In this particular case it might be a question of po-TAY-toe versus po-TAH-toe. Watts and kilowatts among other measures are recognized by the International System of Units (ISU), which has been adopted by the U.S. and most other countries. This system is apparently quite rigid and does not allow the use of subscripts or additional symbols. Nonetheless, investors may see terms like 'watt-peak' from those who want to enhance the ISU with their own nomenclature. Solar power manufacturers use 'watt-peak' to highlight how well their technology performs under full radiation or ‘peak’ conditions.