Lithium batteries or more solar?

[davethedog]

Hello all,

Currently sat here in Bequai and have a question for the community regarding battery discharge and charging etc .

As the weather is quite warm here the fridge and freezer (water cooled)are running a lot more than in the UK, and in the morning before the sun hits the 620w of solar panels we can have used about 130ah overnight running the inverter, movies, fans, fridge and freezer. We have a 510ah 12v gel battery bank and the ah usage and state is measured via the mastervolt shunt and easyview 5 . This also shows we can be down to 80% state of charge some mornings.

When the sun is out all day the solar will charge the batteries without issue and we get to float by about 1400 , but if it is overcast we may not get to float before evening so then we run the generator to get them there l, as well as heat water etc

Few questions;

Is 20% usage normal?

Am I being too paranoid about ensuring the gel batts are at float each day ?

Would I be better off adding extra solar (say 200w more) or switching to lithium batteries? As know the lithium batteries do not need to be fully charged all the time. Nothing wrong with the current gel batteries

Thanks

 

[roaringgirl]

It would certainly be cheaper to add more solar than swap out perfectly good batteries!

Lithium charges faster and is much less fussy about getting back to float. For other batteries, their longevity will be affected by not regularly getting to float voltage.

You could look at it this way: the batteries are there to store your energy, which they're currently doing just fine. Their longevity will be slightly lower by not reaching float every day, at their slightly sooner replacement time, you could consider lithium.

 

[gregcope]

Going lithium (lifepo4) is going to be a significant capital expense.

Adding more solar (or moving from PWM to MPPT) is probably cheaper.

Can you easily add more solar?

 

[davethedog]

We are currently running 5 x MPPT controllers for the solar panels and therefore not too difficult to add a further 2 x 100W panels . May do that to see of that alleviates the small issue during less sunny days then before thinking of replacing the functioning Gel batteries.

 

[gregcope]

Going lifepo4 will harvest more solar than Gell/FLA as it will accept a charge more readily due to its lower resistance especially when lead gets above 80%.

How old are the Gells?

 

[davethedog]

Going lifepo4 will harvest more solar than Gell/FLA as it will accept a charge more readily due to its lower resistance especially when lead gets above 80%.

How old are the Gells?

They are about 3 years old.

 

[gregcope]

Sounds like you might get another three years from the Gells if not longer.

Getting them charged each day will help allot in longevity as will only cycling to 80% DOD so feels like your doing the right thing.

If your struggling to get them to float sounds like adding charge capacity (solar) is the issue, not capacity.

 

[Neeves]

It also depends on your future plans.

If you are to remain where you are - you have defined usage - but if you plan long ocean passages in the next 6, say, months then your usage will increase and your ability to charge will be diminished, less ability to keep panels in sun, AF using more power, nav lights (maybe radar).

You might thus need more charging ability and more capacity.

We have always found Parkinson's Law is applicable. The more capacity you have your usage slowly creeps up to use more than you have, you use more de sal water, you watch an extra movie etc. - basically you reduce your parsimony, have you become more, too, relaxed about usage? Your fridges are the big consumer - could you make them more efficient?

Take note of Geem's thread where he has 2 house banks.

Jonathan

 

[geem]

Hello all,

Currently sat here in Bequai and have a question for the community regarding battery discharge and charging etc .

As the weather is quite warm here the fridge and freezer (water cooled)are running a lot more than in the UK, and in the morning before the sun hits the 620w of solar panels we can have used about 130ah overnight running the inverter, movies, fans, fridge and freezer. We have a 510ah 12v gel battery bank and the ah usage and state is measured via the mastervolt shunt and easyview 5 . This also shows we can be down to 80% state of charge some mornings.

When the sun is out all day the solar will charge the batteries without issue and we get to float by about 1400 , but if it is overcast we may not get to float before evening so then we run the generator to get them there l, as well as heat water etc

Few questions;

Is 20% usage normal?

Am I being too paranoid about ensuring the gel batts are at float each day ?

Would I be better off adding extra solar (say 200w more) or switching to lithium batteries? As know the lithium batteries do not need to be fully charged all the time. Nothing wrong with the current gel batteries

Thanks

Solar is so cheap I would definitely do that first. Even if you went lithium at a later time the extra solar will be useful since you will likely use the battery capacity differently to how you use it at the moment. I have just ordered another 200w of solar to add to my existing 720w. I have recently installed lithium and find that to fully take advantage of the lithium, more solar makes sense

 

[Kelpie]

Hello all,

Currently sat here in Bequai

Well that makes four forumites here now! Whereabouts are you?

If you have space to fit solar, then do it. Lithium batteries aren't so easy or cheap around here. Best bet seems to be getting them via the US and shipped in to St Martin, although I know people have had them sent to Grenada too. Solar is much more readily available.

 

[geem]

Hello all,

Currently sat here in Bequai and have a question for the community regarding battery discharge and charging etc .

As the weather is quite warm here the fridge and freezer (water cooled)are running a lot more than in the UK, and in the morning before the sun hits the 620w of solar panels we can have used about 130ah overnight running the inverter, movies, fans, fridge and freezer. We have a 510ah 12v gel battery bank and the ah usage and state is measured via the mastervolt shunt and easyview 5 . This also shows we can be down to 80% state of charge some mornings.

When the sun is out all day the solar will charge the batteries without issue and we get to float by about 1400 , but if it is overcast we may not get to float before evening so then we run the generator to get them there l, as well as heat water etc

Few questions;

Is 20% usage normal?

Am I being too paranoid about ensuring the gel batts are at float each day ?

Would I be better off adding extra solar (say 200w more) or switching to lithium batteries? As know the lithium batteries do not need to be fully charged all the time. Nothing wrong with the current gel batteries

Thanks

Prior to installing lithium, our 450Ah @12v domestic battery bank was typically at 80% soc each morning. We don't watch movies but we do have a couple of fridges. We always got the lead batteries to float every day but we have 100w more solar than you

 

[Pete7]

Is 20% usage normal?

Am I being too paranoid about ensuring the gel batts are at float each day ?


Thanks

I wouldn't worry, 20% DOD each morning is tiny. Use the gel batteries for another couple of years and when you need to replace, then go LifePO4 at a suitable point.

The good news is you probably won't need the same capacity in LifePO4. You are using 1500w overnight, which could be a pair of say 120Ah or 150Ah LifePO4 batteries and cycling 50%. As already mentioned, it really does charge up so much more quickly and has been a game changer for us enabling mostly electric cooking whilst not needing a huge battery bank on a 31ft yacht. 120Ah of LFP paralleled to a pair of Trojans totally 170Ah. Lowest we have seen is 33% SOC one morning supported with 600w of solar in southern UK. We may need a little bit more LFP and we will know more at the end of this summer. Perhaps 200-240Ah to go full electric cooking.

You could add more solar now, but if the acceptance rate of the gel batteries during the final charging to 100% is low like flooded lead acid, adding more power won't help. If you see the current dropping in the afternoon as the gel batteries approach full, add another load. If the output from the MPPT suddenly increases then the panels aren't the limiting item, there is plenty of extra power available from solar. Its the batteries that can't absorb it that quickly.

 

[Neeves]

Well that makes four forumites here now! Whereabouts are you?

I wondered slightly differently - but with the same prompt.

How many Brits cross the Atlantic to the Caribbean , or America - on an annual basis.

Jonathan

The 'Thread drift police', who cannot think outside the box, will have a field day

Jonathan

 

[Mistroma]

All sensible posts and your figures do look reasonable. Using 130Ah is about 25% of 520Ah, leaving SOC 75%. vs. 80% reported. There are a few possible reasons for the difference but it's in the right ballpark and I doubt your SOC reading is super accurate anyway.

Just a suggestion about charging on cloudy days. It might be worth running the generator in the morning if it is obviously going to be cloudy all day. The generator output will probably be higher than solar at that point. It is also when highest charge will be accepted at lowest SOC. Experience should give a good idea what SOC to aim for on generator and then leave solar to get to 100% during daylight hours.

I have 450W with 450Ah Trojan T-105s and they are usually fine after early season. I try to run the generator earlier in the day if we get several cloudy days. Mid-morning usually works as everyone is awake and I'm not disturbing anyone.

 

[Stemar]

I'd go for solar now, then save up for the lithium when the current batteries die. There are several new battery technologies on the horizon, some of which have the potential to be cheaper and better than lithium. The longer you wait, the better the chance that one of these will be available/affordable.

 

[Baggywrinkle]

Another vote for solar. Capacity doesn't seem to be your problem, and for lead batteries increasing capacity makes sense if you are regularly seeing deep discharges - doesn't seem like this is the case. The advice to run the genny early is good as they will be bulk charging at first when they can make the most use of the genny output. As a rule of thumb I've used 4 days cloud and rain as a means to calculate battery capacity because that's the longest I've sat in an anchorage waiting for better weather. If necessary there is always the genny and the engine.

 

[davethedog]

Well that makes four forumites here now! Whereabouts are you?

If you have space to fit solar, then do it. Lithium batteries aren't so easy or cheap around here. Best bet seems to be getting them via the US and shipped in to St Martin, although I know people have had them sent to Grenada too. Solar is much more readily available.

We are currently anchored here:

 

[davethedog]

Thanks for the replies and all food for thought, just realised that we may have an issue with the fridge/freezer thermostat so sorting that will help.

Think we we get to Grenada I may look at adding a further 2 X 100w panels to the guard rails as easily enough to remove at a later date if needs be. Then see how it goes as can run the generator but do not want to if I can help it.

As for lithium...we will see as the cost if the batteries in Grenada are double the cost in the UK!

 

[davethedog]

Hello all and a quick update.

After some research I realised that I could adjust the temperature range of the fridge and freezer thermostat (by adjusting a little screw in the actual thermostat unit) and now have the freezer at approx - 10 and the fridge at 5 degrees with the compressor duty cycle about 60% so a big reduction in amps usage overnight etc

 

[Kelpie]

Hello all and a quick update.

After some research I realised that I could adjust the temperature range of the fridge and freezer thermostat (by adjusting a little screw in the actual thermostat unit) and now have the freezer at approx - 10 and the fridge at 5 degrees with the compressor duty cycle about 60% so a big reduction in amps usage overnight etc

What kind of freezer/thermostat is that?