Seeking Recommendations for an Off-Grid System

Sunny-HTI · May 2014

Thank you for all the help you provide in this forum. I posted once before regarding this subject, and have done some more research since regarding my load and location.

I am seeking help configuring an off-grid system for a location in Haiti with no grid access. I currently own 4 Sunpower 225 watt Panels (Model SPR-225NE-BLK-D) with the possibility of getting two more.

• Specs: Power 225 W- Vmpp 40.5 V - Impp 5.55 V - Voc 48.0 V - Isc 5.93 A - Rated Series fuse 20

• Daily Load: About 1800 Watt*Hours
Refrigerator 810 Watt* Hours - 24/7
Lighting 140 Watt* Hours - Nighttime
Fan 200 Watt* Hours - Most night
TV 200 Watt* Hours - Mostly Nighttime
Phone + Laptop 350 Watt* Hours - Mostly Daytime
Misc 100 Watt* Hours - Daytime

• Isolation: 6 hour average with panel facing directly South ~ 72° angle from March thru September - 57° angle from Oct thru February .

• Average daily temperature 85°

• Panels will be multi-pole mounted at about 55 ft. from charge controller.

• Available local batteries T-105 RE Deep-Cycle Flooded 20-Hr Rate 225AH

I intended to buy a MPPT Midnite Classic Controller and E-Panel.

What would be the optimal panel configuration, Battery bank ( 24 versus 48 ) , Classic Controller 200 or 250?

Thank you in advance for your help.

Harry

BB. · May 2014

Re: Seeking Recommendations for an Off-Grid System

Can you use this link to double check your solar radiation?

http://solarelectricityhandbook.com/solar-irradiance.html

6 hours of sun per day seem to be more of a peak--At least the one city I checked (Port-au-Prince). However you still have a lot of sun all year round and 5+ hours seems to be a good minimum even with a fixed mounted panel.

Battery bank size:

1,800 Watts * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt bank = 352 AH @ 24 volt battery bank
1,800 Watts * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt bank = 176 AH @ 48 volt battery bank

Hmm... You are looking at ~8x T105 6 volt @ 225 AH batteries for 450 AH @ 24 or 225 AH @ 48 volt battery bank... This bank is a bit larger than your needs. Many folks find that they use more power over time--Might be good to grow into.

If you choose a 24 volt battery bank, you can use parallel panels and grow the system one panel at a time (Vmp-panel~40 volts). If you make it a 48 volt battery bank, you will have to grow the array 2 panels at a time. May or may not be an issue for you.

Also, Vmp~40 volts is not very common. Will you be able to get more 40Vmp panels (at a good price) in the future if you want to expand the array?

I like single strings--But your bank size is OK to go with two parallel strings--And some folks like that (if one battery fails, you still have 1/2 a bank to limp along on until you can replace the bad battery).

24 volt rated breaker/fuses are sometimes easier to get than 48 volt fuses. On the other hand, you can use 1/2 the amount of copper on your battery bus with the higher bank voltage.

The choice of AC inverter (availability, wattage, options) will probably be a factor in the 24/48 volt decision.

Solar array size based on battery bank AH rating and 5% to 13% rate of charge:

450 AH * 29 volt charging * 1/0.77 panel+controller derate * 0.05 rate of charge = 847 Watt array minimum
450 AH * 29 volt charging * 1/0.77 panel+controller derate * 0.10 rate of charge = 1,695 Watt array nominal
450 AH * 29 volt charging * 1/0.77 panel+controller derate * 0.13 rate of charge = 2,203 Watt array cost effective maximum

And based on your 1,800 WH per day and 5 hours of sun minimum:

1,800 watts * 1/0.52 system derating * 1/5 hours of sun minimum = 692 Watt array minimum

You can do nicely with a 847 Watt minimum array (battery size, WH per day), but since you do have significant loads during the day, you should have more solar panels to maintain the minimum charging current for the battery bank.

Because of this, I would like to see you closer to the 1,695 Watt array (10% rate of charge)... If you can figure out your daily average watts (say like 120 watts fridge + 30 watts computer + 20 watts misc

like 170 Watts nominal daytime load:

170 Watts * 1/0.77 panel+controller derate = 221 Watt panels to maintain loads
221 Watts daytime loads + 847 min batt charge = 1,068 Watt array functional minimum

Of course, you have to look at the ratings of your MPPT charge controller:

1,068 Watt array * 0.77 panel+control derate * 1/29 volts charging = 28 Amp controller minimum

So, if your loads and array stay relatively "small", you could possibly get away with even a 30 amp MPPT charge controller on a 24 volt battery bank.

A Classic 150 would work fine--Especially if you stay at 24 volt battery bank.

If your solar array needs to be a 10's to 100+ feet away from the battery shed+charge controller, then you may want more than a Vmp-array~80 volts (two panels in series+parallel strings). Three panels in series is Vmp-array=120 volts-- and Voc-array~144 volts--You are on an island that probably does not get very cold--But that is getting pretty close to too high for a 150 VDC limit controller. Then you would need the Classic 200 for the higher voltage array.

If you ever plan on dramatically enlarging the system, you probably want to seriously look at 48 volts.

If the system will remain about the same capacity (say less than ~3 kWH per day), then you may be able to stick with 24 volt battery bank (especially if you can get larger Amp*Hour rated cells at a good price--1/2 the number of cells to maintain).

You should do both designs on paper and see what makes best sense for you.

-Bill

Cariboocoot · May 2014

Re: Seeking Recommendations for an Off-Grid System

Sunny-HTI wrote: »

I intended to buy a MPPT Midnite Classic Controller and E-Panel.

What would be the optimal panel configuration, Battery bank ( 24 versus 48 ) , Classic Controller 200 or 250?

Thank you in advance for your help.

Harry

This should work.
You will have a 900 Watt array which is capable of about 28 Amps on 24 Volt system. Four T-105's in series. The array should be capable of 2+ kW hours per day based on 5 hours equivalent good sun. The batteries could supply 1.3 kW hours per day @ 25% DOD and your nighttime loads seem to come in at 540 Watt hours plus 400 or so for 1/2 the refrigerator use. All is good.

You do not need a Classic 200 or 250. Looking at the 55' distance and based on 12 Amps maximum an array configured with two parallel strings of two in series and 10 AWG wire will give you a V-drop of less than 2%. You could use a Classic 150 without any problem as cold temperatures obviously are not an issue.

You could also use a MidNite Kid if you are not planning on any expansion as it would handle the expected output current of 28-29 Amps fine. If you wanted to expand later you can parallel two Kids, or replace with a larger controller.

mike95490 · May 2014

Re: Seeking Recommendations for an Off-Grid System

Now is the time to decide if you will expand the system or not.

Personally, I would go with a 48V system, 2 panels in series, 2 parallel strings. If you add 2 more panels, you WILL need combiner box with breakers.
It makes the batteries a simple, single string of cheap golf cart batteries.

You want an e-panel with breakers for each side of the charge controller.

Choosing an inverter, look for one with AC charger built in, so you can charge from a generator on rainy days.

Cariboocoot · May 2014

Re: Seeking Recommendations for an Off-Grid System

Right now he has two limitations which prevent him using a 48 Volt system: four 225 Watt panels and T-105 batteries. If you put eight T-105's in series to get 48 Volts you will not charge them from 900 Watts of panel.

If he goes with 24 Volts it can be expanded to double capacity with the same battery type by putting in two parallel strings. In addition if he uses a Kid controller then adds a second of the same then the new panels need not be an exact match to the old (as is so often the case).

48 Volt systems have advantages, but they also have disadvantages.

Sunny-HTI · May 2014

Re: Seeking Recommendations for an Off-Grid System

BB. wrote: »

Can you use this link to double check your solar radiation?

http://solarelectricityhandbook.com/solar-irradiance.html

6 hours of sun per day seem to be more of a peak--At least the one city I checked (Port-au-Prince). However you still have a lot of sun all year round and 5+ hours seems to be a good minimum even with a fixed mounted panel.

Thank you Bill for your reply. You taught me well; that was the link I used to determine solar radiation. The reference city is Les Cayes, which is 10 miles away from my location. Highest irradiation is 7.01 in July and lowest 6.01 in November when panels are positioned accordingly. Also the average daily temperature is 85° high and 70° low.

Battery bank size:
1,800 Watts * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt bank = 352 AH @ 24 volt battery bank

1,800 Watts * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt bank = 176 AH @ 48 volt battery bank

Hmm... You are looking at ~8x T105 6 volt @ 225 AH batteries for 450 AH @ 24 or 225 AH @ 48 volt battery bank... This bank is a bit larger than your needs. Many folks find that they use more power over time--Might be good to grow into.

I found out the Trojan L16RE-A - 325 AH batteries are available as well. However they are double the price of the T-105's (225 AH). Advantage would be 4 batteries in series instead of 8 batteries in series-parallel for a 24 volt system, less cable, less cells to maintain, and perhaps a superior battery. Disadvantage I guess would be 125 AH less for the same money, and costlier to upgrade.

If you choose a 24 volt battery bank, you can use parallel panels and grow the system one panel at a time (Vmp-panel~40 volts). If you make it a 48 volt battery bank, you will have to grow the array 2 panels at a time. May or may not be an issue for you.

Also, Vmp~40 volts is not very common. Will you be able to get more 40Vmp panels (at a good price) in the future if you want to expand the array?

I like single strings--But your bank size is OK to go with two parallel strings--And some folks like that (if one battery fails, you still have 1/2 a bank to limp along on until you can replace the bad battery).

24 volt rated breaker/fuses are sometimes easier to get than 48 volt fuses. On the other hand, you can use 1/2 the amount of copper on your battery bus with the higher bank voltage.

The choice of AC inverter (availability, wattage, options) will probably be a factor in the 24/48 volt decision.

As much I was interested in a 48V system, it seems a 24 volt battery bank would be the more cost effective and reasonable solution. I can't foresee my daily load going over 3 KWh for a long time.
You are absolutely right, I have realized Vmp~40 volts is not very common, and it won't be easy to get similar panels. I am still trying to get 2 or 3 more from a guy that had a couple extras, but it's not definite..Regarding the inverter, I am considering the Outback VFX3524 3500 Watt Sine Wave, what do you think?

Of course, you have to look at the ratings of your MPPT charge controller:
1,068 Watt array * 0.77 panel+control derate * 1/29 volts charging = 28 Amp controller minimum

So, if your loads and array stay relatively "small", you could possibly get away with even a 30 amp MPPT charge controller on a 24 volt battery bank.

A Classic 150 would work fine--Especially if you stay at 24 volt battery bank.

If your solar array needs to be a 10's to 100+ feet away from the battery shed+charge controller, then you may want more than a Vmp-array~80 volts (two panels in series+parallel strings). Three panels in series is Vmp-array=120 volts-- and Voc-array~144 volts--You are on an island that probably does not get very cold--But that is getting pretty close to too high for a 150 VDC limit controller. Then you would need the Classic 200 for the higher voltage array.

I was looking at the Classic 200or 250 because I thought if I had 6 panels I would need to do 3 in series in order to reduce the number of parallel strings

Question - what's the ideal # of PV parallel strings ? .

Thank you,

Harry

vtmaps · May 2014

Re: Seeking Recommendations for an Off-Grid System

Sunny-HTI wrote: »

Regarding the inverter, I am considering the Outback VFX3524 3500 Watt Sine Wave, what do you think?

I was looking at the Classic 200or 250 because I thought if I had 6 panels I would need to do 3 in series in order to reduce the number of parallel strings

Question - what's the ideal # of PV parallel strings ? .

I like my VFX3524

Two of those panels in series is better. For a 24 volt battery bank, the ideal input voltage for a classic is 36-60 volts. The higher your input voltage goes, the LESS efficient your classic will be. Less efficiency means it makes more heat and runs hotter.

You seem to understand that parallel strings of batteries are not the optimal solution for a battery bank... but that's NOT true for solar panels. No problem having as many parallel strings as your wires and controllers can handle. You do need a combiner box to combine the parallel strings of panels, and each string should have a circuit breaker. Take a look at Midnite's combiners. Look at the ones with 150 volt breakers. Avoid the ones with 600 volt fuses... you don't need them and they take up more space in the combiner box.

--vtMaps

BB. · May 2014

Re: Seeking Recommendations for an Off-Grid System

What vtMaps said... The typical reason for going with more solar panels in series is to raise the Vmp-array voltage because the array is "far away" from the battery bank+charge controllers (higher voltage, lower current, thinner wire you can use from array to charge controller).

-Bill

Dave Angelini · May 2014

Re: Seeking Recommendations for an Off-Grid System

The other real nice thing about 24 V is there are many 24 V appliances (freezers), pumps, fans, and DC lighting that can be run without the inverter. Most inverters are around 75% efficient with loads of less than 200 watts or so. You can with the right choices later, enable the home to run in your absence without the inverter on or in a inverter failure. I have client down in Mexico that lost all the solar electronics to lightning. They were making ice that night with solar panels hooked straight to their battery bank.

I spent quite a bit of time down in your country sailing around. A beautiful place for sure! 24V will give you some flexibility that 48V will not. I do large 48V systems often, but I still think after all these years that 24V is often a better choice for alot of people. Good Luck ! Living offgrid full time is about as good as it gets!

Sunny-HTI · May 2014

Re: Seeking Recommendations for an Off-Grid System

vtmaps wrote: »

I like my VFX3524

Thank you vtMaps for your input. Hearing you like your VFX3524 is music to my ears. Buying a nearly $2000.00 inverter seems almost like a marriage ; one has to choose wisely

Two of those panels in series is better. For a 24 volt battery bank, the ideal input voltage for a classic is 36-60 volts. The higher your input voltage goes, the LESS efficient your classic will be. Less efficiency means it makes more heat and runs hotter.

If I understand correctly, with 4 panels, I should have 2 parallel strings of two PV in series, and with 6 panels I should wire them in a three parallel strings.
4 panels - Vmp = 81 V ; Voc = 96 V and Imp 11 V (2 parallel strings)
6 panels Vmp = 81 V ; Voc = 96 V and Imp 16.5 V (3 parallel strings)

I must admit I am a little bit confused by the "the ideal input voltage for a classic is 36-60 volts". The two panels in series already have a Vmp of 81 V

What would be the ideal charger controller that could accommodate the two configurations aforementioned? - Distance combiner to controller 55 to 60 ft .

You do need a combiner box to combine the parallel strings of panels, and each string should have a circuit breaker. Take a look at Midnite's combiners. Look at the ones with 150 volt breakers. Avoid the ones with 600 volt fuses... you don't need them and they take up more space in the combiner box.

Would a combiner like Midnite Solar MNPV3 (http://www.solar-electric.com/mnpv3.html) be fine, or should I look at one with a bit more room for growth?

Could I substitute the combiner by Multibranch Mc4 Connectors (http://www.solar-electric.com/mumc4colam.html) if I plan to buy an E-panel like MNE250AL-PLUS E-Panel ( http://www.solar-electric.com/mne250al-plus.html ).

I am learning a lot by reading the replies. I just have to digest the info. Thanks again to all of you.

Harry

Sunny-HTI · May 2014

Re: Seeking Recommendations for an Off-Grid System

Dave Angelini wrote: »

The other real nice thing about 24 V is there are many 24 V appliances (freezers), pumps, fans, and DC lighting that can be run without the inverter. Most inverters are around 75% efficient with loads of less than 200 watts or so. You can with the right choices later, enable the home to run in your absence without the inverter on or in a inverter failure. I have client down in Mexico that lost all the solar electronics to lightning. They were making ice that night with solar panels hooked straight to their battery bank.

Thank you Dave, very good info. It could be challenging to get the necessary parts if something goes wrong, especially for where I plan to do the installation.

I spent quite a bit of time down in your country sailing around. A beautiful place for sure!

You are absolutely right, Haiti is a beautiful place despite the odds. If you've been sailing around, I am sure you probably have been to Ile-a-Vache, a real jewel straight from God's hands 8)

Good Luck ! Living offgrid full time is about as good as it gets !

I currently live in the US, and on the grid and that allows me to fully appreciate living off grid.

Harry

vtmaps · May 2014

Re: Seeking Recommendations for an Off-Grid System

Sunny-HTI wrote: »

I must admit I am a little bit confused by the "the ideal input voltage for a classic is 36-60 volts". The two panels in series already have a Vmp of 81 V

What would be the ideal charger controller that could accommodate the two configurations aforementioned? - Distance combiner to controller 55 to 60 ft .

81 volts will be fine. Your voltages are a bit higher than most common panels these days (which typically run Vmp = 30). I used 60 volts as optimum because that would be two panels in series. With your panels, you could actually put them all in parallel, a Vmp = 40.5 is adequate to charge a 24 volt battery.

BUT... with a distance of 60 ft you will need some heavy cable. One advantage of putting more panels in series is that you can get by with thinner cable (higher voltage = less cable loss). However, it comes at the expense of reduced efficiency of the controller. On your scale, my opinion is that you would be better off with two panels in series. If you have three strings of two panels per string, and use 60 ft of #8 gauge copper cable, you will have a very reasonable voltage drop on 1.6%.

To get that same voltage drop with 6 panels in parallel, you would need #2 gauge copper.

Sunny-HTI wrote: »

Would a combiner like Midnite Solar MNPV3 (http://www.solar-electric.com/mnpv3.html) be fine, or should I look at one with a bit more room for growth?

Could I substitute the combiner by Multibranch Mc4 Connectors (http://www.solar-electric.com/mumc4colam.html) if I plan to buy an E-panel like MNE250AL-PLUS E-Panel ( http://www.solar-electric.com/mne250al-plus.html ).

I like my MNPV3. Do NOT substitute multibranch connectors for a combiner. The combiner has circuit breakers for each string (required if you have three or more strings). Also, the combiner is a good place for a lightning arrester.

--vtMaps

Sunny-HTI · May 2014

Re: Seeking Recommendations for an Off-Grid System

Another question regarding the Sunpower 225 watt Panels (Model SPR-225NE-BLK-D) and grounding.

As I kept perusing the forum, I found some old posts regarding Sunpower modules and positive ground. I am not even sure if the ones I have (Sunpower 225 watt Panels - Model SPR-225NE-BLK-D) fall in that category. Should I be concerned, or are there easy solutions if my panels require positive ground?

I have to ship those panels soon to Haiti. Although shipping/customs is not cheap, but it will be cost effective due to the fact I bought the panels at a very good price from a location that went out of business.

If those panels are going to be a pain to deal with, I would rather cut my losses , and get something else that's easier to deal with.

I am hopeful the forum can help me put this grounding question to rest.

Thank you

- harry

vtmaps · May 2014

Re: Seeking Recommendations for an Off-Grid System

Sunny-HTI wrote: »

Another question regarding the Sunpower 225 watt Panels (Model SPR-225NE-BLK-D) and grounding.

As I kept perusing the forum, I found some old posts regarding Sunpower modules and positive ground. I am not even sure if the ones I have (Sunpower 225 watt Panels - Model SPR-225NE-BLK-D) fall in that category. Should I be concerned, or are there easy solutions if my panels require positive ground?

According to this spec sheet:
www.prezon.nl/docs/Sunpower_spr-%20230_ne_blk.pdf
Positive ground is not required.

--vtMaps

jcheil · May 2014

Re: Seeking Recommendations for an Off-Grid System

Sunny-HTI wrote: »

Thank you vtMaps for your input. Hearing you like your VFX3524 is music to my ears. Buying a nearly $2000.00 inverter seems almost like a marriage ; one has to choose wisely

You will not regret going with the Outback Inverters. I (and many others) have learned the hard way, that if you are going to do it right, just do it right COMPLETELY from the beginning. Besides, unless you are going to go with some cheap made in China inverter, you are going to find that 24v PSW Inverters of any kind of quality is still going to set you back $1,100-ish. Then you have to buy a stand alone charger like the Iota, another $200-ish, then a bigger generator because the Iota has poor power factor, and an external transfer switch (another $100+), and additional breakers, etc.

Everything you need is in the Outback inverters in one nice neat package; inverter, power corrected charger (that you can adjust to be sized with a smaller generator if needed) & transfer switch. Mount it on a Midnight E-Panel (WELL worth the money) everything fits in about 3 sq-ft of wall space.

BB. · May 2014

Re: Seeking Recommendations for an Off-Grid System

Solar power is not cheap.

(Grid Tied power is actually almost cheap).

You need enough money in the bank for repairs if things go south (back up fuel for genset, replacement parts, cost of shipping units for repair, etc.).

If you do not have the finances to repair/maintain the system, revisit and see if you can live with something smaller.

That is why we focus so much on reliability, people have spent lots of money and time trying to get/keep the cheap stuff running (plus the damage to appliances/home when failures do occur).

-Bill

Sunny-HTI · May 2014

Re: Seeking Recommendations for an Off-Grid System

Sunny-HTI wrote: »

Another question regarding the Sunpower 225 watt Panels (Model SPR-225NE-BLK-D) and grounding.

As I kept perusing the forum, I found some old posts regarding Sunpower modules and positive ground. I am not even sure if the ones I have (Sunpower 225 watt Panels - Model SPR-225NE-BLK-D) fall in that category. Should I be concerned, or are there easy solutions if my panels require positive ground?

I have to ship those panels soon to Haiti. Although shipping/customs is not cheap, but it will be cost effective due to the fact I bought the panels at a very good price from a location that went out of business.

If those panels are going to be a pain to deal with, I would rather cut my losses , and get something else that's easier to deal with.

I am hopeful the forum can help me put this grounding question to rest.

Thank you

- harry

vtmaps wrote: »

According to this spec sheet:
www.prezon.nl/docs/Sunpower_spr-%20230_ne_blk.pdf
Positive ground is not required.

--vtMaps

I just found an old email reply from Sunpower when I contacted them in January after buying the panels from Craigslist:

Tech from Sunpower: " We don't recommend to use the panel for the off-grid. If the battery system is a positively grounded, it is possible to use but the off-grid system is usually a negatively grounded."

On another note, Midnite Classic Charge controller is designed to work with positive ground - below is an excerpt from their manual. However I am wondering if there will be other complication regarding the rest of the system. I just found 3 more panels that could bring my "planned" system to 1350 Watts (using only 6 panels), but I would like to be certain there wont be complication with positive ground before I pull the trigger.

"DC System Grounding

The Classic charge controller is designed to work with Negative Ground, Positive Ground or Ungrounded power systems. In grounded systems, dc negative may be connected to ground either externally or by using the Classic’s internal grounding jumper, shown on figure 2.1. The internal grounding jumper should only be installed when the Classic’s GFP is enabled. In a system with multiple charge controllers the grounding jumper should be installed on every charge controller. In Positive ground or Ungrounded systems the GFP jumper must be removed. See Figure 2.1 Also note that with Positive ground there will be items still referenced to battery negative that can complete a short circuit of the battery bank. These items include but are not limited to the USB Cable and the Ethernet jack. Please contact Technical support for assistance on Positive ground systems. "

-harry

KeithWHare · May 2014

Re: Seeking Recommendations for an Off-Grid System

One important consideration in Haiti is what you can get there and what you need to carry in.

If you already have the solar panels in Haiti, great! Shipping them in could be a lot more complicated.

I have a suitcase that will hold an e-panel if packed carefully. Charge controllers are OK in carry-on luggage. I've even carried in an Outback transformer in carry-on luggage.

Inverters are a bit more problematic. A Magnum MS4024 is about 60 pounds, which could lead to excess baggage costs.

Wire is readily available a couple of places in Port au Prince, not sure about elsewhere.

Where in Haiti will this be located?

Keith

Sunny-HTI · May 2014

Re: Seeking Recommendations for an Off-Grid System

KeithWHare wrote: »

One important consideration in Haiti is what you can get there and what you need to carry in.

If you already have the solar panels in Haiti, great! Shipping them in could be a lot more complicated.

Thank you Keith. You are absolutely right, getting equipment there can be complicated sometime. I have used a few reliable shipping services in the past, and I plan to use their services again.

Inverters are a bit more problematic. A Magnum MS4024 is about 60 pounds, which could lead to excess baggage costs.

Excess luggage can be pricey - 60 lb in checked luggage is $100.00 extra and $200.00 between 70 and 100 lb .

Wire is readily available a couple of places in Port au Prince, not sure about elsewhere.

I have bought THHN 10 AWG building wire cheaper than in the US in last year. of course you have to know where to buy. However this time I will be shipping PV wire.

Where in Haiti will this be located?

This will be in the South , near Les Cayes.

Harry

Seeking Recommendations for an Off-Grid System

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