Help required to design off grid system

Re: Help required to design off grid system

Also, if your bank is "sulfated" (sulpher is permanently locked in with lead into a crystalline form), you will also see low Specific Gravity.

And for a "sanity" check--Check a couple car batteries too and see what they read. It is not unusual for a hydrometer to not be calibrated, or some other issue (such as dirty/sticking float) affect your readings.

What was the solar array size (wattage), and what was the battery bank rating (volts/Amp*Hours, and per string--if you are disconnecting a string or more)?

Basically, batteries are pretty good during much of the charging cycle. If you take 100 amp*hours out, you need to return around 100-120 AH back.

And, once the battery reaches Absorb set point (say ~58 volts or so), you should hold it for ~2-4 hours or so to ensure that the battery is fully charged (the last 10-15% of battery charging takes time, the battery charging current slowly falls during this last part of the cycle).

Just reaching ~58 volts is not enough. "Shallow" cycling, perhaps 2 hours of "absorb"... Deep cycling, or trying to recover a "troubled" battery bank may need 4-6 hours of absorb voltage... As always watch battery bank temperature... You do not want to exceed the mfg. operating temperature (around 45-55C maximum temperature or you will risk battery damage).

-Bill

Re: Help required to design off grid system

syedbukhari wrote: »

I am using 12 batteries
each battery has 12 volt and its capacity is 200 Ahr
Total watts for 12 batteries are 28800

• 4 batteries in series, gives you 4*12v=48 volt battery bank.
• 3 parallel strings give you 3*200AH=600 AH battery bank @ 48 volts
• 600 AH * 48 volts = 28,800 WH = 28.8 kWH battery bank.

Yes 3 panels in series with 4 strings in parallel with 2 panels unused.

• 12 panels * 220 Watts = 2,640 watt array

I am using aprox. 14000 w*hr energy

Per Day???

You are using about 50% of your battery bank's capacity every day:

• 14,000 WH used / 28,800 WH battery bank = 0.49 / 49% of capacity used

That is a pretty heavy load for a battery bank... It will probably not last quite as long and you will have to be very careful to get it fully recharged at least a couple times a week.

More or less, your charging will be:

• 14,000 WH * 1/0.80 battery eff * 1/0.77 panel+controller losses * 1/2,640 Watt solar array = 8.6 hours of "noontime equivalent" sun per day

There are very few areas in the world were you will get that much sun, constantly, every day.

In north America, we use ~4.0 hours of sun per day as a, sort of, minimum assumed value to size a power system... If you are in a very sunny region, you may get 5 hours pretty consistently for 9 months a year.

My 0.80 (80%) flooded cell battery efficiency may be on the "conservative" side--And if you do things right, you may get closer to 90% efficiency (at least while the batteries are in very good shape--older batteries can become more inefficient) or:

• 14,000 WH * 1/0.90 battery eff * 1/0.77 panel+controller losses * 1/2,640 Watt solar array = 7.7 hours of "noontime equivalent" sun per day

At this point, your desired loads (I am assuming you are telling me 14 kWH of 48 volt DC loads, if it was 14kWH per day of 230 VAC AC loads, you would have another 1/0.85 for inverter losses too) and size of solar array are probably not sustainable. You need either to cut back on loads and/or add to your solar array.

In some ways, if you are using your AC power during sunlight hours (i.e., service station)--You are saving some battery losses (i.e., you don't have the 80% battery efficiency issues when the sun is up and, more or less, powering your loads from the solar array).

However, this can be an issue as this also reduces charging current to the battery bank which can be a problem too (we recommend ~5% to 13% rate of charge to a battery bank) and if you are drawing Y,YYY Watts during the day, you don't want the Z,ZZZ watts available for battery charging to be less than 5% rate of charge.

For example, a 5% minimum rate for a 600 AH @ 48 volt battery bank would be:

• 600 AH * 58 volts charging * 0.05 rate of charge = 1,740 watts to battery bank

Which leaves:

• (2,640 watt array * 0.77 controller+panel derating) - 1,740 Watt 5% batt charging = 293 watts average daytime DC load supported by array

And, I think, your DC loads during the daytime are probably much larger.

Many of our rules of thumb assume charging during daylight and discharging at night (at work during day, home at night cooking, TV, homework, lighting, etc.).

When you start mixing significant daytime loads into the design requirements, we need to make sure that all this continues to work together well.

Assuming that much of your power is daytime use, your battery bank may be OK with its current size--And you "just" (I know, adds a lot of cost for you) enlarge your solar array--Probably roughly double in size (just a guess at this time).

Yes you are right distance and language is problem to elaborate my views.

And yet, your posts have fewer errors in English grammar than mine (my only language).

-Bill

Re: Help required to design off grid system

There are just too many options/models/manufacturers to generalize that "all VFDs" can take DC input or not...

For your needs (AC pump + VFD + Solar array--lowest costs, least amount of maintenance)--You will really need to work with a local supplier or a manufacturer that is willing to work with you in country.

There is a very good chance that with your experimenting and experience you will be gaining--That you can make this a business and help others with their pumping/solar needs (more than a few people here have created solar based businesses after going down that road on their own first).

What I would suggest--Try to find a used 3 phase motor that would meet your needs (fit pump, correct size, etc.) and then send the motor/pumping specifications to a couple manufacturers and/or local representatives and see what they can do.

Also, if you know somebody with the local paper and/or somebody that writes on the Internet--You could "suggest" that they may get some free advertising out of assisting you. If you have a local university (or even trade school)--You could try enlisting their help/prestige too .

AC power, and especially 3 phase/poly phase power is a very complex subject (lots of math--I mean a very lot of math). There is probably little you can do to "help" or "play around" with a generic VFD to convert it to your needs unless you have a lot of engineering/electronics experience. Add trying to direct couple to a Solar array (which is a "current source" rather than a voltage source--that most equipment is designed to connect with)--And you should do much better with equipment designed for your needs--rather than trying to convert.

If, instead, you go with solar+battery+AC inverter (more expensive, less efficient, more maintenance), then as long as your solar PV AC system is large enough--Then you can probably run a "generic" VFD (single phase AC in, poly phase AC out to motor).

-Bill

Re: Help required to design off grid system

You probably will have to contact the mfg/representatives... But, some links:

Hyundai N 300 200 or 400 VAC 3 phase input--No direct from solar array that I can see
Lenze 8600 appears to support DC input (could it be programed for solar power input?):

3 x 480 V AC, 45 to 65 Hz
Permissible voltage range: 330 ... 528 V
(alternatively 470 to 740 V DC supply

Yaskawa 616 G3 Do not see any DC input option

I don't think any of these will really do what you want them to do... The Lenze unit may be programmable to measure the DC input voltage/current, then a program could perform some sort of MPPT (maximum power point tracking) and control the pump based on how much solar power there is at the panels. But I would not think this would be easy.

If you have contacts with anyone that sells these VFD's, I would suggest you look at the links I gave you for solar pumping (perhaps even the article) that they can send back to the factories. I think that would help them understand your needs better.

Solar arrays are not "solar batteries"--They are sort of like the most ugly power you can imagine (current sources that vary with the amount of sun and temperature of the array).

It would be better to find/use an VFD designed and tested to run from a solar array (directly) rather than trying to program a standard VFD or "play" with one to see if you can get it to work (unless you have the experience and workshop to do such experimentation/reconfiguration).

-Bill