Solar Heated/cooled Lunch Box

Summer or winter, some lunches taste better when they're cool and fresh, other when they're hot.
To be able to heat/cool your lunch wherever you are, I made a solar heated/cooled lunch box.
The solar panels charge the batteries, hidden below it.
Half an hour before lunch starts, you press the switch, either to heat or to cool.
The power of the batteries heats up or cools down the Peltier element at the bottom of the lunch box.

Components:

-Solar panel and batteries (taken from a IKEA SUNNAN lamp)
-Peltier element (taken from a camping cooler)
-Lunch box
-Switch with 3 positions (has to be able to switch polarity)
-2 metal plates (cut out of a biscuit box)
-2 polystyrene sheets (material of a CD jewel case)
-Soldering iron
-Glue

Draw the contour of the solar panels on the upper side of the lunch box.
Remove the inside of the contour with a cutter.
Place the solar panels.
Fix the panels to the top with glue (I prefer a glue gun).

Draw the contour of the switch on the upper side of the lunch box.
Remove the inside of the contour with a cutter.
Place the switch.

Draw the contour of the Peltier element on the bottom of the lunch box.
Remove the inside of the contour with a cutter.
Glue the first metal plate on the bottom.
Glue the Peltier element inside the removed contour onto the first metal plate.
Cut out a sheet of insulation and place it around the Peltier element.
On top of the Peltier element, place the second metal plate. (These plates conduct the heat and spread it)
When everything is in place, make sure the wiring is correct and the Peltier element works (both heating and cooling).

Glue a sheet of polystyrene (or any other plastic that is safe to be in contact with food) on top of the second metal plate and seal up the sides by melting it with an old soldering iron.
Repeat the previous step for the top of the lunch box.

Enjoy eating your lunch, whether it's hot or cold!