Solar Efficiency

The short answer to the questions from the last section is, No. Take a look at the Chart from the National Renewable Energy Lab below.
(Click to get a better view.)

[1]

At first glance, it is a little confusing since there are so many types of solar technologies. It also appears that some are still improving their efficiency curves.

Of the 20 lines on the chart, two lines matter. These lines account for 85% of all Solar energy installed today (as we will see in the next section).

The two lines are the dark blue line in the middle with the solid blue squares, Crystalline Si Cells (Single crystal, non-concentrator) and the dark blue line just below it with the open blue squares, Crystalline Si Cells (Multicrystalline).

Global Silicon Market Share ^[2]

The top line (Crystalline Si Cells, Single crystal, non-concentrator) has an efficiency of 25% in the lab.

In the real world, it's widely accepted to be closer to 15%.

85% of Solar energy installed today has a top-line efficiency of 15%, and it's essentially been flat since 1995. It is stuck, and it is not going to improve much beyond this level.

The reason it has been stuck for so long is that it is close to reaching its theoretical limit. The Shockley-Queisser Limit is the maximum theoretical efficiency of a solar cell. The limit is 33.7% ^[3]

You may think, hey wait a minute, look at Multi-Junction PV and other Emerging PV! Unfortunately, neither is close to being a significant portion of the install base, and neither shows any sign of changing that fact. We cannot include them in any strategic plans at this point in time.

Maybe 15% efficiency is enough to provide for a significant portion of our energy needs. Efficiency may turn out to be irrelevant. However, efficiency improvement is an important factor in predicting Solar energy growth possibilities, and it is clear that efficiency has been stuck at 15% for 20 years, and unlikely to improve much in the future (assuming majority of install is Crystalline Si Cell).

Next, let's take a closer look at the various Solar technologies. It's simpler than it looks in the NREL chart.

Next: Solar Technologies >

Sidebar 2: Moore's Law

Is Solar just like Moore's Law?

Moore's Law is the observation by Intel Co-Founder, Gordon Moore, that the number of transistors on an integrated circuit doubles every two years. His observation describes the key reason behind the boom of computers, the Internet, mobile phones, and all sorts of wonderful consumer electronics.

It is often stated that there is a similar dynamic with Solar energy, and therefore if we give it time, Solar energy will reward us with its own version of the iPhone.

Let's look at this more closely.

Moore's Law observes two key aspects: 1., Increasing the number of transistors in a given space, and 2., Increasing performance (until recently, roughly 40% every two years).

Solar energy has Swanson's Law, and it states that the cost of each solar cell is reduced by 20% with each doubling of manufactured solar cells. This addresses cost, but it does not squeeze more solar cells in a given space or increase performance.

The basic building block of an integrated circuit is the transistor. The more transistors added in a given space, increases the work done in that space, and performance is increased.

The basic building block of Solar energy is the Silicon electron. The Sun's energy knocks them free to become the current in electricity. We do add Phosphorous electrons to Silicon to form the N-Type layer, but we can not add more electrons than we already do today.

There is no parallel between Moore's Law and Solar energy. Integrated circuits continually increase performance because engineers have continually been able to increase the number of transistors in a given space (This will not last forever. Once transistors reach the size of an Atom, the game is up.)

There is a theoretical limit described by the Shockley-Queisser limit that pegs the limit of Silicon's ability to convert Sun energy into electricity at 33.7%. We have achieved 25% efficiency in the lab, but that has essentially been flat since 1995, indicating we are butting up against the limit, and further improvement will be extremely incremental.

References