OR... may be this is the explanation: if they hit the 2019 target, the need for a bigger version will go away (and they can build more with the same tooling, if not in the same location as before)? Once there is an order placed.
"the largest mass by far is the battery,” says Tom Cleaver, R&D programme manager at OXIS. “By increasing the specific energy of the cells to 425Wh/kg, the battery can be made lighter which will allow it to fly higher and therefore cover more of the globe.
These cells are lithium sulphur (Li-S), an innovative battery chemistry that has a theoretical energy density five times greater than lithium-ion, with lighter weight and longer life-cycle characteristics. OXIS is carrying out extensive materials research, production process development and cell performance characterisation in order to improve the specific energy of the Li-S cells and hit the cycle life targets that Airbus has set. This will be done in an iterative manner in order to integrate the improvements the company will be making to each element.
Increasing energy density further is one of the greatest challenges for a programme such as Zephyr, and requires the reduction of the dead mass of the cell – such as current collectors, pouch materials or tabs – to the absolute minimum and increasing the amount of active materials and the utilisation of them.
“[Since] the project started in November 2016 research work has commenced and is progressing, with the first built integrated cell having demonstrated 380Wh/kg against the 425Wh/kg target. We are now full speed on research and development, so we plan to make improvements to the cells. We have a target end date for the project of January 2019 but we are keen to beat this.” ["]