Need advice on off grid system

[larrybc1]

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

[Designer_Mike]

Hi Larry and welcome,

8000 watt is not the proper unit.
A watt is a measure of power at a given time. To do the calculations properly you will need to calculate the "energy" requirements most likely in watt-hour (or kilowatt hours). Which is just as simple as it sounds. If you are consuming 8000 watt for one hour, you have consumed 8000 watt-hour.

If you expect to consume 8000 watt for 24 hrs a day, you will need to generate 192 kilo-watt hours a day. Hopefully you are talking about consuming 8 kilo-watt hours!
Sunking is the calculation wiz when it comes to battery and generation requirements so I'm not even gonna try!

I'm sure he'll be along in a minute and crunch the numbers in his head in no time but he will need clarification about 8000 watt per day.

[larrybc1]

Hi Larry and welcome,

8000 watt is not the proper unit.
A watt is a measure of power at a given time. To do the calculations properly you will need to calculate the "energy" requirements most likely in watt-hour (or kilowatt hours). Which is just as simple as it sounds. If you are consuming 8000 watt for one hour, you have consumed 8000 watt-hour.

If you expect to consume 8000 watt for 24 hrs a day, you will need to generate 192 kilo-watt hours a day. Hopefully you are talking about consuming 8 kilo-watt hours!
Sunking is the calculation wiz when it comes to battery and generation requirements so I'm not even gonna try!

I'm sure he'll be along in a minute and crunch the numbers in his head in no time but he will need clarification about 8000 watt per day.

Hi Mike..My mistake I should have been clearer..I meant to say that in a 24 hr period i expect to use 8000 watts of energy..so i am trying to generate enough power for using 8000 watts per day total..also I need to store 2-3 days worth in case of no sun etc..I hope this clears it up a little bit..thks Larry

[Mike90250]

Buy first, Research 2nd. Welcome to the Club.

Get a couple spare panels, while you can - Evergreen is going out of business.

So, I'd suggest 2 arrays, 5 panels in series,(2 strings of 5) in each array. Use either a 60 or 80amp charge controller. With the heat you have, it's best not to run stuff too near it's max limit. This also gives you a bit of redundancy - 2 separate arrays w/controllers.
20, 210w panels will produce about 80% of their nameplate in the heat. So I'd expect to see a total of 3360watts, or 1680w per array if you split in 2. An interesting idea you can use, is to face one array 20deg east of south, and the other 20deg west of south. This will give you more power, spread over the whole day, and may give a better top off charge, while you have one array a bit toward the sunset, the other catches sunrise. Check out the specs on the PV watts site for how the 2 setups may differ !

Gee this is all backwards, Your loads drive the battery size, and the battery size drives the solar array.

Batteries: (rule of thumbs for quick and easy design)
So you have roughly 3.3Kwh at hand, maybe 5 hours (maybe 6) sunlight gives you nearly 17KWh daily harvest. You can only use half of that ! The rest is wasted in system losses. Ouch. That's 8500 kwh is the max you can use.

Battery discharge. We shoot for about 20% daily discharge, If you have a 100ah battery, you can use 20 amp hours, leaving 80ah in the battery. This gives you longest battery life. Also a large battery bank that will last through 2 cloudy days before you need to fire up your backup genset. If you go with 50%, and have a cloudy day, you may find yourself running a lot of fuel through your genset, to keep the batteries alive. Discharge them way down, and you only get a dozen cycles. Deep cycle batteries are not !
8,500wh = 177ah at 48V. So you need at least an 800ah battery bank. Tall case L-16 size batteries are 6V @ 400ah (some brands are 350ah, some 420ah) So you would need 2 banks of these.
If you use the 200ah AGM batteries, you may wont get 1 year (365 cycles ) of 95% discharges. Maybe 200 cycles at the most.

Ouch !

[larrybc1]

Buy first, Research 2nd. Welcome to the Club.

Get a couple spare panels, while you can - Evergreen is going out of business.

So, I'd suggest 2 arrays, 5 panels in series,(2 strings of 5) in each array. Use either a 60 or 80amp charge controller. With the heat you have, it's best not to run stuff too near it's max limit. This also gives you a bit of redundancy - 2 separate arrays w/controllers.
20, 210w panels will produce about 80% of their nameplate in the heat. So I'd expect to see a total of 3360watts, or 1680w per array if you split in 2. An interesting idea you can use, is to face one array 20deg east of south, and the other 20deg west of south. This will give you more power, spread over the whole day, and may give a better top off charge, while you have one array a bit toward the sunset, the other catches sunrise. Check out the specs on the PV watts site for how the 2 setups may differ !

Gee this is all backwards, Your loads drive the battery size, and the battery size drives the solar array.

Batteries: (rule of thumbs for quick and easy design)
So you have roughly 3.3Kwh at hand, maybe 5 hours (maybe 6) sunlight gives you nearly 17KWh daily harvest. You can only use half of that ! The rest is wasted in system losses. Ouch. That's 8500 kwh is the max you can use.

Battery discharge. We shoot for about 20% daily discharge, If you have a 100ah battery, you can use 20 amp hours, leaving 80ah in the battery. This gives you longest battery life. Also a large battery bank that will last through 2 cloudy days before you need to fire up your backup genset. If you go with 50%, and have a cloudy day, you may find yourself running a lot of fuel through your genset, to keep the batteries alive. Discharge them way down, and you only get a dozen cycles. Deep cycle batteries are not !
8,500wh = 177ah at 48V. So you need at least an 800ah battery bank. Tall case L-16 size batteries are 6V @ 400ah (some brands are 350ah, some 420ah) So you would need 2 banks of these.
If you use the 200ah AGM batteries, you may wont get 1 year (365 cycles ) of 95% discharges. Maybe 200 cycles at the most.

Ouch !

Mike..thks for the help..So do you think I have too many solar panels for what I want to do..My plan was to have 20 panels but as of now I only have 16 evergreen 210 watt panels..Do I need to get the other 4 panels? I understand what you are saying about the batteries..less discharge= longer life..what if the 200 ah AGM batteries are only discharged 30-50% how long will they last? might be hard to get the trojans in the Phils..thks Mike Larry

[russ]

Routinely only discharge to 20% (80% remaining) with a 50% DOD as a maximum once in a while is the normal recommendation for best battery life.

[Mike90250]

Mike..thks for the help..So do you think I have too many solar panels for what I want to do..My plan was to have 20 panels but as of now I only have 16 evergreen 210 watt panels..Do I need to get the other 4 panels?

Define your loads, and assume they will be 20% more
Then redo the numbers I did, and see if you can get by with 16 panels. Wire them 5 in series, 3 strings, and you have a spare in case of breakage. Will work with 1, 60a charge controller

I understand what you are saying about the batteries..less discharge= longer life..what if the 200 ah AGM batteries are only discharged 30-50% how long will they last? might be hard to get the trojans in the Phils..thks Mike Larry

battery chart for your batteries can be obtained from the mfg. 50% discharge will, if you are lucky, give you a couple hundred cycles.

[russ]

About battery discharge recommendations - from http://www.boatelectric.com/sulfation.htm

---** In industrial usage batteries the recommendation is to avoid discharging batteries no more than 80% of their capacity and then charging them to 100% immediately after the discharge. If drained lower than 80%, a quantity of lead sulfate will be created more than desired. Also, hard lead sulfate will start forming within 2 days if batteries are left discharged. To avoid sulfation buildup, the battery must be charged back to 100% right after discharge. Equalization charge should take care of the hard sulfation, but there will be some sulfation left over that the equalization charging misses.

[larrybc1]

Define your loads, and assume they will be 20% more
Then redo the numbers I did, and see if you can get by with 16 panels. Wire them 5 in series, 3 strings, and you have a spare in case of breakage. Will work with 1, 60a charge controller



battery chart for your batteries can be obtained from the mfg. 50% discharge will, if you are lucky, give you a couple hundred cycles.

thks Mike for all the info..so I should plan on only a 20% discharge for the batteries to last? also will look for industrial type batteries--forklift style thks larry

[Sunking]

Larry you do understand by going off-grid in the Philippines you are volunteering to pay about $3 to $4 per Kwh for electricity the rest of you life paid up front in cash in 5 year increments as you continually replace batteries?

To generate 8000 watt hours you will need a 3000 watt solar panel array, 60 Amp MPPT charger, and 40 Kwh battery.

In the USA just that equipment alone cost around $12,000 with $5600 of that in batteries to replace every 5 years or so. I would imagine where you are at will cost at least twice that much plus that much more in other equipment to support it like a generator.

[larrybc1]

Larry you do understand by going off-grid in the Philippines you are volunteering to pay about $3 to $4 per Kwh for electricity the rest of you life paid up front in cash in 5 year increments as you continually replace batteries?

To generate 8000 watt hours you will need a 3000 watt solar panel array, 60 Amp MPPT charger, and 40 Kwh battery.

In the USA just that equipment alone cost around $12,000 with $5600 of that in batteries to replace every 5 years or so. I would imagine where you are at will cost at least twice that much plus that much more in other equipment to support it like a generator.

Hi derck.. Thks for the reply. Yes I realize the cost but right now I pay $350-400 a month for diesel not including maintenance and for only 10 hrs of power.. So even replacing batteries every 5 years for $5000 is cheaper then diesel at $4000 per year.. Plus I will have power available for 24 hrs.. I would go on grid if that was a possibility but it never will be as I am on a remote island location.. Thks Larry

[Sunking]

OK Larry I thought you had access to the grid.