[{meter:"MeterA",date:"2021-05-01",hourlyConsumption:[0,0,1,1,1,2,2,2,4,4,4,4,3,3,3]},{meter:"MeterB",date:"2021-05-01",hourlyConsumption:[10,10,10,10,10,10,10,10,10,10,10,10,10,10,10]}]

db.collection.aggregate([{$unwind:{path:"$hourlyConsumption",includeArrayIndex:"hour"}},{$group:{_id:{date:"$date",hour:"$hour"},hourlyConsumption:{$sum:"$hourlyConsumption"}}},{$sort:{"_id.hour":1}},{$group:{_id:"$_id.date",hourlyConsumption:{$push:"$hourlyConsumption"}}}])