Battery bank sizing with Lithium

[rslifkin]

Originally Posted by noelex 77

There is an important factor that has not been mentioned in this thread. If you are using solar as your primary means of electrical generation the amount of day to day variation in solar insolation is of great importance in determing the required battery bank size.

In places like the Caribbean and the Mediterranean (in summer) the solar insolation is very consistent so consequently you can manage comfortably with a very small battery bank. If you want to cruise some other parts of the world, a larger battery bank is needed to average out the days and sometimes even weeks of poor conditions, with the better times.

A “solar” boat cruising Scotland in summer will need a much larger bank than an otherwise identical boat, with the same electrical needs cruising the Caribbean in winter. The average solar insolation is similar, but Scotland has a much higher variability.

On the same note, the boat in Scotland will want a larger solar installation for the same daily power usage (assuming they aren't already running as much solar as they can fit).

[GILow]

Originally Posted by noelex 77

…

Australia is a large country, but many areas have a reasonably high variation in solar insolation from day to day. I think 200Ahrs of lithium is insufficient to contemplate all electric cooking with a boat that is primarily dependent on solar power.

Having wintered in the southern end of Tasmania and spent numerous summers in Adelaide, I can confidently say I’ve seen the extremes of variation in solar input on offer in Australia.

The battery bank I am contemplating is not adequate for solar-only in winter in Tasmania, but I figured that’s easily fixed. Don’t do winter in Tasmania again.

[noelex 77]

The average solar insolation primarily affects the size of the required solar panel array while the variation in solar insolation from day to day primarily affects the required battery bank size (assuming the vast majority is power is generated from solar).

Tasmania has a significantly lower solar insolation than South Australia so requires a larger solar panel array, especially in winter. The variation is also slightly greater than South Australia so the battery bank size also needs to be greater, but only slightly.

The solar panels make the energy. The batteries only store the energy made by the solar panels. The most the battery bank can do is average out the production over a limited time frame.

[GILow]

Actually, the main issue in Tasmania was that the sun is rather lazy down there and doesn’t bother to get out bed properly. During winter it barely makes five fingers above the horizon all day. This problem was addressed by tilting the panels. Took some monitoring, where possible I used the kedge to hold the boat steady at anchor. Tilting the panels doubled the output of the tilted panel.

[noelex 77]

Originally Posted by GILow

Attachment 271088
Actually, the main issue in Tasmania was that the sun is rather lazy down there and doesn’t bother to get out bed properly. During winter it barely makes five fingers above the horizon all day.

Scotland in winter is more of a challenge .

15° further from the equator hurts.

It does show how far modern solar, battery, and electrical systems have come when you can still cruise in these environments without a generator, but closer to the equator is recommended in winter for sensible people .

[GILow]

Originally Posted by noelex 77

Scotland in winter is more of a challenge .
.

As we say in Australia… “yeah, nah”.

I’m eyeing off the Tropic of Capricorn as a suitable cruising latitude.

[noelex 77]

Originally Posted by GILow

I’m eyeing off the Tropic of Capricorn as a suitable cruising latitude.

This is a great winter cruising ground.

The Whitsundays is a good starting point, but it has been many years since I have cruised these waters. The days of being able to anchor freely and in solitude at Butterfly bay or Bait Reef are sadly long gone. Compulsory moorings have filled these and many other areas.

To stay on topic, the solar conditions are quite variable in Australia even at these latitudes. Many consecutive days of heavily overcast conditions are not uncommon. If you are planning on depending on electric cooking primarily via solar, you will need a battery bank larger than 200 Ahrs.

[GILow]

Originally Posted by noelex 77

This is a great winter cruising ground.

The Whitsundays is a good starting point, but it has been many years since I have cruised these waters. The days of being able to anchor freely and in solitude at Butterfly bay or Bait Reef are sadly long gone. Compulsory moorings have filled these and many other areas.

To stay on topic, the solar conditions are quite variable in Australia even at these latitudes. Many consecutive days of heavily overcast conditions are not uncommon. If you are planning on depending on electric cooking primarily via solar, you will need a battery bank larger than 200 Ahrs.

Yes, I’m eyeing a 280 AH kit. Eve cells and a good quality smart BMS.

But much of what we “cook” is raw and we often go days without using the stove.

As long as I have power for the coffee machine, that bit is non negotiable.

[Sailing Ohm]

You’ve failed to mention/calculate your daily total anticipated watt draw which is the most crucial piece of information when sizing a bank.
As someone who builds battery banks for homes,boats and buses Id say thats a really small bank especially for having such high loads. Especially if you are living aboard. Most lithium installations I do are in the 15-20KW range for power hungry users which replaces 5-6 traditional lead acid batteries (size wise)
Quality lithium banks can easily handle 1C discharge but it really all depends on the BMS.
Any voltage drop will be comparatively minimal until the bank gets down to 20-30%charge. Remember lithium starts at a higher voltage and always has a linear voltage drop. Peukerts law doesn’t apply here. But you still want a large bank to hold plenty in reserve and decrease you load percentage of capacity.

It’s all about watts. The issue is you expect to run a 4 or 3 KW load on a 4.8KW battery. How often are these loads running? Is this once a day multiple times a day? Are they running when the no source of charge can happen? Have you factored in the power used by the inverter?
Anyways, I still maintain This is to undersized for such things especially in the long term unless you plan on charging it with a generator consistently. If on renewable you have to have a few days backup energy in case the sun/wind isn’t providing power. Get more batteries and don’t live life on the edge.

[boat driver]

Originally Posted by GILow

So, on another thread I asked for ideas about running a dual 12/24 volt system for the boat. Long story short, it seems to be the way to go.

However, I am making some assumptions about the capabilities of lithium batteries that are based purely on what I've read, so I'd like to test those assumptions by running them past peoplei who are using lithium batteries on their boats.

The assumption that is most critical is about voltage drop (or sag) under load.

My anticipated peak load would be 4kW, and that would be for maybe one or two minutes at a time. Sustained loads of up to 3kW for maybe twenty minutes at most.

This would be provided at 240 v AC by a decent quality pure sine wave inverter, probably rated at 5 kW continuous and running from 24 volts.

I would expect to use a battery bank of four 12 volt 100 AH(nominal) lithium batteries, each with a 100 amp BMS. So, two parallel pairs of two batteries in series. (At this stage I am assuming I will buy a decent set of commercially made 12 volt drop ins, but I have not ruled out making my own batteries)

So, that's asking up to 80 amps per series string for short bursts and 60 amps per string for longer periods of time.

In the experience of people using lithium batteries, how well are they likely to cope with this sort of use and is voltage sag likely to be an issue, given inverters tend to be a bit fussy about this sort of thing?

Lithium batteries are both advantageous and often mishandled.
Research the negatives. Start with another car carrier caught fire over weekend in Asia tim due to lithium car batteries.
They can not be mistreated, must be properly design installed, and when age approaches replaced.
Don’t worry about all the technology’s advances- that is anticipated. Worry about overheating, thermal
Runaway, and the fact that they cook at 2500+F .
That is a great accelerator for fiberglass.

[wholybee]

Originally Posted by boat driver

Lithium batteries are both advantageous and often mishandled.
Research the negatives. Start with another car carrier caught fire over weekend in Asia tim due to lithium car batteries.
They can not be mistreated, must be properly design installed, and when age approaches replaced.
Don’t worry about all the technology’s advances- that is anticipated. Worry about overheating, thermal
Runaway, and the fact that they cook at 2500+F .
That is a great accelerator for fiberglass.

You have fallen into the same trap and MANY others. Lithium Iron Phosphate, the Lithium batteries used on boats, are a totally different battery than what is used in automobiles, cell phones, hoverboards, etc. They are very difficult to get into thermal runaway. You can abuse them all you want, and it just isn't going to happen. You can even set the boat on fire, and the LFP batteries will not go into thermal runaway, or even contribute to the fire. Subject them to a direct short, and they will burn, but at a lower temp than what is required to set wood on fire, and remove the short and they self extinguish. In pretty much every way, LFP are safer than lead-acid (which can explode) and some have made the comparison that they are safer than a 2x4.

Unfortunately, people hear "Lithium" and that is all they hear.

[GILow]

Originally Posted by Sailing Ohm

You’ve failed to mention/calculate your daily total anticipated watt draw which is the most crucial piece of information when sizing a bank.
As someone who builds battery banks for homes,boats and buses Id say thats a really small bank especially for having such high loads. Especially if you are living aboard. Most lithium installations I do are in the 15-20KW range for power hungry users which replaces 5-6 traditional lead acid batteries (size wise)
Quality lithium banks can easily handle 1C discharge but it really all depends on the BMS.
Any voltage drop will be comparatively minimal until the bank gets down to 20-30%charge. Remember lithium starts at a higher voltage and always has a linear voltage drop. Peukerts law doesn’t apply here. But you still want a large bank to hold plenty in reserve and decrease you load percentage of capacity.

It’s all about watts. The issue is you expect to run a 4 or 3 KW load on a 4.8KW battery. How often are these loads running? Is this once a day multiple times a day? Are they running when the no source of charge can happen? Have you factored in the power used by the inverter?
Anyways, I still maintain This is to undersized for such things especially in the long term unless you plan on charging it with a generator consistently. If on renewable you have to have a few days backup energy in case the sun/wind isn’t providing power. Get more batteries and don’t live life on the edge.

No, I’ve done my numbers. After five years on board I know a lot more about my power needs than you. The bank size is more than adequate.

My question was about sizing for peak load, not storage capacity. But thanks for the patronising lecture on wattage, it made me laugh.

[GILow]

Originally Posted by boat driver

Lithium batteries are both advantageous and often mishandled.

Research the negatives. Start with another car carrier caught fire over weekend in Asia tim due to lithium car batteries.

They can not be mistreated, must be properly design installed, and when age approaches replaced.

Don’t worry about all the technology’s advances- that is anticipated. Worry about overheating, thermal

Runaway, and the fact that they cook at 2500+F .

That is a great accelerator for fiberglass.

Save it for another thread, my question was about voltage sag under peak load.

[Cwens]

Originally Posted by rslifkin

On the same note, the boat in Scotland will want a larger solar installation for the same daily power usage (assuming they aren't already running as much solar as they can fit).

On another note, I've been told that no true Scotsman would turn on his water heater, as showering in warm water only makes you soft and weak and an easy pushover for lean, hungry barbarian invaders.

[MVDarlin]

Where is Oz?