How best to find the "best" small solar panel of a particular size?
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I just completed a battery-free outdoor node reporting temp/humid based on the information in this thread. Works great, thanks to @NeverDie for his insights. Node is a sensebender micro, RFM69W, 10F supercapacitor, and 5V solar panel. Reporting every 4 minutes it sends temp, humid, supercap %, & solar V. Uses the simple tiny solar charger schematic from @NeverDie shown above.
Results: The supercapacitor cost $2 at Digikey, is about 2/3 the size of a AAA battery, and lasts 40 hours without the solar panel connected. The 40 hours is when the supercapacitor reaches 1.9v as the low end for operating the node. Easily gets through the longer dark winter nights.
The solar panel is from China, Ebay, 110mmx70mm, 5V, 1.25W. The panel works great also. It reaches 4V in the smallest amount of light, and 5.45V (no load) in modest indirect light. In fact, it will fully recharge the supercapacitor in the morning before the sun even rises above the horizon, just from the sky brightening. (From the ~20% overnight discharged state.) It seems to charge a fully empty supercap in ~10 minutes under average light.
Bottom line: no longer walking through 1ft of snow in 10 degrees (F) to get the node, bring it inside, remove water seals, and change the batteries. This is the solution I was looking for.
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
This site is excellent, such great talent, thank you all!
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@novas said in How best to find the "best" small solar panel of a particular size?:
@novicit Could you share schematic and software of your node?
also links to the hardware would be appreciated ;)
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I just completed a battery-free outdoor node reporting temp/humid based on the information in this thread. Works great, thanks to @NeverDie for his insights. Node is a sensebender micro, RFM69W, 10F supercapacitor, and 5V solar panel. Reporting every 4 minutes it sends temp, humid, supercap %, & solar V. Uses the simple tiny solar charger schematic from @NeverDie shown above.
Results: The supercapacitor cost $2 at Digikey, is about 2/3 the size of a AAA battery, and lasts 40 hours without the solar panel connected. The 40 hours is when the supercapacitor reaches 1.9v as the low end for operating the node. Easily gets through the longer dark winter nights.
The solar panel is from China, Ebay, 110mmx70mm, 5V, 1.25W. The panel works great also. It reaches 4V in the smallest amount of light, and 5.45V (no load) in modest indirect light. In fact, it will fully recharge the supercapacitor in the morning before the sun even rises above the horizon, just from the sky brightening. (From the ~20% overnight discharged state.) It seems to charge a fully empty supercap in ~10 minutes under average light.
Bottom line: no longer walking through 1ft of snow in 10 degrees (F) to get the node, bring it inside, remove water seals, and change the batteries. This is the solution I was looking for.
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
This site is excellent, such great talent, thank you all!
@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
I'm not aware of any advantages to cycling a LiPo battery. As mentioned by Gohan, though, charging to just 80% does seem to extend lifespan.
Better yet, use a LiFeP04 battery. They're safer, and you don't need to down convert their voltage because their max charge is 3.6v.
I prefer supercaps mainly because they should last practically forever.
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@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
I'm not aware of any advantages to cycling a LiPo battery. As mentioned by Gohan, though, charging to just 80% does seem to extend lifespan.
Better yet, use a LiFeP04 battery. They're safer, and you don't need to down convert their voltage because their max charge is 3.6v.
I prefer supercaps mainly because they should last practically forever.
@NeverDie Did you look at @ceech solar harvesting boards?
My experience with solar panels is this. There are so many of them with the claiming same spec,. but behaving differently in real life. I think the same reason is quality. I have a weather station using ceech's board with temp/hum/baro/lightning/light sensors and nrf24l01+, 5V 1.2W solar panel and 3.7v 400mA LiPO. This has been running for some time. I was actually surprised that the battery is being charged even on a dark winter day. Some harvesting even is possible without the sun.Now I have been looking at replacing LiPO with a solar harvesting board and a few supercaps. Do you think 10F would be enough? Or shall I go for something higher like 20F or 50F?
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Interestingly, in direct sunlight they all measure at an open circuit voltage of 7v +- 0.1v. So, go figure as to why the range is so much wider under dim conditions.
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@NeverDie were they all at the same angle to the light source? If you laid them out on a table and shone a lamp, theynwill be at different angles and have different results.
@wallyllama I would say that in the similar circumstances different solar panels do behave differently due to quality solar cells, i.e. manufacturing quality as well as efficiency.
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@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
I'm not aware of any advantages to cycling a LiPo battery. As mentioned by Gohan, though, charging to just 80% does seem to extend lifespan.
Better yet, use a LiFeP04 battery. They're safer, and you don't need to down convert their voltage because their max charge is 3.6v.
I prefer supercaps mainly because they should last practically forever.
@NeverDie said in How best to find the "best" small solar panel of a particular size?:
@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
Thanks for the pointer to Ceech. I hadn't been aware of him, but I see that his Ebay store has a lot of interesting boards, including this one:
http://www.ebay.com/itm/Solar-Energy-Harvesting-power-supply-w-LTC3108-and-super-capacitor-storage-/331974364829?hash=item4d4b36ce9d:g:tXwAAOSwmLlX4Osy
which I may order just for fun.Impossible for me to really answer your question, as it all depends on what your current drains are. A 10F supercap isn't really much compared to a 400mah Lipo.
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@NeverDie said in How best to find the "best" small solar panel of a particular size?:
@novicit said in How best to find the "best" small solar panel of a particular size?:
Also have a 2nd outside node in testing using the Ceech solar board (A great PCB also!), a 18650 battery and the same solar panel. So far the battery has gone 2 months and is at 3.85V without the panel connected. In testing, the solar panel has no problem charging the battery. In fact so much, I am going to add a FET to disconnect the solar panel periodically to allow the battery to cycle some.
Thanks for the pointer to Ceech. I hadn't been aware of him, but I see that his Ebay store has a lot of interesting boards, including this one:
http://www.ebay.com/itm/Solar-Energy-Harvesting-power-supply-w-LTC3108-and-super-capacitor-storage-/331974364829?hash=item4d4b36ce9d:g:tXwAAOSwmLlX4Osy
which I may order just for fun.Impossible for me to really answer your question, as it all depends on what your current drains are. A 10F supercap isn't really much compared to a 400mah Lipo.
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That's a simple circuit, but it lacks the balancing of the supercaps or at least the individual overvoltage protection
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It's a buck converter. Here's the datasheet for the chip that's on it: http://cds.linear.com/docs/en/datasheet/35881fc.pdf
So, it's for the case of having a solar panel that produces more volts than the target device can handle. It's a larger solar panel than the ones we've been discussing.
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Even with a 5V panel you still need 2 supercaps in series or get the 5v supercaps but they have less capacitance. I have ordered those 5v 4F too so I'll have to see how they behave
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Even with a 5V panel you still need 2 supercaps in series or get the 5v supercaps but they have less capacitance. I have ordered those 5v 4F too so I'll have to see how they behave
@gohan said in How best to find the "best" small solar panel of a particular size?:
Even with a 5V panel you still need 2 supercaps in series or get the 5v supercaps but they have less capacitance. I have ordered those 5v 4F too so I'll have to see how they behave
It depends on how you want to handle the charge termination. If all you want to do is use a blocking diode, as in the sparkfun schematic, then yes. However, remember that if you put two capacitors in series, they have half the capacitance. Furthermore, if you do charge them to 5v, you'll have to step down that voltage one way or another, or else you'll fry the radio on your node. That's why I've gone the direction of using a larger supercap, but terminating the charge when it gets near its rated limit. Yes, you can buy supercaps that are rated up to 5.5v, but they're relatively expensive compared to the 2.7v rated ones.
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it is all a matter of what components you want to use: if you go 5v you can still use a LDO to power your devices, otherwise you need a boost converter at least for arduino. As soon as I receive those buck-boost converters I'll put them to the test, but so far they are in an unknown place (tracking shows they left china a month ago and still missing any further info)
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it is all a matter of what components you want to use: if you go 5v you can still use a LDO to power your devices, otherwise you need a boost converter at least for arduino. As soon as I receive those buck-boost converters I'll put them to the test, but so far they are in an unknown place (tracking shows they left china a month ago and still missing any further info)
@gohan said in How best to find the "best" small solar panel of a particular size?:
it is all a matter of what components you want to use: if you go 5v you can still use a LDO to power your devices, otherwise you need a boost converter at least for arduino. As soon as I receive those buck-boost converters I'll put them to the test, but so far they are in an unknown place (tracking shows they left china a month ago and still missing any further info)
Well, yes and no. I think the challenging case is how to make it as small as possible but still low cost and fairly simple.
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@gohan said in How best to find the "best" small solar panel of a particular size?:
it is all a matter of what components you want to use: if you go 5v you can still use a LDO to power your devices, otherwise you need a boost converter at least for arduino. As soon as I receive those buck-boost converters I'll put them to the test, but so far they are in an unknown place (tracking shows they left china a month ago and still missing any further info)
Well, yes and no. I think the challenging case is how to make it as small as possible but still low cost and fairly simple.
