In January, the solar panels I installed four months ago at home produced more energy than I consumed (I repeat, in January!). After compensating what I took from the grid, the electricity company even withheld, for free!, part of the energy I produced…

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In January, the solar panels I installed four months ago at home produced more energy than I consumed (I repeat, in January!). After making up for what I took from the grid, the electricity company even withheld, for free!, some of the energy I produced.

According to Plato, “knowledge without justice should be called cunning rather than wisdom”, so here are some astrophysical considerations (I leave materials engineering or environmental and sustainability issues to the specialists), to define knowledge about what is or would be fair, about what cunning implies and what wisdom really would be in this matter of solar panels.

I start strong: nuclear energy (and gravity) is the foundation of life on Earth. Everything we know on the face of our planet obtains its vital energy, its source of energy if we play on words between engineering and biology, directly or through intermediaries, from the great nuclear fusion plant that is the Sun. The Sun reaches Earth between 1361 and 1362 watts per square meter (physicists are lazy and write W/m²), which implies that the Sun is tremendously stable (sorry for the series Blackout, which also doesn’t tell a big lie, the thing can happen). It is also inferred that if we had a solar panel of one square meter (those that are usually 2-3 square meters) we could simultaneously supply energy to 136 LED lamps of 10 W (a lot of light for a house!), or 5 powerful refrigerators, or 9 televisions, or almost 2 washing machines, or half an induction cooker, or a more normal combination of all these appliances. The sun gives a lot of energy!

The problem is that all of the above calculations are wrong for many reasons. We leave aside the efficiency of solar panels (that is, how much energy coming from the Sun they are able to convert into electricity and how much is “lost”) and enter more astrophysical concepts. We already gave one: those 1,361 W/m² is what is called the solar constant (we should add “terrestrial” to that, Uranus has a solar constant 1,000 times smaller). The 1,361 W/m², which is a power per unit area, which is known as flux (if it’s already hard to understand the difference between energy and power, here’s another physical concept), is what you receive from the Sun out there of our atmosphere. But we are under the atmosphere and it is not completely transparent.

Nuclear energy (and gravity) is the basis of life on Earth. Everything we know on the face of our planet is powered by the great nuclear fusion powerhouse that is the Sun.

In fact, the atmosphere is opaque, thank goodness, to the sun’s most energetic rays, gamma or ultraviolet rays. It is not fully transparent to blue rays, which explains why the sky is blue (we never talk about it in this section, but there are so many articles on the subject!). Our atmosphere is quite transparent, but not totally transparent to the light we are more used to and which gives us the colors of everyday life, all those of the rainbow. Then it becomes opaque again in the mid-infrared, where rays reaching us from the cosmos serve to heat and excite water molecules and nothing reaches Earth’s surface (which explains why we send the James Webb telescope into space).

Solar panels in Lavapiés, Madrid.

Finally, it becomes transparent again in radio waves. The atmosphere is very much his and he lets go of what he wants. Something that carved our existence is not trivial. Therefore, the solar panels that we can put on our homes or work buildings receive much less energy than the solar constant implies. If the Sun were high in the sky, at zenith, they say, the atmosphere would typically consume 20-60% of the solar constant. The exact value varies in minutes or hours, depending on whether we are talking about blue or red photons, and what is in the atmosphere at that time. If there is dust, the blue photons can disappear almost completely, if there are clouds, much less photons will arrive (but not 0! Since there is sunlight on cloudy days, this is a good topic for another article).

The atmosphere has carved our existence, it is not trivial: opaque to the most energetic rays such as gamma or ultraviolet. It is not transparent to blue rays, which explains the sky

But the Sun is normally not at the zenith, this only happens once a day in intertropical latitudes, not in Spain. In Peninsular and Balearic Spain, forgive me my Canarian friends, the highest point the Sun reaches, right at the summer solstice, is at a height of almost 75 degrees, the height of the stars is measured in angles from the horizon, with the zenith at 90 degrees. At the winter solstice, however, the Sun only rises to a height of about 25 degrees.

And why is the height of the Sun important? Imagine yourself in a swimming pool. They want to get to the bottom. If they dive vertically they will arrive sooner, they will cover less distance. But if you dive obliquely you have to go further to reach the bottom and it’s easier to run out of air. Well, the same thing happens with photons from the Sun. If the Sun is at its zenith, it is said that they must “pass through an atmosphere” to reach the surface. If the Sun is at a height of 30º, the photons pass through 2 entire atmospheres, and if it is at 45º, about 1.4 atmospheres. In total, the lower the Sun, the less photons reach the surface, and also the problem is not linear, the number of photons that the atmosphere eats grows exponentially as the Sun descends in height. This effect is exactly what we see in solar panel insolation curves, for those who already own them or have seen those energy graphs produced in a bell shape.

Production and consumption of electricity at user level.Pablo G. Perez González

As the Sun gets higher and higher as we approach the summer solstice, the peak energy output will be higher and higher. December 21 is when the Sun reaches the lowest maximum height of the year (in the northern hemisphere), 25º in Madrid. Not that day, it was cloudy in Madrid, but on the 26th, my panels produced 3kW at peak, noon; astronomical noon, defined by that maximum height of the Sun, nor clock noon, nor heretical noon that many call lunchtime. At the lowest output, photons from the Sun must pass through the equivalent of 2.4 atmospheres. On the 17th of February we go to 4 kW at the peak, the Sun reached 37º of altitude, equivalent to 1.7 atmospheres. By the time we get to the summer solstice, the photons will only travel 1.04 atmospheres and we should reach 7kW at peak. But that, if the atmospheric conditions are the same, and they won’t be, maybe there will be more dust from the Sahara, more ozone, whose levels rise in summer, less particles of pollution from warming…

Once knowledge is dealt with, where is the justice and cunning we spoke of at the beginning? Justice: why has compensation for surpluses, that is, energy produced that is not used and injected into the general grid, been paid for months? Winter is not the same as summer, it should be divided into a year, the astrophysics of the problem works like this. Was there no astrophysicist reviewing the law governing self-consumption?; or someone with common sense, the question of when it is sunniest is not so unknown either. And cunning: the answer to the previous question involves her.

I’m afraid there are many interests in the subject, from a new way of producing energy that is doing away with models that last decades (remember the “solar tax”), to this new business opportunity that many are making a lot of money with. And they will want to earn more. There are already distinguished minds that remind me of the millionaire of Contact (Robert Zemeckis, 1997) or the Weyland-Yutani corporation, speaking of mat the Sahara of solar panels.

Corollary: I prefer a wise way of producing energy than applying our knowledge unfairly and cunningly, we will have to be vigilant. So far this edition of cosmic voidpublic service version with useful information for everyday use.

cosmic void it is a section in which our knowledge about the universe is presented both qualitatively and quantitatively. It is intended to explain the importance of understanding the cosmos not only from a scientific point of view, but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that the universe is and is, for the most part, empty, with less than one atom per cubic meter, despite the fact that in our midst, paradoxically, there are quintillions of atoms per cubic meter. , which invites us to reflect on our existence and the presence of life in the universe. The section is made up of Pablo G. Perez Gonzálezresearcher at the Center for Astrobiology; Eva Villaver, researcher at the Center for Astrobiology; It is Patricia Sanchez Blazquezprofessor at the Complutense University of Madrid (UCM).

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