What happens to excess power produced by panels after batteries are full?

[Spoonathan]

Hi there. Super noob here. I just got my first solar system set up and I had a question about where my excess power is going. I looked around the forum and couldn’t find exactly what I was looking for so if anyone could answer my question in layman's terms I would be very grateful.

My panels were producing about 1000w and they charged my battery bank to full in no time at all. When my batteries reached full, my BMS enabled over-voltage protection and disabled them from being charged any further. So far so good? Anyway, I’m now left with my panels still producing 1000w of power and it has nowhere to go. The bms won’t allow it into my battery bank, so does that mean it’s all getting pumped directly into my SCC? If so, is that going to somehow damage my SCC? Is it getting burned off as heat?

I just can’t quite wrap my head around this. Any insight would be greatly appreciated. Thanks!

 

[bones1]

It just opens the circuit like unhooking a wire off of a battery. The voltage is still there but not used.

 

[rmaddy]

Power is pulled by things that need it, not pushed by things that provide it. Your solar panels are not pushing 1000W into the SCC when unneeded. The SCC stops taking power from the panels no matter how much sun there is.

It's like all of the outlets in your house. Electricity isn't being pushed out of unused outlets.

Nothing is being damaged in any way if you are not making use of any potential solar power.

When my batteries reached full, my BMS enabled over-voltage protection and disabled them from being charged any further.

I hope this isn't the case. Your charger should be setup correctly so it does not cause an over-voltage of your batteries. If your BMS really is shutting down then you have a problem that must be fixed. A BMS is only meant to be a last line of defense when all else has gone wrong. It is not meant to be the normal path. A properly setup SCC will not cause a BMS shutdown.

 

[Bud Martin]

What kind of SCC do you have? Make and Model? Settings parameter?
The BMS should not have gone into shutdown if you set the charge Voltage properly, some SCC do not like to have have the panels still connected bu the batteries are disconnected which can damage the SCC.

 

[mikefitz]

Your battery BMS shouldn't be used to control charging, the solar chargers should be set up to determine battery charging and terminate the charging process.
The solar regulators automatically determine what power is needed to charge the battery. When the predetermined voltages and or charge current that determines a full battery is reached, the controller shuts off power from the panels.

Mike

 

[frd]

I am also a bit puzzeled about this question now, that I have been reading Wikipedia about MPPT. In german wikipedia it states:

In practice, the optimal operating point is set and continuously tracked by an electronic circuit, the MPP tracking - in principle a DC/DC converter specially optimized for this task. This is connected on its input side to the solar cell, which is always operated with power adjustment by the MPP tracking algorithm in the event of varying internal resistance. On the output side, this maximum gained power has to be taken off; usually a battery is charged, whose voltage changes only slowly, but whose charging current varies according to the delivered power. A direct supply to a consumer is only possible if this consumer can take the entire power currently generated. At the inverter, it must always be possible to deliver the entire power to a grid. The connection of only one consumer (stand-alone grid) is not possible without a battery buffer. In solar inverters, the MPP tracking and inverter functions are combined in one device.

Translated with www.DeepL.com/Translator (free version)

Maximum Power Point Tracking – Wikipedia

de.wikipedia.org

From my understandig, it should be possible that the output power is reduced to the needs of the consumer, when cell voltage raises over the max.Power Point even up to zero. Altough Wikipedia says this is not possible this makes me confused at the moment.

 

[RCinFLA]

A PV cell is a diode clamped illumination based current source. Illumination current is either shunted down the cell's inherent diode, if no external load, or delivered to external load if load is such that the cell's voltage is kept at higher end of cell's inherent diode conduction voltage, which for silicon is about half a volt. A panel stacks a number of PV cells in series to get greater voltage.

Voc is unloaded panel voltage where all the illumination current is shunted down the cell's inherent diode. Vmp is the point of maximized cell diode voltage times externally extracted load current allowing just a slight amount (about 5%) of inherent cell current shunting. You want to maximize cell voltage without allowing too much inherent diode shunt current waste to extract maximum power from cell.

The silicon PV cell's inherent diode voltage is a function of temperature, getting lower when hot, and greater when cold. This causes Voc and Vmp to change with panel temperature.

The question that usually follows is does this damage PV panel. Answer is not to any significant degree. PV panels are in the ballpark of 20% efficient in deliverable electric power. At most, no panel loading causes about 20% more heating power to be consumed by cells. This is not a significant additional amount of panel heating.

 

[12VoltInstalls]

should be possible that the output power is reduced to the needs of the consumer

The inverter does that. Some are meant for that. The higher end stuff can enable that, and even my inexpensive 1012LV-MK can use ‘solar first.’

A battery-less system, however, would be a total exit gland suffering experience, a hemorrhoid needing surgery imho.
The battery system buffers output for passing clouds or low light conditions instead of dropping out and being a bum on the street.

 

[Zil]

Ask a specific question that you have.

 

[Spoonathan]

What kind of SCC do you have? Make and Model? Settings parameter?
The BMS should not have gone into shutdown if you set the charge Voltage properly, some SCC do not like to have have the panels still connected bu the batteries are disconnected which can damage the SCC.

Thanks for your reply. I have the Renogy Rover 40a MPPT. I am not really sure what optimal settings should be for charging a 24v lithium system. Could you give me some advice on what a good cutoff voltage would be as well as optimal charging voltage?

 

[Bud Martin]

I have to download the user manual to see what kind of settings parameters can be done with your SCC.
What are your settings right now?

 

[Spoonathan]

I have only changed the voltage to 24v and the battery type to lithium. I haven’t changed anything else

 

[12VoltInstalls]

What are your settings right now?

I haven’t changed anything else

List the parameters