The gas system can potentially absorb, store and distribute large volumes of fluctuating energy production from renewable sources such as wind and solar PV, when the power production from these are converted to hydrogen through electrolysis. The project has demonstrated transportation of up to 15% hydrogen in natural gas in a closed-loop high-pressure system, consisting of components and infrastructure from both the transmission and distribution grids. The test has shown that there is no increased leakage of hydrogen from the system compared to natural gas and that the tested components from the gas system are capable of handling hydrogen in the tested concentrations without major modifications. The project has also produced detailed knowledge on the effects on electrolysis systems from long-term standby periods.