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Old 10-12-2011, 18:47   #1
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625ah Battery or 450ah and 400 Solar ?

I had planned on installing 625ah of wet cells, but just found a deal on solar. For just a bit more than the cost of two of the batteries, I can get 400 watts of solar. We only have 60w now and a 400 watt rated air x. We also currently only have 225ah in the main bank. I want to increase this, but now I don't know which way to go. Any thoughts?
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Old 10-12-2011, 18:51   #2
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Re: 625ah battery or 450ah and 400 w solar?

First you need a large house bank. Then solar. There are a lot of cloudy days out there.
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Old 10-12-2011, 19:01   #3
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Re: 625ah battery or 450ah and 400 w solar?

Agreed. Run your electrics from a house bank. Use solar to recharge it.
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Old 10-12-2011, 19:04   #4
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Battery capacityis must storage, like a fuel tank. You need power generation so that you can charge them, like filling the fuel tank. Solar panels can help fill batteries a bit.

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Old 10-12-2011, 19:16   #5
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Re: 625ah battery or 450ah and 400 w solar?

So what is the ideal ratio or percentage of Amp hour storage to consumption in 24hrs?
10% 15% 20%.... ?
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Old 10-12-2011, 19:22   #6
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Quote:
Originally Posted by engele
I had planned on installing 625ah of wet cells, but just found a deal on solar. For just a bit more than the cost of two of the batteries, I can get 400 watts of solar. We only have 60w now and a 400 watt rated air x. We also currently only have 225ah in the main bank. I want to increase this, but now I don't know which way to go. Any thoughts?
What is your daily average energy budget and how long do you want to go before needing charging?

Doubling the house bank capacity and adding charging capacity as you propose seems a reasonable thing to do. You double your time between charging need and add a relative ton of charge capacity.
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Old 10-12-2011, 19:22   #7
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Re: 625ah battery or 450ah and 400 w solar?

The basic rule of thumb is to have 1/3 your AH in battery storage in solar AH. The problem is that some panels are rated at higher voltages, and thus, your actual solar AH are less. My 45W panels would be expected to put about almost 3W at full power, but are really around 2W. They are rated at 22V, not at 12V.

I have about 440 AH in house banks and 2X90W in panels and a 600W windmill. The starboard bank died after about 4 or 5 overcast days, and the only load was an unloaded inverter. Could have started that period with some work that used some of the capacity. I always thought it was almost unlimited. These are brand new batteries.

So, I can say that the rule of thumb is OK, but you have to monitor your system and maybe use the wind generator or fossil fuel generator to top up the batteries if necessary.

My brother has something like over 5 kilowatts of solar on his house in Hawaii. He is neutral to positive in his application.

One of my voyaging friends said, when people are aboard and it's overcast, and there's not much wind blowing, we have to run the generator.

Probably the main contibutor in the tradewinds is the windmill. At sea a watermill will do well. I have one but the internal magnets are cracked and I have to restore it. It dates from 1978.

This time of year, in the Florida Keys, or in the Caribbean, you might have those excellent conditions with generally strong winds, and good sunlight during the day. An optimum condition for power generation.
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Old 10-12-2011, 19:25   #8
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I totally understand needing storage. We would still be doubling the size of our main bank if we added the solar. One of the things that really got me thinking was that six six volt batteries is a lot of weight. This summer we lost our shore power charger and our alternator at the same time. We were able to get by but I had to shut the fridge off for most of the day. We lasted a week and a half until my new alternator showed up and we could recharge (I was waiting on a replacement charger from Marinco at the same time). The new alternator is a 100a model. Our house loads are mainly the fridge, chart plotter, and when we get to Mexico probably the watermaker. The fridge draws 6a when it runs, but doesn't run often. The Watermaker has up until now never been needed. It draws around 8-10a. I have a new Xantrex link ah counter meter, but haven't installed it yet. Our current bank is only 225 ah. We are going to add more. Now it is just a question of how much?
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Old 10-12-2011, 19:29   #9
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Quote:
Originally Posted by Pelagic
So what is the ideal ratio or percentage of Amp hour storage to consumption in 24hrs?
10% 15% 20%.... ?
I was thinking the same thing. Another way stated. What is a rule of thumb for How long I should be able to go without charging?

1 day, 7 days? What is reasonable?

If I am drawing 100 amps a day 600 ah seems a lot of capacity.

If I deplete 600 ah and then bulk charge at 60 amps I am looking at well beyond 10 hours to charge it when I consider absorbtion and float stage.

I personally would be looking to supply more of my daily needs on a daily basis and have fewer stored amps.

And if it rains for a week? Well sometimes we'll just have to motor or have a genset option...
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Old 10-12-2011, 19:32   #10
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The watermaker puts out 1.6gph. If we use 4 gallons a day (we never have so far), that's 2.5 hours of watermaker time (at somewhere around 9a) to stay at a full tank. More likely we will try to run the watermaker when the engine is and power up for those few hour runs. That said it is a big draw when it's running. I am conflicted.
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Old 10-12-2011, 19:33   #11
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We will have a little Honda or Yamaha generator on board as well.
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Old 10-12-2011, 19:39   #12
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Re: 625ah battery or 450ah and 400 w solar?

It would be a no-brainer decision for me - get the solar. 450Ah is a decent bank and you have a good alternator for cloudy weather. Many boats your size have that sized bank and no solar.

Having said that, I don't believe you can get the solar for the same price as two extra 6V flooded batteries. Remember, you will need a regulator for those panels and if those 400W are not 17V OC panels, you will need a MPPT controller to run them.

Two flooded 6V are between $200-300. No way you are getting 400W of panels, a controller, large gauge wire and fittings and mounting hardware for that price.

But get the solar anyway.

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Old 10-12-2011, 19:40   #13
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So here's another bit. We are currently living aboard, but in January we leave for an indefinite amount of time. For the past several years we have always eventually came back to the dock and charged up. So far our needs have been mostly met by the 225ah we have (though I've killed the bank twice on extended trips). Not ever going to a dock (or rarely), may increase our need for both storage and generating capacity. It's easier to buy now than it will be once we leave. I do feel we need more storage and generating capacity both.
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Old 10-12-2011, 19:46   #14
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The panels are nominal 12v (wouldn't need MPPT regulator). They are priced at $1.28/w from sunelec.com. I have no idea of the quality though. Has anyone bought from them? The batteries I've been considering are Trojan T105s that sell here for about $130 and a $25 core charge.
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Old 10-12-2011, 19:50   #15
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Thanks Mark. Unfortunately their aren't a lot of choices for 12v panels, and they are more expensive than the ones that require a MPPT controller. I thought that $1.28w was a good deal. You are right that the panels are more, they just aren't so much more that it ruled the option out. Thanks
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