Saturday, 29 November 2014

Astrophysics Corner, Part 13 - Simplified Basic Astrophysics of Solar Panels

We have been kind of busy lately with our solar panel install. It’s a little tough, doing an early winter job, but that’s when the installer was available, so that’s what we are doing.  It's tricky with the weather, but things look to be warming up soon.

Of course anything we can do, Kati of Terra has probably already experienced in her universe, and at a much more advanced level of technology. Here’s a excerpt from Kati of Terra Book 3 - Showdown on the Planet of the Slavers:
Finding Mikki’s was easy… there were, indeed, expanses of objects on the roof which Lank took to be the solar panels that the guard had mentioned. They were not quite the streamlined, flat circles that the Lamanians used, but then, those were the super-efficient ones that the Shelonians had perfected over a long time; these had probably been manufactured on Wayward itself, or another Fringe planet. No matter, they spoke of the owners desire to be self-sufficient when it came to electricity; Lank guessed that such a desire was a positive quality in Salamanka, at least in terms of what he was looking for.
So, how much energy will the panels on the hotel roof in Salimanka, on the planet Wayward produce? That depends on a number of factors:
  • First off, there is the solar irradiance that the planet experiences from its star. That’s measured in energy per square area, above the planet’s atmosphere. For the Earth, that’s about 1360 Watts/meter squared, above the Earth’s atmosphere.
  • The solar irradiance is basically a combination of the star’s energy output and how “diluted” that energy has become as the radiation has spread out, as it radiated away from the star.
  • The amount of energy that the star produces is dependent on the star’s chemical makeup and it’s mass.
    • Basically, large stars burn hot and bright (and burn out fast), while small stars burn cooler and dimmer (and last a long time).
    • Along with the mass of the star, its chemical makeup affects the types of nuclear reactions that can go forth, and those have different energy outputs. All of this affects the temperature and colour of the star.
    • The sun is a sort of middle class star - not nearly as hot and short lived as the really big blue O or B class stars (which might burn out in only a few hundred million years), nor as small and dim as red M class stars (which might last hundreds of billions of years or more). The sun is a yellow G class star, likely to last about 12 billion years and is roughly half way through its lifespan as an active star.
  • The degree to which the star’s energy is dissipated is a function of the planet’s distance to the star and how circular its orbit is.
  • The amount of energy that actually makes it to the surface of the planet is also affected by its atmosphere, of course. This is most obviously due to cloud cover, as on Earth, but the presence of different atmospheric components (e.g. aerosols, ozone) can also affect the amount of sunlight that makes it to the planet’s surface.
  • The latitude of the location of the panels is obviously important. Essentially, the solar flux that is experienced on the surface varies with the latitude of the site as the sine of the sun’s elevation above the ground. The farther from the planet’s equator, the smaller that angle will be, and the smaller the sine of that angle will be (the sine is 0 at 0 degrees, .5 at 30 degrees, about .71 at 45 degrees, about .87 at 60 degrees and 1 at 90 degrees).
  • That will be further compounded by the tilt of the planet’s axis, relative to the plane of its orbit around the star. The greater the tilt, the more the elevation of its sun will vary throughout the year, so the solar panels output will be greater or lesser as the season’s progress.
  • The amount of energy that can produced from the solar irradiance then depends on how efficient the solar panels are. For current Earth technology, typical efficiencies are in the high teens to high twenties (percentages).
  • Obviously, Lamanian/Shelonian technology is much more mature than ours - perhaps they have achieved the 50% or so efficiency that is theorized to be a maximal threshold. Or, perhaps they have come up with breakthrough physics, as hinted at by the reference to “streamlined, flat circles that the Lamanians used”, in the quotation above.
  • There are also some electrical engineering factors that might be considered - for example, whether the planet tends to use AC or DC technology, which will affect whether or not the panel setup needs to use inverters, which can also affect efficiency of the overall system.
At any rate, those are some of the simplified considerations for solar energy usage on different planets.

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