Help needed choosing a solar system

kARTechnology

Hi all.

I am looking to buy a solar setup that could save me from powercuts (which happen sometimes in a month, say 6-7 times for 1-6 hrs)

the location is for a business workplace so night time backup isn't a concern

Actual Load Peak= 36KW

Lighting and Fans, Water Pump = 5KW

Only Essential Load= 3KW

I am confused to go for a hybrid setup, or a separate ongrid+battery inverter setup.

1. Infini V 5KW
2. Longi 375Wp Mono PERC  = 16 nos
3. Exide 12v SolaTubular 150Ah = 8 nos 

 

• Please suggest if any better options available. Also I would like to use some monitoring software. I find the ICC site inaccessible from India. I think i have to build something that uploads to PVOutput website using some ESP32/Raspberry/Laptop. Serial Command Set Information available?
• How is the reliability of the Infini V? Life?  is the low voltage Solar DC input a disadvantage compared to the true Infini series?
• This doesn't seem to have a 4 stage/multi stage charger - so hows the battery life with this Inverter? Battery Equalizer required?
• I read here that the inverter consumes around ~125W to keeps itself running? if yes isn't that a loss on the energy generated? I think all inverters do not consume such high power.
• The fans are in reverse - against natural convection - is it recommended to switch the directions?
• Are there any other better options available?
• I hope the on-grid will help to reduce electricity bills due to the production on Sundays & offset when not using much load that compensates when running Air Conditioner.
• Or is the Axpert VM II 5KW with 5KW Solar Power is suitable for my usage, offgrid & buy more batteries?

BB.

Welcome to the forum KT,

Can you tell us a bit more about your location and energy needs? I guess you are in the Andhra Pradesh state, India?

Many people around the world have afternoon power outages fairly often. And the typical solution (starting point) is an AC battery charger, battery bank, and AC inverter (or inverter-charger). Basically make a UPS system for your home or business.

The above can be a relatively small(er) and cheap(er) system than going full off grid solar power system.

Basically, the battery bank is sized for 2 to 4x larger than your "daily" load (2x for emergency backup and/or if you have AC power to quickly recharge the battery bank--4x your 24 hour loads if you are truly looking for solar power--Solar panels have limited hours of sun per day, something like 6+ hours of charging per day during the summer and less in winter or monsoon season).

You are on the right track looking at conservation first--It is generally much less expensive to conserve power than to generate it.

And while LED lighting and Laptop computers, and (especially DC) ceiling fans are good starts for conservation, Refrigerators/Air Conditioning, major water pumping, etc. are very large usages of power--Both peak Watts (starting  and average power consumption), they also run for many hours per day... They drive your battery bank and AC inverter larger. If you are only supplying power for 6 hours per day instead of off grid power for 24x7--The system can be much smaller (run fans, don't run A/C, if practical).

You can always begin with the battery bank + AC inverter-charger system... And add solar panels (and a backup genset) later--If needed/still desired. And this kind of system will be a fraction of the costs off a full time off grid solar power system (batteries last 5-7 years typically, unless you go with higher end industrial/traction batteries). And if you have a hot climate, hot batteries have a much shorter life (for every 10C increase over 25C, the life is cut by 1/2).

-Bill

kARTechnology

BB. said:

Welcome to the forum KT,

Can you tell us a bit more about your location and energy needs? I guess you are in the Andhra Pradesh state, India?

Many people around the world have afternoon power outages fairly often. And the typical solution (starting point) is an AC battery charger, battery bank, and AC inverter (or inverter-charger). Basically make a UPS system for your home or business.

The above can be a relatively small(er) and cheap(er) system than going full off grid solar power system.

Basically, the battery bank is sized for 2 to 4x larger than your "daily" load (2x for emergency backup and/or if you have AC power to quickly recharge the battery bank--4x your 24 hour loads if you are truly looking for solar power--Solar panels have limited hours of sun per day, something like 6+ hours of charging per day during the summer and less in winter or monsoon season).

You are on the right track looking at conservation first--It is generally much less expensive to conserve power than to generate it.

And while LED lighting and Laptop computers, and (especially DC) ceiling fans are good starts for conservation, Refrigerators/Air Conditioning, major water pumping, etc. are very large usages of power--Both peak Watts (starting  and average power consumption), they also run for many hours per day... They drive your battery bank and AC inverter larger. If you are only supplying power for 6 hours per day instead of off grid power for 24x7--The system can be much smaller (run fans, don't run A/C, if practical).

You can always begin with the battery bank + AC inverter-charger system... And add solar panels (and a backup genset) later--If needed/still desired. And this kind of system will be a fraction of the costs off a full time off grid solar power system (batteries last 5-7 years typically, unless you go with higher end industrial/traction batteries). And if you have a hot climate, hot batteries have a much shorter life (for every 10C increase over 25C, the life is cut by 1/2).

-Bill

You were right about my location.

UPS system, I have 2x 1kva units with each 150ah 12v battery(i know its too small for a reasonable backup)

I could go with 10x12v 150ah @120v batteries and a huge 3 phase 10 kva inverter that can run all my essential load + elevator @ $2.5k, BUT

the power bill for charging these batteries, and additional there are no other benefits.

If i go for a hybrid 5KW + 6KW Solar, with 8x12v 150ah @48v i could be able to run my loads for longer time during the day without hurting the battery, if excess is generated sell it to the grid, avail solar tax benefits

in commercial place we cant conserve power bill as more lights=better look.

I am not going to buy a genset that's noisy, requires maintenance and drinks lots of fuel (very expensive diesel@ 1$/litre)

All lights are 18W LED. water pump is used once per day for 20 min.

Temperatures here are 40-45degrees in summer. cant live without AC. AC currently are 3 phase and there is no scope of running off solar other than offsetting with a on-grid inverter.

I have a quote for $7.3k for the following

1. Infini V 5KW
2. Longi 375Wp Mono PERC  = 16 nos
3. Exide 12v SolaTubular 150Ah = 8 nos 

What do you say?

BB.

I can help a little bit--But you probably need a knowledgeable local electrical engineer to scope your system and oversee the installation and initial qualification/maintenance plans/etc.

For example, you have an elevator you need to keep running. Having no idea about your system, just the lift motor can easily (at a minimum) be ~3-10 kWatts.

I can give you a rule of thumb to initially size the system and (roughly) predict its average output and capabilities. But for anything this large, you need a competent engineer to design and install such a system.

Typically, the component that costs most for an off grid capable system is the battery bank. And for such a large system, you ideally want to look at industrial batteries (such as those for electric forklifts and other tracton type batteries). For example, instead of a bunch of "small" 150 AH @ 12 volt batteries-4x series times X parallel banks, you would look at lower voltage batteries (6 volt, 4 volt, or even 2 volt single cells of large AH capacity)--This sorts of cells make for a more reliable battery bank:

https://www.solar-electric.com/fullriver-dc1150-2-agm-sealed-battery-2v-1150ah.html

The above is just an example of a 2 volt @ 1,150 AH (AGM in this case) cell. You would put 24 of them in series for a 48 volt @ 1,150 AH battery bank. In any case, you need to work with a local battery supplier--You are not going to use our host to ship to India. Having lots of parallel strings of batteries is possible, but I suggest that it is not optimum. Battery life and safety issues with lots of parallel strings, and expense of wiring+fuses/circuit breaker per string, balancing charging/discharging currents, monitoring/inspection of the bank to locate bad cells and wiring, etc. Using large single cell batteries in series (I would suggest 1-2 parallel strings is optimum and avoid more than ~3 if possible with local battery suppliers and their products) is the way large systems are usually configured.

You are sort of all over the map here in terms of sizing a system... 5 kW, 10 kW, potentially even 40 kW to support an elevator.

Back to system design. The peak (running) wattage is one design point. Another is how many hours per day will you be running the load and various other requirements (how many solar panels, do you get full sun/no shade on the panels from at least 9am to 3pm, what about cloudy days/monsoon season--Solar panels only collect lots of energy in sunny weather. Do you have a battery bank that can, for example, supply your loads for 2 days of "no sun" and 50% maximum battery discharge (for longer battery life). Can you keep the batteries cool (batteries are designed for 25C usage. At 45C battery temperature, the life is ~1/2*1/4=1/4 life ... Or an 8 year battery life at 25C is 2 years at 45C--Engineering Rule of thumb, for every 10C rise in temperature, things "age" about 2x faster).

OK--I will go really quickly through the math for a 5 kWatt off grid (hybrid) AC inverter assuming 2 kWatt average load * 6 hours of utility power failure in the afternoons, solar power only with Flooded Cell Lead Acid Batteries.

• 2,000 Watt average load * 6 hours per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max discharge * 1/48 volt battery bank = 1,176 AH @ 48 volt battery bank
• 1,176 AH / 150 AH batteries =7.8 parallel strings ~ 8 parallel strings
• 8 parallel strings * 4 batteries per string (12 volts * 4 = 48 volts) = 32 x 12 volt @ 150 AH batteries

The above is a conservative battery bank design... If you do not have daily outages and can use utility power to recharge the battery bank, then you could go down to 1/2 the size of battery bank (4 parallel strings, 16x batteries total). But if you are going solar and assume near daily power failures, too small of battery bank is difficult to fully/quickly charge from 50% state of charge to 100% in one day with only solar panels.

Next, you need to do two calculations for solar panels. One is based on the size of your battery bank (larger battery banks need more charging current). The typical rule of thumb is 5% rate of charge minimum for weekend/sunny season usage... 10% minimum (to 13% to 20%) for full time usage (daily usage all year long). Note, for our math, we use the battery bank's 20 Hour discharge rate--There are other ratings, but this works out well for our needs.

• 8 parallel strings * 150 AH per string = 1,200 AH @ 48 volt battery bank
• 1,200 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 9,195 Watt solar array (nominal)

And then there is sizing the array based on your daily power usage and hours of solar energy per day. Just to have some numbers (pick city near your location), fixed array, facing south, with a 77 degree angle from vertical:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Chennai
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 77° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.82	6.50	6.64	6.04	5.82	5.06
Jul	Aug	Sep	Oct	Nov	Dec
4.51	4.44	4.78	4.57	4.52	5.00

Your minimum average sun is 4.44 Hours per day for August. The solar array would be (at a minimum for "break even" solar):

• 2,000 Watts * 6 hours per day - 12,000 WH per day
  
• 12,000 WH per day * 1/0.52 off grid solar system eff * 1/4.44 hours of sun (August) = 5,198 Watt solar array minimum

And for a business (or even a home), that your "base loads" (loads you need every day and cannot turn off during bad weather), that you use only 50% to 65% of the above "predicted output", or:

• 5,198 Watt array * 1/0.50 base load derating = 10,395 Watt array recommended (especially if no genset/backup power)

From the 9,195 Watt array based on 10% minimum rate of charge, and the 10,395 Watt array for "base load" sizing, the number of solar panels would be:

• 10395 Watt array * 1/375 Watt panels = 27.7 ~ 28 panels suggested array

The exact panel configuration depends on your solar charge controller specification (maximum array input voltage, maximum current/power, etc.).

Anyway--Some math that lets you size your system based on your energy needs and assumptions about where you are located and how you will use the energy (average loads, hours per day, etc.). The above is not "right or wrong", but just a suggestion for a relatively conservative fully solar power system based on my first pass guesses.

Your thoughts, corrections, and questions?

-Bill