This research is aimed at designing and optimising a fully renewable energy system for the GCC countries of the Arabian Peninsula for the year 2050 . This includes deriving the energy potential of open-field PV and wind technologies in the region. Apart from the electricity demand of the power sector, the hydrogen demand of the steel, ammonia and road&rail transport sectors is also considered, as well as the export of hydrogen in the liquid form. Different scenarios are considered for a better understanding of the operation of the system. Li-ion batteries and gaseous hydrogen vessels are employed to balance production and demand, while reconversion technologies are also part of the system together with powerlines and hydrogen pipelines. The study shows that the potential of onshore wind and solar energy is way greater than total energy demand, while offshore wind potential is of a comparable size to total energy demand. On average, solar energy is the cheapest source of electricity at 2.9 €c/kWh, followed by onshore wind at 4.9 €c/kWh and offshore wind at 9.9 €c/kWh. However, the minimum cost registered by solar and onshore wind technologies is almost the same at around 2.2 €c/kWh, while offshore turbines do not fall below 5.0 €c/kWh. In a cooperation scenario considering local electricity and hydrogen demand, total annual costs are equal to 130 €bln/year, 21% less than a similar scenario where countries are isolated from each other. Twice as much electricity is produced through wind turbines than PV farms under the cooperation scheme, whereas solar energy slightly dominates the electricity mix in the isolation scenario. Besides, the system relies more on curtailment and battery storage than reconversion. The coupling of the power and hydrogen sectors leads to a total costs reduction of 7%. The LCOE found for the system is of 6.1 €c/kWh, which is around 20% more than the current LCOE of modern gas turbines in the region. The LCOH of gaseous and liquid hydrogen at the port is of 2.5 and 3.0 €/kg respectively, which is 2-3 times more expensive than crude oil and several times more expensive than LNG based on current breakeven costs in the region.