False. Basic thermodynamics, a black body radiates, a white body doesn't. There's no way that two objects in radiative contact can spontaneously take on different temperatures, and that implies absorption (blackness) is required for thermal radiance.
The best efficiency for storing solar energy is feeding it into the mains network and counting the the quantity of oil or coal not burnt.
Jeroen Belleman
-the-market/
Have you ever actually learned anything about that? It creates problems fo r the utilities and is starting to be a significant problem for California. If the solar contribution continues to increase they will need to start w asting it if they can't find a practical way to store it.
Rick C.
Yes, I'm aware of that. Utilities don't *want* to 'store' energy. They want to run at full capacity, if at all possible. Their economic model is based on that. And yet, producing and storing H2 from solar is going to be more expensive still.
Jeroen Belleman
on-the-market/
for the utilities and is starting to be a significant problem for Californi a.
They need to buy power storage hardware to soak up short term excess genera ting capacity, and store the power until the network can use it. They don't want to invest the capital so they complain about having a significant pro blem, rather than getting on with solving the problem. It's not as if an of f-shelf solution doesn't exist, so the significant problem is an unwillingn ess to spend money.
wasting it if they can't find a practical way to store it.
There's no problem about finding a practical way to store the energy, but t here are huge problems in finding the money and persuading the regulatory a uthority that it's okay to spend it.
-- Bill Sloman, Sydney
That's location dependent. Currently it helps to have lots of high hills, which are lacking in the UK.
E & SE Australia are different, I believe.
Such costs should be added to the cost of the renewable electricity. At the moment they tend to be ignored.
Is that why you can burn your feet walking barefoot on a black asphalt street in summer? Because black asphalt radiates heat away better than white concrete?
The visible-white sheet or mirror won't get very hot from sunlight, and it does return most of the incoming sunlight back to space. Conservation of Energy is basic thermodynamics too.
It's been noted that painting roofs and streets white in cities does reduce local heat-island effects. Most paints are black at thermal wavelengths, so will radiate some heat, especially at night; the night sky is pretty cold. Sunlight energy peaks in the visible.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
on-the-market/
Is it? I realize the focus on H2 has been for autos. But there may be oth er uses and in particular there is nothing to say that H2 can only be gener ated at large, industrial facilities. If the H2 is generated directly from sunlight, it may well be practical to use on a very small scale for fuelin g autos at home or work.
Don't know, it's still early days obviously, but there is no reason to limi t you thinking. There are no small number of EV owners who install PV sola r so that their car can be charged without involving the grid.
Rick C.
That saves some fuel, but the system still needs 100% generating capacity for times when there's no sunlight.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
The green-nuts still say "but sunlight is free." It's hard to argue with logic like that.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
But turning it into useful energy isn't.
NT
No, the foot-burning is due to heat transport by conduction (your feet are in contact with the asphalt, not radiatively coupled). Yes, black radiates heat away better, but DAYTIME the solar insolation is twice the terrestrial average out-radiation, wile in NIGHTTIME the out-radiation remains the same (on average) half-as-much-as-sunlight-during-day leve, when insolation is absent.
There's three ways to move heat: conduction, convection, and radiation. Radiation alone moves heat to and from a planet in the vacuum of space. Any quasi-steady-state temperature relies on balancing the influx and outflux. The hot asphalt just represents a daily cycle sampled at peak, when the trough is ignored.
Citation? I've never heard of a roof-painting experiment on the city scale. Was it an experiment or a projection based on some particular paint? Or are you just making things up?
If your pet theories need the protection of repeated falsehoods, science offers a solution: euthanize that pet.
It requires capital investment - currently about the same per kilowatt gene rated as the equipment required to burn fossil carbon and convert the energ y released into electricity to drive the grid.
At present solar cells provide about 1% of the electricity generated around the world. Increasing the scale of manufacture by a factor of ten would ha lve the investment per kilowatt of generating capacity - as it has twice in the recent past - and make solar power decidedly cheaper than any other so urce - making the next factor of ten scale-up pretty much automatic.
-- Bill Sloman, Sydney
White concrete and black asphalt conduct heat to your foot about the same. The asphalt hurts more because it's hotter.
The hot asphalt will dump most of its heat by convection into the air, and maybe conduction down into the soil. Either way, that heat stays on Earth.
The visible light reflected off the white concrete goes mostly back into space.
Get some white-painted cardboard and some black-painted cardboard. Put them out in the sun. Which do you think will get hotter?
(Use latex paint; both will be black at thermal wavelengths.)
-- John Larkin Highland Technology, Inc lunatic fringe electronics
So, no citation. "in the sun' means you're trying to look at the upswing during the day and ignore the downswing at night. Naughty, mustn't ignore the signal !
Latex, tempera (egg), or oil paints have color from pigments. Your expectation is unfounded, and I actually DID waste time looking at your 'citation' on this issue last time: no useful info there at all.
Paint a solar panel backside white, and another black, and hang 'em both off a space station. Which will run coolest when the panels face the sun?
The Earth is like that; there's a DAY side, and a NIGHT side, and both matter.
The unreliable solar energy is cheap as long as the consumption matches hour by hour with the production. Trying to make it a reliable all around energy source is going to be very expensive.
The most obvious thing is to look at the consumption variation between day and night. It makes sense to build solar capacity for that difference. Depending the country, the variation can be 10-30 % of peek load and even more, if there are no 24/7 industries in the country.
The peak consumption should occur in the summer, when the sun is highest and this is true in low latitude countries.
However, in high latitude countries, the peak is in the winter when very little or no solar power is available due to low solar angle, cloudy winter days and ultimately with one meter of snow on the panels:-). The annual production from a panel is only 1/3 of the production at low latitudes, making the panel cost three time more calculated for annual production.
It is interested to note that in countries in the Alps, the consumption peaks are in the spring and autumn, so the Alps are the northern limit were it makes sense for a large scale solar power employment.
Why do you need a citation? You can do the experiment yourself.
You could also feel white cars and black cars in the sun.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Whit3rd, no offense but you seem to have forgotten reflection. (which is part of radiation I guess) We all agree that black is a better black body. (It radiates more.) But reciprocity then tells us that it's also a better absorber. And that the white absorbs less... energy balance then demands that what isn't adsorbed is reflected*.
The arctic covered in ice reflects more sunlight than the arctic with no ice. We paint weather boxes white, so they don't over heat in the sun.
George H.
*well, assuming no transmission.
Sunlight energy peaks in the visible, where visually white and black things will absorb energy and scatter it locally, or reflect it back into space.
IR emissivity can be very different from visual wavelengths. Water and ice are essentially black at thermal wavelengths. Most organics, like plastics and paint, are too. Shiny metals are usually very reflective at thermal wavelengths.
The older Stevenson boxes were whitewashed, and the new ones are painted with latex paint. They both *look* white.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Then lots of people will do it and get rich.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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