Watts used by plant life on earth

[Cardinal]

I’m trying to create a HS lesson that has kids calculating what percentage of the sun’s energy output humanity consumes. I’m stepping it down by levels: Bill Nye says earth gets about 1/2bill. of the sun’s energy at all. I’m stuck at finding the plant life energy usage so that we can make that into Watts used, and then I need to find the Joules or Calories consumed by humanity. Even if these are rated per year, I can then divide by seconds per year and get Watts per year.

I’ve been using Google, but I’m stymied by the fact that “energy” and “plants” are used all the time in discussing things like electricity output. Can someone help?

[Anaglyph]

Solar radiation striking the earth on an annual basis is equivalent to 178,000 terawatts, i.e. 15,000 times that of current global energy consumption. Although photosynthetic energy capture is estimated to be ten times that of global annual energy consumption, only a small part of this solar radiation is used for photosynthesis. Approximately two thirds of the net global photosynthetic productivity worldwide is of terrestrial origin, while the remainder is produced mainly by phytoplankton (microalgae) in the oceans which cover approximately 70% of the total surface area of the earth. Since biomass originates from plant and algal photosynthesis, both terrestrial plants and microalgae are appropriate targets for scientific studies relevant to biomass energy production.

from here. The trick is to google “photosynthesis” rather than plant, the above mentioned site thas the first one I got when googling the terms photosynthesis global energy