When and how you combust the fuel can give you different fuel efficiencies as well. For instance, the Brayton cycle can achieve easily over 50% fuel efficiency. But in order to achieve this, you need a special housing (jet engines uses this cycle) to be able to compress the fuel to the specific pressure and also handle the pressure. Also, special fuel is required. These two things makes it not really practical for the standard consumer.
On a tangent, Internal combustion engines is probably one of the funnest and hardest class I took in graduate school...
https://arstechnica.com/cars/2016/05/turbulent-times-for-for...
Ceramic, for example, can operate at far higher temperatures, so in theory a ceramic engine can be more efficient.
However, ceramic is harder to work with, and not as durable as steel, so it's not a practical alternative.
Don't research/industries usually come up with unambiguous terms and units for these things so they can compare metrics? e.g. Our prototype showed 94% VSE. VSE: "Visual Spectrum Energy" is the input energy between 400-650nm as measured by ... "
I can't remember the name of the article. It may have been in one of my engine/automobile design books. Don't know. Sorry.
The discrepancies is often due to fact we're defining "solar panels" quite different for each application and also the definition of input energy is different.
A great example is engines. The theoretical (Carnot) efficiency is limited by the heat difference between the source and the sink. You can burn fuel at a higher temperature and pressure which will give you great efficiency, but it's not realistically possibly due to physical constraints (usually the steel that houses the explosions). That's why steel engines are often said to have a maximum fuel efficiency of 37%.
This same idea applies to solar panel but it's even more convoluted. What is input energy? Is it all the energy from the sun or is it only the energy within the energy band that the panel can "see"? What is efficiency? The efficiency for different energy band is different for each solar panel as well. Worst of all, this efficiency changes for different temperature and is effected by hysteresis! By the time you store the energy, you also lose efficiency depending on the internal resistance of the energy storage (That's why MPPT exist and fun fact of the day, from what I know, there is still no reliable analytical method to account for this. Most MPPT trackers are done empirically).
Sorry for the long rant, but yeah, solar panels are confusing and there is a surprising about of research that still needs to be done!