4 ms·

Isn't exponential growth where the growth rate becomes more rapid as the stock of the thing gets larger (and, more precisely, the growth rate is a function of t

Isn't exponential growth where the growth rate becomes more rapid as the stock of the thing gets larger (and, more precisely, the growth rate is a function of the stock)? How is growth in solar capacity exponential? Wouldn't it actually be logarithmic, all other things equal?

schiffern 3y ago
The graph looks rather exponential (and decidedly _not_ logarithmic) to me.[0] The story is actually "the growth rate becomes more rapid as you accumulate experience manufacturing, which also grows as a function of the stock." AKA Wright's Law.[1] You may notice this is faster than your definition of exponential growth, because Wright's Law also counts the decommissioned panels too. The industry still got that manufacturing experience, even if the panels don't count as 'stock' today. So technically the growth rate scales with total all-time production, not current stockpile size. [0] https://en.wikipedia.org/wiki/Growth_of_photovoltaics https://en.wikipedia.org/wiki/Growth_of_photovoltaics [1] https://en.wikipedia.org/wiki/Experience_curve_effects https://en.wikipedia.org/wiki/Experience_curve_effects
- pfdietz 3y ago
  PV has been growing with a time constant short compared to the lifespan of PV modules, so most of the cumulative production is still in operation today. This is also why PV recycling hasn't had a chance to really get going -- very limited potential input to the process yet.
  - schiffern 3y ago
    Yes that's true. My point is simply that solar (in this early phase) does show exponential growth. Spangry's "the growth rate becomes more rapid as the stock of the thing gets larger" was confused enough to made exponential growth sound vaguely absurd, but in fact it's perfectly expected (and indeed observed).
_ph_ 3y ago
Because the more solar gets deployed, the less the costs are. So each increase in growth triggers a reduction in costs which then enables larger growth and so on.
- pfdietz 3y ago
  The key point here is that the potential market has been increasing exponentially with reduction in price.

schiffern 3y ago

The graph looks rather exponential (and decidedly _not_ logarithmic) to me.[0] The story is actually "the growth rate becomes more rapid as you accumulate experience manufacturing, which also grows as a function of the stock." AKA Wright's Law.[1] You may notice this is faster than your definition of exponential growth, because Wright's Law also counts the decommissioned panels too. The industry still got that manufacturing experience, even if the panels don't count as 'stock' today. So technically the growth rate scales with total all-time production, not current stockpile size. [0] https://en.wikipedia.org/wiki/Growth_of_photovoltaics https://en.wikipedia.org/wiki/Growth_of_photovoltaics [1] https://en.wikipedia.org/wiki/Experience_curve_effects https://en.wikipedia.org/wiki/Experience_curve_effects

pfdietz 3y ago
PV has been growing with a time constant short compared to the lifespan of PV modules, so most of the cumulative production is still in operation today. This is also why PV recycling hasn't had a chance to really get going -- very limited potential input to the process yet.
- schiffern 3y ago
  Yes that's true. My point is simply that solar (in this early phase) does show exponential growth. Spangry's "the growth rate becomes more rapid as the stock of the thing gets larger" was confused enough to made exponential growth sound vaguely absurd, but in fact it's perfectly expected (and indeed observed).

_ph_ 3y ago

Because the more solar gets deployed, the less the costs are. So each increase in growth triggers a reduction in costs which then enables larger growth and so on.

pfdietz 3y ago
The key point here is that the potential market has been increasing exponentially with reduction in price.