Solar Panels
- Thread starter diceyface
- Start date
riumplus
Still Fresh
Right, let's sort out this issue once and for all with some hard numbers (I'm an Energy Efficiency Assessor by trade so I've got this data in filing cabinets beside me).
Here's some assumptions I've made from the wiki or my own knowledge: The Pandora has a 4000mAH battery at 3.7V or 14.8 watt-hours, there's 116cm^2 of usable solar panel space (14cmx8.3cm; you can double that if you're putting panels on the back), the amount of sunlight being 1000W per m^2 for 6 hours (rough average for varying sunlight intensity/time between location, weather, time of year and rough bestcase stationary panel orientation). Battery charging is normally 90% efficient and battery discharging is normally 95% efficient, with small voltage converters being around 80% efficient.
First off, doing this won't save the planet at all. If you're doing this solely to charge up your Pandora and are only having the panels visible for a small amount of light per day, the energy required to manufacture the solar panels won't offset the small amount of energy it will produce. If you want to do the best to save the planet, get solar panels on your roof. If you care about carbon emissions, charge it from the cigarette lighter in your car when you're driving around during the day - the electricity necessary to power the cigarette lighter is normally wasted otherwise thanks to not many cars having smart alternators (though this is completely ignoring the fact you're driving :wink: ). If you care about minimum energy consumption, charge it from the USB port on a desktop computer - that usually has the highest efficiency ratio. If you really want to be good for the environment, turning your air-conditioner off for around thirty seconds will save the same electricity as charging your Pandora's battery completely from flat (based on a 1.9KWh air-conditioner, which is slightly below the average size).
The Pandora may be black by our eyes, but we can only see around a third of the light the sun pours down when weighted against how much energy the various wavelengths contain. I've got a neat example I use to demonstrate this to people of two identical metal boxes, one white and one black. The white one gets hotter faster when left out in the sun and the only difference in the two is the paint. Without knowing its full spectrum absorption plus the material's conductance, convectance and radiance properties (even with estimating at it being generic matte black plastic) it's difficult to say how much it would heat up but it's almost certain that attaching a solar panel onto it would lower its temperature compared to just bare. But either way it's going to get pretty hot in direct sunlight; hot enough that it might cause damage if left in full sunlight for a long period of time in Summer. I recommend against it. Keep it as a separate panel with your Pandora in the shade (preferably indoors where it's secure and weatherproof) or don't put it in full-on direct sunlight for an extended period of time.
Average solar panel efficiency varies greatly. Because collection space is limited you'll want higher-efficiency panels than can be gotten from most integrated systems, since you'll be pulling it apart to mount onto your Pandora anyway. Even still, given the limited size you're looking at around 10% efficiency once the panels warm up. Covering the top in panels, best-case you'll get 1.16W, which is 5v @230mA (which means with the bottom covered too you could just keep it running without the battery if they contantly see full sunlight and no clouds pass overhead but you'd have to be lying on your back). Leaving it in full sunlight for the ~14 hours of "potentially usable" light, which equates to around 6 hours of full light, and you'll only get around ~3 hours of playing time out of it. For 14 hours of collection time in a best-case scenario. You're better off getting a larger, cheaper dedicated panel with an external battery you leave outside/on your backpack all day if you want to be "off the grid", then charging your Pandora from that battery at night. Though really, just having a battery-to-USB adaptor and taking some batteries with you will be much easier unless you're going to be away a very long time. You'll get around an hour of playtime per AA-battery or four hours of playtime per D-battery (eg. 4 hours from 4 AA's or 16 hours from 4 D's).
Short version - doable? Yes. Worth it? No. An external battery pack is a better idea.
I'm sleep-deprived, apologies for any errors here
Here's some assumptions I've made from the wiki or my own knowledge: The Pandora has a 4000mAH battery at 3.7V or 14.8 watt-hours, there's 116cm^2 of usable solar panel space (14cmx8.3cm; you can double that if you're putting panels on the back), the amount of sunlight being 1000W per m^2 for 6 hours (rough average for varying sunlight intensity/time between location, weather, time of year and rough bestcase stationary panel orientation). Battery charging is normally 90% efficient and battery discharging is normally 95% efficient, with small voltage converters being around 80% efficient.
First off, doing this won't save the planet at all. If you're doing this solely to charge up your Pandora and are only having the panels visible for a small amount of light per day, the energy required to manufacture the solar panels won't offset the small amount of energy it will produce. If you want to do the best to save the planet, get solar panels on your roof. If you care about carbon emissions, charge it from the cigarette lighter in your car when you're driving around during the day - the electricity necessary to power the cigarette lighter is normally wasted otherwise thanks to not many cars having smart alternators (though this is completely ignoring the fact you're driving :wink: ). If you care about minimum energy consumption, charge it from the USB port on a desktop computer - that usually has the highest efficiency ratio. If you really want to be good for the environment, turning your air-conditioner off for around thirty seconds will save the same electricity as charging your Pandora's battery completely from flat (based on a 1.9KWh air-conditioner, which is slightly below the average size).
The Pandora may be black by our eyes, but we can only see around a third of the light the sun pours down when weighted against how much energy the various wavelengths contain. I've got a neat example I use to demonstrate this to people of two identical metal boxes, one white and one black. The white one gets hotter faster when left out in the sun and the only difference in the two is the paint. Without knowing its full spectrum absorption plus the material's conductance, convectance and radiance properties (even with estimating at it being generic matte black plastic) it's difficult to say how much it would heat up but it's almost certain that attaching a solar panel onto it would lower its temperature compared to just bare. But either way it's going to get pretty hot in direct sunlight; hot enough that it might cause damage if left in full sunlight for a long period of time in Summer. I recommend against it. Keep it as a separate panel with your Pandora in the shade (preferably indoors where it's secure and weatherproof) or don't put it in full-on direct sunlight for an extended period of time.
Average solar panel efficiency varies greatly. Because collection space is limited you'll want higher-efficiency panels than can be gotten from most integrated systems, since you'll be pulling it apart to mount onto your Pandora anyway. Even still, given the limited size you're looking at around 10% efficiency once the panels warm up. Covering the top in panels, best-case you'll get 1.16W, which is 5v @230mA (which means with the bottom covered too you could just keep it running without the battery if they contantly see full sunlight and no clouds pass overhead but you'd have to be lying on your back). Leaving it in full sunlight for the ~14 hours of "potentially usable" light, which equates to around 6 hours of full light, and you'll only get around ~3 hours of playing time out of it. For 14 hours of collection time in a best-case scenario. You're better off getting a larger, cheaper dedicated panel with an external battery you leave outside/on your backpack all day if you want to be "off the grid", then charging your Pandora from that battery at night. Though really, just having a battery-to-USB adaptor and taking some batteries with you will be much easier unless you're going to be away a very long time. You'll get around an hour of playtime per AA-battery or four hours of playtime per D-battery (eg. 4 hours from 4 AA's or 16 hours from 4 D's).
Short version - doable? Yes. Worth it? No. An external battery pack is a better idea.
I'm sleep-deprived, apologies for any errors here
Yay! Someone with hard data!
The thing to keep in mind about this part of the argument though is that without a solar panel there's no reason to put it in the sun in the first place, the panels aren't there for heat-mitigation. The basic assumption of how the Pandora is being used and stored changes with the addition of the solar panels. Sun exposure while in-use is less a factor, as the nature of the beast is to be used when it's needed/wanted, and the effect of the sun on the screen (the primary function being to display stuff) is unaffected by the addition of a solar panel, so a Pandora -in use- will get the same exposure or lack thereof regardless of any mods. Where the comparison matters is where the device is left -in storage-.
We're not talking about the difference between a Plain Pandora and a Solar-Pandora both in direct sunlight, but a Plain Pandora in a pocket, backpack, belt-case, or next to your PC or bedside table with incidental sunlight exposure, and a Solar-Pandora purposefully placed for optimal exposure to sunlight.
This all said, I doubt that anyone is still arguing that integral solar panels are a good idea, we're all just engaging in the intellectual exercise of determining exactly how bad an idea it is.
The thing to keep in mind about this part of the argument though is that without a solar panel there's no reason to put it in the sun in the first place, the panels aren't there for heat-mitigation. The basic assumption of how the Pandora is being used and stored changes with the addition of the solar panels. Sun exposure while in-use is less a factor, as the nature of the beast is to be used when it's needed/wanted, and the effect of the sun on the screen (the primary function being to display stuff) is unaffected by the addition of a solar panel, so a Pandora -in use- will get the same exposure or lack thereof regardless of any mods. Where the comparison matters is where the device is left -in storage-.
We're not talking about the difference between a Plain Pandora and a Solar-Pandora both in direct sunlight, but a Plain Pandora in a pocket, backpack, belt-case, or next to your PC or bedside table with incidental sunlight exposure, and a Solar-Pandora purposefully placed for optimal exposure to sunlight.
This all said, I doubt that anyone is still arguing that integral solar panels are a good idea, we're all just engaging in the intellectual exercise of determining exactly how bad an idea it is.
axenzoku
Still Fresh
- Joined
- May 27, 2009
- Messages
- 51
If I wanted a solar panel charger, like this one, I would use it to charge up when I have nowhere to charge it. For example, if I was out-and-about say at a WiFi hotspot like McDonalds or Starbucks or something, I could sit outside in a chair or at a table with my coffee and keep the solar charger plugged in so I can keep surfing, listening to music, watching youtube, chatting, or playing a game... It would just kinda give me a feeling of security and less-stress when it comes to worrying about my battery running out... Not really worried about the whole environmental aspect of electricity, personally I think everything should run on electricity (because electricity itself doesn't pollute, just the way people decide to generate it).
