"It would be very unwise for HGO to use shareholder funds to...

"It would be very unwise for HGO to use shareholder funds to develop the PHES project and this would be a clear signal to divest our holdings."

Yes HGO does not have the expertise to develop a pumped hydro system on its own however it could JV with companies experienced in turbine installations and electrical sales
I had a farm and developed a quarry on the side with an experienced earthmover, it took negligible input from me financially or in time just some surveillance as I was on site 24/7 the earth mover supplied the crushers and excavators and ADTs and then we took a royalty from the quarry which worked out well for everyone similar approach could work here .