Connect with us

Charging 10xAA batteries with a solar panel

Discussion in 'Power Electronics' started by scutty247, Mar 17, 2013.

Scroll to continue with content
  1. scutty247

    scutty247

    8
    0
    Feb 12, 2013
    Hi there,

    I'm trying to work out how powerful a solar panel I would need to charge 10 x AA NiMH batteries in 8 hours.

    The batteries are 1300mAh 1.2v.

    Lets presume the conditions are very sunny as its being designed for a sunny environment.

    Has anyone got any ideas how I work this out??
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    1300mAH 1.2V
    = 1.3 AH 1.2V
    = 1.3 * 1.2Wh
    = 1.58 Wh

    10 batteries = 1.58 * 10 Wh
    = 15.8 Wh

    If you want to charge them in 8 hours 15.8 Wh / 8h = 1.975W

    So the simple answer is "About 2 watts"

    However, the real answer is more complex.

    Firstly, you have to provide the correct voltage to the batteries, and this may not match the voltage at which the panel provides the most current, so you need a larger panel, or a MPPT regulator. Let's assume you go for the latter.

    The MPPT regulator might be 90% efficient, so your panel now needs to be 100/90 * 1.975W = 2.194 W

    The batteries require more energy to charge than they gave up whilst being discharged. Let's say these batteries require 25% more power.

    So the panel needs to be 2.194 * 1.25 = 2.743W

    In addition to this, you'll never get 100% of the output from your panel, and you'll never even get a constant value.

    I have solar panels on my roof. There are "5kW" of them. Pictures tell the story far better than words.

    [​IMG]

    Here is a nice sunny day. I never hit 5kW, and I get about 10 hours of generation per day, but most of it is during a 6 hour period.

    But, it's not always that good.

    [​IMG]

    Sometimes it rains.

    [​IMG]

    Sometimes it's cloudy.

    [​IMG]

    And even on a fine day you get less hours of sunshine some months.

    So, how could we calculate how much power we would get?

    OK, here's a monthly graph from January:

    [​IMG]

    We could say that conservatively, You can expect a maximum of just over 30kW from a 5kW system -- that equates to the equivalent of 6 hours of full sun per day.

    But let's get more conservative...

    [​IMG]

    Here's winter. There's more variation, but let's call it an average of 10kW per day (it may be generous).

    That's the equivalent of only 2 hours of sun per day! Some days we get the equivalent of less than 40 minutes!

    It's very clear if we look at it over a year:

    [​IMG]

    The actual shape of these graphs will be different depending on where you are (can you guess where I am?)

    The point is, if I were wanting around 22Wh per day, I would need an 11W panel to give me that (on average) in winter. Given that a couple of days had under 1 hour of equivalent sunshine, a 25W panel would almost guarantee me that I could charge those batteries in a day.

    And 25W differs by almost an order of magnitude from the 2.75W calculated above.

    p.s. I live in a very sunny place.
     

    Attached Files:

  3. scutty247

    scutty247

    8
    0
    Feb 12, 2013
    Wow! Thanks very much, that's awesome infomation. Where abouts do you live?
     
  4. scutty247

    scutty247

    8
    0
    Feb 12, 2013
    I'm going to guess Australia from the shape of your graph
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    Good guess :)

    I hope the information helped you.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-