5 ms·

>the total energy extractable from humans per pound load is lower than solar Whilst that may be true, don't forget that the energy output is in kinetic form, s

by scoot 13y ago

>the total energy extractable from humans per pound load is lower than solar Whilst that may be true, don't forget that the energy output is in kinetic form, so for comparison you'd need to factor in the weight of motors, and for a "permanent" presence, some form of energy storage for night time use (and batteries are far from light!)

ChuckMcM 13y ago
Yup, now do the math. 1 sq meter of monocrystalline cells (approximately 2kg) deriving about 166W/hr over a 6 hr solar "day" (1000 W.hrs) stored in LiFePo batteries (about 1kG/100 W.hrs) so 10kg of betteries, with .5 kg of electronics (battery charger) and wires, delivered over 24hrs or 12.5kg/41watts continuous. Human athelete lets call it 165 lbs, so 75kg, or 6 * 12.5 or 246 continuous watts over a 24hr period, or a total of just over 5.9Kwh per 24hr period. So basically anything a human can power, an equivalent mass of solar power infrastructure can power. The interesting bit is of course that you can use it all at once (like a human sprint) or spread it out over time. It will have more surface area however which often limits the ability to just swap solar cells for other forms of power.
- HNJohnC 13y ago
  What about the weight of the motors?
  - ChuckMcM 13y ago
    The efficiency linking human motion to desired motion vs linking an electrical motor to the desired motion is pretty similar in my experience. Brushless motors are relatively light and pretty efficient (hence their use in models today). The human linkages (gears/chains/etc) are comparable in weight. Bottom line connecting the human energy to motion is different but from a weight/volume standpoint similar in both cases.
    - carlob 13y ago
      Yeah, but you still have to account for the motor converting electrical to mechanical in the power output.
- scoot 13y ago
  I did: Your batteries have to provide 600W continuous for 18 hours (actually more as that was the power needed for a controlled decent), and your solar panels have to provide that same energy in your 6 hour 'solar day'. In addition, the solar panels would need to provide another 600W for 6 hours in order to run the motors whilst charging the batteries. So that's 10.8KWhrs of batteries, and 2400W/hr or 14.5sq m of solar panels. That translates to 108KG of batteries and 29KG of solar panels using your weight to power ratios - 137KG in total, compared to the rider at 75KW, so your 24 hour solar bird is a sadly flightless before even adding motors, gearboxes electronics and cabling.
  - ChuckMcM 13y ago
    Can you say more about how you got the 600W number?
    - scoot 13y ago
      There's a power / height chart in the world record claim form (as well: https://dl.dropboxusercontent.com/u/5093348/Draft%20Atlas%20World%20Record%20Claim.zip https://dl.dropboxusercontent.com/u/5093348/Draft%20Atlas%20... More considerations are the additional power needed for control inputs and to resist wind, and to compensate for thinner air at altitude, and the weight of a craft strong anough to operate outdoors.

by scoot 13y ago

ChuckMcM 13y ago

Yup, now do the math. 1 sq meter of monocrystalline cells (approximately 2kg) deriving about 166W/hr over a 6 hr solar "day" (1000 W.hrs) stored in LiFePo batteries (about 1kG/100 W.hrs) so 10kg of betteries, with .5 kg of electronics (battery charger) and wires, delivered over 24hrs or 12.5kg/41watts continuous. Human athelete lets call it 165 lbs, so 75kg, or 6 * 12.5 or 246 continuous watts over a 24hr period, or a total of just over 5.9Kwh per 24hr period. So basically anything a human can power, an equivalent mass of solar power infrastructure can power. The interesting bit is of course that you can use it all at once (like a human sprint) or spread it out over time. It will have more surface area however which often limits the ability to just swap solar cells for other forms of power.

HNJohnC 13y ago
What about the weight of the motors?
- ChuckMcM 13y ago
  The efficiency linking human motion to desired motion vs linking an electrical motor to the desired motion is pretty similar in my experience. Brushless motors are relatively light and pretty efficient (hence their use in models today). The human linkages (gears/chains/etc) are comparable in weight. Bottom line connecting the human energy to motion is different but from a weight/volume standpoint similar in both cases.
  - carlob 13y ago
    Yeah, but you still have to account for the motor converting electrical to mechanical in the power output.
scoot 13y ago
I did: Your batteries have to provide 600W continuous for 18 hours (actually more as that was the power needed for a controlled decent), and your solar panels have to provide that same energy in your 6 hour 'solar day'. In addition, the solar panels would need to provide another 600W for 6 hours in order to run the motors whilst charging the batteries. So that's 10.8KWhrs of batteries, and 2400W/hr or 14.5sq m of solar panels. That translates to 108KG of batteries and 29KG of solar panels using your weight to power ratios - 137KG in total, compared to the rider at 75KW, so your 24 hour solar bird is a sadly flightless before even adding motors, gearboxes electronics and cabling.
- ChuckMcM 13y ago
  Can you say more about how you got the 600W number?
  - scoot 13y ago
    There's a power / height chart in the world record claim form (as well: https://dl.dropboxusercontent.com/u/5093348/Draft%20Atlas%20World%20Record%20Claim.zip https://dl.dropboxusercontent.com/u/5093348/Draft%20Atlas%20... More considerations are the additional power needed for control inputs and to resist wind, and to compensate for thinner air at altitude, and the weight of a craft strong anough to operate outdoors.