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Old 14-07-2019, 00:56   #1
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The “Myth” of 100% by Midday

It is often stated on this forum that it is impossible for solar panels to achieve 100% charge by noon using solar alone. When members post that they regularly achieve these results, it is suggested that their battery monitor or solar regulators are misleading by falsely indicating 100% or by dropping to float too early.

So I thought I would post an example showing 100% charge before noon to prove this was achievable.

At this time of year we are close to the summer solstice in the northern hemisphere. With long daylight hours, 100% before 9am is usual. By noon the batteries have usually been sitting on float for several hours.

This morning I photographed the battery monitor app (a Pico). The solar regulators actually dropped back to float before I could take the photo. So I started another absorption cycle to show that the end amps had been reached.

So here the battery monitor is showing 100%. The solar controllers are regulating. The battery voltage is at the absorption voltage for these gel batteries. The end amps are at 4.36 amps, which is 0.7% of the nominal 600AHr battery capacity.

There are many definitions of 100% full lead acid batteries. The reality is actually that the battery SOC approaches the 100% in such a gradual way that a realistic definition is hard to standardise. The most common definition is when the battery charging drops to float, providing this is done at the correct point.

Most battery manufacturers suggest when the end amps reach 2-3% is the correct point. Many people suggest charging more aggressively holding the absorption phase for longer until the end amps reach 1 or even 0.5%. For gel batteries 1% is a good number so the 0.7% suggests the absorption phase has been held a little too long for this battery chemistry, but in practice the difference is only slight. At this SOC the end amps drop very rapidly so the difference in the time when these various definitions are reached is only small.

Note the time is 8:17. Noon is still over three and half hours away.

This will not be achieved all year. We spent winter in Scotland and at this time of year and these lattitudes, 100% was only achieved late in the solar day (although as sunset was around 4pm, this was not really late ) and of course there are days where 100% is not reached.

So solar can charge the batteries to 100% by noon. This is easily achieved by many marine solar systems, at least at the time of year when conditions are good.
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Old 14-07-2019, 01:19   #2
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Re: The “Myth” of 100% by Midday

But how much did you use overnight? You guys seem like pretty light users and probably barely dent your battery bank in 24hr.

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Old 14-07-2019, 01:28   #3
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Re: The “Myth” of 100% by Midday

We regularly get to 100% by midday with our 2250w of solar but then continue to shove 40amps and dropping for a few hours more.

On a cloudy day, if we just get to 100% by 4pm we will have low voltage alarms trip at 5am
On a sunny day with the 100%+ happening, no alarms tripped.
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Old 14-07-2019, 01:43   #4
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Re: The “Myth” of 100% by Midday

Noelex,

I’ve posted our solar panel results with photos several times on this forum, only to be called a liar by many members. Just because their systems are old, cheap, inefficient, poorly monitored and/or poorly maintained, those naysayers assume everyone else is doing the same.

We have 450w of Solbian flex panels, five controllers, 400ah 24v house bank and regularly get back up to 100% and float status daily without using the generator, even though we cook using all electric (induction and infrared), make 34 gallons of water per day and live totally in anchorages without ever plugging in; I even have the hot water issue figured out, we produce 10 gallons of piping hot water daily for dishes and showers.

I thought more people on this forum would be interested in how we achieve this, rather than throwing stones and making insulting comments.... but it seems I was wrong. It’s good to see someone else backing up my claim who’s also using a modern efficient system and monitoring device.
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Old 14-07-2019, 02:34   #5
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Re: The “Myth” of 100% by Midday

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Noelex,

I’ve posted our solar panel results with photos several times on this forum, only to be called a liar by many members. Just because their systems are old, cheap, inefficient, poorly monitored and/or poorly maintained, those naysayers assume everyone else is doing the same.

We have 450w of Solbian flex panels, five controllers, 400ah 24v house bank and regularly get back up to 100% and float status daily without using the generator, even though we cook using all electric (induction and infrared), make 34 gallons of water per day and live totally in anchorages without ever plugging in; I even have the hot water issue figured out, we produce 10 gallons of piping hot water daily for dishes and showers.

I thought more people on this forum would be interested in how we achieve this, rather than throwing stones and making insulting comments.... but it seems I was wrong. It’s good to see someone else backing up my claim who’s also using a modern efficient system and monitoring device.
I WANT YOUR SOLAR PANELS 😁 Seriously, you inspired me when I saw them couple days ago, already hard at googling suppliers

As for the rest, of course it is so variable... We only have 450 of old tech solar, plus 450 wind, and lots of fridges.electronics, rice cooker bread machine induction stuff... On a good summer day we're 100 percent by 4pm, but that's from 80% overnight. Otherwise gennie for an hour every few days. (till I add some of those panels Ken has)
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Old 14-07-2019, 03:13   #6
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Re: The “Myth” of 100% by Midday

We only drop to 90%-92% overnight on a regular basis June-end of August here in the Med, mostly sunny days; it usually takes until about 4pm to achieve 100% when the solar controllers indicate float status. Also, we haven’t been using the large deep freezer this year which makes a HUGE difference; the regular upright fridge has been doing a good job with its small freezer section. I usually run the watermaker, after the batteries are at 100% or late in the day, so the solar is powering only the Spectra and not attempting to power multiple devices.

I purchased the Solbian panels directly from the Solbian factory outside Torino, Italy and they did the install.
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Old 14-07-2019, 03:57   #7
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Re: The “Myth” of 100% by Midday

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But how much did you use overnight? You guys seem like pretty light users and probably barely dent your battery bank in 24hr.
Our night time loads are a small fridge, LED anchor light & spreader lights & interior lights, usually a couple of movies (28 inch screen and a low power draw computer), Vesper anchor alarm with the NMEA bus powered (therefore wind speed, depth, heading, SOG, STW, rudder angle). Our tablets are on for most of evening. Miscellaneous other items such as music, phone charging etc. The Zeus chartplotter is usually (but not always) turned off when we go to bed. The Vesper gives us all the relevant data such a distance to anchor, depth etc if we need to check this overnight.

The higher draw devices such as washing machine, induction cooktop etc are normally run after the batteries have reached float. The electric kettle is the exception. But morning and evening cups of coffee do not draw many amp hours even though the short term current required is high.

For most of the year solar provides a significant excess of power even on relatively cloudy days. The long daylight hours ensure the battery has to do very little work.

During winter in higher lattitudes we do start to economise. Winter in Scotland was the poorest solar conditions we have ever seen. At its worst, the sun barely skimmed the horizon with a maximium elevation below 11°, official sunset was around 4:30pm but at anchor the sun was often below the hills before 3pm.

In these conditions there is some need to reduce average consumption. The yacht systems ensure we can economise reasonably easily without a significant impact on our lifestyle. For example, the chartplotter is often not left on all day at anchor (although the Vesper is still on). We move to cooking and boiling water via the Reflex diesel heater or propane. We did turn off our fridge off for a short time over the depths of winter in Scotland, but outside tempertaures were as cold as the inside of the fridge so food could still be kept fresh by storing in the lazerette, or under the doghouse.

The backup plan is to use the large alternator. It supplies over 100 A @ 24v (it is actually a 175A alternator @ 24v but is derated by the alternator controller). So far we have not had the need to start the engine just to charge the batteries, and we do not do much motoring or motor-sailing, but in winter the alternator contribution motoring in and out of the anchorage evens out the higher consumption from the autopilot and radar on sailing days.
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Old 14-07-2019, 04:59   #8
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Re: The “Myth” of 100% by Midday

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Our night time loads are a small fridge, LED anchor light & spreader lights & interior lights, usually a couple of movies (28 inch screen and a low power draw computer), Vesper anchor alarm with the NMEA bus powered (therefore wind speed, depth, heading, SOG, STW, rudder angle).
I believe the question really was, at least for me, is what was your battery amp-hours out before the solar charging started.
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Old 14-07-2019, 05:54   #9
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Re: The “Myth” of 100% by Midday

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I believe the question really was, at least for me, is what was your battery amp-hours out before the solar charging started.
My battery monitor does not record the minimum overnight SOC, only voltage. Usually, at this time of year by the time I am awake, solar production has started, but I would guess at around a 15-20 Ahrs @24 v at the start of solar production would be typical. The solar days are long.

Our daily production is well recorded by our solar regulators. The average is 3.5 kWh per day when at anchor in summer. This is around 125 Ahrs @24v or the equivalent of 250 Ahrs @12v. This varies from day to day, mainly depending on the use of high demand appliances such as the washing machine and induction cook top. Much of the time the controllers are in regulation so these numbers are governed by how much power we use rather than the maximium priduction available. Actual AHr usage will be slightly lower than solar production due to battery inefficiency.
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Old 14-07-2019, 06:04   #10
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Re: The “Myth” of 100% by Midday

Wouldn't a better measure of full charge be when the acceptance current levels off? If they are accepting 1% the 2 hours later are accepting 0.5% and another 2 hours later still accepting 0.5% could they really be charged at 1%? Possible that will change with age and temperature?

Anyway, I can just get my 225Ah 2 x T105s charged from around 80% to full before sunset with 300W of solar, or what was once 300W with some shading. Pity I can't find a screenshot from at anchor but this shows the current leveling off on the mains from slight discharge. I take level current acceptance as fully charged and set float to bulk @ 14.9V. From happy hour charts I doubt many people actually get to fully charged very often.

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Old 14-07-2019, 06:16   #11
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Re: The “Myth” of 100% by Midday

I think the problem may be in understanding the criteria.

If you use 10amp-hr out of 1000amp-hr bank with a 1000w of solar panels, I don't think many would argue you can hit 100% by mid morning.

Change that to 300amp-hr used overnight and without some good explanation, the math doesn't add up to be fully charged before noon.

Those are kind of the extreme ends but it sounds like you are running much closer to the low end of the use case where it's quite easy to hit 100% early on in the day.

Assuming you've sized your system to accommodate 2-3 days with little or no solar (to cover overcast days) followed by a good solar day topping the bank up (or pretty close), it's not surprising if most days, you will hit 100% by around noon.
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Old 14-07-2019, 06:22   #12
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Re: The “Myth” of 100% by Midday

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Old 14-07-2019, 06:32   #13
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Re: The “Myth” of 100% by Midday

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My battery monitor does not record the minimum overnight SOC, only voltage. Usually, at this time of year by the time I am awake, solar production has started, but I would guess at around a 15-20 Ahrs @24 v at the start of solar production would be typical.
Well at only -20AH I fully accept that solar can have the batteries fully charged by noon. That was the key piece of the puzzle as at that low of a discharge you will be in absorption by 9-10 am and 2-3 hours later could be mostly fully charged.

But in the morning I'm normally -70-90 AH and don't get to absorption till a lot later and aren't going to be "fully" charged till around 3pm (defining "full" as absorption voltage and less than 0.5C amps charge).

Heck I'm currently on shore power but still have the solar on and it daily does it's full cycle (have the time in absorption turned to only 15 min) and it gets to "full" charge by 10am.

It's all in the details.

BTW - all this requires acceptance that "full charge" isn't really 100% charged but close enough for those of us who are more interested in using batteries than being slaves to them
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Old 14-07-2019, 07:11   #14
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Re: The “Myth” of 100% by Midday

100% float status was achieved by 2pm today, so I’ve been making water for the past three hours for a total of 51 gallons, entirely off solar.
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Old 14-07-2019, 07:59   #15
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The “Myth” of 100% by Midday

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We regularly get to 100% by midday with our 2250w of solar but then continue to shove 40amps and dropping for a few hours more.

This is key here, anyone can take pictures of their amp hour counters showing “full” but if your bank is still accepting charge at absorption voltage, are you full, or just indicating full?

Then of course if your well North in the middle July, that’s a bit different than mid latitudes in December.

But yes if you only use 15 to 20 Ah overnight, which is 30 to 40 if your 12V and are way North so that charging begins when, maybe 7 am?
Then yes you are really charged by Noon assuming a nice sunny day of course.

However if your Joe average and use about 1/3 of your banks capacity over night and it’s Winter time when a lot cruise to avoid the heat in the tropics, it’s unlikely you will achieve a full charge at all, and certainly not by Noon, which is what a lot think, cause their battery monitor tells them they are.

It’s really not much more complex than answering do you have more than 6 hours of Good charging a day, that’s good charging not 6 hours of the panels making 1 amp more than your using.

Take look at this, US in Dec, flat panel.
https://rredc.nrel.gov/solar/old_dat...tlas/serve.cgi

This is July
https://rredc.nrel.gov/solar/old_dat...tlas/serve.cgi

Depending on where you are on that map. There is up to a 400% difference in power made from Dec to July.
I’m sure there are World maps, but US is easy and it shows a pattern that is average. Of course if your straddling the equator, then that’s different.

So yes, cherry pick your data points and you can easily do it, but is that the point?
I have pictures to prove my boat is a 10+ kt boat, cause it has done it.
But it’s certainly not even close to a 10+ kt boat, especially on average, on average she is close to a 5 kt boat. but in surfing conditions it has exceeded 10 kts, I have the pictures to prove it.


Nolex, I respect you and know you know what your talking about with Solar, and I’m sure you really are 100% fully charged, and you stated this is an unusual case due to you being so far North and it’s middle of Summer.
It’s not for you that those of us that say you can’t get there with Solar alone, it’s for the guys down in the Bahamas in December who’s Solar Charger drops to float every day around Noon and they think they are full, but 60 days into their cruise they are asking on the radio to borrow a “battery tester” cause they must have a bad battery that needs replacing because the low voltage alarm goes off in the middle of the night and it didn’t used to, so they must have a battery that needs replacing.
I wished I had a dollar for every time I heard that request on the radio in Georgetown, I wouldn’t need investments to cruise.
They know they have good Solar, it couldn’t be that, cause the green light was on everyday by noon.
Or they run the engine for an hour every afternoon before going to bed, so they must be charged, right?

Joe Average is better served by locking his Solar controller into absorption voltage, because he rarely gets to full, and those times that he does, he doesn’t sit there for hours at absorption voltage, but minutes.
It’s less harmful for a battery to sit at absorption for an hour every now and again than it is to be chronically undercharged, that is why some try to say that you can’t get to full charge on Solar alone, because Joe average can’t, but his controller drops to float prematurely every day, convincing him that he is fully charged.
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