Isn't 11-trans-retinal more stable than 11-cis-retinal? 11-cis-retinal can be found as a part of rhodopsin and it is the non-excited form of retinal. By absorbing light, retinal goes to a higher energy state and converts to 11-trans-retinal. At least I understand it so.
If all above is correct, I just don't get one thing. Shouldn't the cis form be less stable than trans (due to steric hindrance)?
Cis-retinal is less stable than the trans isomer.  The carotenoids ingested by the body are all trans.  Enzymes in the body convert them to trans-retinoic acid, then turn them into a fatty ester which is then converted by the enzyme retinoid isomerohydrolase to cis-retinal.  The higher energy state of the cis isomer makes it prone to photoisomerization back to the lower energy trans isomer.