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Old 30-08-2013, 22:48   #1
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Battery/Solar size

Hello all,
I have done a search regarding a lot of things I needed to know regarding a new battery solar system I wish to install but I just wanted to check with the collective wisdom of everyone here. We have done some limited local coastal cruising with no problems with our 120 AH house battery but next year we are undertaking what I hope will be the first of many extended cruises. I have calculated that my daily consumptions is about 117 AH and based on many resources have multiplied that by 3 to work out a battery capacity of approximately 350 AH. We have a 80 amp alternator and also intend to install 2 by 200 Watt Solar panels. We have to run the motor once a day for the fridge. The question I have do you consider this is sufficient battery and solar power for our needs. I can get a very good deal on two 6 volt 410 AH batteries which then gives me a fudge factor in my battery supply. I have a separate start battery for the motor. I would rather have more power than not enough. Many thanks in advance for any suggestions or advice.
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Old 30-08-2013, 23:02   #2
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Re: Battery/Solar size

ozsailer, who makes a 6 volt 410 a-hr battery? I know Trojan's model L16RE-B is rated at 375 a-hr on the common 20 hour rate and at a 100 hour rate it is 410 a-hr. Heavy battery at 118 lbs. I never like to go heavier than I can lift without injury. If it is a really good sale, go for it. I used to use L16s for remote off the grid cabins/homes for awhile, but switched to 2 volt cells for higher a-hr capacity in a smaller package.
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Old 30-08-2013, 23:37   #3
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Re: Battery/Solar size

1)Batteries shouldn't be discharged below 50%, so for 3 days worth of capacity you'll actually want a 700 AH bank.

2) 400W of solar panels should deliver 1600 watts per day, so your solar should come close to keeping your batteries fully charged

3) 117 AH/day without refrigeration is a LOT. You'll probably save money in the long run if you can reduce this. At a minimum, LED lighting.

4) If you have to run your engine for a few hours everyday anyway then the solar might not be buying you a whole lot. How many AH do you expect to generate from the alternator each day?
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Old 31-08-2013, 01:38   #4
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Re: Battery/Solar size

Factors to consider. Where will you be cruising? look at the solar insolation map or talk to others to see what they are getting per day from their panels. Realize you wont get the ideal solar output advertised for the panels on a sailboat due to shading, not able to maintain the right tilt for your lattititde etc. Maybe 60-80% even on sunny day.
As you've stated need more amp-hr bank so all the decisions of flooded vs AGM vs lithium. When I have to replace my current 500 amphr AGM bank; definitely going lithium.
My 320 watt solar setup, 80 amphr daily energy budget (with fridge), 500 amphr AGM bank(250 amphr useable) in the PNW works well for me.
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Old 31-08-2013, 01:51   #5
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Re: Battery/Solar size

Back again,
I did my calculations twice, just to make sure they were accurate. I am a qualified electrician but I do not have much experience in 12 but load calculations are very similar. I already have LEDs through out the boat but the main items consuming power are the auto pilots , Stereo and TV. Even though we are not big TV watchers the wife likes her comforts and its a little luxury I have no problem giving to her.. I have put in a fudge factor to cover any shortfall. At the moment I am getting people telling me I have am calculating to much power and then those telling me not enough power . 900 AH of power storage requires some serious storage. Anyone with storage ideas would be most welcome as well. I am thinking of building a new battery box behind my current saloon ladder which will see no extra space being taken up. Susswein, the 6 volt batteries 410 AH batteries are marketed by a mob here in Oz called built by Giant. Each weigh 55 KG each. I would love Lithium but to me there are still a few concerns over their safety. It worries me that the manufactueres are still putting warnings on their products relating to uneven charging of cells may lead to fire. Not a good idea on a boat, especially mine

Greg and Sue
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Old 31-08-2013, 02:08   #6
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Re: Battery/Solar size

i can only tell you what we do -- we have been out 6 years and rarely go into marinas except in the hurricane zones where we have to wait out the season or to secure the boat while doing inland travel -or as we will do this winter when we winter over in tunisia -- othewise we try and stay on the hook
we have circum the caribbean and crossed the atlantic and now in the med -
we sail a jeanneau ds40 and have 6 trojan t105 with a seperate starter battery -- we have 3 135 solar panels and i wish i had one more - generally that is sufficient to keep the batteries except when it gets cloudy for a couple of days running -- and like you our biggest energy users are the reefer, the computer (we do not have a tv) and the autopilot - but we almost never have the ap and computer on at the same time -
the problem now is the Univ of Cincy bearcats play football and we can watch on the computer but it is at night so a big energy user --

just our opinion
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in cartagena spain
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Old 31-08-2013, 02:16   #7
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Re: Battery/Solar size

Quote:
Originally Posted by ozsailer View Post
...... I would love Lithium but to me there are still a few concerns over their safety. It worries me that the manufactueres are still putting warnings on their products relating to uneven charging of cells may lead to fire. Not a good idea on a boat, especially mine

Greg and Sue
Southerly Miss
Lake Macquarie
Oz

Remember in the news recently when the new Boeing Dreamliner was grounded for months because of a fire on one jet? THAT was caused by a lithium-ion battery catching fire. I wouldn't put one on my boat either, not untill the technology is improved and proven safe!
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Old 31-08-2013, 02:18   #8
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Re: Battery/Solar size

If you can get a good deal on 6v 410AHrs batteries that sounds ideal for your set up. The 6v batteries are usually good deep cycle batteries. (Note 2 x 6v @ 410 AHrs = 12v @410 AHrs. Some people get this wrong and think they will have 820AHrs)

The rules on battery size are just general guidelines. It depends very much on the area you are cruising (some areas have very consistent sun conditions, like the Med in summer, and a much smaller battery battery capacity is fine. Other areas have wide variations and a larger battery capacity is needed to cover the long periods of bad weather)

The amount of solar power also makes a difference. A large solar array (in relation to the power used) can reduce the required battery size. If you produce all the power you need even on bad days a very small battery bank is fine. Some traditional battery formulae suggest the opposite increasing the battery capacity as the solar size increases. This shows the limitation of a simple formula.

With 400w of solar in many areas you will produce more than the 117AHrs you need, but it depends on the insolation of the area you will be cruising.
If you are not meeting the requirements making efficiency improvements, if this is possible, especially the fridge, is much better than running your engine.

You will be close to reaching the blissful state where you boat is energy independent without running engines unnecessarily. It is a worthwhile goal.
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Old 31-08-2013, 02:39   #9
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Re: Battery/Solar size

Quote:
Originally Posted by MTLandlocked View Post
Remember in the news recently when the new Boeing Dreamliner was grounded for months because of a fire on one jet? THAT was caused by a lithium-ion battery catching fire. I wouldn't put one on my boat either, not untill the technology is improved and proven safe!
There is a lot of confusion about lithium batteries.
Some types of lithium battery are dangerous. Even the conventional lithium ion batteries you have in your mobile phone are not very safe (think about that next time you put your mobile in front pants pocket )

The lithium batteries that are being used on boats are very safe, safer than lead acid. So safety concerns should not be a factor preventing conversion.

The Dreamliners batteries were not LifePO4.

However, the set up of lithium batteries does require a reasonable amount of electrical knowledge. They cannot just be substituted for lead acid, without changes. For these reasons I would not recommend them to most users yet.

The OP requirements are very undemanding on batteries. One of the biggest advantages of lithium is their high charge acceptance, which has little relevance to the OP who will get most of his charging from solar.
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Old 31-08-2013, 02:52   #10
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Re: Battery/Solar size

Noelex, thanks for the clarifications. In my very limited knowledge of the subject I had forgotten about there being different types of lithium ion batteries. Yes, I've seen videos of the back of iPhones and similar other devices like tablets and other smartphones bubbling out b/c of the battery inside and read stories about the devices spontaneously combusting because of it.

Knowing that the lithium batteries used on boats are a different variety makes all the difference, thanks! I may have to consider their use in the future then when I add solar. Do you think the benefits outweigh the cost of litium batteries?
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Old 31-08-2013, 03:26   #11
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Re: Battery/Solar size

There are a couple of great threads on CF:

Lithium Batteries (for the rest of us)

New Lithium-Ion Batteries

To install lithium batteries you need to be prepared to wade through most of these discussions and understand the issues involved. There is little safety risk, but if you get the details wrong, particularly the charging voltages, its possible to damage an expensive battery bank.

I think this level of commitment is too much for most boat owners who just want a plug and play system.

In the USA flooded lead acid batteries are very cheap and easy to get.

In more remote areas lead acid batteries can be expensive. They are heavy and dangerous to transport. The long life of lithium batteries is attractive for the long distance cruiser. The very high charge acceptance is very beneficial for those boats with generator charging and the batteries also cope much better with high power demands like microwaves that are likely to be fitted to such boats.

If you have a generator equipped boat (particularly a cat) I think its worth the effort to install lithium now. For most users I think the effort/cost ratio is just too high at the moment, but that will change over the next few years.
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Old 31-08-2013, 03:31   #12
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Re: Battery/Solar size

Greg,[Ozsailor]
I've sent you a PM.
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Old 31-08-2013, 09:22   #13
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Re: Battery/Solar size

I use LiFePO4 and will never go back to lead.
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