He's using some pretty heavy duty prismatic Lithium Ion cells.

Then presumably it's 8 kW. I wonder what the base rating of the solar panels is; it might be 60-70 kW.

(If it's just the panels shown in the photo, then those are probably 8kW on a sunny day.)

26 panels at 300 W / panel is indeed about 7.8KW with some leeway if it is cold they will do a bit better and when it's warm they'll do a bit worse. Rural Canada is quite far North, so your sunlight will not quite reach the 1KW/square meter that you can expect elsewhere due to the longer path the light needs to take through the atmosphere which causes some attenuation.