Inverter=Bought, now panels????

rdg1

Looking for some more help.

I purchased the Outback FlexPower One, (3648), and now looking at panels.

I found a local resale outfit that have a bunch of panels at a very competitive price. I am looking at picking up 6 of these:

Model Number REC310PE72

STC Rating 310.0

PTC Rating 283.7

Open Circuit Voltage (V) 45.3

Short Circuit Current (A) 9.02

Frame Color Silver

Power Tolerance 0/+5%

Weight (lbs) 59.5

Length (in) 77.5

Width (in) 39.0

Height (in) 1.75

CEC PTC Rating of 283.7

72 REC PE multicrystalline cells

Weatherproof anodized aluminum frame

US import duty-free

3 strings of 24 cells w/ by-pass diodes

Solar glass with anti-reflection surface treatment

Double layer highly resistant polyester backsheet

MC4 cable connectable

Any thought about the panels?

Best way to wire them?

Thanks for your help.

Estragon

You'll need to check temp compensated Voc and Vmp for your climate.

3 in series might be getting too close to CC limit (150v?) if you get cold. 2 in series may not be high enough Vmp with hot panels for a 48v nominal bank, but should be ok for 24v bank.

rdg1

the location of the system is in Baja California, (closest City is Mulege). Cold is not a concern for this install.

Planning on a 48V battery bank.

Thanks

Estragon

Cold likely isn't a problem, but Voc 45.3 x 3 = 136v is at 25°C. I'd do the arithmetic using record low temp for your location just to be sure though.

48v bank with hot climate, 3 in series is likely best, especially if there's some distance from array to CC.

rdg1

Record low temp for my area is 43 degrees F, high is 105.

Only about 20' to 30' from array to CC

To be brutally honest, the VOC, Vmp, etc, does not mean anything to me, hahahaha. Guess that is why I am reaching out to this forum and smarter folks than I.

Estragon

Voc is the voltage with little/no current flowing. It generally happens around first light when the panel is coldest and there's just enough light to create voltage but not enough for the controller to wake and do much.

If voltage goes over the controller limit, it may log the event to void warranty, and can damage the controller.

There should be a temp coefficient spec for the panel you can use to adjust max string Voc to be certain this won't happen.

jonr

 > the VOC, Vmp, etc, does not mean anything to me

Then I recommend getting some local professional help to install the system so it's safe.

rdg1

Thanks for the recommendation about a local professional but did I mention this property is WAY off the beaten track in Baja California? Have you ever seen electrical work in Mexico? And I am talking about the local electric company folks. Not opposed to learning and there is a lot of information on the internet I can get at. I was just hoping that I could mimic a setup someone already has.

I am very experienced with the typical 120/240 electrical systems for residential homes.

I have picked the brains of my neighbors but very little help there.

BB.

The 50,000 foot picture is that solar panels can have a very wide range of operating voltage. From Voc-cold (which in sub freezing weather can be ~1.25x Voc-std) to Vmp-hot which can be 80% of Vmp-std (0.8*Vmp).

With solar charge controllers, they have an operating range (that changes with the voltage of the battery bank).

You don't want Voc-cold to exceed the maximum Vpanel-input voltage of the controller, as Estragon says, the controller may log that as a warranty violation, and it can "fry" the switching transistors in the charge controller (different controllers such as Outback and Midnite have dramatically different requirements/limitations on Vpanel-input max ratings).

And on the other side, on hot days, Vmp-hot-array falls, and can drop below minimum Vpanel-input to harvest full power from the array and send it to the battery bank.

More or less, for a Vmp~30 volt panel, the output voltage range can be from (very rough worst case example) from (0.8*Vmp-std) 24 volts to (1.25xVoc-std of ~40 volts) to 50 Volts.

You need Vmp-hot>minimum input voltage for your battery bank (12/24/48), and ~1.3x Vbatt for MPPT controllers to work well. And Voc-cold to be less than Vpanel-input maximum voltage rating for controller.

This stuff is very important so that you have a reliable system that will give you good energy harvest over the year.

Not trying to pick on you--This gets a bit complex and confusing. And why we highly suggest you do a paper design of your system, and look at "each block" in the system to make sure it all plugs and plays together correctly.

This is complex enough, and important enough, that major solar charger manufacturers have "string sizing tools" to make sure that this is all done correctly:

http://outbackpower.com/resources/technical-support/string-sizing-tool (Outback)

http://www.midnitesolar.com/sizingTool/index.php (Midnite solar's larger controllers)

http://www.midnitesolar.com/sizingTool_kid/index.php (Midnite's smaller controllers)

-Bill

Estragon

FWIW, I went from knowing zero to installing a system on my own that meets my needs adequately. This stuff isn't rocket science, but does have a bit of a learning curve. Buying stuff as you learn can be expensive. Doing paper plans is cheap.

jonr

Figure that those panels will vary in voltage from about 48V to 33V.

softdown

It may be fine to learn and do your own work over time. It is not fine to buy bits and pieces as budget allows and deals pop up. You should find somebody that can recommend a system for you that is compatible.

The good news is that your inverter choice is a fine one. Your location appears extremely remote. Should be very sunny and provide a wealth of solar energy.

I'd start with a basic book about solar energy. I read a few but they all instructed the reader to hire a pro. Good advice for most. With an electrical background, a handy person can do it however. I would give myself a few months of studying up on it though. My system works great and I braved it alone. Though it felt like giving birth for the most part.

People are referring to the possibility of cold weather related "hyperVOC". That will not be an issue for you. 3 panel strings should be fine. I ran two panel strings here due to exceptional cold weather events.

I keep meaning to drive down the Baja and keep postponing the trip. I was raised in Spain for a bit so Mexico seems very comfortable. Oddly - I don't speak much Spanish at all. Muy muy pequito.

rdg1

Thanks for all the responses.

From I can gather, and using the Outback FM80 MPPT controller, for these panels, 2 strings with 3 panels in series each would be the optimal setup for my application. (referred to Midnight string calculator since I could not get the Outback one to download).

BTW, I never feel picked on when I am ignorant.

BB.

We all started at the same place in life.

I am still learning (and starting to forget) more and more every day. 😣

-Bill

softdown

https://forum.solar-electric.com/discussion/comment/395705#Comment_395705

Seems you did more homework than we knew about. How many watts are the panels rated at? Remember to derate everything by about 20%. Refrigerators are the big power consumers. You may have energy to run an electric if you play your cards right - Energy Star fridge in a cooler area.

As I recall your area should be a solar paradise.

Can't go wrong with Outback charge controllers and inverters. People tend to murder their first battery bank so I would not buy the best batteries the first time. Golf cart batteries work quite well.

rdg1

my loads are going to be fairly lite since it is just my wife and I:

800 sqft concrete home, Roof is concrete as well,

12 cuft LG inverter fridge

all LED lighting

Couple of ceiling fans

couple of pedestal fans.

No Microwave

I am not expecting the system to run any AC. I currently have a 6000 BTU window AC that I plan on upgrading to a mini-split. We normally only run the AC at night, during summer months, and I use a Honda 3000is when we do.

softdown

Loads run while the panels are receiving energy are not an issue. Nothing wrong with a lightly used microwave - in my opinion.

Those inverter fridges are expensive. They keep down the surge but seem to use a similar amount of power - from what I have seen.

A concrete home in the Baja? You folks should survive most anything. I'm considering a concrete earth home - only the south side to have windows.

BB.

Details do matter... And, for example, there are fans that are very energy efficient (a few tens of watts) vs those that are less so (>100 Watts).

Getting a Kill-a-Watt meter and/or DC AH/WH meter, a good place to start (there are lots of version/similar of these meters):

https://www.solar-electric.com/kiacpomome.html

https://www.rc-electronics-usa.com/ammeters/r102-amp-hour-specs.html

Nominally, I would suggest that you look at ~3.3 kWH (3,300 WH) per day as an initial planning number for a very energy efficient home/family with a "near normal" electrical life... Full size energy star refrigerator, LED Lighting, Laptop computer, LED TV, cell phone charging, clothes washer, "solar friendly" well pump. Running a Microwave for 10-20 minutes a day is not a big issue...

Using a quick rule of thumb for a reliable cabin system. Design battery bank to support loads, then design the solar array to give enough charging current for the battery bank (5% to 13% rate of charge), and finally, design the panels to support your loads based on hours of sun per day and seasons.

Battery bank: Assume 2 days of no-sun, and 50% maximum discharge for your loads:

• 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 324 AH @ 48 volts

To charge the battery bank, need 5% to 13% rate of charge, and suggest 10%+ rate of charge for full time off grid home occupied year round. 5% rate of charge can work for a weekend/summer/sunny weather cabin.

• 324 AH * 59 volts charging * 1/0.77 panel and controller deratings * 0.05 rate of charge = 1,241 Watt array minimum
• 324 AH * 59 volts charging * 1/0.77 panel and controller deratings * 0.10 rate of charge = 2,483 Watt array nominal
• 324 AH * 59 volts charging * 1/0.77 panel and controller deratings * 0.13 rate of charge = 3,227 Watt array "cost effective" maximum

And there is sizing the array for hours of sun you get per day, by season. I have never found a good listing for hours of sun per day for Baja California... If you can find your city/similar weather conditions in the link below, or have another source for data, we can use that:

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

Let's guess that 5 hours a day, on average for 9+ months a year (use genset, less fans, etc. in cooler "winter" to make up extra power during poor sun):

• 3,300 WH per day * 1/0.52 off grid AC system eff * 1/5 hours per day sun = 1,269 Watt array "break even"

Normally, your base loads (loads you need to run every day), you should only plan on using 50% to 65% of predicted output... So, uprating fudge factor:

• 1,269 Watt array * 1/0.65 fudge factor = 1,952 Watt array 65% fudge factor
• 1,269 Watt array * 1/0.50 fudge factor = 2,538 Watt array 50% fudge factor

My first guess would be a ~2,483 WAtt array could work very nicely--Based on my 3.3 kWH per day suggestion. If your energy usage is less/different, you can plug in different numbers. And give you a lot of "extra energy" during the day (running fans, etc.) if you need it.

If you are in a very sunny area, you could downsize the battery bank and solar array some. Also, if your winter hours of sun is still very high, a smaller array could work OK too...

In general, solar panels are relatively cheap and batteries are relatively expensive (and easy to damage or ruin if you over discharge them)....

Anyway, just a starting point for discussion. Your thoughts and/or corrections to my guesses.

-Bill

rdg1

Bill,

Thanks for the time and effort put into your post.

The numbers you came up with are not too far from mine. The home is more of a "vacation/get out of CA retreat" and as such, I am thinking energy usage will be a bit less. I got the "larger" inverter/CC thinking I could always add more panels and batteries if need be.

Thanks again for your informative post. Makes me more comfortable with the numbers I am working from.

littleharbor2

BTW, I believe most people who live or regularly spend time in Baja don't refer to it as The Baja. Some do but it sure sounds incorrect. When I head home I don't say I'm going back to The California. 😎

softdown

Baja is incredibly sunny unless I am missing something.

rdg1

Still looking at panels and would appreciate some opinions.

72 cell verses 60 cell.

Another forum member suggested that I might be better served by 60 cell panels. One thing that is appealing to me is the size and weight of the 60 verses the 72. I will have to lift these panels, (although only six of them), up onto a roof top that is about 14 feet up. At least my roof is flat, lol...

• other than the panel listed above above, I have been looking at this one, Longi-Solar LR6-60-290M
• STC Power Rating 290W
• PTC Power Rating 267.7W 1
• STC Power per unit of area 16.5W/ft2 (177.4W/m2)
• Peak Efficiency 17.74%
• Power Tolerances 0%/+5%
• Number of Cells 60
• Nominal Voltage not applicable
• Imp 9.15A
• Vmp 31.7V
• Isc 9.71A
• Voc 38.8V
• NOCT 45°C
• Temp. Coefficient of Isc 0.06%/K
• Temp. Coefficient of Power -0.41%/K
• Temp. Coefficient of Voltage -0.128V/K
• Series Fuse Rating 15A
• Maximum System Voltage 1000V

Any thoughts?

Thanks in advance.

mcgivor

The choice of cell count depends on the controller, PWM favor 72 cell, MPPT 60 cell, it's related to the voltage output, particularly the VOC and VMP, it seems MPPT controllers are designed to use 60 cell panels, for economic reasons because 60 cell are used in commercial applications and are/were less expensive due to supply and demand.

rdg1

McGivor, So..... Since I have the Outback FM-80, (MPPT), your opinion is that the 60 cell would work better.

For some reason, I thought the 72 cells were primarily used for commercial applications.

BB.

The big issue is that 2x 72 cell (or 60 cell) panels in series is not high enough Vmp-array for an MPPT controller to work optimally.

3x 60 cell panels for Vmp-array-std~90 volts will work great on a hot day or cold day (Voc-cold) on the Outback/MPPT controller with Vpanel max input voltage of 140-150 VDC.

3x 72 panels Vmp is fine (hot or cold), but the Voc-cold can be a problem for very cold climates (3x Voc-72-cold panels can exceed 150 VDC).

Roughly, at 45F, 72 cell panels, Voc-cold 3x panels in series would be around 143 volts. Below the max startup voltage of 145 volts, and below the max not to exceed voltage of 150 Volts for the FM80.

For you, either 60 or 72 cell panels will work fine. Both size of panels are currently popular, but as single panel wattages continue to climb, they probably will go more to 72 cell (and larger cell counts). From what I can see, the panel mfg. are trying to limit current in the panels/panel wiring and avoid creating larger and larger solar cells (each cell is cut from a solid ingot that is X inches in diameter). The easiest way to create higher wattage panels is to add more cells in series.

For GT systems, where even home size systems work with Vmp-array-std voltage in the 200-400 VDC range (typical, max input Vpanel~600 volts), they can can put one more or less panel in series and have the array voltages work out fine.

For the "typical" (historically popular) MPPT solar charge controllers, they have picked 150 VDC (typical) max input voltage. And the minimum Vmp-array voltage is based on ~1.3xVbatt (where Vbatt is ~15/30/60 volts when charging). These "lower voltage" MPPT controllers have a relatively small window of acceptable input voltage. 60 Cells fits the window very nicely, 72 cell panels have a voltage that can to too high for 48 volt battery systems in colder climates.

There are higher Max input MPPT charge controllers--It is just that these controllers are more expensive and/or have somewhat lower rated output current--They work fine, but can be much more expensive (for example, $500 for 150 Vmax/80 amp vs $1,200 for 600 Vmax/80 amp Schneider/Xantrex MPPT solar charge controllers).

-Bill

rdg1

Thanks Bill....

So, for a system using 60 cell, 2 strings of 3 panels, (panels mentioned above), the system "on paper" would work well for my application and location.

Am I reading this right?

Estragon

Yes, strings of 3 with 60cell should work well.

IMHO, 60cell are (just) managable for one person (me) to safely handle. I have some 72cell as well for a pwm "winter" array, and although they aren't much heavier, the size makes them much harder to handle, at least for me.

cow_rancher

For building a shed purpose, is there a "standard" size for 60 cell or 72 cell panels? Or maybe I should say is there a "popular" size? And I understand that as cell size increase that the panel will increase, however is there a size out there that most MFGs have settled on?

Rancher

littleharbor2

Typical 60 cell 39" x 65". Typical 72 cell 39" x 77" Different brands will vary, usually the variation will be in the height due to different buss tabbing configurations.

BB.

There seem to be few standards for solar panels any more... The 36 cell panels are commonly used for PWM charge controllers and 12/34/48 volt battery banks.

When MPPT became hot, they were able to leverage off of GT Solar Panels (larger format, high volume, cheaper to purchase). 60 cell were the most common... 72 Cell seemed to come and go (Evergreen made 72 cell panels, but went out of business).

More or less, it seems that solar panels have a ~18 month to 24 month manufacturing life. And the next round may or may not match the Vmp/Imp of your existing array. Sometimes, the differences are large enough, that a person has to purchase a second MPPT charge controller to make a second array to match the new set of panels.

Sometimes, you can find/purchase older panels. However, many times, those older panels can cost 2x or more per Watt vs new production panels. Leaving you with design and purchase choices to make (old expensive panels with old array, buying a new controller with new/cheaper panels, etc.).

10+ years ago, GT panels were $10 per Watt... Today, you can find them for $1 a Watt (+/- USA/China tariffs). Why pay >$2 a Watt for a 'matching' old panel, or >$2 a watt for a 36 cell "12 volt" (Vmp~18 volts) panel / Array.

Do your pencil and paper design(s) first... See what works out best for you.

-Bill

softdown

Concrete solar powered house deep in the Baja with a CA owner. This sounds like a survivalists dream.