Off grid design

diallodjeri

Hello folks,

I have a few questions about my system design.
I want to set up a system in region where there is an abundant sunlight throughout the year, precisely in west Africa. I might just not have enough storage to harness all that beautiful sunlight in order to power all my appliances at night, may be just enough storage to power the essential appliances at night.

I’m planning on buying 21 panels, Trina 265 Watts, that should give me around 5kw in shining day.
I want to set it up in way so I can power all my appliances during the day when there is plenty of sunlight to crank all the panels and also to fully charge my battery, Simpliphi PHI 3.4kWh (Lithium Ferro Phosphate). I want to know how can I set up my system so the appliances will only draw power from my panels and not from the battery during the day when the sun is shining, and this way I will draw power from the battery for my appliances that need to be on at night. I want to make sure this setup doesn’t impact negatively my battery life at all.

The dealer told me that I will be needed two charge controllers if I get 21 panels or one charge controller if I get 18 panels, and in that case the charge controller will be running at full capacity all time which is not a wise thing to do.

The dealer suggested an Outback 80 Amp 12/24/48/60 Volt Flexmax 80 MPPT Charge Controller and Outback Radian 3500 Watt 48 VDC Inverter / Charger .
The dealer said that I can connect my 21 panels in string of 3 panels with 2 charge controllers or 18 panels in string of 3 with 1 charge controller.

I would like to know how can I accomplish this goal.

Dave Angelini

Nice choices!  You may be overthinking the way an offgrid power system works. Once the battery is close to full you automatically power all your appliances. On most days you do not even think about it where you are located. Only in winter, bad weather, or a wildfire does one have much concern. Get as many panels as you can. Outback is also coming out (soon) with a high voltage charge controller that may make this alot easier, if you can wait a bit. You may want a battery monitor for the Simpliphi as it does not output Soc. If you give some estimated power consumption it may be helpful.  Good Luck!

Estragon

As Dave said, solar will automatically power loads once the battery gets close to full, BUT only to the extent loads plus charging current are less than the panels are producing at the time. If your loads include air conditioning, electric clothes dryer, electric stove, etc., you could exceed pv output and draw from the battery during the day.

System design always starts with the loads.

Photowhit

Several things. You can expect about 75% of your panel rating when they are in direct sun. So with 18 - 265 watt panels or an array of 4770 watts, you can expect about 3575 watts when in direct sun.

Your battery bank is tiny for the size array you have. Lithium battery banks can charge quickly, but with an 80% usable capacity of (3.4 x .8=)@2.7 Kwh's that's still likely a higher rate than they can charge at... Recharging in under and hour!

You will have loads during the day and evening, but you should discuss these first! 

If you choose to setup this system, I would angle your panels so that 1/2 are facing East and 1/2 are facing west. This will give you a reasonable output throughout the day.

Please talk about your loads! In comparison, I have a 5Kwh array and @12Kwh's of available storage. In a hot environment 3Kwh's of storage is not likely to run a room air conditioner and a fridge over night!

Dave Angelini

Example of a system using less than 3KWh of storage running about 6KW of panels. Been doing this since my mini-split heat pump came out in 2007. Large refrigerator and typical home loads with air temp at night about 76F or 24C. It does take me a bit more than an hour

Photowhit

Dave Angelini said:

Large refrigerator and typical home loads with air temp at night about 76F or 24C. It does take me a bit more than an hour  

Don't know about Africa, or where in Africa...lol. 

It might work here in Missouri, though we do get hot muggy nights when the air runs most of the night....

...but I'm from North Florida, Where 75 degrees at night means for 30 minutes when it drops through the dew point and it's not breathable and foggy..... Most of the night is 80+ and the ac runs pretty steady. Also remember he is likely closer to the equator, so won't have the longer days in summer to help buffer the over night draws... (as I said we need more info)

Dave Angelini

We don't know much about the OP, but as everyone has asked, what is his expected usage of energy? That is a really nice battery that can be expanded at anytime, as long as he has a supplier there. Even if he buys from the store here, it can depend on the exact country he is in.

The screen shot is the heat-pump cooling with the refrigerator cycled on. About 96% efficient.

We spent 6 months in Florida on our boat, that was enough of that

Raj174

Dave,
How does your system handle the 80 amp+ charger output (6000 watt array) to a battery with a max recommended charging amperage of 33 amps? Is this handled automatically?

Rick  

Solray

Lol. I have to run a heater to get it to 76 at night.

Dave Angelini

Hi Rick,

I turn off ["run off" -BB. ?] an array most of summer, except last week when we had wildfires and very smokey skies. It is the strategy I use with many of my clients also. We do not want to run a generator and live in a place that can do that in winter. The LG Resu10 has a continuous charge rating of 57 amps and a peak of 119a, for less than a minute. I have been running it since Christmas. It was a great present BTW. That battery has not caused one problem for me.

Raj174

Thanks for the information Dave.
Yep, I like the Resu 10 also. Hope it continues to perform well.

Rick

diallodjeri

I don't have a hard number of my consumption yet, but I think is going to be 2 mini split AC, where one is 1350watts and the other is 580watt plus one refrigerator and one freezer. These are the appliances that will be running of the system. It looks like my battery may not be big enough for the project.

Photowhit

The mini split's will cycle on and off and use less energy depending on the outside temps and insulation. Modern fridge and freezers will be more efficient than many are use to. It would be good to look at the total system costs, typically investments in modern appliances and insulation will allow for a smaller system.

While I do think your storage is under sized, Dave has more experience. I just hope to add some insight as to things to consider. Certainly and East and West facing array (slightly north east if south of equator and south east if North)

Raj174

Outback recommends a minimum 300AH battery if grid tied and 200AH if off grid per the manual. I have the Radian  GS4048A which is somewhat equivalent to the 3500 watt EU version, and have a 195AH LFP battery bank (10 kWh).
My system supplies enough power over night and into the early morning for a freezer, refrigerator, TV, lights, ceiling fans and the occasional microwave usage. I would think that a 200AH battery is close to what you need. If it's a AGM battery then 300 to 350AH. It might be possible to run the smaller mini split at night for a short time also. Splitting the array east and west is a great idea. The charge controller amperage output may need to be limited if the battery bank isn't large enough for the midday sun (80 amps), but splitting the array east and west will go a long way to keep that restriction to a minimum.

Rick 

diallodjeri

If you don't mind can you elaborate little bit on the reason why one would face panels to different direction; and also what are the requirements to create a battery bank. Do all the characteristics of the batteries have to be identical in order to combine them?

Dave,
Do you have any idea in regard to when Outback is planning to come out with bigger charge controller.
Thanks!

BB.

Lead acid batteries need around 2-6 hours at "absorb" voltage (around 14.75 volts for flooded cell lead acid batteries at room temperature) to get fully charged.

The "optimum" is to use a 2 axis tracking solar array to follow the sun across the sky and collect as much current (wattage) at the beginning and end of the day.

However, tracking arrays are relatively expensive (structure, large concrete in-ground base) and have electro-mechanical components which do require some maintenace (at the very least, needing a few pumps with a grease gun every 6 months).

When solar panels were expensive ($10+ per Watt), using a 2 axis tracker was not a bad way of getting more bang for the buck--And had the added advantage of more hours of useful sun per day. The battery bank "likes" 10% or so rate of charge and >8 hours of charging per day. Charging at 13-20%+ rate of charge in the middle of a shorter day is not as useful for flooded cell lead acid batteries.

If, on the other-hand, you install a 2x larger array with 1/2 your array facing south east and the other 1/2 south west (in the northern hemisphere), you can get a lot of the advantages of a 2 axis tracker (many hours of sun per day), with less complications (fixed array, simpler mechanical structure) and less costs ($1 per watt or less for solar panels). You get, can be called, a virtual tracking array.

You can use a program like PV Watts to compare the various options (fixed, tracking, split, etc. arrays). PV Watts also has hour by hour output so you can mix the two array planes together to see how you can "extend" your day with a virtual array.

http://pvwatts.nrel.gov/

-Bill

Estragon

To give a bit of "feel" to what bill said, I'm currently looking at a lovely early sunset. The sun is about 25° from setting, but I'm getting next to no solar power because the array is just west of south, so the angle is too acute to produce much.

If I had part of the array facing west-ish, I'd still be getting some production from pv.

In my case it doesn't matter much. Most of the big loads are mid-day by design. In your case, it's better to have a flatter production curve so pv can power loads and charge batteries for longer. You just have to size things to be sure both happen.

diallodjeri

I often heard people talking about programing the inverter, for intense the Outback Radian GS3548E. I was wondering what kind of programming you can do with that piece of equipment.

Raj174

@diallodjeri
Off grid, the Radian is very much like any other off grid inverter. However, when grid connected it has several modes of operation, a couple of them can be very useful. Backup mode is default and it would be desired if grid power is not reliable, failing multiple times daily. When a grid failure occurs, the Radian will automatically transfer the loads to the batteries. You may not even know an outage has occurred. Obviously, the battery needs to be large enough to supply the loads for the average duration of the outage or longer. Also, backup mode can be used without solar power installed. Batteries would be charged from the grid between outages, which can be set to occur automatically.

Grid Zero mode allows a blend of grid power and battery power to offset grid consumption. The amount of power taken from the batteries is adjustable and is set using the Mate3, which is the remote and communications controller. All of the modes are described in the Radian operator manual. Here is a copy of the GS3548E manual and an Outback application note on the function of Grid Zero.

Rick

 

Dave Angelini

diallodjeri said:

If you don't mind can you elaborate little bit on the reason why one would face panels to different direction; and also what are the requirements to create a battery bank. Do all the characteristics of the batteries have to be identical in order to combine them?

Dave,
Do you have any idea in regard to when Outback is planning to come out with bigger charge controller.
Thanks!

I can't really say as some of it is in confidence but the trade show SPI is next month in Vegas and that is when the firm dates get out there.
Outback will start selling when Outback is ready. It is a big step for them as they have zero experience above 150 vdc. They have also slipped Skybox from this year to next.

The system I have in the above screen shots, has been producing a HV mppt for almost 7 years and it is rock solid. Their CSW 4024 is probably the most affordable inverter/charger on the market. It is being tested for the LG chem RESU series right now and field tested also by yours truly and a few Australians. The Bridge for Li-ion will work for other battery makes but not simpliphi as it does not output internal BMS data.

It sounds like you will need more storage, get a second Simplyphi or make do with a generator until you can. Many do it that way.

diallodjeri

Hi folks,
I'm really glad I can come to you guys with my solar energy questions.
I want to learn as much as possible before I can start spending my money with confidence.

My daily consumption should be around 3.5 kWh and the night consumption should be around 1.5 kWh to 2 kWh, but I'm buying enough panels that can generate at least 5 kWh which should be enough to charge my battery and satisfy my load at the same time during a day.

I want to know if I should still be concerned about having a too small battery for too big panels as long as I have a good charge controller seating between my panels and the battery.
If I understand the design, the charge controller should be protecting my battery from over charging as well as from over discharging. I can see how the over charging mechanism would work because the charge controller is seating between the panels and the battery. I just don't understand how the mechanism against over discharging would work though.

I was looking to buy (2) SimpliPhi 3.4 kw, 24v battery which would give me a combine storage of 6.8 kw for almost $7000, but I have seen some used forklift battery online with similar capacity for half of this price. I don't know much about a used forklift battery other than it's not sexy, it's bulky and heavy, but I'm willing to sacrifice the sexiness for efficiency. Does anyone knows about a forklift's lithium ion battery. Is that battery a good investment?
Whatever battery I'm going with has to be a lithium ion battery because of its safe technology.

I just want a system with a good critical components such as panels, charge controller, inverter and battery; I don't need all those belts and whistles like communication hub, remote control feature, or any other extra fancy feature, but I do really want a good reliability plus a basic monitoring of the system to see if everything is working like they supposed to. In order to accomplish that, what sort of basic monitoring device do I need?.

Photowhit

diallodjeri said:

If I understand the design, the charge controller should be protecting my battery from over charging as well as from over discharging. I can see how the over charging mechanism would work because the charge controller is seating between the panels and the battery. I just don't understand how the mechanism against over discharging would work though.

The charge controller will only protect the battery from over charging and only with current passing through it. If you are using a generator to charge the battery bank through an inverter/charger then it should protect the battery. I don't know of their designed charging parameters with lithium technology.

diallodjeri said:

Does anyone knows about a forklift's lithium ion battery. Is that battery a good investment?
Whatever battery I'm going to go to buy has to be a lithium ion battery because of its safe technology.

I have and use a forklift battery, It lives outside along with the charge controller, breakers and inverter and is about as safe as can be... Not sure what you fear with Lead Acid batteries, they have been round a long time and their dangers are well understood. I doubt their are lithium forklift batteries available used at this point, but perhaps...

A lithium battery would need to be inside where weather gets below freezing, this would also likely bring other aspects of your system inside, charge controller like to be near the battery bank (or at least have a battery voltage sensor going to the battery) 

Raj174

@diallodjeri
Ok, is your estimate of power usage over a 24 hour period 5 to 5.5 kilowatt hours? 
Also, in your post you mention two 24 volt SimpliPhi batteries, yet in a previous one you mentioned a Radian inverter. The Radian is 48 volt only.

To use the SimpliPhi battery with the Radian inverter, you would need the 48 volt version. The SimpliPhi battery can be wired in parallel to increase the amp hours, but they can not be wired in series to double the voltage. The battery manual describes this in detail. I will attach the document at the bottom of the post for you to read up on. Also, if you need to buy 2 batteries they need to be ordered together and balanced to work together before they are delivered.

 Over charging the battery is not usually an issue if your system is designed properly and the charge controller settings are correct for the type and size of your battery. 
Battery size is not only determined by your daily power usage but also number of days of desired autonomy. You may want to make it large enough to cover one or more days of bad weather, little solar production.

In response to system monitoring, Outback provides monitoring capabilities with their equipment. It requires internet access, registration on their website and the Mate3 remote communications controller. This is required to change settings on the inverter also. 

If you can verify your power usage we will have a better idea of what it will take to meet your needs.
Lastly, are you currently connected to the grid?  
 
 Rick

Dave Angelini

diallodjeri  Many confuse the power storage that is needed. The power you use during the day does not generally matter (except during bad solar days), the number you need is the amount you need to store overnight. You may want to add on to this number if you need to have some in the bank for bad weather. If you are home during this time and can start a generator, it is not as important and you would not be the first who started out this way.

 If I were you I would go back and read all the posts and sum up everything in a new post. It can help!

Dave Angelini

You always match the max charge requirement of the battery by current limiting the charge source. Always!
 This is programmed in by the owner/installer at commissioning.

A max charge spec of 33 amps sounds like your battery is not matched well for a 6kw array size.

I would want to see a max charge spec for a battery with at least 100 adc for a 48v 6kw inverter.