Are solar power plants really a good solution for energy production ?
Everywhere you hear it's a clean way to get energy. So let's see if it really is.
As an introduction, a few words about how the sun heats the earth and how a solar panel works.
The infrared part of the solar spectrum (wavelength > 700 nm, about 50% of the energy) is directly responsible for heating the Earth's surface and air. This kind of solar radiation exposure on the Earth is considered normal.
Photovoltaic (PV) panels operate in the visible part of the solar spectrum: from 350 nm to 750 nm (approximately). It is this part of the solar spectrum that does not normally heat the environment (the part between 700 and 750 nm does). Energy from this range of radiation is partially (14-22%) converted into electrical energy and the rest (78-86%) is converted into thermal energy.
PVs thus act as a converter of the visible part of the sunlight spectrum (not infrared) to heat (infrared). In other words, they increase the amount of heat compared to the transmitted infrared portion of sunlight. To simplify the estimation, let's assume that 16% of the energy consumed by PV is converted into electrical energy. The rest is dissipated in a form of heat. Data about the operational power produced by solar panels are given in units of electric power generated by Photovoltaic (PV) systems. I.e. 84% of the energy dissipated into heat is not included in these values.
Story nr 1 - local:
The first bad effect, fully local one, is a local increase of temperature near solar power plants The Photovoltaic Heat Island Effect: Larger solar power plants increase local temperatures. Another interesting article about a super solar power plant in the Sahara, taking into account the local effects of large heat dissipation around solar panels was written by Jack Marley Solar panels in Sahara could boost renewable energy but damage the global climate – here’s why.
Story nr 2 - global:
Now let's try to look at things globally.
the number of solar panels on earth is growing almost exponentially every year. According to the Renewable Capacity Statistics 2021 website, at 12.2.2021 the world had 714 GW of operational Photovoltaic (PV) systems. Let's try to translate this value into a carbon footprint by treating all operating PV systems as one.
Some assumptions at the beginning:
- 80% of initial radiation is dissipated by the solar panel into heat.
- 1 kW of Solar Panel System covers an area about 8 m2 .
- Solar irradiance: the averaged over the year and the day, the Earth's atmosphere receives radiation 340 W/m2 from the sun
The PV systems are distributed across the earth, so I assume that the average solar radiation used in the calculations is: 150 W/m2
- Average equivalent of the carbon footprint of the 1 kWh as 0.5 . Obviously, we have different CO2 emission intensity for different countries per 1 kwh. The value 0.5 corresponds to the average values over sunny countries.
More detailed data by country and region is available on the website https://www.carbonfootprint.com/.
- Conversion from W to kWh: 1 W == 0.001 kWh
The 714 GW of operational PV systems creates a total surface (St) equal to: St = 5712000000000 m2 = 5 712 000 km2 .
It corresponds to the area size between India (3 287 263 km2) and Australia (7 741 220 km2). Going furthermore, considering the surface of the earth, the surface of the solar panels is 1.1% of its surface. Since we are talking about energy produced by the operational PV systems, we can assume that this is 16% of the energy converted into electricity. Therefore, the dissipated energy into the heat energy (Ht) produced at the same time is:
Ht = 714 [GW] (84 [%]/16 [%]) = 3748.5 [GW].
Now let's calculate the carbon footprint of this amount of heat. Using the conversion from W to kWh (1 W == 0.001 kWh), our amount of heat energy (Ht) is equivalent to 3 748 500 000 kWh ~ 3.75 GWh .
This value corresponds to the carbon footprint (assumption that the carbon footprint of the 1 kWh is 0.5):.
1874250000 kg CO2 /hour.
16 418 430 000 000 kg CO2 / year ~ 16.4 GT /year.
This is a huge value and corresponds to the 52% (!) of total CO2 emission in 2020 (31.5 GT / year) ! Thus, we have an unexpected situation because it looks like solar panels are far worse at producing energy than fossil fuels. Let's see a comparison of the increase in operational energy of PV systems to the change in global temperature anomaly as a function of years. Temperature data from https://climate.nasa.gov/vital-signs/global-temperature/.
Please note the different scales of the data presented in the figure. The operational power generated by solar panels is shown in red, the temperature anomalies in blue. Almost perfect correlation !
- Is CO2 really responsible for warming the earth ?
- The correlation between temperature anomalies and the amount of energy produced by PV systems is surprising to say the least !
- By building PV systems, we create smaller or larger heat islands around them, disturbing the natural energy balance in such an area. The PV systems produce more than 4 times more thermal energy than they produce in the form of electricity.
- By producing solar panels we pollute our environment (+ the need to recycle).
The final conclusions rather indicate that solar power plants do more damage than conventional ones.
Now, the natural question is whether we are already seeing a correlation of climate change with the increase in heat islands around solar power plants.
- Is there a correlation between the heat energy produced by the increasing number of solar plants and the increase in air temperature via the Heat Islands effect ?
- Is there a correlation between the frequency of Heat Waves and the thermal energy produced by solar power plants ?
I would be grateful if someone could point out to me the error I am making in the above approximations.
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