Dinorwig 1.7GW pumped storage located in Wales was constructed beginning in 1974 costing £425 million and took 10 years to complete. The yearly operation cost after construction completed was £5 million. If the plant runs at 0.3 capacity factor per year and selling electricity at £0.025/kWh:
1) Calculate the simple payback period and ROI within 20 years of operation
2) Discuss the local environment, economic and social impact of the project.