Say for example an inexpensive solar calculator or other such similar device with what appears to be lets say a single 2.4V 6uA (microwatt) panel? Is an MPPT used to get the most panel rather than using the panel directly? Is there another solution for this class of panel?
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\$\begingroup\$ was hoping someone would know off hand what alternatives land in between panel diode cap and load vs panel mppt cap and load for this class of product. Clearly I need to buy some different mcus as the one I have runs fine with a dozen or two uA, but has a startup requirement that one panel cannot deliver (unless you charge the cap up before applying the load). \$\endgroup\$– old_timerCommented May 25, 2017 at 13:44
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3 Answers
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When you're talking about "inexpensive" consumer devices like solar powered clocks and calendars the answer (in general) is no.
However, there is a new generation of energy harvesting devices that are very high efficiency designed to extract much more of the energy from devices like a small solar panel.
You can see an example of such a device here: TI Energy Harvesting Device
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\$\begingroup\$ Yeah, was thinking along those lines, the almost free calculators, some are if it is trade show swag. At that level is it something like a panel a diode and a super cap perhaps? or something more complicated...thanks for the link... \$\endgroup\$ Commented May 23, 2017 at 0:31
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You have to balance:
- Price of the MPPT circuitry (which is not that cheap) versus...
- Price of a larger solar cell
For a solar calculator, which draws very little power, the extra solar cell area required is likely much cheaper than a smart MPPT circuit.
For other devices which use energy harvesting, like a dynamo-crank flashlight, this is also likely... because you're going to buy the whole thing for $2 on aliexpress or in a supermarket, which will purchase it at a cost of about $1 from china. And their manufacturing cost does not change if you got to crank it a little harder because it is inefficient.
Now if you have $200 worth of solar panels, then it is extremely likely that the addition of a MPPT circuit worth a few $ in quantity will be highly profitable.
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\$\begingroup\$ No prob, it's all about price/performance! These calculators draw µA so it's just a tiny panel and a cap, not a supercap mind you, for such a low current a cheapo cap of a few hundred µF is plenty... you can disassemble one of these calculators if you have on lying around. \$\endgroup\$– bobfluxCommented May 23, 2017 at 1:16
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\$\begingroup\$ I have a uamp mcu now, problem is with this mcu at least the startup power is too much for the panel, once up and running then it works just fine, maybe its only a problem with the mcu I am using...and this is an mcu that came out in the last year or two, claimed lowest power on the market (seems like everyone bests the last one every year or so many months these days). \$\endgroup\$ Commented May 23, 2017 at 1:19
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\$\begingroup\$ note, these are all good answers, could only pick one as when I read my question cost is the correct answer when I was really curious more of the solution, thanks for the reply! \$\endgroup\$ Commented May 25, 2017 at 13:46
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To add to @peufeu's answer in addition to cost issues there is the fact that MPPT can only improve the efficiency by a limited amount - say 10-20% and it takes power to run. If it takes more power to run than the additional power it provides there will be a net loss.
With high power arrays the overhead of the MPPT circuitry is acceptable, I doubt if you could run any MPPT circuitry on the 10uW or so you mention in the question.
answered May 23, 2017 at 2:06
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\$\begingroup\$ Good to know, thanks. With the power (or lack of) consumption of the current "lowest power" mcus for example, trying to understand still how decades ago, calculators, clocks, etc were able to run. Some had a hole in the case which could imply it was charging a cap when not in use, but most do not. Custom chips, yes I get that as being part of the solution. \$\endgroup\$ Commented May 23, 2017 at 14:05
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\$\begingroup\$ I assume there is more than the panel, blocking diode, cap for storage and the load. \$\endgroup\$ Commented May 23, 2017 at 14:07
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\$\begingroup\$ note, these are all good answers, could only pick one as when I read my question cost is the correct answer when I was really curious more of the solution, thanks for the reply! \$\endgroup\$ Commented May 25, 2017 at 13:46