Shelley was a key member of a close circle of visionary poets and writers that included Lord Byron; Leigh Hunt; Thomas Love Peacock; and his own second wife, Mary Shelley, the author of Frankenstein.
If the 900 watts means the input power, then 1000 w inverter would be ok. If the microwave produces 900 w of cooking power, you will need a bit more, maybe 1200-1400 w if you don't know what the input power rating of the microwave is.
Microwaves dimensions vary in width, heights, depth and capacity. There are no strict standards and actual measurements depend on a type of microwave. Every kitchen appliances manufacturer offer its own specifications for a particular product and microwaves will range in sizes from small compact with 0.4 â 0.5 cu. ft. (11.5 â 14.2 liters) capacity to a few times bigger dimensions.