6 ms·

Admittedly, there still a lot of room for solar panel research for the upcoming years which is pretty exciting! The discrepancies is often due to fact we're de

Admittedly, there still a lot of room for solar panel research for the upcoming years which is pretty exciting! 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!

nojvek 10y ago
I heard about carnot energy but didn't realize the calculation was this simple. Suppose we say we get a insulated material that is string enough to handle high temperatures. We can beat the 37% right?
- pjc50 10y ago
  Yes; I believe this is why jet turbine engines have blades made of single crystals of exotic materials.
- syntaxing 10y ago
  It's a partial yes. You have to worry about pressure as well. You can burn fuel at a higher temperature by igniting the gas at a higher pressure. But there are certain constraints due to the fuel. If the pressure is too high, the fuel will spontaneous combust. That's why there are different octane rating of fuels and why higher octane fuel gives you better fuel efficiency (given your engine has some sort of valve timing like VTEC). This is also why Diesel engines tend to have better mileage than gasoline engines. Even though gasoline engines will perform better at the same pressure as Diesel, there just no way to bring the gasoline to the same pressure that the Diesel can handle. 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...
- paulddraper 10y ago
  It's mostly about the max temperature. If combustion in a steel engine runs at 250 C and operates in a 50 C environment, the max efficiency is 1-325K/525K = 38%. 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.
- tzs 10y ago
  There's a good explanation and derivation of Carnot's results on the efficiency of heat engines in the Feynman lectures [1]. [1] http://www.feynmanlectures.caltech.edu/I_44.html http://www.feynmanlectures.caltech.edu/I_44.html
- kirrent 10y ago
  You can, but it's worth pointing out that cars don't really run on the Carnot cycle because, unlike your air conditioner, they're not reversible. Usually they use something like the Otto cycle. To improve efficiency you can change your cycle or push the limits (temperature, compression ratio, etc.). The current generation Prius apparently uses an Atkinson cycle and achieves 40% efficiency. Some F1 engines notably have a thermal efficiency of 47%. https://arstechnica.com/cars/2016/05/turbulent-times-for-formula-1-engines-result-in-unprecedented-efficiency-gains/ https://arstechnica.com/cars/2016/05/turbulent-times-for-for...
rebootthesystem 10y ago
It's even worst than that in practice. I remember an article from many years ago where the author went through the actual efficiency of the various components in a gasoline-powered car. The conclusion was that the entire system was somewhere around 18% efficiency. 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.
wyldfire 10y ago
> 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 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 ... "
jartelt 10y ago
These things are well defined in the research community and they don't have any issues with this. The input energy is all the energy from the sun that is incident on the panel. Efficiency is electrical power generated by the panel divided by the power from sun (~1000 W/m^2). For the NREL efficiency records, the measurements are all taken at the same temperature at the NREL facility. To find the max power of a device you just sweep the voltage applied to the device and measure the current output and determine which voltage produced the most power (P=V*I). Then operate your cell at that voltage.

nojvek 10y ago

I heard about carnot energy but didn't realize the calculation was this simple. Suppose we say we get a insulated material that is string enough to handle high temperatures. We can beat the 37% right?

pjc50 10y ago
Yes; I believe this is why jet turbine engines have blades made of single crystals of exotic materials.
syntaxing 10y ago
It's a partial yes. You have to worry about pressure as well. You can burn fuel at a higher temperature by igniting the gas at a higher pressure. But there are certain constraints due to the fuel. If the pressure is too high, the fuel will spontaneous combust. That's why there are different octane rating of fuels and why higher octane fuel gives you better fuel efficiency (given your engine has some sort of valve timing like VTEC). This is also why Diesel engines tend to have better mileage than gasoline engines. Even though gasoline engines will perform better at the same pressure as Diesel, there just no way to bring the gasoline to the same pressure that the Diesel can handle. 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...
paulddraper 10y ago
It's mostly about the max temperature. If combustion in a steel engine runs at 250 C and operates in a 50 C environment, the max efficiency is 1-325K/525K = 38%. 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.
tzs 10y ago
There's a good explanation and derivation of Carnot's results on the efficiency of heat engines in the Feynman lectures [1]. [1] http://www.feynmanlectures.caltech.edu/I_44.html http://www.feynmanlectures.caltech.edu/I_44.html
kirrent 10y ago
You can, but it's worth pointing out that cars don't really run on the Carnot cycle because, unlike your air conditioner, they're not reversible. Usually they use something like the Otto cycle. To improve efficiency you can change your cycle or push the limits (temperature, compression ratio, etc.). The current generation Prius apparently uses an Atkinson cycle and achieves 40% efficiency. Some F1 engines notably have a thermal efficiency of 47%. https://arstechnica.com/cars/2016/05/turbulent-times-for-formula-1-engines-result-in-unprecedented-efficiency-gains/ https://arstechnica.com/cars/2016/05/turbulent-times-for-for...

rebootthesystem 10y ago

It's even worst than that in practice. I remember an article from many years ago where the author went through the actual efficiency of the various components in a gasoline-powered car. The conclusion was that the entire system was somewhere around 18% efficiency. 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.

wyldfire 10y ago

> 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 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 ... "

jartelt 10y ago

These things are well defined in the research community and they don't have any issues with this. The input energy is all the energy from the sun that is incident on the panel. Efficiency is electrical power generated by the panel divided by the power from sun (~1000 W/m^2). For the NREL efficiency records, the measurements are all taken at the same temperature at the NREL facility. To find the max power of a device you just sweep the voltage applied to the device and measure the current output and determine which voltage produced the most power (P=V*I). Then operate your cell at that voltage.