PV Input Wattage Without Load Amperage?

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RealityRipple
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PV Input Wattage Without Load Amperage?

Post by RealityRipple »

Is it possible to calculate, estimate, or display the PV's current wattage on the MATE3 without maxing the amperage out with a load?

When deciding whether to run heavy loads (such as pumping or running a washing machine, instant pot, or microwave), I currently have to keep an eye on the wattage during the morning's charge cycle to tell if the panels are making enough on a particular day to handle the load, and then see if the battery shunt's got a positive or negative amperage after starting the task to know if I can continue safely or if I should immediately stop to prevent discharge in the middle of the day, due to clouds, fog, or haze rolling in after the charge cycle is done.

On my old 12v Lead-Acid MATE1/MATE2 system (which I did not put together or program myself) it always showed the PV wattage as a maximum that could be used. I have no idea if it was constantly using that wattage, since I don't think the batteries ever went into float; I think they may have just stayed in a permanent absorb after bulk, if they ever got there. (They were big and slow and unpleasant, of course. However it was set up, the batteries survived for nearly 20 years, though.) But whatever the reason, it did provide an exact "this is how much you have to work with" number that was extremely useful for daily decision-making.

The new system, of course, shows only the drawn wattage, so that the displayed value is "500 watts in" in the middle of the day, with no details on what the PV could actually provide at the time - whether it be 600 watts or 1800. The PV amperage is reflective of the load, and the voltage is basically always peak (90%-some of open circuit) with a minimal load, so I don't see either of those providing any indicator of sunlight. Do I need to get a "sunlight strength meter" weather station installed next to the panels or something to get this info?

PS: My MATE3's Ethernet cable plug is kaput. Only the built-in display can be used.
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Re: PV Input Wattage Without Load Amperage?

Post by raysun »

On my old 12v Lead-Acid MATE1/MATE2 system (which I did not put together or program myself) it always showed the PV wattage as a maximum that could be used. I have no idea if it was constantly using that wattage, since I don't think the batteries ever went into float; I think they may have just stayed in a permanent absorb after bulk, if they ever got there.
I've never heard of the Mate showing PV Array potential power, though its a good bet the Mate itself isn't deriving the value, rather, its from the Charge Controller.

If such a value could be derived, I'd imagine it would have to come from an MPPT "sweep" so would be a static value until the next "sweep".

Climbing into the Way Back machine and looking at the Mate/Mate2 docs, here's the CC status:
Screenshot_20210729-081209_Drive.jpg
Do those parameters ring a bell? I didn't see a reference to any other PV array related metrics.

I'm also guessing the 20 yo system had an MX60?
Screenshot_20210729-082723_Drive.jpg
The closest metric I see in the MX60 manual is the daily Max array power produced.

From the rest of the description in the OP, I'd guess the max PV array value was the actual value in the Bulk phase of the charge cycle.

I don't think "permanent Absorb" is possible, as it will always be limited by Absorb Time.
Last edited by raysun on Thu Jul 29, 2021 11:39 am, edited 4 times in total.
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Re: PV Input Wattage Without Load Amperage?

Post by JRHill »

RealityRipple wrote: Thu Jul 29, 2021 10:45 amIs it possible to calculate, estimate, or display the PV's current wattage on the MATE3 without maxing the amperage out with a load
Well yes, If I understand your question. Mate3 Hot key for Solar. Then for battery. But I'm not sure I understand the question. Please explain this: "without maxing the amperage out with a load." All of it should be in the Mate3 Hot Keys. What do you not get that you want?
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Re: PV Input Wattage Without Load Amperage?

Post by provo »

RealityRipple wrote: Thu Jul 29, 2021 10:45 am
Is it possible to calculate, estimate, or display the PV's current wattage on the MATE3 without maxing the amperage out with a load?
I don't see how that could be done without some kind of photometer (a 10W solar panel would do) mounted right next to your array at exactly the same orientation. It would do as you say, drawing the max possible current and feeding that value into a microprocessor (Arduino?) to calculate the max that your array could produce at that instant. Even that would be an approximation, but you could calibrate it.

I'd buy one :grin: ....
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Re: PV Input Wattage Without Load Amperage?

Post by raysun »

provo wrote: Thu Jul 29, 2021 11:45 am
RealityRipple wrote: Thu Jul 29, 2021 10:45 am
Is it possible to calculate, estimate, or display the PV's current wattage on the MATE3 without maxing the amperage out with a load?
I don't see how that could be done without some kind of photometer (a 10W solar panel would do) mounted right next to your array at exactly the same orientation. It would do as you say, drawing the max possible current and feeding that value into a microprocessor (Arduino?) to calculate the max that your array could produce at that instant. Even that would be an approximation, but you could calibrate it.

I'd buy one :grin: ....
All that would be fun for some hacker who's grown tired of playing Minecraft, but how about simply deploying sufficient PV panels such as to make "penny pinching" watts immaterial?

OP, forgive my being snarky, but with two FM80s and a bunch of 123 watt panels, there's a serious "underperformance" situation. Its kinda like trying to guage the maximum horsepower from a 20 year old Yugo.

On a good day, fresh out if the showroom, those
Sharp ND-L3EJE would crank out about 100W, at 12% conversion efficiency. How long have they been enjoying the California sun? I'd imagine the usable power has declined somewhat.

Your battery should be able to handle 130 - 140A of charging current, the twin FM80s can easily deliver at that level, so the system limit right now is a bunch of decaying silicon.

Have you given any thought to upgrading the arrays?
Last edited by raysun on Thu Jul 29, 2021 12:04 pm, edited 1 time in total.
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Re: PV Input Wattage Without Load Amperage?

Post by provo »

raysun wrote: Thu Jul 29, 2021 11:52 am
All that would be fun for some hacker who's grown tired of playing Minecraft, but how about simply deploying sufficient PV panels such as to make "penny pinching" watts immaterial?
....
Have you given any thought to upgrading the arrays?
Oh, I don't know -- even with a ton of panels, you might want to know what they'd be able to output in some very low sun situation. I think somebody, not me, should market it....
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Re: PV Input Wattage Without Load Amperage?

Post by raysun »

provo wrote: Thu Jul 29, 2021 12:02 pm
raysun wrote: Thu Jul 29, 2021 11:52 am
All that would be fun for some hacker who's grown tired of playing Minecraft, but how about simply deploying sufficient PV panels such as to make "penny pinching" watts immaterial?
....
Have you given any thought to upgrading the arrays?
Oh, I don't know -- even with a ton of panels, you might want to know what they'd be able to output in some very low sun situation. I think somebody, not me, should market it....
You're right. It would be another useful gadget. As obsessive / compulsive as I am, I'd be all over that, right?

Not so much. A well-sized lithium battery has created a bit of "set and forget" attitude, I guess.

😁

As far as assessing the array potential - during Bulk charge, the max array power is being delivered, unless the charging amps are purposely throttled (mine is, at 225A). During Float, I don't care. If there's power being wasted, so be it, if something is running (dishwasher, clothes washer, water pump, etc.), so be it. I don't advise the Domestic Empress on when or what to run. If I think there will be an issue at EOD, I check SoC around 4PM, if the battery is low enough to cause concern, I fire up the generator for a bit.
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Re: PV Input Wattage Without Load Amperage?

Post by JRHill »

Now, now, be nice.
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Re: PV Input Wattage Without Load Amperage?

Post by RealityRipple »

The location of the arrays is something that's going to make replacing them extremely difficult; plus I don't want to replace them until absolutely necessary. 1.8 kW tends to be enough for all my needs, anyway, and while getting 12 new 650w panels for a near 8kW system would be amazing, the minimum purchase order is 16, and my current frames can't handle 16 of the new dimensions (not to mention they're like 80 pounds each instead of 40 or 50), plus I'd have to add more charge controllers to the system because each FM80 is limited to 4kW @ 48v.

Pretty sure the deal with the old batteries was that they never got to absorb or float; just stayed in Bulk all day. The batteries never got above about 12.9 during sunlight hours; only running the generator would get them into the 13s and 14s. And yes, it was an old MX60 setup, but no, it wasn't the daily totals - because it was always in bulk, it would always say exactly what the maximum the panels could provide was. Like I said, though, I didn't set it up, and never really looked through the programmed settings; just got used to what was displayed.

I live in a canyon right off the coast, so clouds and fog love to roll in and roll out unexpectedly quickly, so it was a great advantage to know when things were safe to start and when they weren't. Even with all new panels, the chances of having to use the batteries out of the blue on what were previously clear days is pretty high. And since the panels are a couple hundred feet from the house, sometimes they're cloudy when the whole house is bathed in sunlight, or vice versa. It's very much not a set-and-forget type setup.
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Re: PV Input Wattage Without Load Amperage?

Post by raysun »

because it was always in bulk, it would always say exactly what the maximum the panels could provide was.
That makes sense, when in Bulk, the PV array is providing maximum output. The normal metrics would reflect that.

I guess I'm not following the need behind monitoring potential solar array output. In most places, I'd think coastal California included, it would be so variable as to not be useful for any operational decisions.

I don't imagine, if the array potential was its full 1.8kW at a given moment - enough to start the laundry - that it would be practical to shut the clothes washer off if array output dropped to 150W, would it?

The lithium battery is about 12+ kWH capacity, isn't it? Is the concern if discharged by an amount during the day, there's not enough reserve to cover overnight loads? Does the system have a battery monitor?

Here's one "quick and dirty" way to see full array output:
20210729_145452.jpg
Cloudy afternoon, battery in Float, 500W load (dishwasher doing the breakfast and lunch dishes.) Array can deliver, at minimum, the amount demanded by the loads.
20210729_145519.jpg
Turn on a small heat pump air conditioner. Load = 1.2kW. Array increases output to its current maximum of 750W. If it would have increased to 1200W, I would have turned on another load.
Last edited by raysun on Thu Jul 29, 2021 6:07 pm, edited 4 times in total.
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Re: PV Input Wattage Without Load Amperage?

Post by fcwlp »

raysun wrote: Thu Jul 29, 2021 5:19 pm I don't imagine, if the array potential was its full 1.8kW at a given moment - enough to start the laundry - that it would be practical to shut the clothes washer off if array output dropped to 150W, would it?
I am missing the logic in this thread. The PV input has nothing to do with starting or running a load, the power to do so comes from the battery.

There are plenty of 60-cell panels that weigh about 40 pounds. If you are living with likely 1,200W from your degraded panels, 3,000 to 4,000W will give you the freedom to splurge on use.
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Re: PV Input Wattage Without Load Amperage?

Post by RealityRipple »

Because we have days where it's mildly hazy before noon and I might only make 1.4kW (I still achieve 1.8 - 1.9 at peak hours on the panels I've got), which means I'll decide not to pump water even though it might clear up by 2 - I just wouldn't notice because the batteries finish charging by then on an average day. And when I put a bit more of a load on that's less than the current maximum, it's really nice to know how much I have left - if I can run the washer and the dryer at the same time, for example.

The idea is to not take out of the batteries during daylight hours, so that in case it clouds up all of a sudden and there's no more sunlight for the rest of the day, I'm in the best shape possible for the night and possibly the next day if it's particularly cloudy.
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Re: PV Input Wattage Without Load Amperage?

Post by raysun »

Is there a battery monitor on the system?
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Re: PV Input Wattage Without Load Amperage?

Post by RealityRipple »

Yeah, a FNDC. But since the batteries are lithium, it's not the best at percentages. And yes, after the fact, I can tell if I'm making more or less than the PV is providing. But like I said, that doesn't let me make informed decisions. It lets me regret uninformed ones.
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Re: PV Input Wattage Without Load Amperage?

Post by raysun »

RealityRipple wrote: Thu Jul 29, 2021 7:17 pm Yeah, a FNDC. But since the batteries are lithium, it's not the best at percentages. And yes, after the fact, I can tell if I'm making more or less than the PV is providing. But like I said, that doesn't let me make informed decisions. It lets me regret uninformed ones.
Hmmm... that hasn't been my experience with the FNDC. I was likewise concerned that its Lead Acid legacy would not work well with Lithium (specifically LiFePo4) and did a great deal of testing. I was pleasantly suprised it was substantially more accurate than I presumed going in.

Even now, I run it in series with a Victron BMV700 specifically configured for lithium. The longest PSoC interval was 14 days. At the end of that time, the FNDC read 2.5% lower than the Victron. Both were about 2% and 4.5% off the measured AH required to bring the battery back to 100% SoC. Assuming 98% charging efficiency, the Victron was a shade high in its PSoC reading and the FNDC was low. A metering error of 5% after 14 days of charge/discharge without sync is pretty good in my book.

I can definitely make informed decisions off the data presented.

To monitor in the manner you are aiming for is going to take equipment not in your system, or any home energy system I'm aware of.

@provo suggests an indirect method that may work. Using an external device to measure solar irradiance at the array, and temperature; one could develop a table of estimated array output. Sounds like a fun project for someone who writes programs.

Another approach might be these guys: https://solcast.com/solar-forecasting/
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Re: PV Input Wattage Without Load Amperage?

Post by SandyP »

raysun wrote: Thu Jul 29, 2021 7:43 pm ../.. Using an external device to measure solar irradiance at the array, and temperature../..
It you have ever wanted a weather station then the Vantage Pro2 may also help you with getting the solar info you want.
It measures (and can log) :
- Temperature
- Rainfall
- Humidity
- Barometric Pressure
- Solar Radiation
- UV
- Wind Speed/Direction

Or something like this : https://int.rsdelivers.com/product/rs-p ... er/1232219
-------------------------
http://spwebcam.myddns.me/
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Re: PV Input Wattage Without Load Amperage?

Post by JRHill »

I've had a Davis Vantage Pro2 for many, many years. This year I added the UV and Solar Radiation sensors to the ISS (sensor suite outside). At this time of the season the Solar Radiation sensor can reach 700+ watts per square meter. But other than telling me the sun's IR intensity it doesn't help with how much power I'm making - or not making because the batteries are already full (set at 56.4) and I'm in float (set at 53.5 now) before the day's maximum intensity has peaked. Earlier this season I did calculate the approximated square footage on the panels but I didn't keep the calculations of the energy potential. Suffice it to say its a huge amount more than the panels do make but I knew that would've been the result anyway.

You already can approximate the production potential if the sun is out and you've got x# of panels feeding into the FM. Knowing what it could be if the panels were more efficient doesn't do much more than make you grit your teeth. If the batteries are full and I'm only producing 500 to 700 watts and I turn on the vacuum, micro, etc and the watts produced zing up well, that's all I can ask for. And with the lithiums there's about no way I'm going to draw enough power to Re-Bulk (set at 51.0). If I did re-bulk I'd probably be hurting that night/next morning cause its doubtful I'd fill the batteries back up.

So about all you can do is add the new panels up to your FM's max and enjoy the production on a day that's not so bright.

One last thing: it would be nice to over populate with panels, staying comfortable below 150v, but with way more than a possible 80a so on those cloudy days you'd be able to harvest more. Unfortunately, for me, its not cost effective to add another CC.
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