regulators, etc. if your worried about leaving a battery charger on and damaging the other charge sources, donít be. None of the charge sources care where the voltage theyíre sensing is coming from, they just react to it.
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Old 15-06-2020, 07:21   #4
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Re: solar vs shore

Quote:
Originally Posted by USMCOrdO View Post
What is the preference for power at the dock when not aboard, having shore power turned on, or leave off and let the solar panels and MPPT keep the boat powered and batteries charged.


If I use shore power, does it negatively affect the solar panels or MPPT?


Thanks,
Jay
S/V Encore
C36 1993 #1245
Imo, why risk any extra potential problem when you can just rely on your panels to keep things topped up? Unless you have some big sources of drain connected while you're not there I don't see the point of connecting to shore power.
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Old 15-06-2020, 07:23   #5
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Re: solar vs shore

People will of course argue this, but the least expensive source of power is the power grid. Unless staying for a day and the rate increase for power is significant I always plug in, it keeps from cycling the batteries, and they only have x number of cycles in them, plus it’s the time to equalize the bank if if needs it.
Now if I’m at the dock long time, like now for instance I always plug in, our power is metered and we only pay what it cost the Marina where I’m at, no jacking up the price.
But having a source of unlimited water and power is nice, and middle of Summer in Fl 20 miles or so from the Ocean it would be pure misery without AC.

There is no potential problem anymore than there is if your motoring. However to ensure that I use the panels whenever they are making power I have the float voltage on my Solar controller set to .1V higher than my shore power chargers, that means that whenever the panels can supply the power, the shore power charger doesn’t use any power.
Right now I’m using 9 amps of DC power and all of it is coming from the panels, of course it’s a drop in the bucket compared to the AC power the AC is using.
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Old 15-06-2020, 07:28   #6
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Re: solar vs shore

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Originally Posted by a64pilot View Post
People will of course argue this, but the least expensive source of power is the power grid. Unless staying for a day and the rate increase for power is significant I always plug in, it keeps from cycling the batteries, and they only have x number of cycles in them, plus itís the time to equalize the bank if if needs it.
Now if Iím at the dock long time, like now for instance I always plug in, our power is metered and we only pay what it cost the Marina where Iím at, no jacking up the price.
But having a source of unlimited water and power is nice, and middle of Summer in Fl 20 miles or so from the Ocean it would be pure misery without AC.
No argument there, shore power is cheaper for sure. But if there is no significant drain, then you just have two systems that could go wrong while you're not there instead of one.
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Old 15-06-2020, 07:37   #7
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Re: solar vs shore

My boat hasn't been hooked up to shore power in years. The solar keeps the batteries up.

Plus, I wouldn't want that extra little electric bill charge each month from the marina.

It's nice to know the exact amount without that.
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Old 15-06-2020, 07:42   #8
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Re: solar vs shore

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Originally Posted by Captn_Black View Post
Imo, why risk any extra potential problem when you can just rely on your panels to keep things topped up? Unless you have some big sources of drain connected while you're not there I don't see the point of connecting to shore power.
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My boat hasn't been hooked up to shore power in years. The solar keeps the batteries up.

Plus, I wouldn't want that extra little electric bill charge each month from the marina.

It's nice to know the exact amount without that.
I'm in this camp. If you already have the solar, and it is adequate, then not having the shore power connection reduces the chances of stray currents and all potential troubles that come with those, and reduces (in our locale anyway) the marina charges.

Having said that, when laying up for the winter we also run a dehumidifier and have shore power connected to keep that alive. When in warmer climes we generally don't ever use shore power.
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Old 13-07-2020, 18:47   #9
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Re: solar vs shore

Interested to know the panel power and battery capacity you have installed. Do you have anything else powered on apart from the battery float charging?

We've noticed that panel installations can be under capacity. It might look ok day to day, but if the weather is off or at extreme latitudes the hours of sun are limited, then the daily charge is marginal for keeping batteries healthy.

The risk is that a run of days with low sun that the batteries may either self-discharge or something on the boat is taking a trickle current sufficient to run them down. It might look OK for a week or two, but in these cases isn't long term reliable. The situation can run-away as solar is OK to keep batteries topped up, but doesn't have enough grunt to properly re-charge them.

Interested to hear others experience.
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Old 13-07-2020, 19:05   #10
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Re: solar vs shore

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No argument there, shore power is cheaper for sure. But if there is no significant drain, then you just have two systems that could go wrong while you're not there instead of one.
No not really you actually have one backing up the other, so if one fails, the other keeps the batteries charged.
Set your Solar to .1V higher float than your shore power charger, and during the day it will carry all the load, then as it quits, voltage drops .1v and shorepower picks up the load and the batteries are never cycled.
But at .11C a kilowatt hour, it’s insignificant really, how many Kilowatt hours can your Solar make, multiply that by 11 cents and see how much money you save.
I pay where Im at 11C a kilowatt hour, your rate may be different so use your rate of course, but the answer will likely be less than $10 a month, probably way less as we are only taking about the power used at night.
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Old 13-07-2020, 19:13   #11
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Re: solar vs shore

Shore power with AC/heatpump set to 72f/30% humidity, trickle chargers on.
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Old 13-07-2020, 19:23   #12
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Re: solar vs shore

We have more than enough solar power to run everything on the boat when we are living on the hook for months at a time in normal conditions. We rarely ever plug in even when we are staying at a marina for a couple of days, which we don't often do unless we need something that can't easily be done from on the hook.

It is usually not at all worth the bother to drag out the shorepower cord from deep in the lazarette and run it across the boat and over to the power pedestal, then wind it all back up again neatly to put it away before leaving.

There are some other disadvantages to being plugged in. Unless you have a galvanic isolator or an isolation transformer you could pick up stray current in the water from other boats nearby that have bad wiring and this could eat your sacrificial anode in short order, or worse yet eat your prop or sail drive if the anode gets used up and you don't know it. If you aren't plugged in then that path to ground through your plugged-in cord is not there. Stray voltage can still go through your boat in and out different points but the danger is not as high as being plugged in to a good ground on shore.

Also, a shorepower cord only has so much life out in the sun before the cable jacket gets burned crispy by the sun's UV. Unless you have some sort of special covering over your cord or regularly apply UV sunscreen it will get chalky, faded, and stiff -eventually cracking and splitting. Marinco and 303 both sell special UV protectants and conditioners made especially for power cords but they need to be applied regularly and are fairly expensive.

Water also eventually gets through the best of seals and gaskets and into the contacts in the olug ends and eventually the conductors themselves, contributing to corrosion. The lifespan of an expensive shorepower cord is simply reduced when exposed to the elements compared to being stored in the dry and the dark of the well-found locker. Left outdoors, day after day and year after year it's going to have a shortened useful lifespan. Take a walk down the dock and look at the ragged shorepower cords most people are using. Most are pushing the end of their useful lifespan. Much of that time spent really doing nothing out in the elements for no good reason.

We only plug in when we need to run electric heat, AC, or do a lot of work with power tools when doing projects. Right now we are plugged in because of the need to run AC since it is sauna right now in the Chesapeake. But this is an anomaly, hopefully it doesn't last too long and we will be out cruising again and not camped out at a marina.
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Old 14-07-2020, 05:41   #13
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Re: solar vs shore

john mcd- I have 2 - 12v 100 watt panels installed with a 40AMP MPPT connected to 4 6V 110AH AGMs connected in series and parallel to give me 12v 220AH.

Only intentional draw from batteries is my 12v Fridge/freezer, and the 12v fans to help circulation.

Additionally, I have a microwave plugged in and a dehumidifier plugged in to the AC side which obviously these two wouldn't work if I turned off shore power when not on the boat.

I was just making sure that I wasn't doing harm by having the solar not really doing much. Since posting this, I have made sure that my solar charger is .1 above battery charger setting. I will continue to monitor this.
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Old 14-07-2020, 06:02   #14
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Re: solar vs shore

I only plug in when I will be using more than solar will provide.
  • One less thing to do, coming and going. This is the big reason.
  • Solar is free once installed. Less CO2 and all that. Tiny, but why not?
  • Probably less chance of accidents (fire and shock) although both should be trivial if properly installed.
  • Less risk of galvanic corrosion if there is a dock wiring fault. Also accidents.
  • Less wear and tear on plugs and me.
But if I need more I plug in.
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Old 14-07-2020, 06:25   #15
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Re: solar vs shore

I leave my shore power on to run my AC in dehumidify mode and keep the battery charger in float mode. I would point out one item of caution. My Morningstar solar controller senses "night", that is a time period when no output is coming from my solar collectors, and when the sun comes up it automatically goes to absorption voltage for 3.5 hrs. This controller only detects absorption time and does not read a shunt. This results in severe overcharging of the battery if I leave the solar controller in its normal mode when plugged into the dock. I learned a lesson by frying a set of AGMs by overcharging. I can program this controller with custom charging profiles and made one with the float absorption voltage just .01V above the float voltage. During the day any 12v requirements are easily met by the solar panels while the 120v charger holds the float voltage at night and even though my controller "thinks" it is giving me absorption voltage for 3.5 hours every morning, I am not frying my batteries.
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