Qs about designing a pv system

sdharrat
sdharrat Registered Users Posts: 6 ✭✭
hello everyone 
i have a problem about designing a pv system
my customer has a  building ( office building) the building has 2 floors, he ask my to design a pv system that can run 2nd floor only. the floor consist 6 offices. he asks the system should run without batteries as the the offices are open from 8am to 2 pm and the batteries are expensive

when i estimated the load i found it needs about 8kw and for 6hrs the total load will be 48kwh
if i used kw i will need 14 panel (panel = 265 w)
but 48 kwh i will need more panels more that 70
so because the roof building is small is about 180 sqr m 
 i decided to install 14 panels
so my question is it possible to use panels to feed 8kw with out using batteries or connect system to grid? 
i mean is it possible to run this system as stand alone without batteries from 8 am to 2 pm? with consideration the building is in Africa so we have a sufficient solar irradiation and a lot of sun hours even in winter. And after 2pm the building is closed so no need for power in evening  or night 

Comments

  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    Really need baterys .  Inverter needs start up voltage and smoothing of dc voltage. You could try a smaller than normal battery .. but it could well die early.what inverter have you looked at?
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    You will need a means of supporting the load when, for example, clouds obscure the sun, wether it's batteries or using the grid as a battery, equipment will be needed to address this problem, there are ways to use solar to supplement the grid through AC coupling. Some  equipment can support a limited load without battery support but 8Kw is not within their capabilities, to the best of my knowledge.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • sdharrat
    sdharrat Registered Users Posts: 6 ✭✭
    hi
    the system is like this

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    The system outlined in the diagram would never work successfully for various reasons.

    Firstly, the panel output is non linear, anything outside the 2 hours around noon, there would be less current, so let's say at 8 am the inverter is turned on, if the capacitors don't sag the voltage and shut the inverter down, and somehow it manages to start, the auto transfer switch will operate, connect to the loads, which collapses the input voltage  causing a low voltage shut down and transfer back to the grid.  This will repeat itself until the array can actually carry the loads, if ever, near noon, but a cloud passes and everything shuts down again.

    Secondly,  because the charge controller actually needs battery power to operate it would fail to boot and or if auto voltage. It may boot selecting  the wrong voltage using PV voltage as a reference.

    Thirdly, a charge controllers algorithm will not be well suited to an inverter's needs.

    Batteries have enormous current potential with reletivaly stable voltage exactly what an inverter needs as a source, there are a few options which could assist with loads such as AC coupling with grid support, but this needs specialized equipment and still requires batteries.



      

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    14 panels at 265w is ~3.7kw.  At normal operating temperature, actual output in full sun might be ~3kw.  With controller and inverter losses, more like 2.5kw.  No way it runs 8kw load, even at noon.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • sdharrat
    sdharrat Registered Users Posts: 6 ✭✭
    mcgivor said:
    The system outlined in the diagram would never work successfully for various reasons.

    Firstly, the panel output is non linear, anything outside the 2 hours around noon, there would be less current, so let's say at 8 am the inverter is turned on, if the capacitors don't sag the voltage and shut the inverter down, and somehow it manages to start, the auto transfer switch will operate, connect to the loads, which collapses the input voltage  causing a low voltage shut down and transfer back to the grid.  This will repeat itself until the array can actually carry the loads, if ever, near noon, but a cloud passes and everything shuts down again.

    Secondly,  because the charge controller actually needs battery power to operate it would fail to boot and or if auto voltage. It may boot selecting  the wrong voltage using PV voltage as a reference.

    Thirdly, a charge controllers algorithm will not be well suited to an inverter's needs.

    Batteries have enormous current potential with reletivaly stable voltage exactly what an inverter needs as a source, there are a few options which could assist with loads such as AC coupling with grid support, but this needs specialized equipment and still requires batteries.



      

    thank you for responding 
    if i removed charge controller and i found at the morning will meet the loads. is it going to work?
    if i increased the number for panels to 20 for example does it will be fine?
    like i said my country in africa and most of days is shine only problem is in winter
    for this if i put 20 panels will meet in winter but in summer the array will produce a lot power 
    will this be harm to system?

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    edited December 2018 #8
    You are asking "if it is possible"... The short answer, is yes it is possible. If you have a large enough solar array, and enough sun, it is possible for a solar array to power an off grid AC inverter and produce (relatively) stable output power. It will be safe, and it will be (electrically) reliable.

    The problem is the realities that you have a highly variable amount of input energy (power)--Sun hitting the solar array--That goes from 0% to 100% input power. And you have the office loads... Which consume energy based on the amount of energy (power) that any person using the office needs.

    Say you have a car. And you have a 3 year old kid playing with the accelerator (gas pedal). And you want to drive from point A to point B. And you are driving in city streets, highway, etc. And the only control you have are the brakes. You can control the car's maximum speed (and even stop and go), but you cannot control the minimum speed. Sometimes the kid will not press the accelerator hard enough for you to reach the speed limit, or even go up the hill. So your choice is to give him a larger engine (bigger solar array) to ensure that you have enough energy to do your minimum stuff.

    There are systems that work very well on direct solar=>Magic Box=>load... One of the most popular and useful is Water Pumping. A typical application is a large solar array, a VFD (variable frequency drive--Which is really a variable output frequency DC to AC inverter), and a 3 phase water pump). Here, the speed of the water pump varies with the amount of solar energy available. Little solar energy, the pump spins slowly. Lots of solar energy, the pump spins fast. And when the water tank/storage pond is full (or they have enough water), the pump is simply turned off.

    In an office environment, you don't really have that option to run the lights, computer, phone system, directly from variable input power (one person uses the computer at 8am, the rest of the 10 can start using it at 10am to 2pm, then fewer people after that--Only make copies during the middle of the day, etc.).

    WIth the water pump, the "water tank" is your "battery"/energy storage. You could use laptop type computers (that have their own internal battery with something like 8-10 hours of storage, like my little Chromebook Computer I am using to type this post right now). The battery keeps the computer running, and the solar panels both recharge the battery, and support the computer during the middle of the day.

    Would that work for your office environment? I don't know. And you would still need some sort of battery system to run your router, lights, printers, etc. to buffer them during the day.

    You can use a program like PVWatts to model the "typical" solar energy available in 1 hour slices for all 365 days a year:

    https://pvwatts.nrel.gov/

    For example:
    TRIPOLI, LIBYA
    20x265 Watt panels = 5,300 Watt array = 5.3 kWatt array (k=kilo=1,000 factor)
    Fixed array
    33 degree tilt of panels (typical year around best harvest)
    Facing south (180 degrees)
    77% system efficiency (no batteries, just solar=>AC inverter=>Available AC power or 23% losses

    Press a few buttons, 

    MonthSolar Radiation
    ( kWh / m2 / day )
    AC Energy
    ( kWh )
    Value
    ( $ )
    January4.14489N/A
    February4.70500N/A
    March5.57643N/A
    April6.14676N/A
    May6.24689N/A
    June6.70700N/A
    July7.08755N/A
    August7.12758N/A
    September6.33661N/A
    October5.20575N/A
    November4.25470N/A
    December3.61429N/A
    Annual5.597,3450
    More or less, you get around 3.61 to 7.08 hours of "full sun equivalent per average solar day... And if you use 100% of the energy, you can harvest ~400 to 750 kWatt*Hours per month.

    Of course, in reality, you are going to build a much larger solar array to because you can only use a fraction of the available solar energy (large enough array to power 8am loads--And have way more than you need for Noon Time loads.

    If you look ~2/3rds of the way to the bottom of PVWatts, you will see an "hourly" button that will give you a CSV file you can bring into a spreadsheet. I will pull up a January 1st day to show you what it looks like (my Chromebook only has enough processing power to load about 1/2 of the file in Google Spreadsheet):

    PVWatts: Hourly PV Performance Data
    Requested Location: benghazi libya
    Location: TRIPOLI, LIBYA
    Lat (deg N): 32.67
    Long (deg E): 13.15
    Elev (m): 81
    DC System Size (kW): 5.3
    Module Type: Standard
    Array Type: Fixed (open rack)
    Array Tilt (deg): 33
    Array Azimuth (deg): 180
    System Losses: 23
    Invert Efficiency: 96
    DC to AC Size Ratio: 1.2
    Average Cost of Electricity Purchased from Utility ($/kWh): No utility data available
    Capacity Factor (%) 15.8
    Month Day Hour Beam Irradiance (W/m^2) Diffuse Irradiance (W/m^2) Ambient Temperature (C) Wind Speed (m/s) Plane of Array Irradiance (W/m^2) Cell Temperature (C) DC Array Output (W) AC System Output (W)
    1 1 0 0 0 10 3.7 0 10 0 0
    1 1 1 0 0 9.8 3.4 0 9.8 0 0
    1 1 2 0 0 9.5 4.3 0 9.5 0 0
    1 1 3 0 0 9.2 3.5 0 9.2 0 0
    1 1 4 0 0 8.9 2.8 0 8.9 0 0
    1 1 5 0 0 8.6 3.3 0 8.6 0 0
    1 1 6 0 0 7.8 2.9 0 7.8 0 0
    1 1 7 0 0 7 2.6 0 7 0 0
    1 1 8 0 23 9.1 2.9 21.373 7.767 94.29 65.523
    1 1 9 268 100 11.2 3.3 269.894 15.949 1121.191 1069.577
    1 1 10 599 100 13.3 3.6 568.833 25.258 2297.607 2210.728
    1 1 11 768 85 15.1 3.1 770.961 33.005 3019.787 2906.449
    1 1 12 810 92 17 2.6 876.037 38.861 3339.311 3213.1
    1 1 13 818 92 18.4 1 893.031 47.003 3265.336 3142.169
    1 1 14 778 96 20 1.5 819.654 44.21 3037.91 2923.861
    1 1 15 697 85 20 1.5 659.644 39.745 2490.372 2396.789
    1 1 16 509 76 19 1.5 418.348 31.647 1620.193 1554.806
    1 1 17 126 42 17 2.1 108.868 19.471 434.529 399.012
    1 1 18 0 1 15 0 0.919 12.54 3.972 0
    1 1 19 0 0 14.5 2.6 0 14.5 0 0
    1 1 20 0 0 13 3.1 0 13 0 0
    1 1 21 0 0 11 0 0 11 0 0
    1 1 22 0 0 11 0 0 11 0 0
    1 1 23 0 0 11 0 0 11 0 0

    The 3rd column is the time (like 0800 hours) and the last column is the total harvest (8-9am, 65.523 Watt*Hours or 0.065 kWH for that 1 hour period).

    And from ~1100 to 1500 hours, you will average a minimum of (almost) 3,000 Watts from your solar array. And by 1800 hours, the sun has set.

    (continue next post)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    I see you have utility power available... Is this system designed to "save money" (pay less for utility power) or is it designed to keep the office running because utility power is "unreliable"?

    A "Grid Tied" (Utility Interactive) system is a very simple Solar Array=>GT Inverter=>Main AC power Panel

    Cheap, reliable, relatively easy to install and maintain system (almost no maintenance required unless something breaks).

    And the way a GT system works--It pumps in all of the available power from the solar array into your AC mains panel, and that power is both shared by your in-building loads, and if you have extra power available, it goes back out to the utility while "spinning your meter backwards". Think of the AC Utility as being a "giant AC Battery"... Sometimes you draw energy from the battery and sometimes you "recharge" that giant AC battery. Of course, there is no AC battery at the utility company, but from your GT system of view, that is pretty much how it works.

    However, the utility polices and design of the electric meter make the billing more complicated, or may even make GT Solar "illegal" for your location.

    There are "hybrid" AC inverter systems that do sort of what you want... Basically they do not feed energy back to the utility, they just feed available solar energy to your loads and recharge the battery bank when extra energy is available. The do work, but at the cost of a local battery bank to buffer energy.

    They could do the same thing without the battery bank, but I am not sure that anyone makes such a system at this time (system would take as much energy as the solar array has available, and if there is any extra, would not use that energy so that there is no energy fed back to the utility). Not sure there is that much of a market for such a system (although, we have quite a few people that ask for just this sort of system).

    Here is a short post with some links to Solar Water Pumping with VFDs. It seems to be getting quite a lot of interest in the last few years.

    VFDs (variable frequency drives) are actually quite common in industry... Take AC power in from the utility and do the VFD "magic" to control 3 phase motors (and other types of electric motors)... All they have to do is a bit of programming to the VFD as most (all?) VFDs convert to DC Voltage internally anyway--Just like solar panel energy is DC too). Add software that is "solar panel" compatible (i.e., vary the output frequency/motor speed based on the available energy from the solar array).

    I hope this helps... It is a complex subject and the difference between "what can be done" and "what is practicable" can be a big gap to jump. For the most part, our computers/offices/homes "need" fixed and reliable incoming energy--And somebody randomly turning on and off the AC power (i.e, variable solar energy) to the office really messes with the computers and peoples' ability to do work.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sdharrat
    sdharrat Registered Users Posts: 6 ✭✭
    BB. said:
    I see you have utility power available... Is this system designed to "save money" (pay less for utility power) or is it designed to keep the office running because utility power is "unreliable"?

    A "Grid Tied" (Utility Interactive) system is a very simple Solar Array=>GT Inverter=>Main AC power Panel

    Cheap, reliable, relatively easy to install and maintain system (almost no maintenance required unless something breaks).

    And the way a GT system works--It pumps in all of the available power from the solar array into your AC mains panel, and that power is both shared by your in-building loads, and if you have extra power available, it goes back out to the utility while "spinning your meter backwards". Think of the AC Utility as being a "giant AC Battery"... Sometimes you draw energy from the battery and sometimes you "recharge" that giant AC battery. Of course, there is no AC battery at the utility company, but from your GT system of view, that is pretty much how it works.

    However, the utility polices and design of the electric meter make the billing more complicated, or may even make GT Solar "illegal" for your location.

    There are "hybrid" AC inverter systems that do sort of what you want... Basically they do not feed energy back to the utility, they just feed available solar energy to your loads and recharge the battery bank when extra energy is available. The do work, but at the cost of a local battery bank to buffer energy.

    They could do the same thing without the battery bank, but I am not sure that anyone makes such a system at this time (system would take as much energy as the solar array has available, and if there is any extra, would not use that energy so that there is no energy fed back to the utility). Not sure there is that much of a market for such a system (although, we have quite a few people that ask for just this sort of system).

    Here is a short post with some links to Solar Water Pumping with VFDs. It seems to be getting quite a lot of interest in the last few years.

    VFDs (variable frequency drives) are actually quite common in industry... Take AC power in from the utility and do the VFD "magic" to control 3 phase motors (and other types of electric motors)... All they have to do is a bit of programming to the VFD as most (all?) VFDs convert to DC Voltage internally anyway--Just like solar panel energy is DC too). Add software that is "solar panel" compatible (i.e., vary the output frequency/motor speed based on the available energy from the solar array).

    I hope this helps... It is a complex subject and the difference between "what can be done" and "what is practicable" can be a big gap to jump. For the most part, our computers/offices/homes "need" fixed and reliable incoming energy--And somebody randomly turning on and off the AC power (i.e, variable solar energy) to the office really messes with the computers and peoples' ability to do work.

    -Bill
    mr Bill
    first of all i really want to thank you for great explanation, really thanks
    like you said in first reply all my loads (light, routers, computers) work continuous and some loads like printer works for seconds 
    so what i understand from first reply at 9 am for example the total power from pv will be about 1100 kwh that particle time 
    so if i want to run the system from this design the pv will give only 1100 kw and the rest of loads will be off and this could be harm on inverter, right?
    for the second reply  i can not work grid tie as is illigal to connect pv to meter in libya (my country)
    and the owner is an Electrical company who is going to sell pv system and he wants this project for commercial purpose to sell the pv system. the reason i didnt choose batteries is base on kwh design i will need a lot of panels which the roof wouldn't handle 

    now i am thinking to multiply the system by   so total power will be 16kwh and add batteries to the system 
    so number of panels will be 34. and rest of need power will take from batteries( spouse what i understand the inverter will take power from batteries even the system is charging, please correct me if i am wrong)
    what do you think mr Bill
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin

    mr Bill
    first of all i really want to thank you for great explanation, really thanks

    You are very welcome SD.

    like you said in first reply all my loads (light, routers, computers) work continuous and some loads like printer works for seconds 
    so what i understand from first reply at 9 am for example the total power from pv will be about 1100 kwh that particle time 
    so if i want to run the system from this design the pv will give only 1100 kw and the rest of loads will be off and this could be harm on inverter, right?

    Just to be clear... Watts is a "rate"... Like a water pump pumping 100 liters per hour.

    Watt*Hour is an Amount"... You run your water pump for 2 hours * 100 L/H = 200 Liters pumped to tank/pond.

    In my example above... for January 1st, the data says from 9am to 10am the system will generate ~1069.577 Watt*Hours (or 1.07 kWH) (just showing all the numbers so you see where I got the from). That may mean that at 9am the system outputs ~500 Watts, and at 10am, outputs ~1,500 Watts... Or an average of ~1,069 Watts * 1 hour = 1,069 WH in that one hour time period. 

    That is why a Battery (or a water pump and tank) is useful for most all uses... The storage device can collect and store the "whole variable" output. If you where using a (for example) ~500 Watt computer (what 9am will generate in "power" (Watts), will be wasted by 11am which is generating ~1,500 Watts (these are "made up" numbers to demonstrate the concept--But probably close enough for discussion).

    In general, "overloading" the inverter will not hurt the solar panels or the AC inverter... If you draw too much energy, the output voltage of the solar array will simply collapse. (power=volts*amps... Drawing 10 amps @ 100 volts from array, then try to draw 11 amps, the output voltage of the array will drop to near 0 (zero) volts... P=0volts*11amp=0 Watts).

    What can be harmed by constant cycling of the AC power--Your refrigerator compressor (induction motor) could overheat). You could also get surge voltages and currents that could damage power supplies, etc. (i.e., damage your AC loads).

    for the second reply  i can not work grid tie as is illegal to connect pv to meter in libya (my country)

    Yes, GT Solar is illegal in some parts of the US too (Hawaii, too many GT solar systems and the grid becomes unstable and unprofitable).

    and the owner is an Electrical company who is going to sell pv system and he wants this project for commercial purpose to sell the pv system. the reason i didn't choose batteries is base on kwh design i will need a lot of panels which the roof wouldn't handle 

    Yes--The person who writes (or pays to write) the laws--Frequently are the ones that benefit.

    However, I will agree with utilities that the "green energy" movement is not a fiscally sound business model. In the US, the rest of the other non-solar customers (and sometimes one or more government taxes) pay for the GT solar subsidies.

    now i am thinking to multiply the system by   so total power will be 16kwh and add batteries to the system 
    so number of panels will be 34. and rest of need power will take from batteries( spouse what i understand the inverter will take power from batteries even the system is charging, please correct me if i am wrong)

    One question I am not sure you answered... Are you doing this to save money? Or are you doing this because Utility Power is unreliable (many places have brownouts/power failures for 2-6 hours on random afternoon/evenings.

    In general, battery backed solar power is relatively expensive (in the US, we pay around USD $0.10 to $0.40 per kWH for our electricity (varies between states/utilities).

    GT Solar power can be very cheap to generate ($0.15 or less per kWH).

    Off Grid solar power (batteries), generally, it costs us around $1.00 to $2.00+ per kWH... Some some people have gotten the power costs down to near $0.50 per kWH.

    You need to calculate the costs of your off grid power... Roughly, batteries last 5-8 years (unless you purchase very good batterie$ and keep them cool), solar panels 20+ years, Electronics (inverters, charge controllers, etc.) ~10+ years. And from a battery based system, you will probably only use ~50% of the "predicted power" (it is almost impossible to use 100% of predicted/available solar power for the average home or business). The system has to be larger than your loads, or you will have blackouts.

    For folks that live in areas with unreliable energy... A common solution is to have a battery bank that support (for example 4 hours of load to 50% state of charge--i.e., batteries are >2x predicted use for longer battery life), and use the utility to recharge the battery bank over night. Have a backup genset (for longer power outages, if needed). And you can add solar panels+charge controller later (as money and time permit to save a bit of utility costs).

    Before you purchase anything... Do a lot of paper designs and costing to figure out how all fits together--And what is the best hardware for your needs (obviously, what is available in the US is not always available/cost effective for you).

    And be clear on what your "numbers" mean/are... 16 kWH... Not sure... But for example, say you have 2,000 Watts of loads for 8 hours per day:

    2,000 Watts (rate) * 8 hours per day = 16,000 WH per day

    2 kWH (rate) * 8 hours per day = 16 kWH per day

    In the above, both above equations are correct and say the same thing... Utilities typically bill in kWH per month... But the calculations we make are typically in Watts and Watt*Hours... You have a factor of 1,000x difference (the "k" vs no "k").

    As an example, if you want to use a 2kWatt loads for 8 hours per day. You need a >2,000 Watt AC inverter (typically around 3-4 kWH minimum) and a 48 volt batter bank capacity of:

    2,000 Watt load * 8 hours per day * 1/0.52 off grid system efficiency (battery based) * 2 days of storage * 1/0.50 maximum discharge (for batteries) * 1/48 volt battery bank voltage = 2,564 AH @ 48 volt battery bank

    The above battery bank would be my suggestion for a full off grid AC power system for your office (plus a bunch of other stuff like solar array, solar charge controllers, AC inverter-chargers, backup genset and/or utility backup power, etc.).

    A 2,564 AH @ 48 volt battery bank is not small or cheap.

    If you were to power your "backup" system only 4 hours and had utilty power to recharge (during random outages), you could probably get away with a battery bank 1/4 the size.

    what do you think mr Bill

    Your thoughts SD?

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sdharrat
    sdharrat Registered Users Posts: 6 ✭✭
    thank you
    for question (Are you doing this to save money? )
    no and i have not  have a problem with lack power
    is just like said this company is electrical company who do construction 
    now the manager of company is going to open a new market which is solar
    he wants to make this project as example to sell and spread the idea of pv

    i mean if someone come to him or some goverment devision ask him to fix or install generator for example
    he wants to say "why you want to do that ? is better to install pv system look to my company is run by pv system, i will design and install pv for price..etc" i mean he is doing for marketing 
    so is not bill or lack of power is just for marketing pv system so he can sell system to others
    his company do installing street lighting transformers and other works and now he wants to enter to pv system
    and this project is going to be an example to other CEO of companies or government organization 

  • sdharrat
    sdharrat Registered Users Posts: 6 ✭✭
    January 1st, the data says from 9am to 10am the system will generate ~1069.577 Watt*Hours (or 1.07 kWH) (just showing all the numbers so you see where I got the from). That may mean that at 9am the system outputs ~500 Watts, and at 10am, outputs ~1,500 Watts... Or an average of ~1,069 Watts * 1 hour = 1,069 WH in that one hour time period

    sorry for this part i dont understand if between 9 to 10 system generate 1.07 kwh how it will be for example 500 at 9 and 1500 at 10 if system generated only 1.07 kwh (2000w 9am+10am grater than 1.07 kwh)


  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    An analogy... Everyone remembers those time/distance problems from grade school math (that most of us hated)...

    At 9am leave point A at 50 kph and slowly increase speed until reaching 100 kph at 10am.

    The average speed is (50+100)/2 = 75 kph average speed.

    And the distance traveled during that time is 75 kph average speed * 1 hour = 75 km traveled.

    Of course, I just guessed the beginning and ending end points... All I know is that we had (in this example) a 1 hour period where the vehicle traveled 75 km. What also would work is:

    (0+150)kph/2 = 75 kph averge speed.

    I used the fact that at that time of day, we see around a 1,000 kWH (per hour) rise in output between 8/9/10... So, assuming a spread of 1,000 Watts between 9:00 am and 10:00 am would be Average Solar Midpoint at 9:30 am ~1,000 Watts with -500 Watts at 9am and +500 Watts at 10 am. I think close enough for our discussion (solar power is at best 10% accuracy when measured with typical field voltage/current/power meters).

    For example... You have a 5 Watt solar cell (or panel) at 18 volts Vmp... The shunt resistor calculation would be:
    • V=IR
    • R=V/I
    • V -- Say you want 0-200 millivolts (0-0.200 volts)
    • P=V*I
    • P/V = I = 5 Watts / 18 volts Vmp panel = 0.278 Amps Imp
    • Isc (short circuit current) ~ Imp * 1.25 ~ 0.2789 Amps Imp * 1.25 fudge factor estimate = 0.347 amps Isc (est)
    • I = Vrange-shunt / Isc panel at full sun = 0.2 volt range / 0.347 ampd Isc = ~0.576 Ohm shunt
    That would give you a 0-200 mVolt range for the recording meter with that arbitrary solar cell/panel.

    Remember that the above solar irradiance data is based on "hourly energy" (Watt*Hour) buckets (Watt*Hours harvested between 9 am to 10 pm). It is not based on 1,070 Watts measured power at 9 am (or 9:30 am, etc.).

    If you are really interested in the details... Any sort of logging voltmeter, a small solar panel, and a low resistance resistor (shunt)--And you can measure the current flow throughout a day. The shunt should be low resistance so that it is near a dead short on the solar panel (reading in millivolts or 10's of millivolts). Within 10% accuracy, the short circuit current of the solar panel is proportional to the amount of sunlight on the panel. Set the solar panel at the angle that you would plan for the array.

    You can probably get a good estimate by using this equation from Wikipedia:

    https://en.wikipedia.org/wiki/Solar_irradiance
    sorry for this part i dont understand if between 9 to 10 system generate 1.07 kwh how it will be for example 500 at 9 and 1500 at 10 if system generated only 1.07 kwh (2000w 9am+10am grater than 1.07 kwh)
    Make sure you understand the data being presented... Again, these are not "point in time" measurement of solar power (Watts -- Rate like kph)... They are "integrated" buckets of solar energy harvested (Watt*Hours -- Amount like km driven).

    1 1 8 0 23 9.1 2.9 21.373 7.767 94.29 65.523
    1 1 9 268 100 11.2 3.3 269.894 15.949 1121.191 1069.577
    1 1 10 599 100 13.3 3.6 568.833 25.258 2297.607 2210.728
    1 1 11 768 85 15.1 3.1 770.961 33.005 3019.787 2906.449

    Jan 1st 0800.......65.523 WH (between 8-9am)
    Jan 1st 0800.......1069.577 WH (between 9-10am)
    Jan 1st 0800.......2210.728 WH (between 10-11am)
    Jan 1st 0800.......2906.449 WH (between 11am-Noon)

    Continued next post:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    I will make a suggested system design since this is purely for demonstration (and training) purposes.

    The system I would propose would support ~100 kWH per month (as people see their power bill). Or:
    • 100 kWH per month * 1/30 days per month * 1,000 WH / 1 kWH = 3,333 WH per day ~ 3,300 WH or 3.3 kWH per day
    That is enough to run a relatively energy efficient refrigerator (typical efficient fridge is ~1.0 to 2.0 kWH per day--Of course, getting the most efficient is better). Will run some LED lighting, charge a cell phone, run a laptop computer, small water pump (perhaps even a in-well pump), and a washing machine... Something like all running at 230 VAC @ 50 Hz, or whatever is standard for your area:
    • 1,000 WH per day efficient refrigerator
    • 30 Watt laptop * 8 hours = 240 WH per day
    • 10 Watt phone * 1 hour = 10 WH phone
    • 8 amp * 24 VDC water pump * 1 hour = 192 WH per day water pump (really DC--more efficient, but assume VAC for less math)
    • 9 Watt LED * 5 lamps * 5 hours per night = 225 WH per night LED lighting (there are DC and AC LED lamps--your choice)
    • Total Base Loads = 1667 Watts daily "base load" (3.3 kWH per day gives you headroom for bad weather, tools, vacuum cleaner, etc. during good weather, fans in summer, etc.).
    Starting with the battery bank design (using our "conservative/cost efficient" assumption of 2 days of energy storage and 50% battery discharge for bad weather--Plus sizing of AC inverter for balanced system design).
    • 3,300 WH per day * 1/0.85 off grid AC inverter eff * 2 days stored energy * 1/0.50 max battery discharge * 1/24 battery bank = 647 AH @ 24 volt battery bank
    Two calculations for solar array size. First based on 5% to 13%+ rate of charge (5% for "backup"/weekend/sunny weather system, 10%+ full time off grid):
    • 647 AH * 29.0 Volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,287 Watt array minimum
    • 647 AH * 29.0 Volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29.0 Volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "cost effective" maximum
    And then there is based on your daily loads and how much sun you get throughout the year. Using a different solar calculator (simple, good enough for basic needs). Fixed array, tilted to average best production, Tripoli Libya:'

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Tripoli
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    3.69
     
    4.72
     
    5.42
     
    6.14
     
    6.38
     
    6.68
     
    JulAugSepOctNovDec
    6.91
     
    6.82
     
    5.99
     
    4.87
     
    3.63
     
    3.33
     
    So, if you are trying to avoid a genset... I would look at December as worst harvest "break even":
    • 3,300 WH per day * 1/0.52 end to end off grid system eff * 1/3.33 hours of sun (Dec) = 1,906 Watt array minimum
    Now--In the US, generally solar panels are cheaper than genset+fuel+maintenance... You have to understand your loads... If base load is 1,667 Watts--You have something like another (3,300 Watt production - 1,667 Watts base load =) 1,633 Watts "extra" in dead of winter... When a few days of cloudy/raining/dust storm weather... If your base loads are really closer to 3,300 WH per day--Then assume that you use something like 50% to 65% of predicted output (i.e., you "need this power" such as running a business--Vs home when you can read vs watching TV during bad weather--not genset).
    • 1,906 Watt array * 1/0.65 base line power needs = 2,932 Watt array for bigger/less genset/no genset winter operation.
    So, something between 1,906 Watt array (minimum based on sun/loads) to 2,437 Watt array (10% rate of charge) to 2,932 Watt array (near maximum "cost effective/useful" array for typical home/office use).

    Sizing the AC inverter... More or less the largest AC inverter (and the typically largest solar array) would be around 500 Watts per 100 AH for a 24 volt flooded cell lead acid (FLA) battery bank (other types/chemistries can vary/be smaller--But this is good starting number for paper design):
    • 647 AH (24 volt) * 500 Watts * 1/100 AH (at 24 volts) = 3,240 Watt maximum suggested AC power supply for FLA bank
    So, the suggested AC inverter would be around 3,240 Watts maximum, and about 1/2 that (1,600 Watts) minimum "useful" for this system.

    This is a very capable system--I will run a very efficient family home (here it would be a remote cabin) with a "near normal" electric life.

    HOWEVER, remember, that we are talking about a 100 kWH per month system... In North America, the typical home uses around 500 to 1,000 kWH per month.

    Energy usage is a set of highly personal decisions... We do not do solar/off grid power to be "green"... We do it (here) because it is the best solution for the job at hand. We try for a "reliable" and maintainable system (i.e., don't have to manage power usage every day based on needs and weather). And we are "cheap". We try to give a reliable system design that won't cost you a bunch of money down the road with dead batteries, etc.

    The first thing to get, is a Kill-a-Watt type energy meter you can plug your loads into (measure the computer load one day, measure lights the next, and so on...). A Watt meter like one of these (if 230 Volt system, I guess Libya does not have country wide standard power yet?):

    https://www.amazon.co.uk/s/ref=nb_sb_ss_i_3_5?url=search-alias=aps&field-keywords=kill-a-watt+meter

    You want to design and build a "balanced system". AC inverters are cheap and you can buy 3 kWatt 12 volt AC inverters. They will not really work well... The maximum wattage (suggested by us) for a 12 volt system is around 1,200 to 1,800 Watts... If you need more power, need a high voltage (and probably higher AH) battery bank...

    Build the ~3.3 kWH per day system and run one or two offices off it, or a conference room and lunch room, etc... Remember that batteries are the weak point for most off grid power systems... If you do not treat the batteries correctly, they will commit suicide (or you will be doing assisted murter) of the battery bank.

    Does this make sense?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    A 3.3kwh per day system is a good midsized system.

    And it is about the largest system I would suggest for a first time self install.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MrM1
    MrM1 Registered Users Posts: 487 ✭✭✭✭
    Bill in your example above, what do you  recommend for a charge controller? With my 24v system I would like to increase the array size but using the midnite solar sizing tool I find I an about maxed out with a 2565 watt (3s3p) array for a classic 150
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    This is where you start to play around and try different configurations.

    For example, you can use 2x solar charge controllers in parallel (each one manages its own array). And your run each controller back to the home battery bus (star wiring... If you "daisy chain", from controller 1 to controller 2 to battery, you have higher voltage drop/larger wiring, and you can have interference between the two outputs sharing one cable--Also, having two controllers and 2x output circuit breakers does give you backup--If one fails, the other controller will help you limp along until the failing unit is fixed/replaced...Just a suggestion).

    Or, you could go with a 48 volt battery bank and  (1/2 * 647=) ~324 AH capacity. Same storage, just reconfigured the batteries (and battery choices) into a higher voltage/lower AH configuration. And now the Classic 150 will support almost a 2x larger array (P=V*I, 2xV and 1/2 AH, same amount of stored energy).

    Then you have to see what 48 volt AC inverter is available (typically higher DC Bus voltage inverters have higher wattage ratings). Also--Sometimes getting 12 or 24 volt DC appliances (LED lighting, smaller DC water pumps, HAM Radios, even DC microwaves are available) is pretty easy, but 48VDC appliances tend to be rare.

    On the other hand, a DC battery bank has quite a wide voltage range. For FLA batteries, it runs ~10.5 to 15 or 16+ volts (12 volt ref). Many DC appliances don't really like to run on such a wide input voltage.

    Using an AC inverter to power your (today, pretty efficient AC appliances and lighting), you let the inverter "live with the battery bank voltages" and your AC loads see a pretty stable voltage. And this costs you roughy 15% larger solar array+battery bank (~85% inverter eff).

    Typically smaller systems (12 volt, 1,200 Watt or less), AC inverter "tare losses" (power consumed by an inverter just On, no loads), it pretty significant (20 Watt inverter tare loss * 24 hours per day = 480 Watt*Hours) Vs the 2,000 to 3,300 WH per day system above. So running an inverter 24x7 on a small system may not be a good idea.

    With larger systems (2-8 kWatt inverter systems and much larger battery banks and solar arrays), you are generally going to run the inverter 24x7 every day (losses become minimal vs rest of system loads)--So the small stuff (like cell phone chargers, general house lighting, etc.) is just as easy to run at 120/240 VAC because the inverter is always running anyway.

    And, with low voltage systems (especially 12 VDC), it is difficult to send much DC power more than 10 feet (3 meters) without using very heavy cables (cost of cables). And there are not a lot of "standard" DC outlets that you can just plug equipment into (other than car cigarette lighter sockets). Sending 120/240 VAC around the home/property is much easier (and standardized outlets).

    After all of the above typing? What would I suggest... It really depends on your needs (and what you want to show the customer, and frankly learn on for your sales and service folks)...

    You are 1/2 a world away from me... And you need a system that works for you. I would humbly suggest that you start with a ~3.3 kWH per day system and 10% - 13% rate of charge. Run it and learn from it (get flooded cell lead acid batteries, use a hydrometer to understand your bank's charging/discharging characteristics). Get a DC Current Clamp DMM (using a DC current clamp meter makes debugging and understanding a system so much easier and safer). Some basic equipment (just starting points for your search--I would guess US products are probably pretty expensive to obtain):

    https://www.solar-electric.com/search/?q=hydrometer
    https://www.amazon.com/gp/product/B019CY4FB4 (DC/AC Current Clamp DMM) (note that AC only Current Clamp meters are more common).

    Adding things like Battery Monitors is nice--But not mandatory (for FLA battery banks).

    Don't spend too much on the basic system. And you can add a few bells and whistles later (Internet monitoring, Battery Monitor, a second charge controller in parallel for more solar/backup).

    Look at the difference between an AC inverter, vs an AC inverter-charger (the single inverter-charger can take AC Utility  Power and/or Genset power to run your loads and charge the battery bank at the same time--Basically a big solar UPS system for you home/office).

    What is it that you (and your customers) want/need for power? When do they need to run the system (summer/winter cabins, 12 months a year)?

    What batteries are available (voltage, AH, $$$ per stored energy, FLA vs AGM, etc).

    Make several system designs and pick some equipment, cost them out (larger/smaller inverter, remote monitoring, flooded cell vs AGM batteries, etc.).

    This a real mix and match project. You will probably have to make tradeoffs (what batteries are available, cost of different levels of equipment.

    Many of us "murder" our first set or two of batteries--So suggest not to get "high end/expensive/sealed batteries for the first bank). Also, it is sort of difficult to adjust the size of a system after it is installed. You generally do not want to mix old and new batteries if you can avoid it. If you need a 3x larger battery bank, you will need a new AC inverter (inverters are 12/24/48 volt battery bus--And larger systems at some point need higher DC bus voltage)...

    After you design your first system--You will learn a lot. And what you would do different on a second system.

    Just to give you some ideas--One of our posters, 2ManyToyz, has a website where he documented his evolving system (solar projects about 1/2 way down page):

    http://2manytoyz.com/

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset