Solar Panel

Discussion in 'General Electronics Chat' started by brian25, Aug 3, 2013.

  1. brian25

    Thread Starter Member

    May 13, 2013
    hi sir/ma'am i have a question regarding in device specifications

    1. how many amperes of lead acid battery i'm gonna use if my solar panel is 50w?

    2. what is the use of charge controller? can i directly connect the solar panel>> lead acid battery>>12v devices?

    3. what's the meaning of specification written in solar panel (Maximum system voltage: 800V)?
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    1. At 50W, the current output is about 4A. If you have, for example, 10 hours of enough sunshine to get maximum output, then you have 40 amp-hours. To get the most out of your system, you need at least 2-3 times that capacity in your battery. I'd say 80 to 120 Amp-hours

    2. The charge controller will charge your battery and insure it doesn't over charge. You might get away without one, but your battery life might be drastically shortened.

    3. Never heard of that one. I'd hazzard a guess, but I'll wait to see if someone else has more insight.
    brian25 likes this.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The question of battery capacity is to be determined by the use you want to make of it. Running some LED lights?, then a very small battery will be OK, but to power a microwave oven long enough to use it for several days would require thousands of dollars worth of battery bank capacity. Solar panel wattage will merely determine the LENGTH of time needed to recharge the batteries you select. 50 watts will take months to charge the large bank of batteries, but could recharge a small 7Ah 12 V SLA in a matter of a few hours. Ideally. one desires to fully recharge his bank of batteries in a single day, but some systems that are merely for short duration back up can be made to recharge over several days, if the system is only used in-frequently.

    A charge controller does what the title says. It controls the charging of batteries using the solar panels output as an input.

    Direct connection requires a device to prevent backward flow of current into the solar panel from the battery. A diode will perform this function in most cases.

    Maximum system voltage is the voltage level you CANNOT exceed, if connecting your panels in series. 12 volt panels can put out a maximum voltage much higher than 12 volts. Lets say in this case it is 22 volts. Using the NEC codes relevant to solar installations we find that Open circuit voltage PLUS 10% is used for calculating max voltage. Now we have 22 volts plus 10%, so 24.2 volts per panel connected in series up to the point where we approach the MAX system voltage. The code also desires us to consider the series string input maximum plus an additional 10%. So if we connect 30 panels in series, we get 24.2 volts times 30 panels for a max series voltage of 726 volts. To this we would again add 10%, so, 726 + 72.6 = 798.6 volts.

    Therefore, if we use the NEC regulations for calculating MAX open circuit voltage and apply that value to the manufacturers stated MAX system voltage. 30 panels would be the most that could be used in the imaginary situation I just described. A real calculation would use the Open circuit max voltage value supplied by the panel manufacturer.
    brian25 likes this.
  4. LDC3

    Active Member

    Apr 27, 2013
    This is a easy calculation for the manufacturer, so why not have it stated both ways so the end user can understand. Like this:
    Maximum system voltage: 800V
    Maximum panels in series: 30
    brian25 likes this.
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    the user must assume responsibility for end use application and suitability of a product for his needs. The end user must assume responsibility for conforming to national, state and local codes and regulations.

    A nation of lawyers and asinine legal codes has created this nonsensical monster of 'I'm not responsible' attitudes due to 'suit happy' parties that will sue for any and all reasons, imaginary or not.

    Yes, it would be simpler, but we all know simple is not how the 'system' likes things, don't we. :)
    brian25 likes this.
  6. brian25

    Thread Starter Member

    May 13, 2013
    sir/ma'am why solar panels have different amperage what's the use of that?

    thanks a lot :)
  7. wayneh


    Sep 9, 2010
    Do you mean, for a given power output, why are different amperages available?

    Power is voltage times current, so the manufacturer has many options when constructing a 50W panel. The general idea is to choose a combination which optimizes the overall power transfer from sunlight to end use. The panel manufacturer has no control over end use, so they allow the user to choose what will work best. If the user wants to charge a 12V battery, a high amperage 10V panel is less useful.

    With modern, high efficiency DC-DC converters, this concern is becoming less relevant.
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    The maximum system voltage is not so simple. You can put more panels in series in Grenada then you can in Greenland because it's warmer there, and they put out less voltage.
  9. DerickInskeep

    New Member

    Oct 17, 2014
    Hello friend bit old thread but thanks for sharing out the vital information..I am looking to get new panels so the details will help me lot.