Parallel Solar Panels With Different Voltages

[PancakeBill]

I have two 250 watt panels mounted on the roof. 33v each. In par the panels capable of providing 500 watts at the 33 volts. But, I have a 200 watt folding panel that is at 23 volts. If the folding and the roof are all connected in parallel, I see that as 700 watts. These feed into a Bluetti Power Station. However what will the voltage show me? Resistors in par will give average resistance, but voltage? fuzzy on that one, and will it make a difference to the charging system?

current is on 250 8.27. on 200 9.92

 

[PancakeBill]

Finally found a good source.

Voltage is limited by lowest in circuit. So my 2 at 33v and 1 at 23 volts will be 23 volts.

The amps will add so 9.92 + 8.27 + 8.27 = 26.46 amps total

amps 26.46 * volts 23 = 608 .58 watts

Now all these numbers are on the optimal side YMMV

Is my logic correct?

 

[Primerump]

yes, basically in a nutshell..
when paralleling dissimilar panels, the voltage will be of the lowest panel and the currents will sum, generally the max wattage will be the combined current times the lowest voltage.
when you series them, the voltages add but the current will be of the lowest panel.
your good source was already here.. lol. just pm me.

 

[PancakeBill]

Here is a question, looking around I see solar disconnect switches, at what point are these needed, or just disconnecting sufficient?

I am curious what panels are producing when the controller is no longer accepting power. Just a curiosity thing. Seeing a number of inline indicators, but not sure if that does what I want, labelled source and load, if there is no load will it still show, or is it more like a shunt?

 

[Primerump]

Here is a question, looking around I see solar disconnect switches, at what point are these needed, or just disconnecting sufficient?

a solar disconnect is usually required by NEC code for residential systems to disconnect the array for safety reasons ( ie: a 500V array not electrocuting fire fighters etc.. ). for an RV where there are no codes to speak of, it's a good addition to isolate the array when working on the system. the lower voltage is usually not considered an issue unless you have series panels that exceed 50V. I always mandate one, it's so much more convinient and a simple way to isolate the array. disconnects MUST be rated for 1.25 times the working voltage and be DC rated. an AC residential breaker will not do, period..

I am curious what panels are producing when the controller is no longer accepting power. Just a curiosity thing. Seeing a number of inline indicators, but not sure if that does what I want, labelled source and load, if there is no load will it still show, or is it more like a shunt?

Panels are a current source, power only flows when there is a current sink, ie: a controller/battery load.
when your batteries approach 100%, the panel current will decrease and the voltage will increase. when no current is drawn the voltage will reach the Voc ( open circuit voltage ).

 

[Lou Schneider]

I'd get a separate MPPT controller for the folding panel and combine it's output with the main system. This will give you full output from all of the panels.

 

[PancakeBill]

I'd get a separate MPPT controller for the folding panel and combine it's output with the main system. This will give you full output from all of the panels.

Not sure what that would do? Right now it is feeding into the power station. Not into batteries.

 

[Lou Schneider]

Not sure what that would do? Right now it is feeding into the power station. Not into batteries.

You didn't say that - just that you wanted to put it in parallel with the roof panels.

 

[PancakeBill]

Have had a chance to experiment. I have discovered the 2 250 watt panels rated at 32 volts and 7.78 amps are under performing. I am getting the 32 volts but clamp meter telling me only about 4 amps, and when you do the math, the charging power shown on panel f power station matches. I am getting the 32, just a bit anemic in the current from stated.


However, I ran my PS down to about 4% overnight and when the overcast came about 3PM I was almost back to 90%. So I guess it will be OK

 

[John From Detroit]

he amps will add so 9.92 + 8.27 + 8.27 = 26.46 amps total

amps 26.46 * volts 23 = 608 .58 watts

Now all these numbers are on the optimal side YMMV

Optimal side.... I think they rate these based on the assumption you are in orbit around Mercury.. but yes. (And yes I'm joking... slightly)

 

[Lou Schneider]

Have had a chance to experiment. I have discovered the 2 250 watt panels rated at 32 volts and 7.78 amps are under performing. I am getting the 32 volts but clamp meter telling me only about 4 amps, and when you do the math, the charging power shown on panel f power station matches. I am getting the 32, just a bit anemic in the current from stated.


However, I ran my PS down to about 4% overnight and when the overcast came about 3PM I was almost back to 90%. So I guess it will be OK

Solar panels only produce their full rated power under ideal conditions - a sunny, intense clear desert day at high noon with the panels pointed directly at the sun. 4 amps from the panels sounds about right for an average day especially if the panels are flat so the sun is hitting them at an angle.