> Temperature delta can be increased by just putting devices in series.
Yes, but depending on efficiency this can scale quite horribly. Multi-stage Peltier coolers, for example, used to be absolutely horrible in yhis regard - a two stage device would need to dissipate 100W at the high temperature side to provide just 1W at the cold side. (I remember doing the math for a project around 2016, don't know how much better it is these days.)
Yes, but depending on efficiency this can scale quite horribly. Multi-stage Peltier coolers, for example, used to be absolutely horrible in yhis regard - a two stage device would need to dissipate 100W at the high temperature side to provide just 1W at the cold side. (I remember doing the math for a project around 2016, don't know how much better it is these days.)