Old situation

JOSI · August 2012

Can i take an array of (12) 190w panels in two strings of 6 which will be Vmp 220v,VOC,271,Imp10.38,Isc 11.12 and parrallel a second array of (12) 130w panels in one string of 12 which will be Vmp 212v,Voc 265v, Imp 7.63, Isc 8.37?

Customer has a sytem with 130w kyro panels that feed a charge controller into a battery bank running a DC irrigation surface mount pump. He is wanting to add a small grid tied system to his house (New array of 190w panels). What he asked is if he can use his old array to back feed to the house also when he wasnt using the irrigation pump. I cant seem to figure out how to make it work without just rewiring his old array to feed into inverter with new array and see if he will just change his Dc pump to an Ac pump. Any suggestions would be greatly appreciated. Oh and he doesnt want to buy two seperate inverters.

Photowhit · August 2012

Re: Old situation

Lots of things, Panels specs are wrong, even with assumed decimal places VMP of 22.0 and IMP of 10.38 will be close to a 230 watt panel, panel with VMp of 21.2 and IMP of 7.63 is about 160 watt panel, so this needs better info, distance between the arrays will be a factor as well.

EDIT; perhaps your talking about the combined string numbers? What is required of the inverter to back feed the grid? They will run at the lower voltage.

If the VMP is high enough for the output, the system would run at the VMP of the lower voltage, and the amperage would add. you would have to have an inverter able to handle the combined output. The client could charge the batteries from the grid for the current DC pump until they failed, and then switch to an AC pump... requiring a charger...

BB. · August 2012

Re: Old situation

JOSI wrote: »

Can i take an array of (12) 190w panels in two strings of 6 which will be Vmp 220v,VOC,271,Imp10.38,Isc 11.12 and parrallel a second array of (12) 130w panels in one string of 12 which will be Vmp 212v,Voc 265v, Imp 7.63, Isc 8.37?

Customer has a sytem with 130w kyro panels that feed a charge controller into a battery bank running a DC irrigation surface mount pump. He is wanting to add a small grid tied system to his house (New array of 190w panels). What he asked is if he can use his old array to back feed to the house also when he wasnt using the irrigation pump. I cant seem to figure out how to make it work without just rewiring his old array to feed into inverter with new array and see if he will just change his Dc pump to an Ac pump. Any suggestions would be greatly appreciated. Oh and he doesnt want to buy two seperate inverters.

First, connecting the two arrays in parallel with Vmp=220/212 volts is not a problem. They should be within 10% difference (20 volts) or less for "close to ideal" matching. (same with matching Imp. Within 10% or better).

The second array with lower Imp rating... You should check the Isc / series protection fuse requirements of the two sets of panels. You may be "forced" to put a Series protection fuse in the lower current string to prevent a short in that string from being fed by the Isc 11.12 rated array). In theory, you would need around an 11 amp (if you can find an 11 amp fuse) to 15 amp series protection fuse for the lower current array. The 11.12 amp Isc rated array should be "wired" as if it could send out 1.25x as much current or 13.9 amps.

So, in practice, a 15 amp fuse on the smaller array (if that is the series fuse rating of those panels) would not do anything helpful and should not be needed (if you do another parallel string, you will need to install a combiner box/fuses/breakers to protect each parallel string of panels).

I have a question or two for you--What voltage/AH rating is the battery bank and what solar charge controller are you using? There are probably only one or two controllers out there that can manage that high of voltage array?

And I am a bit confused about the request... Are you trying for:

A central array+charge controllers+battery bank to power everything?
A new off grid (or is this on grid/Grid Tied/Hybrid GT+Backup Off Grid power) system for the home that can draw excess power from the pump system (which has its own array+controller+battery bank+DC only loads)? Is this excess power from the solar array, or from the solar array+battery bank (for over night use)?

How far between the pump PV system and the home? How much power needed to run the home/draw from the pump PV system?

-Bill

JOSI · August 2012

Re: Old situation

His current array is 3 panels in series 52.8v and 7.39A. 4 strings in parrallel 52.8v and 29.56A Feeding an outback MX60 charge controller. The battery bank consist of 6- 6v 600ah deep cycle batteries. This is watering his small pecan orchord and has been inplace before i met him. He is wanting to add the new array and send to his house which is a fair distance apart. (That is another whole issue im working on.) He doesnt have to water the pecan trees year round and wants to use that system to offset his house also. Neither will offset much of his power as he has a 4000sq home but this is what he wants so im trying to work with him. The two arrays would be right next to each other.

BB. · August 2012

Re: Old situation

I am a little confused about the setup... It looks like a 12 volt battery bank (600 AH)? But, the array is really sized more towards using a ~83 amp MPPT charge controller--and there is only a 60 amp controller there. Some wasted mid-day power it would seem.

IF this is a DC pump currently--I guess it could be a native 18 volt or 36 system too--Which makes finding an inverter more difficult.

The home has grid power?

Does the pumping system need a battery bank or could it be transitioned to a solar panel+DC pumping system (Grundfos, etc.) for daylight only pumping?

-Bill

JOSI · August 2012

Re: Old situation

BB. wrote: »

I am a little confused about the setup... It looks like a 12 volt battery bank (600 AH)? But, the array is really sized more towards using a ~83 amp MPPT charge controller--and there is only a 60 amp controller there. Some wasted mid-day power it would seem.

IF this is a DC pump currently--I guess it could be a native 18 volt or 36 system too--Which makes finding an inverter more difficult.

The home has grid power?

Does the pumping system need a battery bank or could it be transitioned to a solar panel+DC pumping system (Grundfos, etc.) for daylight only pumping?

-Bill

Im sorry they are 400ah batteries. Wired in series foe 48vlts. The pump is a centralfugal 36volt nominal 24.2amps 1089w. I am pulling all this off the documents he gave me although i have seen the system. He doesnt want to purchase a seperate inverter and yes it is difficult to find a gridtied inverter with a 36-48volt startup.

My thinking was to just rewire the old array into a single string (12 panels in series) as first mentioned and see if he would just change the DC motor out to an AC Motor. I believe he is wanting to do the impossible. I have brought this up in a few photovoltaic courses i have taken and even to the engineer group at my distributors (they didnt want to touch it) with no avail. The home does have grid power but is about 400ft from where the arrays are. Which intels the next problem i have to deal with which is he has #4 dorect burial triplex run out there and im afraid the voltage drop will be too much. But i'll worry with that once i get the design problem figured out.

And to answer the last question is yes it needs a battery bank because he waters at night.

BB. · August 2012

Re: Old situation

If this is a 48 volt battery bank, then Vmp~52.8 volts is not good... You should have Vmp>=~72 volts minimum for proper/full charging and equalizing on a 48 volt battery bank.

But if you have 6x6 volt batteries--that would be a 36 volt battery bank????

Regarding the pump--Is this a DC to 3 phase inverter / VFD type system? Or is this a "brushed" DC motor?

If brushed, usually brush changes and turning down the commutator/wear and tear on this types of motors is a real pain--Conversion to AC (perhaps a 3 phase motor with VFD) would be an option...????

-Bill

Photowhit · August 2012

Re: Old situation

BB. wrote: »

But if you have 6x6 volt batteries--that would be a 36 volt battery bank????

I bet you got it! The MX60 will charge a 36V bank, had to find one for a guy wanting to charge a golfcart.

JOSI · August 2012

Re: Old situation

BB. wrote: »

But if you have 6x6 volt batteries--that would be a 36 volt battery bank????

Yes sorry 36volt batttery bank.

Pump Is a SunCentric Solar Centrifugal High Volume Surface Pump.

BB. · August 2012

Re: Old situation

Boy--that is a tough mix of "non-standard" battery bank voltage (for solar) and pumping system (it appears these are brushed motors with a maximum of 12,000 operating hours between brush changes).

I don't see any easy way of sharing power from the existing system unless something "major" is done.

Change pump to 48 or 24 volt model... Use a controller to down converter 36 volt battery bank to a second 24 volt battery bank--then run a standard 24 volt inverter from there to the home (you might be able to get an Exeltech semi-custom inverter for 36 volt operation--that would probably be the best bang for the buck, if possible).

I would suggest using PV Watts and estimating the amount of "off season" power available from the pumping station. Say they only pump 6 months of the year--How much energy will be available during off peak season (assuming ~0.52 end to end derating; from panel to AC available kWH per day/month/season). And compare that with system costs. If the region has "poor sun" in the winter (and/or local shading of the solar array), then $$/kWH cost (spread over 10 years for inverter, 5-8 year for secondary battery bank--if needed, etc.), may make the power costs simply too expensive to add to the home.

Another possibility--Could they run a pipe from the orchard pump to the home/cistern? Perhaps using the pump more would be a good trade-off in costs (although, brushed pump, so running pump more adds significant wear and tear to the motor).

-Bill

Old situation

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