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Solar Panel contd.

March 26th, 2012 Leave a comment Go to comments







Installation of additional 130Wp is in place now to make the power plant worth 300Wp.  The new panel added has a spec of 17Vmp against the 16.4Vpm of the 170Wp panel group.  So eventually I may be losing some power.  I am using 10sqmm copper cable to reduce the transmission losses.  I had measured the impedance of the cable to 1mΩ. So at 20A, I will be losing about 0.4W only.  But the cost of this wire is around 70Rs/m.  I am able to produce about 221W during the mid day, and about 170W around 10AM.  Upon little bit of investigation, it is found that the solar panels shell out less power at increased temperature.  It is also said that at 60-70°C, the efficiency is around 70%, which is matching with my measurements.  So, thinking about a water cooling solution; basically augmenting a solar water heating solution with the solar panel to establish double benefits.  Every day with the solar panels is a day of new learning and I am enjoying it. 🙂
  1. Sai_karthi
    April 21st, 2012 at 17:49 | #1

    Pls share total cost involved (break up), is it connected to an inverter?


  2. sudarsun
    April 21st, 2012 at 23:47 | #2

    The cost break up is the following:
    1. Polycrystalline Solar Panel per watt: Rs 70/watt.
    2. Mount Structure per 100W: ~Rs 1000.
    3. Power cable, if your inverter is farther from panel: ~Rs 90/m
    4. Solar MPPT Charge controller: 12v/20A ~ Rs 5500
    5. 1000VA quasi sine wave inverter: ~ Rs 8000.
    6. Batteries: 12v 100Ah Exide: ~Rs 8500

  3. Sai_karthi
    May 18th, 2012 at 12:39 | #3

     Thanks for sharing the details could you let me know from where can i get the listed products in Chennai.

  4. karthikeyan
    May 18th, 2012 at 17:29 | #4

    Hi Sudarsun,

    I came across this article by shear luck. I had been thinking of using solar power for day to day power consumption. Is there a possibility where the power can be used directly for operating appliances like fan, light, etc and also charge batteries for usage during night or sunset times of the day. I currently use a 650 watts inverter coupled to 12v 150 Ah exide battery.

    Thanks in advance for your response.


  5. sudarsun
    May 18th, 2012 at 18:16 | #5

     Definitely, It is possible to solarify your home, which already uses a 650VA inverter unit.  All you have to get is a set of solar panels and a MPPT charge controller.

    Solar PV Array -> MPPT -> Batteries is the additional electrical circuitry you should install.

    Let the existing Batteries->Inverter->Load setting be as it is.

  6. sudarsun
    May 18th, 2012 at 18:19 | #6

     There are several vendors who could provide the items. But the profit margin these people have is just too much to accept.  It would be expensive if you buy the units in retail.  I have been buying the panels from http://www.akshayasolar.com/, which is based in Hyderabad, but their pricing, support and quality is very good.  For MPPT controllers, you directly buy from ebay.com for retail purchase.

  7. Raghavendra Sondur
    June 8th, 2012 at 12:13 | #7

    I read a report that the PV panel prices may come down by as much as 70% this year.  Raises doubt in mind if one should wait.  Looking forward to your post on water cooling solution for PV panels. Thanks Raghavendra

  8. Subramanian M M
    June 12th, 2012 at 19:13 | #8

    Hi Sudarsun,
    Appreciate your initiative of going for Solar power. I am also planning to go up to 3 KW, but starting with 1KW initially.
    Though I am a mechanical engineer, I equipped myself with little knowledge on Solar Power.
    You have almost shared all details that one may need, I guess. I need some additional tech. specs which will help me designing solar power utilization and cost effectively. Appreciate all your help in this regard. Here is my plan.
    Polycrystalline, 1 Panel 30 V x 8 Amps = 240 watts ; 5 Panels connected in series to generate 150 V x 8 Amps = 1200 Watts. After losses, I am looking for 1000 Watts for 5 PSH. 5KW in total. Of the 5KW generated, I am planning to use 2KW directly and store 3KW for use from 3 pm to 10 am next day. I have my loads planned for this already.
    For storage, I have planned for deep cycle batteries 4 no x 12 V x 100 Ah. With this, I should be able to store 4800Watts. The power discharged will be 3000W which is 62.5%. Hope this discharge level is fine.
    Now, need your help in design.
    Sizing the MPPT – The normal power generated by SPV (connected in series) will be 1200W and slightly above during mid day (right?).
    Charging current = 1200 W (SPV) /12 V (Battery) * safety factor = 100 * 1.2 = 120 A. I should go for 12 V / 120 A MPPT. Is the sizing correct? Is MPPT of such a capacity available? And what would be the approximate price?
    Sizing Inverter – I am planning to go for Pure Sine wave inverter with 5 Kva with a expansion plan in future. Also, how good is the Inverter with ABM (Advanced Battery Management)? Is it better to go for it so that we can eliminate MPPT altogether?
    Battery – I am planning to go for deep cycle 12 V battery. Is the battery voltage need to be aligned with Inverter voltage? Say, if the inverter comes in 48 V / 3 Kva, then I need to connect 4 batteries in series to get 48 V. If so, my batteries have to be in multiples of 4s to build 48 v in future? Is this correct?
    In short, what is the key in sizing & aligning MPPT charge controller, Battery and Inverter?
    One last question. I am planning to do it myself end-to-end with the help of my electrician cum mason. Is it advisable to do? Will there be anything missed out because of the absence of an expert?
    Thanks in advance.

  9. sudarsun
    June 12th, 2012 at 23:15 | #9

    Hi Subramanian,

    You have done most of the ground work yourself and I am very well assure that you are on the correct track.  Moreover, it is absolutely fine to do this project yourself with the help from a good electrician and an understanding mason.  Ofcourse, you need some help from a metal fabricator as well.

    I am noticing one specific problem in your calculation that you have not accounted for “energy (Wh)” and just have played with “power (W)”.  For example, your statement that “store 3kW for use from 3pm to 10am next day” is indeed a rigourous requirement. 

    Let me explain that:  When you say you need 3kW for 19 hours, the energy requirement is 3kWx19h = 57kWh.  So, into order support your night requirement you should be in a possible to produce 57kWh in your morning time (10am to 3pm).  You have also mention your load during the day is 2kW, so it would add an additional 2kW*5h = 10kWh to the energy requirement.  So the total energy to be produced would be 57+10=67kWh in 5hours.  So you should atleast have a solar panel capacity of 67/5 = 13kWp assuming 100% efficiency and sun-tracking device.  In ideal situation, the panels work at 80% efficiency and sunlight peaks only for 2 hours. So, adding a compensation factor of 1.4, you should be having a solar power plant of capacity 13*1.4=18.2kWp.

    That’s the production of power part.  Now let’s see the inverter sizing.  Assuming you would want to go for a 3kVA inverter would not be sufficient. Why?  Inverters typically have 80% efficiency, assuming 70% efficiency and operating at 80% load continuously, you need atleast a 5kVA inverter (3000W/(70%*80%)=5350 ~ 5000VA).

    Let’s see the painful part, Storage!  As we computed, the energy requirement during off sunlight period is 57kWh.  If you wanted to go for a 48VDC system, you would atleast need 57000Wh/48V = 1187.5Ah rating for the battery system. The batteries have atleast 1.3 loss factor, so the modified Ah requirement is 1543Ah.  And as you know the maximum Ah rating available in local stores is 150Ah for deep-cycle batteries.  So you need atleast 10×4=40 batteries, to cover your power requirement for the night.

    In my honest opinion, you should consider going for an inverter system with >=192VDC, so that the current flowing through will be drastically reduced.  When it comes to sizing MPPT, you can do that only after fixing the DC voltage range.  In generate MPPT controllers are rated in current, if you keep the current lower than 100A, you will be able to get a controller easily from China.  But, I would suggest going for Solar Inverter solutions where the MPPT controller comes inclusive.  Consider Liebert Solar Inverters from Emerson (http://www.emersonnetworkpower.com/en-US/Brands/Liebert/Pages/default.aspx).

    Hope the above information helps.

  10. Subramanian M M
    June 13th, 2012 at 10:24 | #10

    Hi Sudarsun,
    Great analysis, thanks for the details and your time.
    I got the key information. First, “When it comes to sizing MPPT, you can do that only after fixing the DC voltage range”. And the next “But, I would suggest going for Solar Inverter solutions where the MPPT controller comes inclusive”. These are really key information for anyone who wants to go for Solar power should know.
    On the power generation part, I understand the difference between 3 KW and 3KWh. It is actually 3KWh what I meant and not 3KW. I am sorry about the confusion.
    In a nutshell, I am planning to install Solar panel of 1200 W. Assuming 5 hours of sun light and considering other losses, I am expecting to get at least 5000 Watts/day. Of this 5KW, I want to store only 3000 watts in battery (keeping the number of batteries not more than 4) and 2000 Watts directly to load during day time. The electrical appliances I am planning to connect are couple of fans, CFLs and Tube lights. All put together consumes not more than 4400 watts/day in peak summer (in winter it may go down as the usage of fans will come down). I am also planning to go for grid interactive, meaning when the battery reaches its cut-off limit, the electrical appliances will get power from grid. So, Solar Power + Battery Power + Grid Power is I how I am planning.
    I request you to go thru my plan / design below and comment on it.
    I am planning to go for high efficiency panels because of space limitation I have in the terrace and more over I am planning to expand the capacity to 3KW later.
    Panels for now – 30 V x 8 Amp = 240 Watts. 5 Such panels connected in series which will build 150 V x 8 Amps = 1200 Watts / hour.
    Battery – 4 No x 12 V x 100 Ah – 4800 Watts should be sufficient to store the needed 3000 Watts. The discharge / day will be only 62.5% (3000/4800), considering the battery life.
    Inverter – I am planning for 5Kva. Assuming a low power factor of 0.8, the output current should be 5 Kva x 0.8 = 4000 Watts. When all the loads (Fans, CFL & T/L) are switched on at a time, it will not be more than 700 Watts. So, going for 5KVa Inverter, including future expansion, should be safe bet for now.
    Solar Inverter is real good suggestion and I will Google on it.
    Thanks in advance.

  11. sudarsun
    June 13th, 2012 at 12:06 | #11

    Hi Subramanian,

    From your description, I understood that your load is 700W and you would want to use as much solar power as possible with 4 batteries as a the constraint.  Here is the calculation:

    a)  Load = 700W
    b)  Solar Power production time  = 5 hours.
    c)  Time for Load on Battery Storage = 19 hours.
    d)  Total energy requirement = 700W * 24h = 16800Wh
    e)  Day use = 700*5 = 3500Wh
    f)  Night use = 700*19 = 13300Wh

    Inverter Sizing:
    1) Power Factor/Efficiency = 70% (worst case)
    2) Load for continuous operation = 80%
    3) KVA requirement = 700/(.7*.8) = 1250VA (~ 1.4KVA)

    Battery Sizing:
    1) Number of batteries to use = 4
    2) DC Voltage range = 4×12 = 48V
    3) Ah requirement for night use = 13300Wh/48V = 277Ah
    4) Assuming 10% loss factor, Ah requirement = 277*1.1 = 304Ah.  [Note: In general 30% loss to be accommodated]
    5) Max Ah rating available in the market = 150Ah.
    6) Number of batteries required = 8 (2 parallel rows of 4 batteries in series)

    Solar Panel Sizing:
    1. Total energy required = 16800Wh
    2. Assuming 80% efficiency, energy requirement = 16.8*1.2 = 20.16KWh
    3. Assuming 5 hours of use day light, Solar Panel Power spec = 20.16/5 = 4KWp.
    4. Assuming 48V Inverter supply, you can consider geting 24v 250W multi-crystalline panels *16=4000Wp and have pairs of panels connected in series and all pairs in parallel.

    MPPT Sizing:
    1. Considering 24v 250W panels, Vmp = 36V and Imp = 6.94A.
    2. Since we connect 2 panels in series, the Solar panel grid voltage becomes 36×2 = 72VDC and the maximum current from the panel would be 4000/72=55.55A.
    3. Since the output voltage of MPPT would be at 48-52VDC (assuming 1V more than 12V per battery while charging), the current to be handled by MPPT should be 4000/52 = 76.9A.  So getting a 48V/80A or 48V/90A MPPT is a good bet.

    Solar Inverters:
    1. The Solar Inverter for 1.4KVA or 2KVA 48VDC may probably come with a 30A MPPT controller, but your requirement is 90A controller.  So, a ready made solar inverter will not fit your requirement.  So, you should consider getting the controller and inverter separately.

    1. Multi-crystalline Solar Panels with 12% efficiency are available at ~64/Watt and 15% efficiency are available at Rs 70/watt (including taxes and transportation).  Don’t go for Mono-crystalline panels, if you are not installing a Sun-Tracking device.
    2. 2KVA Solar Inverter w/30A 48V MPPT controller is available at 15-17K with 2year warranty.  If you go for Liebert, 2KW inverter would probably cost around 40K, which would come with a 35A MPPT controller.
    3. Exide Solar Inverter batteries at 12v 150Ah are available for 15K per battery.
    4. 48V/90A MPPT controller should cost some where around 400$ and you have import directly from China.
    5. Fabrication works for Mounting the panels would cost another 30K atleast.

    hope the above helps.

  12. Subramanian M M
    June 13th, 2012 at 16:35 | #12

    Hi Sudarsun,
    This time, I got another key info “Don’t go for Mono-crystalline panels, if you are not installing a Sun-Tracking device”. I was wondering why not Mono but now I have the answer. Thanks for that.
    Ok, now let us come to the main part. I guess, I mislead you again by giving some Load detail. My apologies for that.
    Let me put it this way. It is NOT Load to Panel design rather Panel to Load design.
    For simplicity of calculation, let us say I have 5 no x 250 W panel (Vmp = 36V and Imp = 6.94A) and also I have 4 no x 12 V x 100 Ah battery.
    With this 5 panels and 4 batteries, I would like to design MPPT and Inverter.
    Now, how to size the MPPT and Inverter?
    What is the best way of connecting Batteries (Series / Parallel) so that all the batteries are equally charged / discharged? And, how does this impact on MPPT/Inverter design?
    Load – I will connect/disconnect appliances based on the power available.
    Thanks in advance

  13. sudarsun
    June 13th, 2012 at 17:02 | #13

    Not a problem Subramanian.  In the process, you have made me document my experience on this blog, which would be very useful for a lot of readers later. 🙂

    I get the point now.  Let’s see how to take this for Supply->Load design.

    You have 1250Wp of Solar panel capacity and have 48V/100Ah battery capacity.  From the Vmp setting, I am presuming that your panels are 24V type.

    Scenario 1:
    1. DC = 48V
    2. You may connect 2 panels in series and put the series connected panels in parallel to achieve 48V capacity, but you will not be able to put the 5th panel to use.

    Scenario 2:
    1. DC = 24V, put 2 batteries in series and put the series batteries in parallel.
    2. You may connect all the panels in parallel, so your Vmp = 36V and Imp = 34.7A, which will also be the input to your MPPT controller.
    3. The output of the MPPT is expected to be at 28V, assuming 2V more than the rated voltage. So the current from the MPPT controller should be 1250W/28V=44.6A.  So you should be getting a 24V, 50A MPPT controller from the market.

    Scenario 3:
    1. DC = 12V, put all the 4 batteries in parallel.
    2. Since your panels are 24V, this would not be possible with a normal MPPT controller as the controller would assume the same voltage systems at both the sides.  But there are Solar inverters available, where panel system and battery system have different voltage levels.

    Regarding the connection of batteries, if all of them are of the same age, connecting series or parallel should not affect the charging behavior.  But one catch is there in 24v systems.  You have two ways of connecting the batteries.

    a) put two batteries in parallel and connect two such banks in series.
    b) put two in series and connect the banks in parallel.

    Here (b) is preferred more than (a).  Because in (b), the current through the bank is uniform for the batteries connected in series.  But in (a), there is no guarantee that the same current is flowing through a pair of batteries.

  14. Subramanian M M
    June 13th, 2012 at 17:58 | #14

    Thanks for your patience Sudarsun.
    This time, I got more important detail.
    For a normal MPPT controller, the Panel system and Battery system voltage should be same. While connecting in series / parallel, I need to ensure this. Right?
    Scenario 2 seems to be best suiting and I will go for that.
    Thanks a lot for your valuable inputs and time.

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