System expansion, long runs, options

hemmjo · August 2014

I work with a mission in the Dominican Republic, many of you have helped me get our well and staff housing systems up and running. Both (separate systems) are working fine.

The staff housing system consists of 4 - 275 watt 36 volt panels wired in 2 - 72 volt strings, Midnite classic controller, 4 - interstate GC batteries in 12 volt strings, and a Kasie 1000w 12 volt inverter.

We have now expanded a little and have a small home for a caretaker family and a group kitchen/dining building. The original plan was to have a system on each building, BUT I am thinking it would be less costly, less maintenance and more effective to expand one system to deliver power to the other buildings.

I am thinking of upgrading the staff building with 4 additional panels in to make 2- 144 volt strings, upgrade to a 24 or 48 volt 2k inverter, and a new 24 or 48 volt battery bank, then move 2 of the existing batteries to each other building. Run 120 volt lines under ground 215 feet to the kitchen to charge the bank for the relocated inverter. Then extend the 120 volt lines another 135 feet from the kitchen to the house to charge the batteries for another inverter. The remote batteries and inverter at each location would provide 12v power for LED lighting and handle surges to minimize the need for large underground conduit and wires.

Things that affect this decision are;

We already own 2 of the inverters, 1 iota 15 amp charger, the batteries would move from staff housing when that is upgraded with new batteries.
I can run #6 wire which will carry 8 amps with about 2% voltage drop for less than just a charge controller.
If I put complete systems in each building I need so much additional equipment and it is much more for people to monitor.
The staff house was designed(roof slope and orientation) for solar panel installation equipment location and battery bank storage.
The other buildings are not oriented as well for sun and there is no good place for a lot of equipment, etc

The new buildings would have minimal electric needs, some LED lighting and small blender for the kitchen. The home needs LED lighting and small TV etc for the home. We are investigating propane refrigeration for the new home.But it may get a small electric refrigerator. The current 1000w inverter which would be moved to this home is running the staff refrigerator just fine.

I have not yet run all the numbers, just looking for comments on the concept for now.

Thank You,

John
http://villagemountainmission.org/

Cariboocoot · August 2014

Re: System expansion, long runs, options

Long runs are overcome by higher Voltage and/or thicker wire. Usually some combination of the two.

If you use high Voltage arrays to charge batteries the charge controller loses efficiency in down-converting. As it is your 72 Volt array would be good for a 48 Volt system but doubling it to 144 Volts is awfully close to the input max on most controllers, even in your hot climate. I wouldn't add more panels in series; put the new strings in parallel.

Running 120 VAC to be reduced to charge batteries then reconverted up to 120 VAC again doesn't make much sense. I would just make it a 120 VAC run from the central power station to begin with. Even if you have to add a second inverter there to accommodate the extra power demand.

Upgrading the one system to 24 or 48 Volts would be a good idea if the majority of loads are 120 VAC. In general 12 VDC loads should be avoided. If they are still necessary consider supplying them with a power supply or converter (if close to the batteries).

First thing you'll have to do is determine just how much additional power is needed.

BB. · August 2014

Re: System expansion, long runs, options

If you want to look at sending the Array power a longer distance... As Marc says, Vmp-array much over ~100 VDC will over volt on cold days (not that you get "cold" days in the DR). You do have options for higher voltage charge controllers:

http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco.html

Midnite Solar "Classic" MPPT Solar Charge Controllers - Basic Specifications

Model
Classic 150
Classic 200
Classic 250
Classic 250KS

Max Input Voltage
150 Volts DC
200 Volts DC
250 Volts DC
250 Volts DC

Max HyperVOC
150 VDC + Battery Volts
200 VDC + Battery Volts
250 VDC + Battery Volts
250 VDC + Battery Volts

Battery Voltage Range
12 to 93 Volts DC
12 to 93 Volts DC
12 to 93 Volts DC
12 to 150 Volts DC

Max Output Current
96 Amps
79 Amps
63 Amps
40 Amps

See the Solar Classic data sheet for complete specifications

and true 600 volt (Vmp-array ~ 400 volts maximum +/-):

Morningstar TriStar 600 Volt 60 Amp MPPT Solar Charge Controller (around $1,300 minimum)
Conext XW MPPT 80 Amp 600VDC Solar Charge Controller (around $1,150 minimum)

The Midnite higher voltage controllers have lower rated output current... And the 600 VDC input MPPT controllers are about 2x the cost vs the 150 VDC maximum input controllers... Choices.

-Bill

zoneblue · August 2014

Re: System expansion, long runs, options

Agreed. 72Vmp, batt and inverters near array, run AC to the outbuildings. 200ft is fine, might need to bump up a wire guage is all.

mike95490 · August 2014

Re: System expansion, long runs, options

We are investigating propane refrigeration for the new home. But it may get a small electric refrigerator.

Make that decision BEFORE you upgrade the system, or you will have to upgrade AGAIN to add capacity for a fridge. I think it was calculated out, that if you plan on using a fridge more than 9 months a year, solar is less expensive than propane tanks forever.

hemmjo · August 2014

Re: System expansion, long runs, options

Thanks for the input guys. After pricing propane equipment, we are going with electric refrigeration. So I will be running upgrading the existing system to provide all of the collection, storage and inverted power requirements. Investigating those anticipated loads now. The current battery bank is typically at 77-82% SOC in the mornings before the sun comes up. Staff has been instructed to charge phones and computers in the morning when the sun is up and NOT to run the washing machine after noon to allow the batteries to be at full charge when the sun goes down. BUT, this does not always happen....

From the classic specifications, the max voltage is 150VDC, the HYPERmax is 150+battery which will be either 24 or 48. Can someone help me further understand why it would be a bad idea to put the additional panels in series with the existing for 108 or 144 VDC input voltage. Depending on the final load figures either 2 or 4 additional panels will be added. IT NEVER gets below 50f especially if the SUN is shining!! This would allow me to use the same wiring into the combiner, the same breakers and wiring into the Classic charge controller?

Next question is in regard to choosing an inverter. The KISAE 1000W 12 volt inverter is taking care of the basic needs for the existing staff housing. The current battery bank is typically at 77-82% SOC in the mornings before the sun comes up. The surge limit warning beeps when everyone has their computers plugged in, the washing machine (it is TINY... pulls 200 watts max in operation) is running and the refrigerator kicks on. The 'fridge only pulls 63 watts in operation as measured with a kill-o-watt meter. I know the surge is a lot more. I know, I should have exact loads but they are not available right now. I anticipate the load will double when the final figures are compiled.

Given the fact that the current inverter is at its limit, I am thinking a 3k-4k will be in the range necessary. As mentioned earlier I would like the batteries to be configured in a 24 or preferred 48 volt bank to eliminate parallel connections.

Thanks again,
John
http://villagemountainmission.org/

Cariboocoot · August 2014

Re: System expansion, long runs, options

hemmjo wrote: »

From the classic specifications, the max voltage is 150VDC, the HYPERmax is 150+battery which will be either 24 or 48. Can someone help me further understand why it would be a bad idea to put the additional panels in series with the existing for 108 or 144 VDC input voltage. Depending on the final load figures either 2 or 4 additional panels will be added. IT NEVER gets below 50f especially if the SUN is shining!! This would allow me to use the same wiring into the combiner, the same breakers and wiring into the Classic charge controller?

The HyperVoc function is to prevent the charge controller from burning up if the Voc input exceeds the operational maximum. This is usually caused by cold temps raising the panel Voltage. Up here we can see a 30% increase in Voc, no problem. You probably won't see that down there.

But the higher the array Vmp is in relation to system Voltage the lower the charge controller efficiency. That is the more important consideration here I think. You could lose 7% of your power just from running higher input Voltage, with no potential gain.

Next question is in regard to choosing an inverter. The KISAE 1000W 12 volt inverter is taking care of the basic needs for the existing staff housing. The current battery bank is typically at 77-82% SOC in the mornings before the sun comes up. The surge limit warning beeps when everyone has their computers plugged in, the washing machine (it is TINY... pulls 200 watts max in operation) is running and the refrigerator kicks on. The 'fridge only pulls 63 watts in operation as measured with a kill-o-watt meter. I know the surge is a lot more. I know, I should have exact loads but they are not available right now. I anticipate the load will double when the final figures are compiled.

Given the fact that the current inverter is at its limit, I am thinking a 3k-4k will be in the range necessary. As mentioned earlier I would like the batteries to be configured in a 24 or preferred 48 volt bank to eliminate parallel connections.

Thanks again,
John
http://villagemountainmission.org/

I think you would indeed be better served by a 24 or 48 Volt system. Exactly which will depend on two factors: total Watts needed at any given time and total Watt hours needed for the day. Remember if you give them X Watts they will demand 2X Watts.

vtmaps · August 2014

Re: System expansion, long runs, options

hemmjo wrote: »

Can someone help me further understand why it would be a bad idea to put the additional panels in series with the existing for 108 or 144 VDC input voltage.

The reason is that the controller becomes less efficient as the input voltage increases. Less efficiency means the Classic runs hotter and can handle less current.

--vtMaps

westbranch · August 2014

Re: System expansion, long runs, options

If the original system is supplying enough power and is at ~ 20 - 25% DoD daily you are right in the sweetspot for your batteries, at this time... so you need to add up the additional power uses and that will tell you how much more battery you will need... more simply doubling your system will allow you to power twice what you do now, and never have to worry about those darn cell phone chargers or the washer

Since all your power was well handled at 12 V I am thinking that 24 V would work well for you. Your choices of inverters will be much less at 24 or 48V.

PS could you please add a signature line with a description of the original system for reference.

thanks

System expansion, long runs, options

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