Solar Electric System for a School

Hi dears,

A school in my area want to use solar energy to power all of its equipments.
A summary of necessary equipment is as follows.

Ceiling Fans: 500 :40,000 Watts
Tube Lights: 800 :32,000 Watts
IT Room: (9 System units, 36 LCDs) : 40Amps @ 220V :about 9000 watts (UPS is installed with one hour back-up)

Currently they are using 100 kVA Diesel Generator to overcome 2~3 hours daily load-shedding for partial load(School opens 6 hours a day). This generator consumes 10 Liter/Hour.

Their Max Electricity bill is PKR 163,329/- for the month of October with 22 working days with consumed units 7480.
P.F is 0.83
......................................

I want to know....
1: Is it feasible to advise this school to shift above load to solar electric system?(Net metering is not allowed in Pakistan)
2: Minimum solar panels required to power this load is 180,000 watt without batteries? (8:00 AM to 1:00 PM)
3: At-least 5 inverters of 25 kVA will be required to power all this load?
4: 125,000 watt solar panels with a larger battery bank is better than a solar system without batteries?
5: Any other option like Hydrogen fuel cell will be less costly with better performance for above system?

I am confused ...

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar Electric System for a School

    Badar, first we need to have you list the consumption in Watt hours, so we know what the loads are over time, without guessing.

    Second I believe that a conservation program might be needed and newer low energy consumption computers, for example, installed as well as new lighting.

    That is just a quick idea of what is needed for that much consumption.

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
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  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School

    Just for the heck of it... Take the amount of panels+inverter+2x your daily usage as a battery bank and cost it out... And compare to the cost of 10 liters of fuel per hour (3-6 hours per day?)...

    I don't think it will make economic sense at this point....

    Like Westbranch suggests--Conservation will be your friend. Get power usage cut by 1/2 (should be possible--cutting lighting by 1/2 is barely noticeable, look at computer energy usage, and other "big stuff" first). The small stuff is probably not where you are spending most of your power budget.

    Also look at the generator power usage--Is the loading somewhere around 50% of generator rating, or near 10%? Sizing the generator to the loads (especially post conservation) can be a big help too.

    A $1,000 to $1,600 USD per month (9 months of the year) is not a "huge power bill" compared to the cost (and maintenance) of an off grid solar power system (I think).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School

    Well here are some calculations

    Electricity bill + fuel expenses for last one year is

    About PKR. 30,000,000/-
    Subsidies on Fuels and electricity are expected to be 0 by this year. So at least 30% increase in prices is expected.

    Rough Estimation of Load
    500 Fans in summer = 40,000 Watt
    100 Lights............ = 4000 Watt
    Expected bill per month PKR 200,000/- and per year 2,400,000/-

    Rough Estimation of Solar panels
    100,000/- Watts panels
    price for each watt PKR 100/watt
    Cost of panels = PKR 10,000,000/-
    Total Installation estimation: 15,000,000/-

    Pay-back period
    4 to 5 years

    Actual problem is load-shedding not bills. for this purpose they have installed 100kVA generator.

    Any suggestion?
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School

    OK--I am still missing the Watts * HOURS per day (or kWH per day)...

    But lets say that, if I understand correctly, you billing/power used is 7,480 kWH per month (note, we use "," for separating numbers into 1,000s etc. and "decimal points" "." for numbers less than zero in the US--Some folks would write as 7 480 to avoid confusion).

    Anyway, using 7,480 kWH per month and a general lead acid battery bank of 2 days of storage and 50% maximum discharge (i.e., you are "off the grid" and all power comes from battery bank in poor weather conditions)--Note I am assuming 7 days per week power usage, if 6 or 5 days per week, may have to adjust sizes a bit (system a bit bigger):
    • 7,480,000 WH per month * 1/30 days = 249,333 WH per day
    • 249,333 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 24,444 AH @ 48 volt battery bank
    In the US, that would be around USD$187,000 worth of fork lift batteries (retail pricing)... the PKR to USD is about 100:1...

    To charge such a battery bank, we would need ~10% rate of charge:
    • 24,444 AH * 59 volts charging * 1/0.77 panel+Controller losses * 0.10 rate of charge = 187,298 Watt solar array
    Using solarelectricityhandbook and assuming you are around Multan PK, fixed array tilted to year round optimum power:
    [h=3]Multan
    Average Solar Insolation figures[/h] Measured in kWh/m2/day onto a solar panel set at a 60° angle (from vertical):
    (For best year-round performance)

    Jan

    Feb
    Mar
    Apr
    May
    Jun


    4.78


    5.38

    5.54

    5.69

    5.66

    5.62



    Jul

    Aug
    Sep
    Oct
    Nov
    Dec


    5.19


    5.20

    5.50

    5.76

    5.15

    4.62




    Using 4.62 hours of sun minimum:
    • 249,333 WH per day * 1/0.52 off grid system eff * 1/4.62 hours of sun minimum = 103,785 Watt array minimum "break even" in December
    A solar array between ~103,785 watts and 187,298 (optimum for battery charging) would appear to work...

    So, now we have a battery bank and solar array basic... The numbers are a bit skewed as I assumed charging during day and using power at night... But in reality you are both using power and charging during the day. And you may have a 5-6 day school week, not 7 day. The modeling will need some more thought--and will be more complex/confusing vs my "simple" model.

    Cooling loads may be less when the sun is behind clouds (don't know about humidity and fan circulation needs). Do you want battery bank big enough to run from batteries during 1-2 days of bad weather before starting up genset? Is system just required to limit generator run time or do you want to "disconnect" from the grid? At this point, I would guess that Grid Power is still "relatively inexpensive" and if you need only 2-3 days of "backup solar power", we could look at a 1/2 sized off grid/backup solar power system.

    Was 7,480 kWH per month power usage correct (kWH=Units of power)? Does this include generator usage, or do we have to add several hours of day genset power too?

    I think the numbers are "close enough" for you to at least do a return on investment calculation--Or if my numbers are way off (or your location is wrong), you have enough information to at least do your own numbers as a first draft to see if this makes sense at all (remember batteries will probably need to be replaced every 10-15 years, at least--And Inverters+Charge controllers should assume ~10 year life between replacement). Solar panels should last 20 years or more.

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School

    Well BB.

    Thanks for your detailed reply. I think your way of calculation is far different from mine :D
    here is my calculation style.

    Assumptions:
    1: utility company is not disconnected from school. It will be used as "back-up" power in poor weather days.
    2: Solar panel gives 40% output at 8:00 AM Local and 100% at 10:00 AM Local in clear skies. (I have checked using meter)
    3: All following load will be operated between 8:00 AM to 01:00 PM Local time. Then there will be no load.

    Power Load:
    APPLIANCE..................... QTY.....................Watt.....................Total Power
    Fans............................ 500.....................100........................50,000 watts or 50kW
    Lights........................... 100......................40.........................4000 Watts or 4kW
    Total Load.............................................................................54000 Watts or 54 kW

    Energy Consumed in one hour:
    54,000W

    AC Amps to run this load
    I=P/V= 54000/220= 245Amp/hours

    DC Amps required to run this load @ 48V
    =Ac amps * 5= 245 * 5= 1225 DC amps/hour

    Battery bank required for 2 hours back
    =DC amp/hours * 2= 1225*2=2450 Amp/hours @ 48v

    Solar Panels requirement
    CS5P-260M (CanadianSolar) gives max 5.27 Amps.
    Assuming that it will give 2.5 amps at 9:00 AM.
    Panels required=DC AH/Panel output= 1225/2.5=490 Panels
    Panels in watt= Qty of panels * power of panels= 490 * 260 = 127,400 Watts of panels required.

    Costing:
    Batteries' cost: 1,440,000/-
    Panels' cost:....12,740,000/-
    Misc...............5,000,000/-
    Total..............19,100,000/-

    Break-even Calculations:
    Total load: 54kW/h..............................= 54 units/hour
    Unites consumed/day...........................= 54*6=324 units/day
    Units consumed /month........................=324*25= 8100 units
    Expected monthly bill on this load...........=Unit consumed * Unit rate = 8100* 22= 178,200/-/Month
    Yealy payment for electricity of this load.=178200*12=2,138,400/-
    Keeping in view, rise in prices, expected break-even would be in 4-5 years for all this installation.


    Am I right?

    P.S: Ignoring power losses. i.e i ideal condition
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Solar Electric System for a School
    Badar wrote: »
    I think your way of calculation is far different from mine :D
    here is my calculation style.
    <snip>
    Am I right?
    P.S: Ignoring power losses. i.e ideal condition

    You should not ignore the power losses.

    Fans (and some lights) have low power factor. This means you need your inverters and wiring and fuses to be larger than the 245 amps you calculate.

    You have not included the cost of replacing the batteries or electronics.

    Because your loads occur during daylight you have a tiny battery bank for the size of the system. You plan to be discharging these batteries at a C/2 rate. Most batteries have their ah rating based on slower discharge. Therefore your battery will probably not last 2 hours. More importantly, batteries should not be drawn down to depletion or they will be scrap in a short amount of time. You need to increase your battery bank size (and possibly use AGM batteries).

    Finally, you should calculate the cost of conservation... what would it cost to put in more efficient lighting and more efficient fans?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School

    As vtMaps says--You cannot ignore losses and "physical" realities... For a pure off grid system, you have to just about double the solar array size because of the losses in the system.

    For the AC side, the PF of 0.82 sounds like it is a bit optimistic for "average" induction motor fans and "typical" florescent fixture... Induction motors can run ~0.67 PF and florescent lighting has been as low as ~0.50 PF (cheap Compact Florescent "twisty" bulbs).

    But if accurate, the AC inverters and wiring would need to be up sized by:
    • 1/0.83 = 1.205 => ~20% larger...
    Badar wrote: »
    Well BB.

    Thanks for your detailed reply. I think your way of calculation is far different from mine :D
    here is my calculation style.

    Assumptions:
    1: utility company is not disconnected from school. It will be used as "back-up" power in poor weather days.

    How many hours do you need to operate from the battery bank per day (worst case)? 2 hours then run generator or you don't usually have power outages on overcast days?
    2: Solar panel gives 40% output at 8:00 AM Local and 100% at 10:00 AM Local in clear skies. (I have checked using meter)

    So--Just to make things "easy" (I don't know when your solar noon is, and solar noon occurs earlier during winter in the northern hemisphere), lets say the power needs go away at noon--So from 1pm on (say 1pm is ~solar noon during late fall thru early spring), you are recharging the battery bank from solar (~1/2 of the day's worth of solar power)--and you can use the utility for recharging if needed (makes system "smaller/cheaper").
    3: All following load will be operated between 8:00 AM to 01:00 PM Local time. Then there will be no load.

    5/6/7 days of power usage?
    Power Load:
    APPLIANCE..................... QTY.....................Watt.....................Total Power
    Fans............................ 500.....................100........................50,000 watts or 50kW
    Lights........................... 100......................40.........................4000 Watts or 4kW
    Total Load.............................................................................54000 Watts or 54 kW

    Energy Consumed in one hour:
    54,000W

    AC Inverter rating:
    • 54,000 Watts * 1/0.82 PF = 65,854 VA (volt*amp9) rated inverters/wiring
    • 65.9 kVA * 1.25 NEC derating = 82.4 kVA rated wiring/breakers (and inverters?)
    In the US/North America, wiring and breakers are designed to not be loaded more than ~80% of rated load (1/0.80 = 1.25). That is why we use the 1.25x derating factor here.
    AC Amps to run this load
    I=P/V= 54000/220= 245Amp/hours
    • I=54,000 Watts / 220 VA = 245 Amps
    Note that Amps and Watts are already "Rates" (like gallons per minute)... So, do not add the Amps/Hours or Watts/Hours -- That is something different (first derivative of Amps or Watts from Calculus, and a mix of seconds and hours units--even more confusing--Amps is Coulombs per second, Watts is Joules per second).
    DC Amps required to run this load @ 48V
    =Ac amps * 5= 245 * 5= 1225 DC amps/hour

    Don't ignore the loss factors--In solar they all add up to "kill" your project numbers (like the 52% solar panel to AC power output derating).
    • 54,000 Watts * 1/0.85 inverter derating * 1/48 volt battery bank = 1,324 Amps at "nominal" load
    Battery bank required for 2 hours back
    =DC amp/hours * 2= 1225*2=2450 Amp/hours @ 48v

    "Typical" Flooded Cell Lead Acid batteries typically are best operated at ~C/8 rate of discharge--You may push this to C/5 if batteries are kept cool. AGM can handle much higher discharge rates but are also much more expensive. For the moment, to stay "conservative", lets use C/8 rate:
    • 1,324 Amps * 1/(C/8 discharge rate) = 10,592 AH "nominal" 48 volt battery bank.
    Solar Panels requirement
    CS5P-260M (CanadianSolar) gives max 5.27 Amps.
    Assuming that it will give 2.5 amps at 9:00 AM.
    Panels required=DC AH/Panel output= 1225/2.5=490 Panels
    Panels in watt= Qty of panels * power of panels= 490 * 260 = 127,400 Watts of panels required.
    For Flooded Cell battery charging, you are looking at a (typically) maximum of C/8 nominal charging rate (our ~13% cost effective maximum rate of charge). Note that a major source of battery losses is they discharge at 48 volts and recharge at 59 volts--P=I*V. Lead acid batteries are near 100% efficient regarding AH of charging/discharging--However, they are around ~80% power efficient.
    • 10,592 AH * 59 volts charging * 1/0.77 solar panel+charge controller losses * 0.05 rate of charge = 40,580 Watt array minimum
    • 10,592 AH * 59 volts charging * 1/0.77 solar panel+charge controller losses * 0.10 rate of charge = 81,159 Watt array nominal
    • 10,592 AH * 59 volts charging * 1/0.77 solar panel+charge controller losses * 0.13 rate of charge = 105,507 Watt array "cost effective maximum"
    This is another issue with Lead Acid Battery sizing... They have a limit to the maximum amount of current you can pump down them for multiple hours before they overheat... It takes a larger battery bank to absorb higher charging currents (or active cooling).

    A 127,400 Watt array is probably "close enough" that it will not cause major problems. When the loads "go away" at solar noon, the output power begins to fall too.
    Costing:
    Batteries' cost: 1,440,000/- * 4.3x larger battery = 6,192,000 PKR
    Panels' cost:....12,740,000/-
    Misc...............5,000,000/-
    Total..............19,100,000/- = 22,492,000

    Break-even Calculations:
    Total load: 54kW/h..............................= 54 units/hour
    Unites consumed/day...........................= 54*6=324 units/day (actually 5 hours per day => 270 kWH per day?)
    Units consumed /month........................=324*25= 8100 units (=> 6,750 kWH per day--6 school days per week?)
    Expected monthly bill on this load...........=Unit consumed * Unit rate = 8100* 22= 178,200/-/Month (6,750 * 22PRK=148,500 per month)
    Yealy payment for electricity of this load.=178200*12=2,138,400/- (148,500 per month * 12 moths=1,782,000 PKR/yr)
    Keeping in view, rise in prices, expected break-even would be in 4-5 years for all this installation.
    22,492,000/1,782,000 PKR per year = 12.6 years

    Add new batteries every 5-15 years, new electronics every ~10 years, and your cost of "solar power" is about the same costs as avoided electric costs--With the down side of a 22,492,000 up front cash payment on install... You can use Present Value/Future Worth calculations (based on assumed inflation), but at a first cut, this is not a "risk free" return on investment (replacement batteries, parts also go up in price over time... Training/maintenance for the system are also real costs).

    Batteries are a real killer in any off grid power system. That is why "net metering" (using the utility like a giant battery bank) looks really nice. Net metering can also be a huge cost for the utility (they have to maintain the infrastructure and 'buy power' at retail when the sun is up, and sell power at retail when the sun is down)--Not really a good investment for them and why governments have to push utilities to do net metering and why the extra costs are passed on to the rest of the customer base.

    The numbers are very fluid at this time--And you can see how one change in assumption makes your payback 2-3 times longer (and approaches never saving money) very quickly.

    Making accurate measurements, reducing power usage/increasing efficiency are (generally) your first priorities. In the US, you can get large savings in costs if your loads can be "interrupted"--In your case, you already have the generator. But, they may interrupt your power anyway and not really look at reducing your billing costs (local customs/laws).

    In the US, commercial customers with "poor" power factor can get charged a whole lot--More or less 1/PF (in a round about way, commercial customers are charged for kVAH, and not KWH.

    In theory, with new fans and lighting (or at least using capacitors to "correct" the motor PF), you could save upwards of 10-20% on your power bill if you have some form of kVAH (or kVR) charging.

    If you are not an electrical/power engineer--Perhaps you can partner with a local university electrical/power engineering department and make this a class project/thesis (at least for the initial project study/paper design).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Solar Electric System for a School
    Badar wrote: »
    A school in my area want to use solar energy to power all of its equipments.
    A summary of necessary equipment is as follows.

    Ceiling Fans: 500 :40,000 Watts
    Tube Lights: 800 :32,000 Watts
    IT Room: (9 System units, 36 LCDs) : 40Amps @ 220V :about 9000 watts (UPS is installed with one hour back-up)

    Currently they are using 100 kVA Diesel Generator to overcome 2~3 hours daily load-shedding for partial load(School opens 6 hours a day). This generator consumes 10 Liter/Hour.

    Their Max Electricity bill is PKR 163,329/- for the month of October with 22 working days with consumed units 7480.

    utility company is not disconnected from school. It will be used as "back-up" power in poor weather days.

    All following load will be operated between 8:00 AM to 01:00 PM Local time. Then there will be no load.
    School operates (22 days / 31 days in October) * 7 days / week = 5 days / week.
    School operates for 5 hours / day.
    School has grid power for 2 to 3 operational hours / day.
    School has no grid power for 2 to 3 operational hours / day.
    Grid electricity consumed in October was 7,480 kWh or 7,480 kWh / 22 days = 340 kWh / day.
    Price of grid electricity in October: 163,329 PKR / 7,480 kWh = 21.84 PKR / kWh = $.21 / kWh.
    Fuel consumed operating generator: 10 l / hour * 2.5 hours * (22 operational days in October) = 550 l / month.

    Does PRK 163,329 include the cost of the fuel to run the generator?

    Does this school operate all year or is there something like summer vacation? If the school does not operate during the summer, then the PV panels should be pointed to favor winter conditions and you need to ensure there is no shading.

    Where would the PV panels be installed?
    If on a roof, is there enough space on the roof for all the PV panels?
    If on a roof, what direction is the roof facing?
    If ground mounted, is there enough space without shade all year? Did you include the spacing required between rows? Because PV panels on ground mounts are more likely to be subject to vandalism and theft, did you plan to put a fence around them?
    Will the PV panels be pointed in a fixed direction or put on tracking mounts?
    Do you need to construct a building to house the electronics and batteries?

    Because the power consumption is between 8 am and 1 pm, the system will likely be more efficient if the PV panels are pointed in a direction that favors morning sunlight.

    For the IT room, is 40Amps @ 220 V the actual power consumed by the equipment, or the power rating of the UPS?

    You need a battery charger to recharge the batteries from the grid.
    3: At-least 5 inverters of 25 kVA will be required to power all this load?
    340 kWh / 5 hours/day = 68 kW
    40 kW + 32 kW + 9 kW = 81 kW
    If the average power factor is .83, then 81 kW / .83 = 98 kW minimum continuous inverter power which is about the same power rating as the diesel generator. Will the inverter's specifications need to be derated due to high ambient temperature?

    If grid-tied PV panels are pointed in a fixed direction to output maximum power at 10:30 am but otherwise seasonly optimal:

    340 kWh/day / (5 hours/day) = 68 kW
    Average power output for 5 hours around optimal direction: ~cos(5 h / 2 * 15 degrees/h / 2 (average)) = 94%
    Seasonal variation in insulation from optimal direction: ~cos(23.5 degrees inclination of Earth's rotational axis) = 92%
    Efficiency of dirty panels, wiring and inverter: 80%
    68 kW / .94 / .92 / .80 = 98 kW of grid-tied PV panels

    There is no allowance for charging batteries, charge controller, shading, atmospheric absorption of sunlight in early morning, clouds, smog, haze, PV power loss from aging, seasonal variation in load, power consumption beginning a little before 8 am nor power consumption ending a little after 1 pm. View this as the absolute minimum sized PV array with an optimal fixed pointing direction. It likely needs to be larger: 98 kW * (81 kW / 68 kW) = 117 kW based on your rated loads.

    Because the grid power is shut off for 2 to 3 hours during school operation, you will probably need batteries, a PV charge controller and a battery charger powered from the grid. To size the grid powered battery charger, you need to know how many hours / day the grid power is available and the size of the battery array. Charging the batteries will be around 75% efficient over the lifetime of the system due to inefficiencies of the batteries, wiring, charger and aging. This inefficiency will be equivalent to about an extra 40 minutes of power drawn from the grid on cloudy days. The 98 kW PV system might output 98 kW * 5.7 h/day * .94 (suboptimal pointing direction) * .75 (efficiency) = 419 kWh during a good sunny day with batteries. Only (419 kWh - 340 kWh) * .75 = 59 kWh would be available for storing in the batteries and later use. A larger PV array would reduce the power drawn from the grid to replace the energy extracted from the batteries on cloudy days.
    Lights........................... 100......................40.........................4000 Watts or 4kW
    Your estimates for the lights has varied from 32 kW to 4 kW and for the fans, from 40 kW to 50 kW. Which is it?
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Solar Electric System for a School

    If the grid power is off for 2 to 3 hours during school operating hours, then you should assume it is off for 3 hours. Wet lead-acid batteries should not be discharged below 50% of capacity.

    81 kW * 3 hours/day * 2 = 486 kWh minimum battery array at 6 hour rate of discharge.

    486 kWh / 48 V = 10.2 kAh = 10,200 Ah minimum battery array at 6 hour rate of discharge which is a heavy load.

    As BB wrote, increasing it to the 8 hour rate of discharge gives 648 kWh and 13,500 Ah at the 8 hour rate of discharge. Because batteries will likely be rated at their 20 hour rate of discharge, you will have to study the prospective battery's discharge curve to determine if it is suitable.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Solar Electric System for a School

    >Ceiling Fans: 500 :40,000 Watts
    >Tube Lights: 800 :32,000 Watts

    This must be a very large school. Assuming 5 fans per classroom, that makes 100 rooms.

    Its going to help you if you can get much clearer about your use of metric units for your loads/demand. 40kW constant for 5hr is 200kWh/day. You need to check/measure these figures very carefully as they are a lot.

    >School has grid power for 2 to 3 operational hours / day.
    >School has no grid power for 2 to 3 operational hours / day.

    Sounds like the third world. Is Pakistan really not resourcing schools with even basic power supply? We whine about the slow pace of fibre installations here. I presume the load shedding is a result of an grid system at/over capacity. Is it a local or regional problem? Are there plans to change the situation that might materially affect your design/investment timeframe?

    In general, it sounds like designing a system based on batterys and grid chargers, will only excerbate the problem... then youll only get 1 hr per day! Conversely, installing solar will alleviate local grid issues, and potentially even support the local grid at times. However in the third world where will the funding for this large and expensive system come from?

    >Grid electricity consumed in October was 7,480 kWh or 7,480 kWh / 22 days = 340 kWh / day.

    340kWh/d is a lot of power being used in an area where there isnt a lot of power. Hence convervation is always generally your first port of call. Have you got the ability to get an energy conservation audit done? I have a friend that does audits for supermarkets and the like. He routinely takes 20% off their power bill, and they pay him a cut. We are talking really big bucks.

    Fans appear to be your big user. Are there any passive deisgn type building modifications that could reduce the heat issues, glazing shading, thermal mass additions, insulation etc?

    Finally if you are serious about a PV system for this school, then you need a consultant. Theres very few people qualified to design and install systems that size, and the guys here are just being friendly offering what little we can in this situation.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School

    Wow.....for such a gracious help.
    ......................................................
    Situation:
    It is Pakistan. Government level corruption, heavy expenses on fighting against terrorism & lack of leadership, has resulted great shortage of finances. Major victim of this shortage is "Electrical Grid". Pakistan has resources to produce 20,000 MW electricity (according to demand), but is producing just 8000 to 12,000 MW.
    So since last 6 years it is a routine for local Pakistanies' to face 8 to 14 hours of daily load-shedding. As a result industry and businesses are under enormous pressure.

    Any signs of improvement?
    Although I am not voter or present government. Yet I feel, they are trying their best to eradicate/minimize corruption, cover line losses, trying to generate cheap electricity from solar/wind. But major problem is terrorism ,shortage of finances and confusion.
    1: Government is facing Rs. 500 Billion Circular debt (money owe to power companies)
    2: Continuous terrorism and series of suicide attacks/bomb blasts/ethnic & religious issues.
    3: A state of confusion. Who is our friend and who is enemy...Taliban or United States.


    So I think government has a little better sincerity and less corruption level, but no vision and determination.
    Next 30 days will decide what the Pakistan will choose. An Army Action or just continue the state of confusion. I hope so.

    Under the sea:
    What I said, was above the sea level. Situation under the sea is that, despite all above poor economic/social performances, average Pakistanies' have reasonable financial potential. Majority of Pakistanies' are just fed-up of governmental level lies and finding their own solutions to run their businesses. Alternative Energy like Solar electric is their first priority. But local sellers like "me" and bad quality panels "made-in-china" have generated bad-will of solar electric system.

    1: Usually there are no certifications like NABCEP offers.
    2: Panels are selling on small shops...even on rice shops. :p
    3: Panels are of very poor quality. last 2 or 3 years. so creating great dis-satisfaction.
    4: I contacted "Solar Distributor" of "CanadianSolar" in pakistan for school. What they replied was just "stupid". I can share their Quotation with you. :)

    What the School is?
    1:School is English medium with intermediate level classes in it, with about 1200 students.
    2:It is known as "Eliot class school" in our area.
    3:It has a board of directors with good/rich people from town and from gulf.

    I am sharing google earth pic here of this school.
    Attachment not found.
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School

    My Designs:

    I am thinking three kinds of designs/installations to suggest them.
    1: Grid free installation for entire load in three phases. One phase for half fans and half lights, second phase for remaining half fans & lights, third phase for IT room & water motors. all installation estimation with & without batteries (Grid as back-up in emergency)
    2: generator replacement for winter season. when only lights are needed. (They originally demanded for this type of information, then requested to give an estimate for entire load)

    YOU CAN THINK OF IT AS A PRE-FEASIBILITY STUDY.

    Climate:
    Climate here is very hot from April to October. (Desert City). very few days with clouds in whole year.

    School Timing:
    0730 PST to 1300 PST (April to October)
    0815 PST to 1330 PST (November to Mar)

    Summer Vacations:
    mid June to mid August
    Electricity bill shows that this school conducts summer camps.

    Max Electricity Bill:
    Max Electricity bill is for October 2013, which is more than 160,000/- excluding generator fuel expenses.

    Client's mood:
    Client is more interested in "battery free" installation.

    Expected Project Approval time:
    Project approval might take many months. at least not before April 2014.

    Chances of winning the project:
    5% :D: As rich people who are also donor of this school wishes to be more rich :D
    I am all doing this research for self learning. :D
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School

    I will share my presentations with you after finalizing, but please can you please tell me if there are any battery less inverters? price range?
    I dont want traditional "grid-tie" inverters used for net metering purpose. Since there is no net metering in pakistan. because I have read that such inverters also disconnects the load when grid is OFF. I want just battery-less inverters. That when there is solar, it operates directly on solar. and when there is no solar then it shifts load to electrical grid.

    Is there any?
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Solar Electric System for a School
    Badar wrote: »
    I dont want traditional "grid-tie" inverters used for net metering purpose. Since there is no net metering in pakistan. because I have read that such inverters also disconnects the load when grid is OFF. I want just battery-less inverters. That when there is solar, it operates directly on solar. and when there is no solar then it shifts load to electrical grid.

    It's not easy to have it both ways. SMA has introduced a new grid-tie inverter that can produce limited power (without batteries) when the grid is down. I have no idea whether that can be scaled up to the level you need.
    Badar wrote:
    It is Pakistan. Government level corruption, heavy expenses on fighting against terrorism & lack of leadership, has resulted great shortage of finances. Major victim of this shortage is "Electrical Grid". Pakistan has resources to produce 20,000 MW electricity (according to demand), but is producing just 8000 to 12,000 MW.
    <snip>
    Government is facing Rs. 500 Billion Circular debt (money owe to power companies)

    The problem I see is the Pakistan consumer (including your school). If you continue to run such inefficient fans and lighting, you will never be able to produce enough electricity. It's always cheaper to conserve energy than to produce energy. That's true for a single residence and its true for a nation.

    I presume (tell me if I am wrong) that your grid electricity is heavily subsidized. That would explain the 500 billion "circular debt". That would also explain why there are electricity shortages... because you would rather buy more subsidized electricity than invest in energy saving appliances.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School

    Badar,

    My answer (and it has gotten me into trouble many times before :blush:) to your "problem" is to change the rules.

    My guess, if you try to do things the "traditional way" (as documented above with panel+charge controllers+batteries+AC inverter+etc...), you will--At best--Pretty much break even when compared to the cost of power from the utility.

    My suggestion, look at each load and see if and how much you can do things non-traditionally.

    First the lighting. LED's have made a huge change in the way light is generated and made large changes in the way lamps work (respond to voltage/available power). I would suggest you get a few commercial LED fixtures and do some experiments.

    For example (websites are examples, I know nothing about the sites or their products), look at AC LED lighting.

    http://www.rabweb.com/product.php?product=FFLED18

    Many fixtures are rated from 120 to 277 VAC--But in reality, may work on 120-277 Volts DC or (factor of srt(2)x) of 170 VDC to 391 VDC. You have to contact the mfg or even just buy one or two and take one apart (second for testing/spare) and see what the input circuitry is.

    Many modern devices use some form of electronic switch power supply input that do not need AC voltage--But instead will work just fine with DC voltage (perhaps a higher voltage by the square root of two). This even applies to many/most computer power supplies.

    In the "old days", everything used a transformer to convert from 120/230 VAC to 12 volt or other low voltage AC before rectifying for use in the device. But transformers use "lots of copper" to make that happen. With the low price of electronics and the high price of copper, AC only transformers are being replaced by AC/DC capable electronics.

    Also, with LED lamps, they maintain their (relatively) high efficiency and similar color temperature even at reduced input power (note, LED's optimally are constant current lamps--they need a fixed current regulator, not a fixed voltage regulator/source). Unlike filament bulbs which go towards "red" at lower power levels or florescent lamps which need AC power to operate reliably (they are Arc Lamps and a DC current will usually destroy the electrical elements inside the tube very quickly). While you could make electronics to change DC to AC for florescent, I would choose the LED just to make things "simpler".

    Another issue with LED lamps is they generate less heat than filament bulbs, and can be slightly more efficient than florescent lamps--Especially if you can use less lamps for "focused" lighting (i.e., more lights on the black board for the teacher, and less light on the students desks. Or task lighting just lighting desks with less flooding on walkways and storage areas. And if you need occasional lights (library book shelves), you can use motion sensors to only turn on lights/zones when occupied (LED lamps can be turned on/off hundreds of times per day, filament and especially florescent will fail an early life if power cycled a lot).

    Another neat thing with LEDs, since they are small--You can sometimes mount them in ways that the heat does not enter the room (install outside and shine through a window, or recessed into a ceiling and avoid heat into the room/living-working space. Room lighting can be a major source of heat into the room, and reducing heat into the room, can reduce heating loads too... However (again using very rough numbers) an adult will add about 100 watts per person to a room's heat load--So a class room with 30-50 students may give you 3,000 to 5,000 watts of heating--More than the heat from lighting--For a school, heating from lighting may be less of an issue (and in many high desert climates, heating from lighting can significantly heat a room on those cold/clear desert mornings (no clouds to reduce amount of radiation of heat back into space--forget "global warming" from CO2--That does not stop/slow back radiation to space).

    So, for lighting, you may be able to (with even commercially produced/lower cost LED Fixtures) simple put 6-12x ~250 Watt panels in series (6x Vmp~30 volts would give you 180 VAC nominal) and enough power for ~60x 22 watt LED florescent fixtures just from sunlight. That would light X number of rooms per array.

    Assuming you get direct sunlight when the school day starts, you will have some light when classes start. You could tilt panels more towards morning sun (raise at an angle, face south east) and have a few less lamps because of less sunlight/energy in early mornings.

    If you really needed, you could put a high voltage DC Battery bank in there too to supplement solar panel power in the AM/cloudy weather (i.e., ~15x 12 VDC batteries) if needed (I would try my best to avoid batteries--They are a whole pile of issues to get right and you still have expense of replacing batteries very X number of years).

    Since you still have AC power (grid/genset), and in many areas of the world, morning utility power cuts are less common, you could perhaps skip batteries completely and just have backup AC power in parallel with the solar arrays (transfer switch AC to DC supply that can parallel with solar array).

    There is also a fall back to make a similar system with low voltage DC (12 volts) and standard M16 LED conversion lamps. These LED lamps are defined/designed to work with 12 VDC power for track lighting, but many of these bulbs will work just fine with 12-18 VDC too:

    http://www.ledlight.com/12-volt-led-track-lighting.aspx

    Same process as above, but use lower voltage solar panels (100-140 watt typically with Vmp~18 volts) and smaller lighting "units" (i.e., only 1-10x 100 watt panels in parallel) per "micro power" installation.

    I believe that the above will not be that difficult to implement (getting samples of various LED fixtures/lighting from different sources, taking a few apart to see how they work, and some experimentation with a DC power supply, meter, small oscilloscope, etc.)--And you can work out the details to build small systems, each capable of lighting a few rooms each (rather than building a central solar lighting power station with a large solar array and sending energy to all the rooms). Smaller systems are "less" complex and can be (if done right) have less issues with safety (large/high voltage power systems require professional electricians to install/maintain, large battery bank are heavy/full of acid/and electrical accidents waiting to happen too).

    You have not said if you where an electrical/electronics engineer/trained or not. Without some good knowledge of electronics, doing the above may be a bit frustrating/require a few months (or couple of years) of self training. However, if you can get somebody with electrical/electronic education, none of the above is that difficult to do the basic research. And the amount of supply's instrumentation is something that could be done with stuff found in a typical school electronics lab.

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: Solar Electric System for a School
    Badar wrote: »
    Ceiling Fans: 500 :40,000 Watts
    Tube Lights: 800 :32,000 Watts

    Just as a note - if you are really running 32,000 watts of light during school hours (the day) then you are far better off with windows/skylights/heliostats than with solar electricity. Just use the solar energy directly and cut out the expensive middleman.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School

    Badar,

    I like your idea of breaking things into separate projects--At least for analysis, if not actual implementation. It makes the problems clearer and, potentially, easier to solve as each problem may need a different solution.

    Fans are the next issue... A typical fan uses an AC Induction Motor. Those types of motors are pretty rugged (and when used in fan type applications) are pretty hard to damage short of hitting with over voltage (a fan, with lower input voltage will simply turn slower--A motor driving a fixed load, like the compressor in a refrigerator, will draw more an more current as the voltage falls--Brownouts will burn out motors used in these types of applications).

    So--Again, change the rules. no 230 VAC at 50 Hz (or whatever your power standard is)--Look at different motors and at "non-traditional" power.

    The simplest motor for your needs would be a "brushed" or "Universal" motor (such as you see in an electric hand drill, the starter motor in a car, etc.). These types of motors can be directly connected to a solar array, sometimes with electronics for higher efficiency/better air flow in mornings/evenings, very cheaply and easily. However, brushed motors will need brush replacement every ~6-12 months and some other issues which make them less than ideal--So forget these motors for this application.

    The next are PM DC motors (permanent magnet) that have electronic commutation (instead of brushes). The are cheap, reliable, and can take variable DC power/voltage from a solar array very nicely. These fans are used in just about every small computer made these days.

    The problem may be trying to find this type of motor (PM with electronic commutation) in the size and fitted to fans for air circulation in a class room. If you can find DC Fans like this--Just connect to a solar array + backup battery (or AC to DC power supply) and away you go. China is making a huge amount of "non-traditional" power devices and they may have things like this... I will look later today, but I am running out of time right now.

    Another way is with induction motors, but different types than you probably have today. There are three phase induction motors (very common, but perhaps not so easy to find in fractional/sub 1,000 watt ratings). These motors can be driven with a VFD (variable frequency supply) very easily from AC power, and there are VFD's that appear to be relatively easy to convert to DC input). Basically, the VFD is a type of DC to AC inverter, but it outputs 3 phase (rotating field to turn motors) and variable frequency (10-50+ Hz) to adjust motor power RPM needed for application or based on amount of DC power from solar panels available.

    And another variation is use the VFD with split phase/capacitor start motors... These motors have an external capacitor that "alters" the single phase input to 2 phase AC for the motor (to provide the "rotating field" needed to start the motor rotation). These types of motors are available in smaller sizes and may be easier/cheaper to make/retrofit into fan applications.

    In any case, read about VFD+Solar powered water pumps. Similar solution for a bigger application vs yours.
    BB. wrote: »
    Some discussions about VFD (Variable Frequency Drives)... Basically a variable frequency inverter with (typically) three phase output. Used to soft start motors (handy for 3 phase well pumps, or pumps with well head starting capacitor) and can also turn an AC motor into a variable speed motor (very handy for pumping applications).

    WELL PUMP and Inverter QUESTION

    Wind/solar for large scale pumping etc (out of my depth!)
    could use knowledge - using Gould jet pump - transfering from 230vAC to ? DC (new link/thread 10/27/2012)
    Help required to design off grid system (information on possibilities to connect "standard VFDs direct to solar panels) (new link 1/13/2013)

    -Bill

    The last link is from user "syedbukhari" -- He is from Pakistan and based on our conversation here has implemented a VFD+solar array water irrigation system, and (I think) is turning this into a business... I would suggest you try contacting him via "Private Message" and see if he can help you with the VFD/Fan questions--And/or even the LED Lighting. If he does not see your PM, let me know and I will send him an email directly. Let us know how it goes with him.

    Regarding the computers--I will leave that conversation for another day... There are "interesting" methods to supply solar power--But the basic solar array+battery bank+AC inverter is probably the best solution. Again, conservation is going to be a big help here--Computers are actually quite heavy users of electric power and, obviously, they need stable power to operate reliably.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School

    And to confirm what Bill von Novak said--Adding skylights/alternative sources of natural light is a good low-tech way fixing many lighting issues. I did this in my home and my in-law's home (dark stairways in middle of home, dark bedroom) and I really liked it.

    Installing LED motion detector lighting would have probably been cheaper. :roll:

    With today's "low E" glasses, you can keep a lot of the heat out of the room. Although, this can be less than ideal in real applications. I have seen these skylights implemented in the US at one school and (assuming no water leak/heating issues) the uncontrolled light can be a pain. In the classrooms I saw, they installed horizontal "blackout shades" under the skylights and they were closed in every class room (was on a weekend, so I don't know if they opened during school days).

    If you try these solutions (add frosted glass/plastic/diffusers to avoid direct sun, etc.)--Do them on a "small scale first" and see what works best for your application/needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School
    vtmaps wrote: »

    The problem I see is the Pakistan consumer (including your school). If you continue to run such inefficient fans and lighting, you will never be able to produce enough electricity. It's always cheaper to conserve energy than to produce energy. That's true for a single residence and its true for a nation.

    I presume (tell me if I am wrong) that your grid electricity is heavily subsidized. That would explain the 500 billion "circular debt". That would also explain why there are electricity shortages... because you would rather buy more subsidized electricity than invest in energy saving appliances.

    --vtMaps

    vtMaps, you are absolutely right.
    Principle here in school is, just like traditional General of 2nd world war, insisting to promote traditional things. I think, he Loves tube lights. :D
    I suggested him to replace all 40 watt tube lights with 5~8 watt LEDs. In this way all 30,000 watt lighting load will reduce to just 3000~4000 watt. He can save not only electricity, but also small sized generator can work best in winter season. so saving fuels expenses also. I told him that he can save PKR 400,000/-~ 500,000/- per year in this way. But I am unable to put things in his mind. :(

    However I am going to add a new chapter in my presentation, after this valid point from you.

    Yes, Grid electricity is heavily subsidized. However, now government, is gradually reducing such subsidies. so a price hike is expected in this year.
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School
    BB. wrote: »
    Badar,

    My answer (and it has gotten me into trouble many times before :blush:) to your "problem" is to change the rules.


    Your thoughts?

    -Bill

    I like your Idea of "Thinking untraditional".

    Regarding my team!
    Actually we are not "learned from university", but we are learned from working. (sorry for my English :D)
    I do the research work and make presentations/quotations(have little technical knowledge and brain storming, graduated in physics), two young boys work professionally as electrician(home/commercial wiring, unfortunately just Matriculate), one is electronics professional (He repairs inverters/UPS or such accessories), My big brother, who was government telephone exchange installer before retirement and electronics hobbyist. A friend of mine is marketing man.
    So when we have a project, we join our hands....

    Thinking Alternatively.
    Basically If I were the principle of that school, I would discuss this problem in following manner.
    1: Fans are basic load in summer for solar electric. Lights are not needed. Rooms are designed to have sufficient sunlight.
    2: IT Room/Computers/Water Pumps should be used in time when grid electricity is present.
    3: In winter, when Fans are not needed, then solar electric can be used to power lighting.
    4: Remove tube lights and install LEDs, to lower the electricity bill.

    Alternative Installation:
    Since principle will not accept our idea of replacing motors, and also, finding motors in Pakistan is very difficult as E-commerce is not developed here. so I changed the design as follows....
    One DC fan of 25 watt costs Rs 3200/- in Pakistan.
    We need, 500 Fans, consumes total power 12,500 Watt=20,000 Watts
    So...

    Cost of Fans:.................... 500 * 3200= ............................1,600,000/- PKR
    Cost of Solar:.................... 20,000 * 100=..........................2,000,000/-
    Wiring etc :....................... ........................................... 500,000/- ~ 800,000/-
    Fixture :..................................................................... 200,000/-
    Expected Total Cost for Fans........................................ .4,300,000/-
    Less: Cash from Selling of old fans...................................(500,000/-)
    Approximate cost of solar electric system:.. .....................3,800,000/- as compared to 20,000,000/- for conventional solar AC electric system.

    Motion Detector Lighting:
    Any state-of-art technology is not feasible, yet, for two reasons.
    1: Authorities will raise objections
    2: Repair/restore in case of any issue will be difficult, as Rahimyar Khan is a small town, with NO Experts.

    Water Pumps:
    10 Water Pumps of 0.75hp are installed to fill overhead water tanks.
    I will suggest them installing solar system for just two pumps. All pumps can be used in pair of two in school time.
    (Separate system will be installed). After School time. All pumps can be used to fill the tanks for next day use.

    IT ROOM
    For It room, I have no idea :s
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School
    Just as a note - if you are really running 32,000 watts of light during school hours (the day) then you are far better off with windows/skylights/heliostats than with solar electricity. Just use the solar energy directly and cut out the expensive middleman.

    School building is designed in such a manner that it has sufficient sunlight, that lighting is not needed in day time. Summer is full of sunlight. Lighting is only needed when there is winter, its fog and its cloudy.

    Each room has one sided ground to roof glass wall. It provides sufficient sunlight. but problem is our "style of wasting energy".
    I think we need to educate students about energy :(
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Solar Electric System for a School
    Badar wrote: »
    Regarding my team!
    Actually we are not "learned from university", but we are learned from working. (sorry for my English :D)
    I do the research work and make presentations/quotations(have little technical knowledge and brain storming, graduated in physics), two young boys work professionally as electrician(home/commercial wiring, unfortunately just Matriculate), one is electronics professional (He repairs inverters/UPS or such accessories), My big brother, who was government telephone exchange installer before retirement and electronics hobbyist. A friend of mine is marketing man.
    So when we have a project, we join our hands....

    You have pretty much everything you need to start with people/knowledge... They may need some lab gear and a bit if money to get different lights/fans/etc. to make some experiments (don't we all just need a little more money:cry:).

    If you can direct their initial path(s)--You will have a good start. The big thing to understand is that solar panels are not solar batteries.

    A battery will hold the regulated/desired voltage (i.e., 12 volt DC or even your 230 volts AC grid/generator output) from zero current to maximum available current. That is the definition of a "voltage source".

    A solar panel/array is a "current source"... For a 175 watt panel with Vmp=17.5 volts (just picking round numbers)--The panel will output (typically) ~10 amps under full sun from 0 volts to ~17.5 volts and as the voltage rises above Vmp, the current of panel will fall until around 21 volts or so.

    Remembering power = Voltage * Current.... At zero volts the panel is outputting around 10 amps (probably closer to 12.5 amps--but it does not matter at this point). But Power=V*I=0v*10a=0watts power... At maximum output voltage, V=21 volts and I=0 amps, so P=21v*0a=0watts--Still no power.

    At Vmp of 17.5 volts and Imp=10 amps, you get the full 175 watts rated output.

    And, Ipanel (output current) is approximately equal to the amount of sun hitting the panel. So, if the sun is behind a cloud a bit, and you have 1/2 the light, then Ipanel will be ~5 amps.

    So--all of the neat things electrical we use every day need to be "rethought"... The fan that always gets 230 VAC and always blows the same amount of air on switch position 2--No longer does that will solar--When the sun is less, the fan (or water pump) will spin less, the lights will not be quite as bright, etc.

    Identifying the devices you want to run (fans, lights, water pumps, computers, etc.)--You have to look at efficiency (lower power usage) and see which ones will work on DC power with varying available current/voltage. It can be done (as in the earlier posts). Get a single solar panel and experiment with a 12 VDC or 24 VDC computer fan (and get a variable DC output power supply--Makes things a bit easier to "characterize" and test on the lab bench).

    Same thing with LEDs... Look for Buck Mode current regulator circuits/chips. And understand how those work and what you would like them to do for LED control.

    This is an interesting chip for a 25 Watt LED setup:

    http://cds.linear.com/docs/en/datasheet/3956f.pdf

    Pick a task and start learning what you need. You will have failures, and you will learn from them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Solar Electric System for a School

    Using Solar Electricity Handbook: Solar Irradiance for Bahawalpur, Pakistan:
    Az = Azimuth
    El = Elevation, 0 degrees points PV panel at horizon and 90 degrees points it up
    Insolation in kWh/m2/day


    orientation of PVJanuaryFebMarchAprMayJuneJulyAugustSeptOctNovDeckWh/m2 /year

    Az south, El 61 degrees, optimal4.965.685.825.895.975.895.595.425.595.625.114.762285

    Az south, El 46 degrees, best winter5.305.875.715.475.265.074.894.935.365.705.415.151949

    Az south southeast, El 46 deg, best for school operating hours?5.175.725.575.335.134.944.774.815.235.565.275.021900

    Az south southeast, El 61 deg4.845.545.675.745.825.745.455.285.455.484.984.641965

    Az southeast, El 46 deg, direction of roofs in photo5.045.585.425.205.004.824.654.685.095.425.144.891852


    This is not the best insolation especially for 28 degrees north latitude. For example, Phoenix, Arizona, USA at 33 degrees north latitude has a peak of 6.83 kWh/m2/day in April. Either the data at Solar Electricity Handbook is inaccurate for Pakistan, or you have more clouds or haze than you think.
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Solar Electric System for a School
    Badar wrote: »
    Lighting is only needed when there is winter, its fog and its cloudy.
    A grid-tied photovoltaic system will be bad for lighting when there is fog or clouds. You will need batteries for that. When I lived in a foggy place, the fog tended to be present in the morning and evaporated away before noon. If it is the same in your location, then pointing the PV panels to favor morning sunlight would be bad.

    Because the lights and fans are complementary loads, it would be helpful for you to determine the electricity consumption of the school for every month of the year. Was that average of 340 kWh / day in October consumed by fans, lights, computers or water pumps?

    The two buildings with half of the roofs facing southeast measure about 32 m by 26 m. The central part that looks like it provides passive ventilation and sunlight is about 9 meters wide. I can not determine the pitch of the roof from the photo. The central portions might have an area of 9 m x 32 m x 2 = 576 m2. With 14% efficient PV panels, you could get about 81 kW of PV panels up there. Because I do not know the pitch of the roof, more might fit. If you use the lower part of the roofs on the southeast side, you could fit more PV panels, but one of the roofs looks like it gets some shade from trees. Because the fans are the biggest loads and if you have fog in the mornings, an elevation near 61 degrees might be best.

    With a grid-tied PV system, no feed-in tariff and a PV system that output enough power to power the school directly, the school would be giving away electricity during the days it is closed. This favors installing a smaller PV array that provides no more than 5 days / 7 (days per week) = 71% of the power that the school consumes during an open day. Hopefully the electric meter would run backwards when the PV system sends power to the grid.
  • BadarBadar Solar Expert Posts: 38
    Re: Solar Electric System for a School

    Ok friends. I have submitted my feasibility report and quotation to the school administration. It will be considered in Board of Governor's meeting. Lets see what happens then.

    Thankyou very much for all of you for helping me
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