We have investigated novel bicyclic diene molecular solar thermal energy storage systems that presently are the ones with the highest predicted energy density. Using a variety of different ab initio quantum chemical methods, we report storage energies, absorption spectra, and reaction barriers for the release of stored energy for a series of bicyclic dienes. The bicyclic dienes are all constructed by modifying the bridgehead of the well-known norbornadiene/quadricyclane (NBD/QC) system. In conclusion, we find it promising that it is possible to significantly amplify the storage energy of the NBD/QC system without seriously compromising other crucial properties by introducing simple modifications to the bridgehead.