The HyDrid does not exclude the electric battery. On the contrary, it facilitates the introduction of a base load electric system that can be much smaller than of current hybrid electric vehicles.
Electric batteries are excellent for storing large amounts of energy, but less fit for handling the large power peaks that occur when accelerating or braking. Batteries need to be bigger than necessary, just to handle such power peaks. The high power loads also reduce the lifetime of the batteries. Ultracapacitors could be a solution for these power peaks, but they are from a cost perspective not attractive.
Hydraulic accumulators are the low-cost equivalent of ultracapacitors. They can easily store large power peaks, at a very high efficiency and at very low costs. When a hydraulic accumulator takes care of the intermitting power demands of a vehicle, this also means that the e-motor that powers the common-rail pump can be designed to the average load of the vehicle, instead of the maximum load. This means a small 5 to 11 kW electric motor can power the vehicle, combined with a smaller battery pack.