Be aware that the CO2e emissions shown in this app give an indication but have pretty big caveats:
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The CO2 emissions of nuclear that are shown are most likely too low. Electicity Maps just used the absolute lowest of a number of estimates.
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The emissions of reservoir-based hydro vary depending on climate and biomass in the reservoir but Electricity Maps uses a single standard value. Some hydro power in warmer climates is connected to methane emissions from the reservoir, because of anaerobic processes at the bottom of the reservoir. Some reservoirs emit as CO2e as a coal plant with a similar capacity. [edited slightly, see below↓]
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They are showing solar/wind emitting emissions when they’re producing electricity. However, solar and wind don’t work that way because they’re not using consumables. Their emissions mainly come from manufacturing and transport. In essence, solar and wind are emitting just as much whether they are producing electricity or not.
Regarding nuclear to put it into numbers: Current estimates average at about 66g CO₂eq/kWh ranging up to 180. This site uses 5 as estimate!
Thank you for the hydro part, didn’t know that yet. It does not seem as bad as you said tough, This paper states up to 73g CO₂eq/kWh which is far below the 400-800 of a stone coal plant.
My info came from Wikipedia. Your source is from Canada, not Brazil which is exactly the point. :)
The source linked by Wikipedia ist not very sound in this case. It is a website with the sensationalist title “Hydroelectric power’s dirty secret revealed” and in its text the magazine mentions a “a study to be published” without title where it supposedly gets its information from.
You are correct, that in Brazil the biomass may contribute more, in this study from 2002 one of the highest emitting reservoirs is examined. Including everything up to the Ants colonies destroyed by the reservoir. However they note that Emissions decrease significantly after a few years as the biomass is decomposed. Also at the time of the article linked above the plant was still installing turbines, increasing its energy output. This obviously leads to wrong estimations when current carbon emissions to current power output is extrapolated over the lifetime. In 2002 a Cambridge article noted that emissions are on par with fossil fuels (which of course is still not great!) A study in 2016 noted that previous estimates of the emissions may have been quite a bit to high as they collected samples during seasons with high activity.
In summary: We don’t know for certain yet how high the emissions are, but 3.5 times fossil fuel emissions seems to be grossly overestimated.
Additionally to your points
-the amount of electricity produced by solar pv is significantly underreported. Because a lot of pv is behin the meter and therefore not included.