# Need advice on off grid system

Solar Expert Posts: 44
Hi everyone..I am new to the forum and want some advice on an off grid system to see if I am on the right track..I have a beach resort in the Philippines and have No Way to get on the grid--and Diesel for the generator is about \$4 a gallon! so here is my plan..!. 1. Loads will be about 8000 watts per day..2. I bought 20 evergreen 210 watt panels..I plan to use the xantrex XW6048, 6000 watt/48 volt inverter charger..for the charge controller I was going to use the outback 80A MPPT charge controller..The batteries are going to be 12 volt 200AH AGM batteries..I was planning on a 48 volt system so I would have a string with 4 batteries in the string..The plan is to have 5 strings of 4 batteries each for a total of 20 batteries.I figure that I can average at least 4 hours of sunlight per day--probably more--I am at 14 degrees North latitude..I would like to know if I have enough panels and if the inverter/charger and charge controller look good..Also if I have enough batteries..Thanks so much Larry

• Banned Posts: 17,615 ✭✭
Re: Need advice on off grid system

Whoa! Let' back up and do the math before you spend any money.

By "Loads will be about 8000 Watts per day" I'm going to assume you mean 8000 Watt hours.
So the first thing you do is try to cut that number in half.

If you can't, a 48 Volt system is the right choice. You will need a minimum of 333 Amp hours of battery, and that's if all goes well. 666+ would be better (gives you that 25% working margin).

Let's say you build your battery bank around those 12 Volt 200 Amp hour AGM's. You'll need at least two parallel strings of four batteries; a total of eight batteries to give you 400 Amp hours @ 48 Volts. Adding more strings to that will increase the Amp hour capacity but also increase the problems with keeping current flow even and require more panel to recharge. You do not want to go with five such strings, as that would be 1000 Amp hours and then you'll have difficulty handling the recharge current for sure: you'll need two arrays and two charge controllers to handle 100 Amps potential peak charge current.

So what would you need to recharge that 400 Amp hour 48 Volt bank from solar? The rule-of-thumb calculation shows 40 Amps * 56.8 charging Volts = 2272 Watts after derating. Now that's the tricky party: the Philippines is known for being hot and moist, so your panels may suffer greater derating than we'd normally expect to see. Typically you can expect 77% efficiency, or a need for 2950 Watts of array. You might do better to size the array and the nearest commercially available combination that exceeds 3kW. Remember: AGM's can take higher charge current than FLA's without consequences.

That brings us to the "harvest potential". Using the Icarus Formula we see a 3kW array producing only 6kW hours per day AC "out the door", based on 4 hours of equivalent good sun. You probably will see more hours than that (check PV Watts International: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/International/inputv1_intl.cgi) but not so good in the heat so it might even out.

So you might want three parallel battery strings (600 Amp hours) and a 4.5 kW array to be sure you have your 8kW hours daily and some reserve capacity. Going above that is probably spending extra money for power you'll not use and adding more complexity you don't need.

Just a suggestion. Others' opinions may differ.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Need advice on off grid system

you should be fine with the pvs you have if it is 8kwh per day usage, but if not you can always buy more pvs. 5 strings of 4 or 4 strings of 5 would work. i agree with the 48v 400ah battery bank (2 strings of 4 200ah batteries) and you may want to go higher if you will need any days of autonomy.

you may need 2 controllers to handle all of that power for 80a x 48v = 3840w and you are feeding 210 x 20 = 4200w in pv. you can try to bank on the losses keeping that down to a minimum, but if it loses very much or very often by the cc limiting at 80a then get 2 controllers.

i think aiming would be interesting for me if around the equator. i would be tempted to lay them out like flat (14 degree tilt to south) on a seesaw to catch morning, noon, and evening sun. if you don't know what a seesaw is it is a thing for kids in a playground that has a long board that is able to swivel in the middle and each kid on either end goes up and down. forgive my description if it didn't suffice.
• Banned Posts: 17,615 ✭✭
Re: Need advice on off grid system

Niel I think you've just invented the world's simplest PV tracker system!

I checked for panel angle in the Philippines and flat isn't too far off; the year-round average would be something like 12.5 degrees (goes -11 in Summer, +36 in Winter). Also, it seems the days are around 10 hours all year long so up to 6 hours equivalent good sun should not be a problem - even without the Teeter-Totter Tracker®.
• Solar Expert Posts: 44
Re: Need advice on off grid system

Thanks for all the great advice..So I guess I need 2 controllers for this set up--2 60 amp??..How would I wire the panels to achieve a 48 volt system? also is there a good book to buy on how to install the system as nobody down there has done it before so I am on my own with the install--I do have a very good electrician to help...As far as the temperature goes it is not that hot where I am at--80-85 degrees year round but high humidity..thanks in advance Larry
• Banned Posts: 17,615 ✭✭
Re: Need advice on off grid system

With 4200 Watts of panel you would only need one controller, providing it's the right one. In all likelihood you would not see 60 Amps from that. Just to be sure you could use an Outback FM80 or one of the MidNite Solar Classic 150 units, either of which is capable of 80 Amps max on a 48 Volt system. Probably output would be around 57 Amps at most. 80-85 degrees will affect panel output, as they are tested at 72 (I think) and any temp above that will have reduced heat dissipation with resulting lower panel power. The manufacturer's specs should have info on the difference.

As for wiring, the nice thing about MPPT controllers is that so long as the Vmp of the array is above the minimum needed for the system Voltage (in this case about 72 Volts) and the Voc does not exceed the controller's input max (in this case 150 Volts) they will work. If you have the specs on these Evergreen panels (Vmp, Voc, Imp, Isc) it would help. I vaguely recall they're a "12 Volt" panel with a Vmp around 18. Voc is probably 23-24. You'd probably wire for four parallel strings of five in series. It is important to have over-current protection (fuse/breaker) on each parallel string - sized according to the Isc (Isc * 1.25 ^ nearest available). Also, the length of wire between the array and charge controller will be important for sizing the wire (reduce Voltage drop and handle maximum current).

NAWS lists and recommends this book: http://www.solar-electric.com/bonewsoelho.html
Maybe some of the other folk here have additional suggestions.
Re: Need advice on off grid system

A couple suggestions... Take a second look at getting AGM batteries. They tend to be way more expensive and not really last as long as a good industrial battery. If you have electric fork lifts in the region (port, factory), you may be able to get some good used batteries (at least as a start).

Second, have you done everything you can conservation wise... Virtually anything you can do to reduce power usage, from an investment point of view, will have a better return than just spending more money on a larger PV system.

Third, I would suggest, besides the standard hydrometer, that you get a decent DC Current Clamp Meter (on "cheap" end of spectrum) and a Battery Monitor (or Victron Battery Monitor)...

Batteries are very often killed by over discharging (taking a battery bank "dead" even once can be enough to kill it).

Given this is a resort--some of the power use may be out of your hands (employees, guests) and you need to make sure that you (and your backup) know the state of the battery bank at all times.

Deep Cycle Battery FAQ
www.batteryfaq.org

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,655 ✭✭✭✭✭
Re: Need advice on off grid system

As to angle, I would angle them for winter! Not even knowing your time of greatest use, a 35 degree angle and rain fall will help clean the panels, while at <15 degrees, someone would want to check them often for bird droppings.

Do you have a sea breeze effect where you are with regular clouds and rain at some point in the afternoon? If so you might want to angle them a bit more to the east as well.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Need advice on off grid system
BB. wrote: »
Take a second look at getting AGM batteries. They tend to be way more expensive and not really last as long as a good industrial battery.
-Bill

i agree about the costs of agms, but who said they don't last? i've lost a bit of capacity on my 1st agm, but it was abused a bit too and it is still going with this year being its 8th year. maybe it would be better to ask him why he chose the agms rather than advise him against them. maybe he prefers the non-gassing so he can put them in his home or he likes the efficiency of them. i would not have made a fuss if your reasoning was that the first batteries in a system tend to get beat up or abused so it's better to iron out the kinks with a cheaper battery, but your reasoning isn't right to give imho.:-)
• Solar Expert Posts: 44
Re: Need advice on off grid system

Hi Neil..Yes I do like the fact that I can put the AGM batteries anywhere and there is no gas..also that is what is available..and if i only discharge them 25% then they should last 5-7 years..does that sound right? thks larry
• Banned Posts: 17,615 ✭✭
Re: Need advice on off grid system

Personally I'm not keen on forklift batteries because they are very large and very heavy which makes them difficult to handle physically. There are also issues with getting the charging values right for RE because they weren't designed for it and the manufacturer's don't have any exact specifications for programming your controller.

I do like using FLA's because nothing beats taking a specific gravity reading for knowing what shape your battery is in. They will also take a lot of "abuse" that AGM's will not tolerate - specifically over-charging and resulting water loss.

Never heard of AGM's not lasting a reasonable amount of time. They can die in an instant if the charge Voltage is too high: the vent pops, the water is lost, the battery is scrap metal. But they will take/give more current than FLA's.

Contrary to what some will tell you, freezing is not an issue with any battery if it's kept charged. AGM's can stand sub-freezing temps even if partially discharged. This is probably not a potential issue in the Philippines. :roll:
• Solar Expert Posts: 6,031 ✭✭✭✭✭
Re: Need advice on off grid system

I think you would be lucky if an AGM could last 5 years in a cycling application with a new user.
"we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
http://members.sti.net/offgridsolar/
E-mail [email protected]

• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Need advice on off grid system
larrybc1 wrote: »
Hi Neil..Yes I do like the fact that I can put the AGM batteries anywhere and there is no gas..also that is what is available..and if i only discharge them 25% then they should last 5-7 years..does that sound right? thks larry

larry,
i think that is quite reasonable for concordes at least, but i'm not sure of all other brands. unless it gets abused by glitches and mishaps in a new system, then it should be fine for that amount of time and even fla types have problems when getting into that 10yr age bracket no matter their warranty.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Need advice on off grid system
They can die in an instant if the charge Voltage is too high: the vent pops, the water is lost, the battery is scrap metal.

coot,
when the vent pops it does not necessarily ruin the battery. it really depends on how much and how long it vents. i have vented mine when i was inbetween controllers as i had placed an unregulated automotive charger on it a few times and forgot it was on. it went close to 16v several times and did not ruin it, but i can't replace what had vented either so this shows itself to be lost capacity. i would venture to say mine is close to the point of not being acceptable by concorde's standards. i might add that even one that is below that 80% point is not ruined, but just not as powerful so there isn't necessarily any instantaneous scrap metal in this event.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Need advice on off grid system
I think you would be lucky if an AGM could last 5 years in a cycling application with a new user.

it's also true of a new user using fla types too as mistakes on a battery are mistakes on a battery. going fla isn't always cheaper either as some are nearly as high priced in some instances, but in any case mistakes or abuse will detract from the life of any battery regardless of type. his 1st batteries may not necessarily end up abused no matter what type they are as 1st round batteries aren't certain to be abused or mistakes made on them. there's no guarantee that the 2nd or even in the 3rd round of batteries that there won't be mistakes or abuse for some cases either.

agms can't have the water added, but some fla types can boil away their water quite fast and deeply exposing the plates so what good does it do to just be able to add the water in such cases? the only difference may be the initial costs when abuses or mistakes are made to batteries. no matter the type of battery involved it kind of hurts to see unnecessary damage occur.
• Banned Posts: 17,615 ✭✭
Re: Need advice on off grid system

Yes, AGM's may survive over-charging.
Yes, FLA's may not survive over-charging.
Yes, the main reason FLA's are recommended as a "first set" is because they usually cost less per Amp hour than AGM's and as such the user won't be out so much money if something does go wrong.
On average FLA's will withstand higher Voltage charging better than AGM's.
At least that's my experience.

All content of this post is deemed accurate at the time of posting unless it is found not to be. Your actual mileage may vary. Professional driver on a closed course. Do not attempt at home. Not an offer which can be made by formal prospectus only. Offer subject to change without notice. Disclaimer ad infinitum ad nauseum.
• Solar Expert Posts: 6,031 ✭✭✭✭✭
Re: Need advice on off grid system
Yes, AGM's may survive over-charging.
Yes, FLA's may not survive over-charging.
Yes, the main reason FLA's are recommended as a "first set" is because they usually cost less per Amp hour than AGM's and as such the user won't be out so much money if something does go wrong.
On average FLA's will withstand higher Voltage charging better than AGM's.
At least that's my experience.

All content of this post is deemed accurate at the time of posting unless it is found not to be. Your actual mileage may vary. Professional driver on a closed course. Do not attempt at home. Not an offer which can be made by formal prospectus only. Offer subject to change without notice. Disclaimer ad infinitum ad nauseum.

Your darn right. Also add the number of cycles in because we are talking cycling daily for offgrid and not some old battery that sat in a garage for years unused.

My favorite example is a customer in Baja who could not get to his house for two weeks after a hurricane washed roads out. Lightning had blown out the inverter and the mx-60 had welded the relay. A 24V set of Surrettes charged daily to near 36v for 12 days. All he did was add water and the batteries were fine.

I would not specify AGM for cycling unless there was a really compelling reason ( UnattendedTelcom) where they will get changed out every 4 or 5 years before they fail.

The main reason a new user has problems is they do not know what their loads are. They have not done this and no matter how many people have tried to estimate the power required, it still is unknown until you have done it! If it were easy, there would not be so many failures !
"we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
http://members.sti.net/offgridsolar/
E-mail [email protected]

• Solar Expert Posts: 10,300 ✭✭✭✭
Re: Need advice on off grid system

yes, i acknowledged already that higher voltage is a weak point on an agm, but that is what a controller is for as i admitted i didn't have a working controller for a spell.

note here that my agms are not just batteies in storage. many agms are deep cycled batteries and telcom batteries are different than the agms from concorde or decca/mk to name a few as telcom batteries don't cycle well and aren't meant to. don't pooh pooh them just because you like fla.

the op is familiar with the types and made a decision as it fit his needs best in his viewpoint. to argue about flas vs agms is moot and i would have had no quarrel with the op if he had chosen an fla type. it seems a few of you may have a grudge against agms that is unfounded and your argument can't be based by telcom batteries specifically as telcoms are different in many respects than other agms. that argument is like saying all fla batteries are no good based on automotive starting batteries.

let's drop this aspect of the discussion as this does not help the op in setting up his system. if you want a p***ing match on battery types then take it elsewhere to a new thread.