# What equipment needed for solar panels on FX 24v inverter

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Re: What equipment needed for solar panels on FX 24v inverter

Should be fine.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

This is what my MPPT 60 says at 11 am.
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

So i just got a message from Serge at Rolls Surette and i asked what i should be charging my 8 rolls S600 batteries and i told him my Outback inverter only shows 14 amps as the maximum charge and he said that my batteries should be charging at 25-28 amps.
Would i need to get another inverter?
right now im running my generator from 8 am till noon then 6pm to 10 pm to keep charging my batteries.
Re: What equipment needed for solar panels on FX 24v inverter

Assuming your array is in full sun, nice cool day, etc... It is outputting roughly 2/3'rds the energy I would expect (assuming 9x 100 watt panels):
• 900 watts * 0.77 derating * 1/14 volts = 49.5 amps
• 900 watts * 0.77 derating = 693 watts typical maximum
Try disconnecting one string at a time and see what the output energy is. Perhaps you have a "dead string" or, perhaps, it is the best they can do...

Look at the Watts, Vmp, and Imp as determined by the controller (make sure the controller has stabilized--I think the Morningstar is faster, some older controllers could take 5-15 minutes to re-measure Vmp/Imp/Pmp).

If your weather is hot and it is hazy--then this may be an appropriate output.

You can also measure the sort circuit current on each string... The output current is most proportional to the amount of energy hitting the panels (current is only slightly temperature dependent). If the strings don't agree--you may have a bad panel somewhere.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

But do i need to program the Mppt controller? i never have done anything to it. i just plugged in the wires.
Re: What equipment needed for solar panels on FX 24v inverter

The target voltage still is >31 volts... Perhaps, the batteries have never reached that yet (equalization) so it will attempt that until the batteries actually get that high.

I don't think there is anything to program just yet... The spread between target and actual battery voltage should indicate that the controller is in MPPT mode and maximizing current (energy) into the battery bank.

It is going to take quite a bit of Amp*Hours to get your battery into the 29+ volt range--perhaps several days and not a lot of DC loads at night.

You can measure the resting voltage of the battery bank and estimate the state of charge (very roughly at ~77F, 12.6/25.2 20% or less charge; ~12.7-12.8/25.4-225.6 volts 100% charged) and estimate how many amp*hours are currently in your battery bank...

For example, 12.06 volts / 24.12 volts resting would be ~50% charged... Assuming you have 24 volts at 900 AH, 50% of that would be ~450 AH or 29v*450AH= 13,050 watt*hours.

Roughly:
• 13,500 WH / 500 watts = 26.1 hours to get to around 90% state of charge...
The last 10% is going to take probably around another 5-10 hours.

Assuming 5 hours of full sun equivalent per day right now--you are looking at 36/5 hours of sun = 6 days of charging (and no loads) just with your current solar setup...

You really do need more panels for the 900 AH / 24 volt battery bank... Do I have your bank size correct?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

should i change the equalization on the inverter from 31 to 33 and run the generator longer?
Re: What equipment needed for solar panels on FX 24v inverter

Sorry, I 1/2 posted and then did some extensive editing--so my previous post probably looks different than when you posted...

At this point, setting the Solar Charge Controller to anything over 29-30 volts is not going to do anything until the battery hits the target voltage--At that point, the charge controller will taper back on current as the battery accepts less and less current (at that 29.x fixed voltage).

If you have a genset and AC charger--You can perhaps get the total current up that you could bring the battery bank up to 30+ volts.

At that point, either the solar charge controller will stop increasing the voltage and taper the current flow--And/or the AC battery charger will hit its programmed point and start tapering back on charging current.

And, it really does not matter which controller tapers back. If the solar charger cuts back (falls out of MPPT mode as output current requirements fall)...

Or the AC charger cuts back... And if you AC generator is at 50% or less load, the reduced output current/power of the battery charger will not really lessen fuel flow all that much on the genset (below 50%, most generators have pretty much 50% fuel flow--Diesels, may have less, but they should not be operated for long periods below 50% or they coke up; and there are the Honda/Yamaha inverter gensets which can reduce engine RPM and conserve some fuel at lower output power levels)...

In the end, the typical "optimum" use of fuel is to recharge the battery bank to 80-90% state of charge in the early morning (turn of genset as setpoint voltage is reached, and the charger is starting to reduce output current) and then let the solar charge controller finish up the charging.

This can reduce fuel usage and generator run-time (maintenance costs).

But--With batteries, their health is paramount... Whatever it takes to keep them above 20% state of charge (below that, you can instantly kill your batteries), avoid 50% or deeper discharge--longer cycling life, and avoid long periods of times below 75% state of charge for days/weeks/months to limit sulphation.

I try to avoid running a 6-12kW genset with a few hundred or 1kW of loading... If you have a large genset and a small AC charger--possibly getting a larger AC charger or using a smaller/more fuel efficient genset (like a Honda eu2000i, or eu1000i) to bump up the genset at 1/4 the fuel flow may be the better answer.

All depends on bank size, your usage patterns, fuel availability (if off-grid), etc.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Re: What equipment needed for solar panels on FX 24v inverter

What is it set for now? If you monitor the current, bank state of charge, you can probably charge C/10 or C/8 (10-13% of AH capacity) pretty safely.

Once your batteries approach 100% charge, I believe Rolls/Surrette recommend a 5% rate of charge for equalization...

Personally, I would watch the bank voltage and charging current... And set the absorb voltage at which your bank reaches ~90-100% state of charge and 5% rate of charge (say a full bank takes 5% current at 30.10 volts)--That is probably what I would set the inverter too... And at that point, you would turn off the genset (if you are looking to reach near 100% state of charge quickly with the genset).

Of course, you can always monitor the bank (using the, example, 30.10 volts for 5% rate of charge) and figure out when the battery is 80-90% full, and let the solar panels take the rest of the charging.

At some point, assuming I have the battery bank capacity correct--you are going to have to make the decision on more solar panels or more genset runtime... No right or wrong answer--unless you let the battery bank "deficit" charge (never get back to 90%+ state of charge a couple times a week due to not enough solar panel/genset runtime).

Sorry to be so wordy...:roll:

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

I tested all of the photowatts and i get 38 v VOC on each one of them . so it may be the best i can get with them. My other question , Could i connect the astros even though im only getting 17.8 volts VOC on each of them to a Morningstar Prostar -30?
Re: What equipment needed for solar panels on FX 24v inverter

Vmp= 16.9 volts is a bit low for the Astro's on 12/24 volt batteries on hot days--but they will work.

You can put two in parallel for ~34 volts and connect the balance in parallel (2/4/6/etc. panel array) behind a PWM or MPPT controller and connect that controller to the battery bank. It is perfectly OK to put several charge controllers in parallel on a battery bank.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

So you mean connect the Astros in parallel in 2/4 or 6? also they should be fine connecting them to The prostar -30?right now i have 2 astros parallel and im getting 19.2 dc volts from the back of the 2 panels.
Re: What equipment needed for solar panels on FX 24v inverter

Yes... 2 in series, then connect them in parallel (up to the current rating of the controller).

Depending on how well they work--It does matter if you are asking about Voc and Vmp... Voc open circuit is the maximum voltage of the panel with no current flowing (not very useful).

Vmp maximum power is with current flowing.

Voc of 19.2 volts seems a bit low for charging a 12 volt battery bank (or two panels in series for a 24 volt battery bank). As the panels heat up, Vmp/Voc falls, plus you have the voltage drop of the wiring and charge controller. So--it is possible that you will not get Imp in full sun on a hot day. So you will have to monitor the setup and see that they are working well enough for you.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

so i sjut rewired the astros and the photowatts and the array current went up and the voltage went down. so now i have 6 astros and 9 photowatts connected in series /parralell.
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Re: What equipment needed for solar panels on FX 24v inverter

hey BB, this is what im gettig today as soon as unplugged the astros and i just have the photowatts in 3x3x3 series parallel. And this is at 10 am eastern with clear skies temperature of 80.
Re: What equipment needed for solar panels on FX 24v inverter

If I remember your system correctly, 1,000 watts and Vmp ~34.4 volts is very close to what you are getting today from 10 panels in 2 series x 5 parallel for the Photowatts...

I am not sure of the panel wiring?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

i have 3x3 in series then parallel. Im only using 9 photowatts.
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

Hey guys , so i finally upgraded to the 48 v outback inverter. My other question is could chaining the Solar bypass Diodes on some of the panels make them better? also right now I'm have the panels hooked 3x3 series parallel. should i have to change the configuration if i changed my inverter from 24v to 48 v?
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Re: What equipment needed for solar panels on FX 24v inverter
castilloj wrote: »
Hey guys , so i finally upgraded to the 48 v outback inverter. My other question is could chaining the Solar bypass Diodes on some of the panels make them better? also right now I'm have the panels hooked 3x3 series parallel. should i have to change the configuration if i changed my inverter from 24v to 48 v?

as to the bypass diodes, unless you know they are bad leave them alone.

it depends on the vmp of your pvs. if they are 12v nominal out then you'd need 4 in series to reach 48v nominal vmp and if they are 24v nominal vmp then it takes 2 in series to make the 48v nominal vmp. i have a feeling you'll have no way to use that 9th pv without either purchasing more similar pvs.
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Re: What equipment needed for solar panels on FX 24v inverter

The vmp of the photowatt are 34.4 at 24v and 17.2 at 12 v I have them currently connected 3 sets of 3.

The Astros are open circuit voltage is 21.1v
Rated voltage is 16.9v
• Solar Expert Posts: 208
Re: What equipment needed for solar panels on FX 24v inverter

So right nowi have my photowatt panels connected at 4 sets of 2 connected series parallel.
My mppt displays my array as being-
Array voltage 66.66 v
Array cuurrent 3.3 amps
Sweep vmp 66.66v
Sweep voc 76.70v
Sweep pmax 218 watts

I also have 6 astro panels not connected.