Need to reduce PV voltage

[somawheels]

I (almost) have an offgrid system setup: A genrator and inverter with batbank powers my home. It will be a while until I get solarpanels (>month)
I happen to have 2 (7 year old) 80w panels, and would like to temporarily connect them to my inverter/charger, so as to keep my batterrybank in good health.
The problem: each panel is 17.6v(Vmp), while my inverter charger has an operating range of 30-32v. Connecting these up in series gives 3.2v too much (35.2v total).
What is a good bodge, but safe way to subtract about 3.2v away from these panels?
Thanks

[sensij]

Without some kind of charge controller, the voltage will be a function of the load and unlikely to be at Vmp anyway. Even with an mppt charge controller, you could expect the voltage to move by 10% or more throughout the day as the panels heat up and cool down. It doesn't sound like you have the right combination of components for what you are trying to accomplish.

[somawheels]

Regardless of the load, these panels have the potential to produce an overvoltage, and I cant allow that as it may damage something. Could I just apply a load to the panels to reduce their voltage? like anything - a motor, heater....?

[SunEagle]

Depends on what is more important to you. If it is the inverter /charger then find new solar panels that match up to it.

If the panels are more important then get a charger and inverter that works with them.

You would be taking a chance of using any device to hopefully reduce the input voltage to the inverter. If it should fail or not work correctly you will probably toast your system.

[sensij]

Regardless of the load, these panels have the potential to produce an overvoltage, and I cant allow that as it may damage something. Could I just apply a load to the panels to reduce their voltage? like anything - a motor, heater....?

No, you misunderstand. You would need a voltage regulator to keep in the inverter charger's narrow range. What charge controller had you planned to use for the full system? It might work here too.

[Sunking]

You have to have a charge controller.

[somawheels]

I have a solar PWM charge controller built into the inverter, however, it's operating range is 30-32V, This is fine if you are buying 24v panels (which I will be), but most 12v panels add up to more than 32v when paired up. are you suggesting I use a second charge controller to feed into that charge controller? I am confused.

[Logan5]

I have a solar PWM charge controller built into the inverter, however, it's operating range is 30-32V, This is fine if you are buying 24v panels (which I will be), but most 12v panels add up to more than 32v when paired up. are you suggesting I use a second charge controller to feed into that charge controller? I am confused.

If the inverter is 24 volts, just get a good MPPT charge controller and skip the limited built in unit. If your inverter is 12 volts, just upgrade the inverter/charger unit.

[sensij]

If the operating range is only 30-32 V, it is not a solar charge controller. What is the model of the inverter charger?

Really, try to understand that a solar panel's maximum power point voltage will vary more than that in just one day. In PWM it does not routinely operate at the maximum power point, but at the battery voltage. With PWM, your upper voltage limit to worry about is the panel's Voc, and for the sake of efficiency, you want the Vmp to be slightly higher than the battery voltage.

[somawheels]

It says
"system voltage: 24Vdc"
"operating voltage range: 30~32Vdc"
"Max solar voltage (VOC) 60Vdc" Should have said this earlier.
I am now unsure what "operating voltage range" means
My 2 panels have a VOC of 22.1V (x2 will be 44.2v) so Im alright there.

The manual says:


It is A cheapo Inverter/charger and solar charger all built into one unit. Some people have had bad experiences and some people have not.

[SunEagle]

It says
"system voltage: 24Vdc"
"operating voltage range: 30~32Vdc"
"Max solar voltage (VOC) 60Vdc" Should have said this earlier.
I am now unsure what "operating range" means
My 2 panels have a VOC of 22.1V (x2 will be 44.2v) so Im alright there.

Even if you through in a cold temp multiplier that will raise the panel VOC a little you should be ok with the charge controller having a 60VDC as the max input voltage.

[sensij]

As long as you are within the voc limit, it will operate at the voltage it needs. The further Vmp gets from the operating voltage, the bigger the hit to efficiency, but it now sounds like you can use your panels in series just fine.

[somawheels]

Great, ThankYou. Can anyone else confirm this to be true?