Some sites like the 5G Space Appeal have been playing with the numbers from a draft of a SpaceX/Starlink document and got some of them right, but others wrong.
The 5G Space Appeal mention a power output of a frightening “5 million watts from thousands of antennas arranged in a phased array” which does indeed sound scary.
They link to a draft of a “…representative subset of the complete system technical data …” which is probably what was available at the time they made the site.
What they got right is that the antenna is a “phased array” which gives it the ability to stear and focus the beam.
What they can’t know is the number of antennas in the arrays since that information is not disclosed by SpaceX for competitive reasons.
Looking at the data the site links to we found that the highest given transmission power is stated as 66.89 dBW which adds up to little less than 5MW (million watts) if you do the math (using one of the online calculators like this one). So they got that right too.
One important thing they missed here though is that what is measured here is “EIRP” and without knowing more about the antenna, like the gain, the radiation pattern etc., it’s impossible to know what the actual radiated power is.
Besides, a power output of 5MW is huge and would require more than 5MW of electricity to achieve. And since the only power source in space is solar panels, it would require an enormous array to produce.
For comparison, the total solar arrays of International Space Station ISS measures around 272 x 104 meters (896 x 341 feet) and they provide between 84 kW and 120 kW in total. Around 50 times less than 5MW and likely 80-100 times less than the actual power that would be needed.
The real numbers
Looking at the final application we see that the output power is set to a max of 29.91 dBW and 20.21 dBW repectively which gives us a power output of 1.000 Watts and 105 Watts respectively which does sound a lot less frightening.
It is stated in the final application that the power on ground will be -105.72 dBW which is the equivalent of around 30 pico Watts per m2 (1 pico Watt is one trillionth of a Watt) which is way less than any ground based antenna.
See also the post Can the power of 5G satellites be turned up to harm people?