The question is why build a power station in a mountain? The answer is a simple one. The designers wanted to minimise the impact that a large power station would make on the countryside and the most suitable site for the power station was on the boundary of the magnificent Snowdonia National Park. Naturally enough, when the scheme was first proposed, conservationists were alarmed by the enormity of the design and its position in one of the country's premier national parks. However, many assurances were given, and considerable modifications and alterations to the original design were undertaken to meet the environmental objections.
There seemed no better way to disguise the station than by hiding it inside the mountain which had already been excavated for hundreds of years by the slate quarrymen.
Another question is why was something of the scale of Dinorwig needed? In the 1950s, the concept of pumped storage came to Britain for the first time with the planning of the Blaenau Ffestiniog hydroelectric pumped storage scheme. This plan was highly successful and demonstrated the importance of pumped storage generation plant. However, it was realised that this power station would be insufficient to regulate the growing electricity demands of the country.
Engineers spent two years investigating possible sites for a large generating scheme. In the end three sites were shortlisted, all of them in North Wales. Elidir Mountain, sited on the boundary of the Snowdonia National Park, had the unique feature of a lake near its peak, Llyn Machlyn Mawr and another, Llyn Peris, at the bottom – ideal for a pumped storage scheme.
Elidir Mountain had long been used for another purpose. At the side of the lower lake, Llyn Peris, were the remnants of another industrial age – the Dinorwig slate quarries. For more than 200 years, mining carried out by thousands of quarrymen had eaten into the side of Elidir, leaving terraces up to a height of over 600 metres and the unsightly scars of industrial waste at its foot. It was the slate industry which dominated the scenery and the lives of the local community by providing the main employment in the area until synthetic materials overtook traditional slate production. At its peak, the Dinorwig slate quarry employed about 3,000 men. Indeed, at the beginning of the 1900's, Dinorwig was the second largest slate quarry in the world, overtaken only by the neighbouring Penrhyn quarry. Demand for slate roofing material became significant during the late eighteenth century and roofing slates from Dinorwig and other North Wales quarries were not only shipped all over Britain but also found their way to continental Europe and North America where they were used to meet the expanding housing needs in the industrial cities. The slate industry reached its peak towards the end of the nineteenth century and in 1969 the quarry finally stopped production.
Having made the decision to build a power station at Dinorwig, consultations began with the local community who, by a large majority, welcomed the prospect of up to 2,000 jobs during the construction phase. They also welcomed a sensitive design which involved hiding most of the power station deep inside Elidir Mountain in underground caverns.
After almost ten years of hollowing out the mountain, creating tunnels, enlarging the lakes and shifting all the heavy machinery into the mountain, Dinorwig was ready to go and was opened by Prince Charles in 1984. Since then Dinorwig has become essential to Britain's power supply; stepping in on those occasions when we all decide to make a cup of tea.