As a point of comparison, current triple junction solar cells are hitting between 40% and 50% efficiency.
Ya, that's about three times as efficient as the ones on the ISS. We could have had arrays 1/3 as long which would have saved us some trouble or generated nearly 100kw per array which also would have saved us some trouble.
If you know a few simple facts you can calculate the maximum solar energy available at any given planet. You just need:
- Suns temperature in K = 5778K
- Suns Radius in m = 695,700,000m
For Juno we need the distance to Jupiter (we'll use the maximum to be considered conservative
- Jupiters distance to the sun in m = 817,000,000,000m
Finally we need two equations:
- Area of a Sphere = 4(Pi)(r^2)
- Stefan-Boltzmann equation = (sigma)(T^4)=power/unit area
- Sigma is the Stefan-Boltzmann constant = 5.6703x10^-8 W/((m^2)(K^4))
So first we plug in our values for sigma and the temperature of the sun into the Stefan-Boltzmann equation.
It gives us a value of
63.2 million watts/m^2 at the surface of the sun.
Next we use the radius of the sun to calculate its surface area and multiply it by our answer above to give us the entire power output of the sun:
3.84x10^26 watts.
Since we want to know how much of that energy is available in orbit around Jupiter and by conservation of energy we know all that energy reaches a sphere of a radius equal to Jupiters distance from the sun, we divide that number by the surface area of a sphere the size of Jupiter's orbit.
We get:
45.8W/m^2 of power in Jupiters orbit.
By comparison earth receives 1360W/m^2 - 30 times more power. Hence the large high efficiency arrays on Juno.
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