What happens to unused energy?

[Thisguy585]

I have a self built solar array hooked to life ol batteries and don’t use it(for loss of power/emergency back up) what happens to the energy it creates if not in use? I have a victron mppt if that makes a difference. Should I disconnect if not in use? Thank you

 

[Ampster]

I don't think they actually convert energy from the sun to current unless there is a load. Disconnection would depend more on how you want to maintain your batteries.

 

[Bluedog225]

I thinks it’s a little waste heat. As I recall, the batteries like to be stored in human comfortable temps and somewhere between 40-90%. Technically probably a good idea to store not hooked up.

Others will have more specifics on the details.

 

[RCinFLA]

All PV generated power must be immediately consumed or stored in a battery.

When load on charge controller is less than potential PV array power the charge controller will back down the power taken from panels by allowing panel voltage to rise in the direction of Voc. When at Voc, there is zero power taken from PV panels.

As PV voltage is allowed to rise above Vmp, more and more of the illumination generated current is shunted across PV cells' inherent diode. The closer the panel voltage gets to Voc, the less the extracted PV array current to charge controller. PV power is consumed as a small amount of extra heating of panels.

Because PV panels are approximately 20% max efficient for electrical conversion, at full re-absorption (Voc) there is about 20% more heating of panels. This is not damaging to panels and does on increase panel temperature very much over what it normally gets to from sun heating.

For reference, Vmp is normally about 81% to 85% of Voc for silicon PV panels. At low illumination levels, shunt resistance of PV cells starts to consume a greater amount of any illumination generated current.

 

[Mattb4]

I have a self built solar array hooked to life ol batteries and don’t use it(for loss of power/emergency back up) what happens to the energy it creates if not in use? I have a victron mppt if that makes a difference. Should I disconnect if not in use? Thank you

When not in use your solar panels create power to run things in the Spiritual Plane.

Kidding aside no power is created until you put a load on the panels.

 

[wattmatters]

what happens to the energy it creates if not in use?

It's not created in the first place.

Think about a wall power outlet. How much energy is it supplying with nothing plugged in and turned on?

You PV system is the same. With nothing to send power to, it doesn't supply any.

 

[zanydroid]

You can also think of the PV as "heat sinking" the solar panel by pulling some of the incoming solar energy out to do something useful as electricity.

If you don't have the PV cell hooked up, the solar panel will heat up same as any other dumb glass brick on your roof.

You might consider disabling RSD for a roof install or turning the disconnect when not in use for a long time, just as a risk management measure. Why energize stuff (with the attendant risk) when there's no value being provided.

 

[Thisguy585]

Thank you all for the reply very very helpful! I do have it hooked up to a battery bank. Will it damage the batteries or will the Mppt handle that as in not charging it if already full

 

[Quattrohead]

Think of it as a bottle of water or preferably a bottle of beer, if you don't take the cap off and use it it ain't harming the bottle.

 

[zanydroid]

Damage batteries? Probably not. Two damage modes I can think of:

• SCC battery settings wrong, and it doesn't stop correctly. This would be a problem even if you are actively using the system
• Lithium batteries don't like long term storage at 100%, they prefer like 60%? Unfortunately this is fundamentally awkward for the backup use case. You would either have to have a system that will charge before a potential outage. Or take the extra wear on the batteries from 100% storage. Or have 2x the batteries and now you can park the 2x more batteries at 50% each. Note that 2x the batteries could well be less rational than taking the extra wear, from a cost-effectiveness perspective.

 

[nc73]

Nothing is the answer

 

[svetz]

Solar radiation that isn't transformed into electricity usually becomes heat.

 

[timselectric]

It bounces back to the sun. And creates global warming.
So stop punishing the rest of us. And find some way to use it all. lol

 

[Thisguy585]

Lol thanks all very helpful and greatly appreciated!

 

[wattmatters]

Will it damage the batteries or will the Mppt handle that as in not charging it if already full

Provided the MPPT charge controller settings are correct, it will not damage the battery. It will simply cease charging and move to a float level voltage. If the battery is not going to be cycled much and is expected to sit there for long periods, you might consider using a low-ish float voltage setting or switching off the charge controller from time to time as it's probably better for battery health to not sit at full charge all the time. A LiFePO4 battery will not lose charge very quickly if left disconnected.

Secondly, the battery should have a BMS which acts as an extra line of defence to disconnect the battery from the circuit should something go wrong with the charge controller and it tried to overcharge the battery.