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Old 20-09-2022, 09:53   #1
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How much lithium is enough for 1000watts of solar?

So I currently have 1,000w of solar on my boat, at some point in the future I think I will have a hard Bimini made which would then allow me to put another 600w on it. I currently have 540ah of lithium and have the space to put another 600ah. We use a fair bit of power but not excessive. We have a couple of decent tv’s (27” and 40”) as well as a small desktop (Mac mini, takes like 25w) and our fridge and freezer. We are considering getting a small (12k btu) AC to keep the master cabin cool at night.

So my question to you guys is; if we are going to be in the tropics is it worth dropping $5k on more batteries. The only generator we have is a 2,000w suitcase one that I pull out when we’ve had cloudy days .
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Old 21-09-2022, 17:19   #2
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Re: How much lithium is enough for 1000watts of solar?

First observation is that the AC is the big variable here.

A typical 12k BTU marine AC is around 1kW consumption when running, including things like the water pump, etc. (assuming you aren't spending a ton to get something like a Mabru or Termodinamica.)

At a 30% duty cycle (not a good assumption when you are cooling the boat down after a hot day), that's about 300W continuous equivalent. If you are a 12 V boat, that's 25A continuous equivalent (with a 100% inverter). So, for this optimistic scenario, 8 hrs of AC knocks out 200Ah. If you have to cool the boat down to get to temp and your inverter is less than perfect, maybe it's more like 250-300Ah. You can reduce the Ah by reducing the cooling time (though I'd contend you have a solid hour to go from daytime temp to sleeping temp => 100Ah floor). So, you are in the ballpark, but barely.

A second observation/factor - some much cheaper, good quality LFE batteries have been arriving. A good example is the new SOK marine rated 206Ah battery for $1030. That puts your battery upgrade at $3,100 plus rest of circuit. There are even cheaper ones that may not have the same rep for quality as SOK.

As for the amount of solar, it's not a comfortable margin. But, I think it comes down to your usage patterns and willingness to run your little generator.

1,000W of solar may be enough if you have consistent sunshine for a lot of the day.

A simple way to think about this is an approximation that 1 hr of 100% solar (1kWh) = 1 hr of AC run time (1kWh). Adjust this downward for other consumption, for panel shading/clouds, for system inefficiencies, etc.

On the other hand, if you are going to add solar, this is only a temporary situation, isn't it?
As with everything, your use will expand eventually to use up everything you add and then some. (OK - maybe not you, but definitely me.)
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Old 21-09-2022, 20:30   #3
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Re: How much lithium is enough for 1000watts of solar?

To Nuro05
At first impression, I would think your current setup (without aircon) is more than ample for your current needs. And not enough to run an aircon overnight.

However, first you need to check how much amperage your equipment is using ie the big TVs and fridge/freezer, autopilot etc. After that one can make a more objective statement if one needs to increase capacity of batteries and/or panels.
540 amp/hr lithium batteries offer approx 80% of usable capacity, that is around 430 amp/hr. Even with a cloudy day, the solar panels will put charge in the batteries ie 300-400 watt/or ~20 to 30 amps at 12 Volt for 8-10 hrs or so).

You mentioned you have to use your genset on cloudy days. Is that for your aircon? If not, you must have equipment that consume lots of electrons.
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Old 22-09-2022, 17:14   #4
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Re: How much lithium is enough for 1000watts of solar?

Quote:
Originally Posted by HankOnthewater View Post
To Nuro05
At first impression, I would think your current setup (without aircon) is more than ample for your current needs. And not enough to run an aircon overnight.

However, first you need to check how much amperage your equipment is using ie the big TVs and fridge/freezer, autopilot etc. After that one can make a more objective statement if one needs to increase capacity of batteries and/or panels.
540 amp/hr lithium batteries offer approx 80% of usable capacity, that is around 430 amp/hr. Even with a cloudy day, the solar panels will put charge in the batteries ie 300-400 watt/or ~20 to 30 amps at 12 Volt for 8-10 hrs or so).

You mentioned you have to use your genset on cloudy days. Is that for your aircon? If not, you must have equipment that consume lots of electrons.
We do not have an AC at this time, I am considering add one. The one I was looking at consumes about 500w (40ah@12v). We have good numbers about our usage but do not have good numbers about how much our panels will actually produce. This is because we have been on the Great Lakes this summer and didn’t get everything set up until about the 2nd week of August, so the sun was already starting to head back south. Also 2 of my panels are partially shaded by the radar dome so the best production I ever saw was about 550w out of the entire bank. The radar dome will be moved next spring and we will be in the Caribbean by summer so hopefully things will be better.
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