How much lithium is enough for 1000watts of solar?

[nuru05]

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 .

[catalystcat]

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.)

[HankOnthewater]

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.

[nuru05]

Originally Posted by HankOnthewater

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.

[T1 Terry]

Realistically, if you have a good quality MPPT solar controller. you can expect to get around 80% of the advertised capacity, so 800w from your 1000w solar array .... you might get a bit more on those scattered cloud days that the glare near blinds you, because the water is reflecting back up to the light cloud and that is reflecting back down .... I've seen 125% of the advertised solar capacity when everything aligns just so .... but that is an exception and not the norm.
Next is the peak sun hrs per day, around the equator you can expect around 6 peak sun hrs, up nth or down south in winter, expect around 2.5 peak sun hrs .... if you go far enough down to reach the ice, it actually gets better when there is sun, but virtually nothing when the sun drops below or right on the horizon.

Using these calculations, determine your total 24hr power requirements and divide that by the expected peak sun hrs, 80% of that is the solar you need to survive just one day. We generally allow 2 .5 days with zero sun to calculate battery capacity and solar to recharge that in 1 .5 full sun days.
Only you know where you will be at what time of yr, so you will have to do the sums.

T1 Terry

[PaulCrawhorn]

1000W of panels in good conditions will make about 300Ah per day available to charge batteries, but of course once the bank is Full they don't accept any more.

Your usage budget is key, I personally want enough bank to give me enough for at least three overcast / rainy days.

More if in latitudes / climate where that is the norm.

[FlyingScot]

1000wp of solar isn't nearly enough to run any air conditioning anywhere on the planet. A/C: you will need 2000 watts or more of high quality solar.
Once you hit the Caribe, your refrigeration amp hours will double too.
Battery size doesn't mean much if you can't refill it.

[Pizzazz]

It is not practical to run AC off solar, especially in the tropics. You would be disappointed. Sell the portable genny and get a small diesel generator if you want to run AC. For everything else you seem to be well set up.

[coriobay]

We have 1000 solar and 600 lithium, we run a Zero Breeze aircon on our Lipari Master Cabin, Because it is portable we can stor away until we need it, it runs on 24v or on supplied 240v stepped down to 24v adaptor, works ok for us and we run off the inverter, it is a cheap option, it will only cool one cabin
specs are here
https://www.zerobreeze.com/products/zero-breeze-mark-2

[ozsailer]

As stated, first thing you must do is work out your boat power load. No use trying to work out anything untill this is done. Ensure you allow for all power usage including radar and chart plotters. This is also about power management. If you leave lights and TVs running inadvertently or the kids enjoy watching movies you will use way more. Weather is another factor to take into account. We allowed enough battery/solar so that we did not have to start our generator/motors for 3 days. On our old Cat we had 1200 watts of solar and 900 AH of battery (AGM) which was ample for our needs. Just my opinion but it would be a waste of money to increase battery and not solar capacity. I very good point was made by a previous poster that in the hotter climates you will use more power when the fridges/freezers will work harder. Personally AC on a boat is a luxury unless you have a dam large Genny or tied to the dock.


Ozsailer

[Adelie]

Originally Posted by nuru05

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 .

Rule of thumb for MPPT controllers is 1/3 of panel nameplate Watts equals average daily Ahr at 12v.
So for 1000W expect about 333Ahr/d into the batteries.

Some days it will be more, some less.

To maximize output have each panel on its own small controller. Shadowing one panel in a string brings down the output of all the panels. At least have 2 controller so panels on opposite sides can be unaffected.

Find out how much power you are currently using. Install an amp-hr counting shunt.

Fridge and freezer are each probably 60Ahr/d draw depending on size and insulation. Autopilot is probably similar.

12k BTU is not a small AC unit, that the largest or second largest you can get before you need to go to 240v service. 5k is the smallest normally available. If you really want AC you need to get a doghouse AC unit (yes that really is a thing), on the order of 300w draw. It will only cool 1 cabin and you would do well to insulate the deck above and all walls/hull.

[T1 Terry]

Originally Posted by FlyingScot

1000wp of solar isn't nearly enough to run any air conditioning anywhere on the planet. A/C: you will need 2000 watts or more of high quality solar.
Once you hit the Caribe, your refrigeration amp hours will double too.
Battery size doesn't mean much if you can't refill it.

Ummm....... we install a lot of systems in RVs so they can run their air con from lithium batteries and solar and we are in South Australia, so not in the best solar collecting area by far.
We have 1600w of solar on the roof of our RB145 Hino (a smallish Japanese market bus) and the house side is 100% electric. household 340ltr fridge/freezer, hot water, split system air conditioning, air fryer, induction hotplates, electric toaster, coffee machine .... there would be a microwave as well but there just isn't the room. We do not have a generator, nor do we plug into power. The solar is overkill, but I had the panels and built a summer roof over the bus to get some protection from the summer heat when we crossed the Nullabour from South Australia to Perth Western Australia and back .... Death Valley on steroids sort of weather.
Solar and battery storage have come a long way, as has the efficiency of air conditioning and refrigeration in general

T1 Terry

[T1 Terry]

Originally Posted by Adelie

Rule of thumb for MPPT controllers is 1/3 of panel nameplate Watts equals average daily Ahr at 12v.
So for 1000W expect about 333Ahr/d into the batteries.

Some days it will be more, some less.

To maximize output have each panel on its own small controller. Shadowing one panel in a string brings down the output of all the panels. At least have 2 controller so panels on opposite sides can be unaffected.

Find out how much power you are currently using. Install an amp-hr counting shunt.

Fridge and freezer are each probably 60Ahr/d draw depending on size and insulation. Autopilot is probably similar.

12k BTU is not a small AC unit, that the largest or second largest you can get before you need to go to 240v service. 5k is the smallest normally available. If you really want AC you need to get a doghouse AC unit (yes that really is a thing), on the order of 300w draw. It will only cool 1 cabin and you would do well to insulate the deck above and all walls/hull.

Maybe many moons back, but that no longer the case if the system uses high solar voltage, a lot of panels in series.
As an example, a Victron 250/100 can control a series string of 12v nom panels, 22.5v open circuit x 11 panels = 247.5v They don't actually produce anything at that voltage, but the controller must be able to handle the open circuit voltage of the series string/s connected to it.
The panels must have bypass doides, but you don't see panels for sale these days without bypass diodes.
The 100 side of the 250/100 is how many amps is the max it can send through to the battery. 1500w x 80% = 1200w expected instant maximum harvest from that size array. 1200w divided by 12.8v (mominal voltage for a 12v lithium battery) = 93.7 amps. That means a single controller can handle 11 x 135w solar panels.
It doesn't matter if you have more solar capacity than 1500w, the controller tops out at 100 amps but any extra just can't pass through the controller. Might sound like a waste of solar, byt that 100 amps is reached earlier in the morning and stays for longer in the afternoon. It also harvests more solar in less than optimal solar days. If you have enough solar you will see charging even when it's raining ..... just not when the black thunder clouds are overhead, the type that turn day into night.
If you need to link a few strings of series panels in parallel into the one controller, be sure to add a blocking diode at the positive end of each string to stop the output of the string with the best harvest at the time, turning all the other panels into heaters.

T1 Terry

[noelex 77]

Originally Posted by T1 Terry

Maybe many moons back, but that no longer the case if the system uses high solar voltage, a lot of panels in series.

Having lots of panels in series is usually the easiest and cheapest system to install, but is also the least effecient in a marine environment with plenty of shaddow sources. A parallel configuration is more efficient especially for higher voltage panels. Multiple controllers are the most efficient.

Originally Posted by T1 Terry

Might sound like a waste of solar, byt that 100 amps is reached earlier in the morning and stays for longer in the afternoon. It also harvests more solar in less than optimal solar days. If you have enough solar you will see charging even when it's raining ..... just not when the black thunder clouds are overhead, the type that turn day into night.

Using an undersized solar controller such as one with 100A limit with a 1500w solar array and 12v system will harvest less energy than using a larger controller (or even better multiple controllers with a larger total capacity). Using an undersized controller will be less expensive but will not harvest more solar in less than optimal days.

[noelex 77]

Originally Posted by nuru05

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 .

The fact that you need to run a generator even occasionally with your current set up means the energy budget is tight.

I notice you do not do any electric cooking, which helps, but even if you add an extra 600w of solar and 600Ahrs of battery capacity, running AC is going to be very limited unless you are prepared to run the generator to provide much of the energy. 1600w of solar is very little to contemplate A/C.

The extra 600w of solar will make more difference than the extra 600Ahrs of lithium so I would prioritise the extra production.