# uW energy harvesting

Joined May 11, 2022
10
hello,

I was reading in multiple papers that some researchers will use a weak power supply to power electronics that are at higher power demand. They do that by using a capacitor and some circuits to store energy and releasing it at once when it is enough. I believe the circuit will maintain the voltage fixed at a level enough to drive their electronics to release the current in the charged supercapacitor.

My application:

I have a weak power source that generates microwatt (uW) and I would like it to store energy and release it into the mW. If someone has done that before can someone recommend a circuit I can build with some analysis to understand what is going on? or recommend a commercial chip if available?

#### ronsimpson

Joined Oct 7, 2019
2,797
What is you power source? Voltage, current, any information will help.
What will you power? Again Voltage, current any information. How long will it need to be powered?

If you have 1uW and you want to power a 1mW thing, you will need to save up for 1000 seconds to run for 1 second. That is if everything is 100% efficient. There will be power loss, so some extra power is needed.

Joined May 11, 2022
10
What is you power source? Voltage, current, any information will help.
What will you power? Again Voltage, current any information. How long will it need to be powered?

If you have 1uW and you want to power a 1mW thing, you will need to save up for 1000 seconds to run for 1 second. That is if everything is 100% efficient. There will be power loss, so some extra power is needed.
I am using a fuel cell. My power will be around 20uW. and I would like to harvest energy until I get to 1~2mA to power up something.

#### Papabravo

Joined Feb 24, 2006
20,618
I am using a fuel cell. My power will be around 20uW. and I would like to harvest energy until I get to 1~2mA to power up something.
I believe that you have some major misconceptions about the potential capabilities of energy harvesting. The thing you keep forgetting about is time. You say you want 1-2 mA of current, but you don't say for how long. The second thing is you have no idea how exponential processes work. The more energy you have stored in a capacitor, the harder it is to add more. The more energy you take out of a capacitor, the quicker the voltage will decay to unusable levels. In short, it is just not worth the effort for the extremely meager yield.

#### ci139

Joined Jul 11, 2016
1,898

#### nsaspook

Joined Aug 27, 2009
12,347
Everyone has it but few are actually useful in a typical home or office environment as most are for solar, not ambient RF harvesting.
https://semiengineering.com/the-limits-of-energy-harvesting/
“If you’re not burning a lot of energy, there is no need for energy harvesting,” Gert Jørgensen, senior vice president of sales and marketing for Delta’s ASIC Division. “And if you do burn a lot of energy, then energy harvesting will not work. Where we see this working is in the 10 milliwatt to 100 millwatt range, but a battery is still 20 times cheaper. Energy harvesting technology is big. You have the harvesting element, power management and storage. If you compare that to a battery, the battery is smaller.”
https://www.maximintegrated.com/con...ology-boosts-battery-life-for-iot-devices.pdf
While some applications in energy harvesting have taken off, much of the vision from that 2012 conference has not been fulfilled. Despite the fact that energy harvesting operates for free, the investment in the systems is not free. Ultimately, energy harvesting may not be the right technique for powering so many smart energy applications.

#### ronsimpson

Joined Oct 7, 2019
2,797
I am using a fuel cell. My power will be around 20uW. and I would like to harvest energy until I get to 1~2mA to power up something.
What is the voltage for the fuel cell? Do you have a data sheet for it? More information!
Also 1-2mA at what voltage? 5V or 3.3V or ?

Joined May 11, 2022
10
I believe that you have some major misconceptions about the potential capabilities of energy harvesting. The thing you keep forgetting about is time. You say you want 1-2 mA of current, but you don't say for how long. The second thing is you have no idea how exponential processes work. The more energy you have stored in a capacitor, the harder it is to add more. The more energy you take out of a capacitor, the quicker the voltage will decay to unusable levels. In short, it is just not worth the effort for the extremely meager yield.
My plan after harvesting and storing the energy is to releasing into a chip. For example, the chip needs ~1mA to operate. so the capacitor will be depleted in ~2s. So, I think time is not a problem. Furthermore, I can connect one or two fuel cells.

#### Alec_t

Joined Sep 17, 2013
14,009
For example, the chip needs ~1mA to operate.
If 'operate' means powering the chip itself, then if the chip is driving a load that load will require additional current. What will the chip be controlling/driving ?

#### Papabravo

Joined Feb 24, 2006
20,618
My plan after harvesting and storing the energy is to releasing into a chip. For example, the chip needs ~1mA to operate. so the capacitor will be depleted in ~2s. So, I think time is not a problem. Furthermore, I can connect one or two fuel cells.
I fail to see the motivation for following that plan. A deep cycle SLA batter will charge faster and last longer at those power levels.

#### ci139

Joined Jul 11, 2016
1,898
you forgot to quote the jewel
Advanced power management capabilities could be built into these devices—dynamic voltage frequency scaling, multiple voltage rails, dark silicon.