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Energy source for hot place on cloudy / rainy days without wind?

  1. Nov 8, 2013 #1
    Say you're in a place either 15 degrees north or south of the equator where average temperatures are over 25C (77F), a large majority of days are either cloudy or rainy and there isn't any wind.

    You need 50Wh a day for your needs and the battery you have happens to have a capacity of 50Wh as well so you need to generate every single day. You can buy things but not a battery with a larger capacity or fuels such as petrol.

    How do you generate electricity?
    (can either use retail products or late stage experimental technology)

    I'm currently thinking of going for some sort of wide spectrum solar cells which are receptive to IR and UV as well a larger portion of the visible spectrum but I have no idea if this technology currently exists in the real world.
    Also, how much less electricity will a normal solar cell generate on a cloudy day?

    This isn't homework, it's a voluntary problem solving project for us to do that doesn't effect our final grades but does have nice rewards.
  2. jcsd
  3. Nov 8, 2013 #2


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    Staff: Mentor

    Are you sure you don't mean 50 kWh?
  4. Nov 8, 2013 #3


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    Staff: Mentor

    It's still schoolwork, so I'll move it to the HH forums.

    Is there any running water available? If it is cloudy and rainy, I'd expect there to be running creeks or streams in the area...
  5. Nov 9, 2013 #4
    I'm pretty sure it's 50Wh (180kJ)

    I understand, I just thought that I would get more replies in the engineering section of the forum.

    Daily water needs are fulfilled by a nearby manual bore-well. No other water sources are mentioned so I guess we have to assume that there isn't any running water.

    I did miss one point in my initial post, your own energy can't be used to generate electricity.
  6. Nov 9, 2013 #5


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    Solar PV will generate on cloudy days if you have big enough panels. In some cases the output is down to 5-10% of what it is on a sunny day. So short answer is to buy really big panels perhaps 10-20 times bigger.

    In the real world it might be cheaper to buy a bigger battery. Depends on how long cloudy days persist and what the implications are for running out of electricity. Is it used to power a refrigerator storing vital medicine or just a reading light?
  7. Nov 9, 2013 #6


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    Look into Peltier modules and the Seebeck effect. A single small module can produce about 1.7W with a small temperature difference. See a demo.

    Temperature differences can be achieved by solar collector or even by heating water (fire!) on cloudy days.
  8. Nov 9, 2013 #7


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    Finally.... A PV question that matches the parameters in my location..... :grumpy:

    My 50 watt panel put out an optimal 0.03 watts 40 minutes ago(1 hour and 20 minutes prior to high noon). It is a cloudy day. Though I'm at 45° north, and your cloudy day might not be my cloudy day.

    So many variables, so little time.......
  9. Nov 14, 2013 #8
    I have done previous research on thermoelectrics and they are a good option.

    I came across a new (for me anyway) form of heat to electricity converter in the form of thermionic emission. This seems interesting because from looking around it may be more efficient than thermoelectricity so you'd need less wood for power production.

    There seems to be quite a bit written about it but are there any commercial products available?
  10. Nov 17, 2013 #9
    I have a question about thermoelectrics which I've been wondering about.

    There seem to be stacked modules when it comes to cooling applications but is it possible to stack modules on top of each other to increase efficiency when generating electricity?

  11. Nov 17, 2013 #10


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    For cooling, modules are stacked because each one produces a limited amount of temperature difference for a given working current. By stacking, these temperature differences can be summed.

    For power generation you're applying a temperature difference and obtaining a potential difference and current. You want to maximize the temperature difference (or at least operate the module at its optimum temperature difference). Stacking doesn't help with this, in fact it would make getting each module to its optimum ΔT more difficult.
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