Solar charge controller not reporting unused solar capacity

Hello all, I have a question as to why my solar charge controller does not report on the available solar power (what the solar panels are capable of producing at a moment in time, not just what they are currently using).

I am relatively new to solar but have an electronics background and I have put together a very small self-consumption system to educate myself before potentially moving to a full-scale system.

I have a few 100W 12V solar panels along with a Victron 75/15 charge controller charging a battery (and some loads).

Shortly after setting this up, I realized that when the battery was not full (or I had a heavy load) I got ~200+ watts from the SCC in full sun.

Then there were days where I saw I was only pulling say ~100Watts (what the SCC reported as producing) when I knew there was full sun. I understand the SCC is like a "battery" it will only supply what is asked for (the load).

Well from just a few weeks of looking at the sun out the window I would know the panels were not producing the ~200Watts that were available in the bright sun, so I turned on a few more loads and sure enough the SCC moved up from say 100 Watts to 175 Watts running just fine. I would manually turn on these additional loads when possible. The wife finally said, "really this can't be automated"?

The Victron CC is loaded with options but not one about "here is the excess power you are not using". I must be spending too much time watching the Victron screen because without looking out the window I can see the solar voltage rise from its running voltage of around 16.x volts to over 20 volts and I know then that it's not producing the full potential of the panels and can turn some loads, and sure enough the running voltage comes back down to 16.x.

After some research I found articles on building dump loads to power a heat water, etc. when the solar panels are not producing their full potential on the primary loads, but it does not seem there is a product to buy, wire in and do this.

I am assuming because this 'feature' is not available on any charge controllers I looked at that there is more involved than a software update to monitor the solar panel voltage/current and use a solar algorithm to do this? It seems like this is a VERY necessary item for self-consumption. Obviously if your attached to the grid you have an "unlimited load" and you push back almost everything you can, but in self consumption its use it or lose it.

I saw a video from Andy in the Off-Grid Garage where he used a handheld solar panel meter. It seemed to run a short MPPT test and tell you what the panels were capable of producing at that moment with that sun. Why wouldn't someone integrate something like that into the solar charge controller with knobs... Every x-seconds or minutes it does this test (yes might drop the solar production for that time, but hey birds or clouds pass by too).. and it could say hey " the panels can produce 190 Watts right now, you are using 70, there are 120Watts not being used". Once this is done then we could trigger relays to use the power or better yet have a charge controller that is capable of power limiting this extra power to another set of contacts.

In my small system there is not really a lot to gain in terms of real power but if I had a couple of Kwatts on my roof I would like to use it efficiently.

Does something like this exist but I just have not found it?

Thanks in advance

Matt

I hear what your saying and it got me thinking of why when I turn my water faucet on, I don’t drink all the water that is coming out of it and all the water that the faucet is capable of producing. /s

When your battery is full, your panels don’t need to produce anything. Its just the way it is. Like when I’m full, I don’t need to keep filling my glass or drink the excess water. If you want to use that additional power than the simplest answer is to USE it. Buy more batteries, use more power or send it back to the grid and you will be able to take advantage of all that unused power that your so desperately looking for. If you are still perplexed with this then I’m not quite sure how to help you. It couldn’t be more automated my friend.

The device your looking for is called a battery. You pull the power you need from them and the solar controller puts what it can back into them. Once the battery is full, it will supply the extra loads any available power that they need and if nothing is needed then the SCC doesn‘t need to run. So in order to find out exactly what your panels are able to produce at the current environmental conditions, they need to be able to put ALL that power into something that can express all of the available voltage and current.

It is like your power meter on your house it cannot tell you how much power is available from the power plant it can only tell you what you are using.

RVLife, thank you for replying and yes, I understand I could add more batteries so that I never waste any solar, but at a certain point you would probably add more solar to make sure the batteries are full. Therefore, sometimes the solar will stand by waiting to recharge the batteries, all I want is the telemetry from the charge controller to know when that is and then do nothing, do something with that info....

Your drinking water could be similar, if the water only came in a few hours a day (and sometimes not that strong) you would make sure you have enough jugs (batteries) to store all the water while it runs during the day so that you could do your water routines in your house when its dark out. You probably would not store enough water to fill a pool or such, but if you knew your jugs were full and still had a few hours of water to run rather than waste it you might turn on your lawn sprinkler system during this time. In my case maybe to heat an electric hot water or whatever.

The topic of this thread is not what to do with extra power but how to measure it.

Thank you

Iabeeman I hear you and do understand that current charge controllers are like a power meter just showing you what you are drawing.

I would like to know what the solar panel array is capable of, if I read what my charge controller was providing for (the load, lets say 100Watts), then disconnected my charge controller and plugged in the solar tester to the array, it would tell me what the highest capacity the array is capable of right then and there with the current sun shining, lets say it said identifies 200Watts. I would then plug the array back into the controller and just know at that point that I was using only 50% of what was available at that moment in time.

Wouldn't you like it if there was another number on the charge controllers display that said, "maximum capacity of the array right now is X" even if you were drawing something else?

The fact that I have not found anything to do this may be because this may not even be possible, but like I said in my opening thread does something like this exist? If you search for solar dump loads you find articles where there are people trying to do similar with additional equipment.

Thanks

Matt

My Bogart TM 2030 battery monitor shows unused solar power (UPr) in watts; however, if nearly all available power is available, the monitor just says “Yes”. Not sure if this addresses your question but i just wanted to throw this out. Not sure if other battery monitors show this information. I would think they would.

I don't think there is any technical way for the solar controller to know how much power is available. There might be a way to calculate it if the solar controller knew the wattage of the panel, the voc, and isc. But that would be a pretty advanced feature, and im not sure how it might work with multiple panels.

Thinking about it, i don't think even that works. If there is no load, there will be no current, and voltage will be near voc, even in lower light. There simply isn't a way to know what is available, only what is being used.

The charge controller can only account for the power it pulls from the panels to charge your batteries and power your loads.

Maybe you could divert excess power to a micro inverter or water heater once your batteries are full. Better yet, opt for a PWM diversion controller in place of your charge controller and use a water heater as the diversion load.

If you have one of these PYRANOMETERS you can calculate the power that you should be generating with your panels. You will have to set the metering sensor on the same plane as the panels.

wholybee said:

I don't think there is any technical way for the solar controller to know how much power is available. There might be a way to calculate it if the solar controller knew the wattage of the panel, the voc, and isc. But that would be a pretty advanced feature, and im not sure how it might work with multiple panels.

Thinking about it, i don't think even that works. If there is no load, there will be no current, and voltage will be near voc, even in lower light. There simply isn't a way to know what is available, only what is being used.

Click to expand...

Again, I am not sure if this addresses your comment about there being no technical way to measure how much power is available, but I bought and have used this WS400 handheld solar panel meter referred to by the original poster of this thread (the meter recommended by Andy in the Off-Grid Garage). I simply plug in the MC4 connectors from the panels into the meter (with no connections to any battery). I have assumed that it does what it says it does (i.e., measure panel amps and volts produced by the panels). Do you think it truly measures what it says it does? Thanks for your help.

https://www.aliexpress.com/item/100...4333a264acbb02b44650b807420&afSmartRedirect=y

It basically MPPT with electronics load that can handle so much power, it takes the measurement for short period of time since the load can burn up if the load is on continuously.
You can see the active devices using as the load in Andy video.
How accurate it is, that is another story.
Features:
Auto MPPT detection: When pressing the AUTO MPPT test button, the instrument automatically adjusts the test interval time according to the current power value and refreshes the digital display. For example when the power of solar panel is 100W, refresh once every 5S, when the power is 300W, refresh once every 15S.

Bud Martin said:

It basically MPPT with electronics load that can handle so much power, it takes the measurement for short period of time since the load can burn up if the load is on continuously.
You can see the active devices using as the load in Andy video.
How accurate it is, that is another story.
Features:
Auto MPPT detection: When pressing the AUTO MPPT test button, the instrument automatically adjusts the test interval time according to the current power value and refreshes the digital display. For example when the power of solar panel is 100W, refresh once every 5S, when the power is 300W, refresh once every 15S.

Click to expand...

Bud, thanks for the explanation. My bogart TM 2030 monitor also purports to measure "unused power". Is there any doubt about whether it does what it says it does? I am trying to understand the previous comment about there being "no technical way to measure how much power is available".

You can measure the power delivery of power source by having load connected that can be adjusted so you can verify if that power source can supply the power as claimed in the published spec, then you have Volt and Amp meters to measure the Voltage and current data to calculate power.
How does Bogart make the power measures the 'Unused Power'? It must have really good size variable load that is switched in and out to accomplish that and good cooling system to keep the load cool, plus how does it know the spec and the Qty. of the panels attached to the system.
Can you provide the user manual that shows how the Unused Power is measured?
In Solar system, you do not have steady Sun radiation so power you see 30 minutes ago will not be the same as 30 minutes later, and the loads may vary to with time.. I am not sure what the Unused power data will be used for.

Bud Martin said:

You can measure the power delivery of power source by having load connected that can be adjusted so you can verify if that power source can supply the power as claimed in the published spec, then you have Volt and Amp meters to measure the Voltage and current data to calculate power.
How does Bogart make the power measures the 'Unused Power'? It must have really good size variable load that is switched in and out to accomplish that and good cooling system to keep the load cool, plus how does it know the spec and the Qty. of the panels attached to the system.
Can you provide the user manual that shows how the Unused Power is measured?
In Solar system, you do not have steady Sun radiation so power you see 30 minutes ago will not be the same as 30 minutes later, and the loads may vary to with time.. I am not sure what the Unused power data will be used for.

Click to expand...

An excerpt from the manual appears below, taken from the manual at this link. http://www.bogartengineering.com/wp-content/uploads/docs/QuickReferenceGuide.pdf

Bud Martin said:

The following three are not shown on front label. They only show when the SC-2030 charger is connected and communicating with the TM-2030, and when the sun is shining on panels.
SOL: Solar amperes: the amount of current being delivered by the solar panels from the SC-2030.
UPr: Unused solar power in watts: shows if extra power is available from the sun that could be used when battery charging is tapering down in the afternoon. Run appliances such as a dishwasher or vacuum when this extra power is available, which would otherwise be wasted. Displays “YES” when nearly all solar power is available for extra use; if a number is displayed, it shows watts available.

Interesting.
So what does it show in Watt of Unused power when loads are turned off (or not connected) on your system?

Click to expand...

As long as the monitor has power from the battery, with nothing connected to the battery except the monitor and charge controller mated to the monitor, the monitor will show unused watts or say "yes"; as described in the manual.

I agree with wholybee who said "I don't think there is any technical way for the solar controller to know how much power is available'.

I agree that it may not know how much total potential power is available without putting a load on the panels, but the CC does know when it's not using all the power available from the panels. I doubt any vendor is going to publish their MPPT algorithm but when the output of the CC needs less than its input it switches their MPPT steps. There might be valuable information within those steps to help identify possible power not being used.

From what I have observed on my system and from other threads on building dump loads, when not using the capacity of the panels (meaning real time with sun) the panel voltage rises above the working voltage. On my panels the published working voltage Vmp is 18.6 the open voltage Voc is 22.3. I find the 'working' voltage is more like 17V, but that could be for a lot of reasons (wire loss from panels with current draw, etc..)

I am attaching a graph from my system yesterday; lots are going on but what is interesting for this thread is that at about 11:30 am the panel output power starts going down (green) (this is because the batteries are getting near full and drawing less amps). The panel voltage starts to rise (yellow) and getting close to 20V, I think this is because of shifting in the internal MPPT steps.

I realized this around 12:30 and put on another load (to prove the Voc theory), the panel voltage dropped to working voltage 16-17V, the CC then put out close to 200Watts instead of ~140Watts previously. I turned off the extra load 1/2 hour later and the solar production went back to what it was doing before the extra load and the panel voltage jumped back to ~20 V (meaning it still had capacity that I was not using). The grey line is the output power of the inverter. The fact that the panels can put out more than what is being drawn is nothing new for anyone but is interesting to see some data on it.



In a prior post I said I wish that the CC vendor would provide info when the panels are not being used fully, well I guess in a roundabout way they are, if you dig into the details, you can figure it out. I will be running these graphs daily now and it should be able to tell me when a day passed where the panels were capable of more power than I used (ok.. step 1 identify that there was extra power).

Step 2- Trigger on this when power is not being used, I am not a software guy so I don't know how to use a Raspberry Pi or such to grab the data, then do some what/if's to trigger a relay, etc... I think this is much more complicated as if this was even all done and a relay was triggered for a dump load, how do you not pull down the primary load (this would need to be a current/power limited solution, and has limited devices to send power to such as a heater that can take only what you give it and make it somewhat useful, or maybe charge a second battery bank)

A request for future charge controllers is to build in a system to the CC that can simulate a load like identified earlier and from Bud Martin identified with an external meter. This would be the best as it could tell you the total power available when it runs. This might be the only way of really identifying the power available at that moment in time. It could give you the health of your solar panels, for me I would graph this over week's months and it would tell me when the panels are losing capacity, wires are broken, panels are dirty, etc...

This 'tester' would only run for seconds and therefore I don't think it needs a huge load like everyone would think, high power MOSFETs like identified in the below video are all that may be needed.
Solar Panel Multimeter WS400A - can it identify faulty and bad solar panels? - YouTube

I used to work for a networking company and when we would identify to the vendors of something we needed that was not provided, they would sometimes give us these feature requests. (Although it did take months or years), not sure if any vendors are watching these threads ;-)

Anyway, if someone know of these kinds of things being worked on / available please advise or just more discussions about this...

I am most interested in the reporting of the data for these items, not just fixing todays concerns.

Thanks

You could use a pilot panel (small wattage) to determine sun intensity. That panel must be loaded with a resistor low enough so the panel is always in Isc. That makes the voltage to current linear. Then compare that number to what the CC is using.

You have now discovered why I use panel voltage to control diversion to heat water.

Thank you for replying efficientPV.

I have thought about the use of a solar irradiance tool (with panel mounted on roof) or sacrificial panel on the roof with full load to give me what the sun was capable of doing and then comparing it to what I was generating. This would only have allowed me to 'see' a difference but not do anything about it yet. After seeing your username "efficientPV" ;-) I looked at some of your other post and it seems like you may be doing something like this already?

So what I think you may be suggesting is to install a smaller panel (ideally in the middle) of the other panels with a resistive load, build a voltage differentiator with some knobs (maybe simple voltage divider, maybe op-amp) and compare this output voltage (the delta of the test panel with my panel's voltage). The output of that could be a voltage where a low voltage may indicate none to a small difference (panels being used close to peak), a higher voltage indicates the panels are not being used as well (or reversed of course).

Ok, so next step how to use a low voltage signal to trigger a load. I saw another post where a voltage could create a PWM signal that then turns on-off MOSFETS, etc.. These pulses then could allow short bursts of current from the load side of the CC (Battery side) to a 'resistive' type load.

Is this what you are suggesting? I see a possible issue with the oscillation in the feedback, when the new load kicks in, the CC will take some time (maybe seconds) to change it steps and lower the voltage which would then change the voltage and lower the PWM on pulses and could create a cycle?

Am I on the right track?

Is there a device that is available (or part of this) that already does this? I don't think I can build a device to create PWM signals (with potential timing parameters needed) out of a voltage.

You got me thinking in a different way, thanks...

Matt