The maximum demonstrated efficiency of a multijunction cell, in a lab, WITH CONCENTRATION is less than 50%. Commercially available cells are lower.
Concentration is an important caveat for two reasons:
First, it implies that you are collecting light from a larger area than the PV panel itself. Second, efficiency grows with increased irradiance (so efficiency will be lower without concentration).
> 3 square meters of lateral area
Lateral area is meaningless. It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck, there is zero probability that you can put 3 kW of irradiance on your panels. Neither of those vehicles will achieve kWh/mile numbers anywhere close to a Prius.
In practice, you need to halve the efficiency and more than halve the collection area you quoted. You also need to account for conversion losses.
This is a theoretical exploration of the hard limits, not an engineering design.
The multijunction theoretical efficiency limit is 87% with infinite junctions, and over 50% with a practical number of junctions. There's nothing stopping you from creating a miniatural concentrating solar device that focuses the light from a 10 cm^2 area onto a 0.5cm^2 cell, we haven't seen such devices because the cost and extra mass exceed what you get from the efficiency gains when you can simply increase area; a very area constrained application with high power requirements might change that.
> It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck
Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the sun, perhaps even unfurl additional area? what about the area of the doors and windows?
Current solar cars can drive 1000 km per day with an average speed approaching 100km/h. It doesn't seem completely out of the realm of the possible to achieve 50km in an hour for a passenger car that can expose similar area while parked.
> This is a theoretical exploration of the hard limits, not an engineering design
You replied to (and even quoted) a comment explaining the practical limits, then doubled-down and said multi junction cells can exceed a number which has never been experimentally demonstrated.
And here you are again saying that multifunction cells can achieve 87% efficiency.
An ICE engine can achieve 100% thermal efficiency with the right Th and Tc. That has about as much relevance to the discussion at hand as 87% efficient solar panels.
Let me be clear: the most efficient cells that have ever been experimentally demonstrated under any conditions are less efficient than the number you originally stated. In real world conditions the number is half of what you originally.
> Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the
> multijunction cells can exceed 50% efficiency
The maximum demonstrated efficiency of a multijunction cell, in a lab, WITH CONCENTRATION is less than 50%. Commercially available cells are lower.
Concentration is an important caveat for two reasons:
First, it implies that you are collecting light from a larger area than the PV panel itself. Second, efficiency grows with increased irradiance (so efficiency will be lower without concentration).
> 3 square meters of lateral area
Lateral area is meaningless. It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck, there is zero probability that you can put 3 kW of irradiance on your panels. Neither of those vehicles will achieve kWh/mile numbers anywhere close to a Prius.
In practice, you need to halve the efficiency and more than halve the collection area you quoted. You also need to account for conversion losses.