Recent content by Sam Lee

Where can we find the articles online? Any web sites?

This body (6300K) that we are talking about could be a thermal stroage body. It is not a solar cell. Solar cells are more efficient if they receive radiation from bodies with higher temperatures.

You are absolutely right. Forget about lens. No wonder big solar projects use mirrors to heat up a body. Now we can really scale things up. We can have a 100m parabolic dish and focus all the energy to a spot. Anyone knows how to work out the maths?

Count Iblis, I was trying to follow your reply. It went on quite well in the beginning but it was difficult to link the end and the beginning together. While the total energy in a system is constant, the amount of energy that can be extracted from it to do useful work is dependent on the...

Great effort. My gut feel is that the 1 meter lens diameter (800W) will not provide enough energy to bring something all the way up to 6300K. The scale is off. It should be more fruitful to look at something much bigger, like 100 meters! Working backwards, in order to receive 9000W, we...

Something is funny here, although I cannot pinpoint where. The case in point is that the body receiving the focused radiation from the sun has a hole for the focused radiation to enter, thereby acting like a black body in absorbing all the radiation that passes through the lens. The rest...

This can be proven theoretically, at least for a start. We know the sun is about 6000 deg C (about 6300K). We also know that the sun radiation is about 1kW/m2. We also know that we can focus the sun's rays using fresnel lens to about 1 cm2 diameter. Now, using a thermal storage cylinder...

Actually we can focus parallel rays on one spot. Like focusing the sun's ray onto a spot. Electromagnetic (EM) radiation is very different from other types of energy. It can actually be focused! Most, if not all, other forms of energy cannot be focused. And EM rays can flow from low...

That is precisely the point. Start using public transport instead of driving whenever feasible. That will save lots of oil and reduce carbon emissions.

From a pure science perspective, a bus is more efficient than a car. A bus carrying a full load of 40 passengers will use less energy than 10 cars, each car carrying a full load of 4 passengers, when they travel the same distances. And 4 people in a car will be more efficient than 4 cars...

Does that mean that 99% of the thermal radiation will flow to the 3K bath? Can you explain more on this? Is it good or no good in relation to what we are trying to do here?

Great inputs from all of you. We are making good progress in harnessing energy from the surrounding. If we take Earth as the radiating body (300K), and outer space as the cooler body (close to 0k), then we have a temperature difference! Say we make use of the roof of a building. We have a...

Harnesing energy from the surrounding is a challenging problem with non-obvious solutions. We have to keep an open mind and continue to exploring. I suppose we can all agree that for black bodies, the radiation is more than 400 W/m2 at 300k. If we take the emissivity of our surrounding to be...

I'm not sure whether we can focus a directionless radiation source. Can someone assist in this area? The price of photovoltaic is about $1000/m2 whereas fresnel lens cost about $150/m2. It's much cheaper to use lens to focus the source before using the more expensive photovoltaic to convert...

Yes, we know that solar energy is significant, but not enough. We need to tap many other energy sources. Based on an ambient temperature of 25 deg C (300K), there is more than 400 W/m2 of ambient (or background) radiation. If we can focus this background radiation somehow, then it can become...