Solar Watts : Daily AH Consumption

[swampbush]

Originally Posted by Pete O Static

My panels total 290 watts.
Located in the Caribbean.
Wired in series.
Controller Victron 100/30 MPPT.
Typically Generate 1.2kwh per day.


Each system is going to yield different results. Using a rule of thumb is very general. Wiring in series vs parallel, PWM vs MPPT controllers, Latitude and shading, there are way too many variables.

With my meager 290 watts I can sit at anchor indefinitely in the Caribbean. It will keep meats frozen in the fridge for weeks. I only start the engine to heat water and I could probably get a 12 volt diverter for the water tank. My lighting is LED, so the fridge and the stereo are my main energy consumers. On passage, totally different story and I need to charge with the engine system to supplement for autopilots, chartplotters, VHF, AIS, etc when sailing through the night.

I never get to "float" by noon and I am always suspect when people say that they do. If you notice, many people will say this, regardless of array size, bank size or energy consumption. If you are charging a 1000 amp/hr bank with 300 watts, while using computers and blenders, no way you should be in float by noon.

Typically, a controller has a setting which once "timed out" will go to float regardless of battery state. Mine was set to a default of 6 hours. Meaning regardless of energy harvested, it would be in float by noon. I removed that restriction by changing the setting to 10 hours. Now I get a full day of Bulk, Absorption and sometimes, finally float at the end of the day.


I verify this with a Balmar Smart Gauge. I am nowhere near back up to 100% by noon and I am willing to bet most are not.

There seems to be a myth on cruisersforum that you can't get fully charged with solar. You just need more panels. I have 1200 watts. 1000 of which is new high voltage panels through a victron controller. The victron estimates absorption time based on start up voltage each morning. It can be adjusted by changing the maximum absorption time. Strangely there is no minimum time. Usually it will do 1 hour of absorption if we are fully charged. First light voltage with fridge and freezer running is about 12.46. Absorption current starts at about 40amps and tapers off. 1 hour is not always quite enough. I extended it today but the current fell to about 16amps net after about 1.5 hours and is now 11 amps after 2 hours. This is on 900AH of T105 flooded batteries.

[Dsanduril]

930W solar into 520AH AGM. Daily usage 150-200AH, mostly depends on AP usage and how much water we decide to make. Usage can go down to about 100AH/day if poor weather (we ration ourselves).

On a good sunny day we can make a lot of water and still get to endAmps by about 1pm. On poor days we lose about 50AH, so 3-4 days before we need to find an alternate charging source.

Energy is 99% solar, we end up running the engine to charge maybe once every month or two. Haven't been plugged into shore power in a long time (don't even remember).

Cruising anywhere from 45S to 60N. Don't have too many energy hogs, although we do have cold (fridge/freezer). Only other big consumer is the AP when underway.

[CatNewBee]

Do not forget the amps. For a long life lead acid batteries want to be charged at least with 0.1C, that said your solar shoud output enough juice in average to meet that requirement.

If you have a battery with 400Ah, your solar should at least provide 40A, better 60A, ( what translates to 600...900Wp ) so the batteries are charged with significant currents.

Then chances are you get to full frequently and the battery has a happy long life.

[john61ct]

Getting to Full is very do-able.

Pumping in optimum amps rarely so on smaller boats, just no room for that much solar.

Not a huge impact on longevity, long as the rest of it's done right.

Of course the first hour's charging done with dino juice can help with everything.

[Pizzazz]

Small boat, 100W of solar on dodger, PWM, 200 AHr house bank (two golf carts), located in Southern California. Rarely get more than 25 AHrs per day from solar.

Daily consumption over 200 AHrs, biggest items are fridge, radar, autopilot and work computer. Power needs met by an 80A alternator that typically feeds batteries in bulk charge mode. I get to 100% SOC when I am in the marina.

I view solar as backup power, in case everything fails, there should be enough power for radio, lights and navigation, light, survival use of watermaker. On a smaller boat, there is just not enough space for a decent solar installation that does not look ugly. Further, small boats have small engines which are similar to diesel genset engines, so it is relatively more efficient to use the main engine with an alternator as the main charging source.

[David Gunn]

We have been cruising for 14 years (42foot monohull) and have sailed from Australia to Caribbean. We have 500Ah AGM batteries house. 1x 125 cranking.
We use about 40-50Ah per day at anchor.
Our fridge (70litres) has a Eutectic tank and Danfoss compressor with good insulation and uses 90% of the power consumed on the boat. We turn the fridge compressor on (automatically on timer) at 0800 and off at 1700 and it keeps the fridge below 5 C usually even in tropical waters.
For long passages we have a WindPilot and a back up is hydraulic autopilot.
We have to run the engine on passage if not using the Windpilot.
We used about 20 litres diesel when crossing the Atlantic because sargasso weed stopped us using the Windpilot and we had to use hydraulic autopilot.
We have 2x 115Watt solar panels that have the batteries fully charged by 1000. They are at 13.1V before sunrise as the only load is the anchor light whilst at anchor.
Our first set of batteries lasted over 7 years and we expect these to last 10 years.

[Jon Hacking]

Originally Posted by KISS

I'm curious if there's a trend among cruisers that could be used as a rule of thumb/sanity check.

So, if you please, post:

Your Solar Watts (nominal) / Your Daily AH Consumption (average)

Also indicate:
-to what extent you rely on solar (contra wind, diesel, etc)
-where you cruise (tropics, high latitudes)

Our son did an energy analysis of Ocelot & discovered a very interesting relationship:

If you divide your nominal solar panels WATTS by 3, you'll get very close to the number of 12v Amp-Hours you'll get into your batteries, for unshaded, horizontally mounted panels in free air in the tropics.
(tax, dealer prep, & destination charges may apply. Your mileage may vary.)

This is an extremely useful relationship, but no solar-panel vendors are likely to give it to you, as it has to be determined empirically. Tilting panels will give more (if you tilt them all the time). Out of the tropics you'll get more reflections off the panels (decreasing performance) but the cooler temperatures may make the panels more efficient.

For us in the tropics, we've got 900W of solar running through a Blue-Sky SB-50 MPPT, & we usually get ~300Ah into the batteries from that (if we need that much). Our nominal daily usage is about 140Ah, & the batteries are usually down about 60-90Ah every morning, mostly from the fridge running at night. While we used to have 660Ah of gels, we've now swapped over to 300Ah of LiFePO4s. We can charge with the engines, of course, but rarely need to. The batteries are usually fully charged by noon.

[a64pilot]

Assuming you have a place to put it, you can get 1/3 of the panels rating in watts as Amp Hours in a good day.
The catch is of course most don’t have a way to use all the panels can make, if your charged by noon, where does the rest of the power go?

[chris in SG]

Originally Posted by billknny

The generally accepted rule of thumb, which is too simple for an internet forum because people can't argue about it is as follows:

For unshaded, horizontally mounted panels, expect the following to hold (about) true:

(Panel rated Watts) * 0.30 = Amp-Hours/ day @ 12 volts.

There will be lots of variation, but as a design rule of thumb, this works.

One of the problems with any discussion around Amp-Hours is that it is really a very imprecise measure of energy delivered and used. We REALLY should ALWAYS talk about Watt-hours. One Amp-Hour at 12 volts has a lot less energy in it than one Amp-Hour at 14.4 volts, but sailors talk about those as if they were the same.

I have 630 Watts of solar panels installed horizontally, with only occasional shading by a shroud shadow. In early May at the latitude of Fort Lauderdale it delivers between 3.5 and 4.0 kW-Hours per day. That's full un-throttled output. You get less, of course, if the batteries go into absorption mode.

Similar experience with 650 Watts of panels in the tropics. The attached record of kWhr per day is for one 300W panel. The 'low days' are when we are charging from shore or engine, so the true solar average is more like 1.25kW hrs per day from 300W panel or 2.7kW hours per day from 650 Watts total panel rating which is significantly down on Billknny's 3.5kw hrs per day but sufficient to be reliant on solar alone to run fridge and small freezer with separate compressors, these being the major power consumption in the tropics.

[john61ct]

So 300W panelage, around ~100AH per day.

Ballpark, depends on many variables the weather, bank sizing etc.

[a64pilot]

I started to post that due to acceptance you will not see anything close to 1/3 rating unless your dumping your excess power to a water heater or something, then I saw he had an LFP bank.
But us lead guys won’t see anything like 1/3

[Stu Jackson]

Originally Posted by Pete O Static

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I never get to "float" by noon and I am always suspect when people say that they do. If you notice, many people will say this, regardless of array size, bank size or energy consumption. If you are charging a 1000 amp/hr bank with 300 watts, while using computers and blenders, no way you should be in float by noon.>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

I verify this with a Balmar Smart Gauge. I am nowhere near back up to 100% by noon and I am willing to bet most are not.

Thanks for your honesty. It's refreshing. Unless, of course, like a64 says, one has a solar array that can produce more than is consumed after the nighttime loads have been replenished.



BTW, float is NOT full.


Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

[a64pilot]

Originally Posted by Stu Jackson

Thanks for your honesty. It's refreshing. Unless, of course, like a64 says, one has a solar array that can produce more than is consumed after the nighttime loads have been replenished.

No, it’s my belief that on average us lead acid guys can’t get to “full” no matter how large the array is, it’s not the size of the array, it’s that on average it takes up to 7 hours to charge a bank, and you don’t on average get 7 hours of Solar.
Note just like the Solar day varies, that 7 varies too, new bank shallowly discharged, maybe five and a half, old pretty sulphated bank, eight or nine, seven is a ballpark average.

However LFP as I understand it will accept all that a Solar array can throw at it and therefore can be “full” much quicker. You stop short of 100% on a LFP bank, or should anyway.

[Stu Jackson]

Originally Posted by a64pilot

No, it’s my belief that on average us lead acid guys can’t get to “full” no matter how large the array is, it’s not the size of the array, it’s that on average it takes up to 7 hours to charge a bank, and you don’t on average get 7 hours of Solar.
Note just like the Solar day varies, that 7 varies too, new bank shallowly discharged, maybe five and a half, old pretty sulphated bank, eight or nine, seven is a ballpark average.

However LFP as I understand it will accept all that a Solar array can throw at it and therefore can be “full” much quicker. You stop short of 100% on a LFP bank, or should anyway.

I agree. My point was that those who say they get to float at noon are usually, but NOT always, FOS, especially with FLAs. And your approach in this post is yet another reason that unless the array is HUGE and the bank is LFP, it ain't gonna happen either.


a64, I really appreciate the input you provide on this and other battery/solar related topics, based on your real life experiences now that you're out there. You have really gained a tremendous amount of knowledge since you started with your boat and these danged elektrisity thingies, thanks for continuing to share.

[a64pilot]

If I just hooked up my systems and accepted the preprogrammed settings, then it will drop to float a little after lunch probably, and voltage is very close to what you would expect from being fully charged, but it’s not. I know that now, and my personality won’t let me abuse equipment like that, knowingly. As long as I was ignorant it was OK of course
I believe that most people buy good quality equipment, have it professionally installed and don’t even read the manual, much less spend hours of reading trying to understand exactly what is going on.
Seeing the little green light come on makes them feel that they made the right decision, and you know what, their bank usually lasts several years too until it’s well and truly dead.

Those of us that obsess over our batteries and try to learn as much as we can and babysit them etc. , operationally don’t gain anything at all, the people who are fully charged by noon still get by, just their bank doesn’t list as long as we hope ours does.

If I could have fit golf cart batteries into my box, I would have, and would have accepted replacing them every three years or so.
I replaced batteries every other year in my powerboats as a matter of course. I don’t remember what kind of shorepower charger they had.
My battery management amounted to not letting them drop below 12V, that was it.

Short cycling a bank, especially a good quality flooded bank works, it has for a long time.
Just I’m cheap and want to squeeze every penny so can out of this bank, now that I’m retired and on a fixed income.