Shore Power use

[Andyaero]

As I am still achieving around 700w a day via the solar, I am staying unplugged for around 4-5 days or until the batteries hit about 20% and then plugging in to charge up, or if we've not been out, to use the immersion or tumble dryer.

Then unplugging again.

Is this worthwhile? Am I using less shore power by doing this?

I guess being permanently plugged in keeps the batteries full all the time, so not particularly good for lithium. Or does the battery management system somehow compensate for this? I'm thinking not, as they are always at 100%.

I have 600ah lithium, 1.3kw solar and victron chargers and inverter.

Thanks

 

Edited December 13, 2025 by Andyaero

[nicknorman]

There are a number of different things at play

 

1)Yes it is better not to keep the batteries fully charged.

 

2)The charger uses some power just to run itself (not much, but some)

 

3) Li battery life mostly depends on the overall amount of charge put in and out. So cycling the battery down to 20% and then fully charging, will wear it out faster than say keeping it around 80% and using shore power.

 

4) Although the charge efficiency of Li is very good (Ah in and Ah out virtually the same), the power efficiency less so (Wh in and Wh out) - although still much better than LA. So running direct from shore power uses slightly less energy than doing so via the batteries.

 

5) Taking energy only from the shore means you are not benefiting from the solar.

 

So I don’t think there is a right answer, it depends on your priorities.

 

One thing to consider might be to reduce the charge voltage on the Victron to about 13.3 or 13.4v and leaving the charger on. The batteries will settle around 50-80% giving headroom for the solar to add more on a sunny day and thus the Victron will charge less. The downside being that if you need to charge in a hurry, you would want to put the voltage back up to 14.4 or some such. So another factor is how easy is it for you to change the Victron charge voltage.

 

[Tonka]

Have you a galvanic isolator or isolation transformer?

[IanD]

2 hours ago, Andyaero said:

As I am still achieving around 700w a day via the solar, I am staying unplugged for around 4-5 days or until the batteries hit about 20% and then plugging in to charge up, or if we've not been out, to use the immersion or tumble dryer.

Then unplugging again.

Is this worthwhile? Am I using less shore power by doing this?

I guess being permanently plugged in keeps the batteries full all the time, so not particularly good for lithium. Or does the battery management system somehow compensate for this? I'm thinking not, as they are always at 100%.

I have 600ah lithium, 1.3kw solar and victron chargers and inverter.

Thanks

 

Dpeneding on your Victron equipment, you might be able to enable solar/wind priority, where solar is used to charge the batteries (which supply any DC loads) and shoreline only supplies AC loads. In this case the batteries only stay fully charged (to float voltage, harmless) while the sun is shining, they then drop overnight.

[magnetman]

700W h per day is good for 1.3kW given that yesterday was the shortest day of the year. 

[Andyaero]

1 hour ago, Tonka said:

Have you a galvanic isolator or isolation transformer?

Galvanic isolator

10 minutes ago, magnetman said:

700W h per day is good for 1.3kW given that yesterday was the shortest day of the year. 

Only 300 yesterday but nearly 500 already today.

Edited December 13, 2025 by Andyaero
overly keen autospell

[Alan de Enfield]

14 minutes ago, magnetman said:

700W h per day is good for 1.3kW given that yesterday was the shortest day of the year. 

 

The 21st December is the shortest day (Winter solstice)

 

Edit for spooling errur

Edited December 13, 2025 by Alan de Enfield

[magnetman]

Oh yes my clock is wrong. Yesterday was the earliest sunset so the days seem longer after that. 

 

 

[blackrose]

2 hours ago, Andyaero said:

 

Only 300 yesterday but nearly 500 already today.

 

I'm on 530Wh so far today from 910w of panels.

 

Edit: 2.45pm with a hazy sky and the sun is going down already. Only 5a being generated by the panels now and I've ended up with 1.01kWh in total today. But it's not bad for a short winter day.

Edited December 13, 2025 by blackrose

[Chris John]

4 hours ago, Andyaero said:

As I am still achieving around 700w a day via the solar

Really?  Seems rather a lot with only 1.3kw of solar 

[Momac]

3 hours ago, magnetman said:

700W h per day is good for 1.3kW given that yesterday was the shortest day of the year. 

Is the shortest day not the day of the winter solstice which is 21st Dec 2025?

[blackrose]

36 minutes ago, Momac said:

Is the shortest day not the day of the winter solstice which is 21st Dec 2025?

 

Yes that was pointed out and conceded several hours ago.

Edited December 13, 2025 by blackrose

[Up-Side-Down]

In terms of LFP battery charging (and indeed all things lithium) I set a fair bit of store by this guy:

 

https://www.youtube.com/watch?v=1G8WxY_jcUM&t=16s

 

https://www.youtube.com/watch?v=K9Tfivf5bAI

 

 

[IanD]

40 minutes ago, Up-Side-Down said:

In terms of LFP battery charging (and indeed all things lithium) I set a fair bit of store by this guy:

 

https://www.youtube.com/watch?v=1G8WxY_jcUM&t=16s

 

https://www.youtube.com/watch?v=K9Tfivf5bAI

 

 

Yep, he really knows his stuff, and unlike many posters on social media he talks a huge amount of sense --  and as he also says, none of this is new or rocket science, and it's all backed up by both LFP theory and research papers and how the batteries are used in real life in solar/boat applications.

 

 But then I would say that, because he's saying exactly I've been saying for several years now... 🙂 

 

Which is that in use like ours (fractional-C use on a boat in the relatively cool UK) there's no need to worry about lifetime or over/undercharging, take them up to 100% SoC regularly to keep them balanced, go all the way down to 0% if you need to, and don't stress about things like trying to keep them forever close to 50% (or below 80%, or whatever).

 

Just use the damn things, whatever you do they'll probably outlast the boat... 😉 

 

 

Edited December 15, 2025 by IanD

[nicknorman]

I only got 1:20 in before he spouted bullshit. Although I agree that he is mostly OK.

[nb Innisfree]

Lots of assumptions are made, I recall a boater trying to figure out his electrical probs, he had removed his batt banks & stated that he could deffo eliminate those on the basis that they were good batts & were fully charged (after all he'd run his engine at least 2 hrs 🙄) When I put a multimeter on them it recorded 11.5v, he refused to admit they were nearly discharged even suggesting my meter was faulty! I politely made my excuses & left. 

 

You can lead a horse to the water etc... 

Edited December 15, 2025 by nb Innisfree

[NB Thistle]

On 13/12/2025 at 14:53, Chris John said:

Really?  Seems rather a lot with only 1.3kw of solar 

So far today (writing this at 12.45) I've had 630Wh off 1.8kW. Even yesterday when it rained almost all day I got 200Wh.

[Gybe Ho]

46 minutes ago, NB Thistle said:

So far today (writing this at 12.45) I've had 630Wh off 1.8kW. Even yesterday when it rained almost all day I got 200Wh.

 

560Wh for me at 1:30 GMT today from 1.33kW of solar. The panels are flat. The daily kWh generation samples from @Andyaero are ahead of mine, I wonder if he is in a marina with big open skies and some panel tilt towards the south?

 

Still working on reducing daily consumption, I might buy a small camping gas stove to lower the electric kettle and air fryer daily consumption. I reckon turning off the invertor overnight would save 0.12kWh. My computer has an average draw of 60W, buying a new generation PC would probably save another 0.25kWh.

[Alan de Enfield]

1 hour ago, Gybe Ho said:

I might buy a small camping gas stove to lower the electric kettle and air fryer daily consumption.

 

But you'd then need to turn on the de-humidifier to remove all the condensation / water vapour caused by using the gas stove.

[NB Thistle]

3 hours ago, Gybe Ho said:

 

Still working on reducing daily consumption, I might buy a small camping gas stove to lower the electric kettle and air fryer daily consumption. I reckon turning off the invertor overnight would save 0.12kWh. My computer has an average draw of 60W, buying a new generation PC would probably save another 0.25kWh.

My boat's base draw is about 20W for the router and fridge. I only turn the inverter on when I need it, mostly that is microwave and coffee machine as apart from printer, projector and cinema sound system everything else runs off 12V. Christmas lights are increasing inverter use somewhat at present though 😂

[Up-Side-Down]

3 hours ago, Gybe Ho said:

I might buy a small camping gas stove

Make sure that (unlike me) it's not sitting on the kitchen worktop when the BSS examiner visits!

 

At least he had the good grace to step back off the boat, ask me to remove it, and then step back on again and begin his examination as if nothing untoward had just happened!!

47 minutes ago, NB Thistle said:

My boat's base draw is about 20W for the router and fridge. I only turn the inverter on when I need it, mostly that is microwave and coffee machine as apart from printer, projector and cinema sound system everything else runs off 12V. Christmas lights are increasing inverter use somewhat at present though 😂

I think there must be something a wee bit muddled here. The best 12V fridge I'm aware of draws 0.4kW in a 24hr period; likewise a decent router, meaning a baseline consumption of 0.8kW over 24 hours. Assuming there is no investor and everything is therefore 12V DC, it is very hard to total less than 1kW when the remaining odds and sods are accounted for.

[blackrose]

57 minutes ago, NB Thistle said:

My boat's base draw is about 20W for the router and fridge.

 

 

That seems pretty low. Your 12v fridge must be very efficient. My mains fridge draws about 4A but I guess it's only on about a quarter of the time, so that 1A + inverter 0.6A + router 0.6A = 2.2A or 26.4w. 

 

The thing is if you have a decent solar system and batteries the base draw is largely irrelevant, given all the other electrical demands. I work from the boat with the laptop & large monitor on all day and even at this time of year I only run the generator once or twice a week to charge the batteries while I run the washing machine. Once spring comes there's no need to run the generator at all until Oct or Nov.

Edited December 16, 2025 by blackrose

[Gybe Ho]

1 hour ago, Alan de Enfield said:

 

But you'd then need to turn on the de-humidifier to remove all the condensation / water vapour caused by using the gas stove.

 

I have been watching the humidity level on the boat since October, not a problem so far, cooking with a diesel range helps. As I don't heat the boat overnight and the range takes an hour to get up to water boiling temp in the morning, an electric kettle has been used. Each boil take 0.05kWh and it soon amounts to a significant chunk of my daily kWh budget, hence my interest in a mini gas or meths powered ring for Nov, Dec and Jan. Meths apparently generates a lot more moisture than butane.

 

I bough some chemical dehumidifiers for the winter and they are still in the sealed wrapping, I check cupboards for moisture and no problem as yet.

[blackrose]

4 hours ago, Gybe Ho said:

 

Still working on reducing daily consumption, I might buy a small camping gas stove to lower the electric kettle and air fryer daily consumption. I reckon turning off the invertor overnight would save 0.12kWh. My computer has an average draw of 60W, buying a new generation PC would probably save another 0.25kWh.

 

Gas-free boats... I think it's a mistake but like everything else it's all down to personal choice.

[Alan de Enfield]

19 minutes ago, Up-Side-Down said:

The best 12V fridge I'm aware of draws 0.4kW in a 24hr period;

 

That, in theory, equates to ~32Ah.

 

I have measured the actual 24 hour usage of my 12v dometic fridge at 30Ah on a number of occasions  but obviously depends on the battery voltage the ambient temperature, number of door openings etc etc.