The first bible translated into Welsh has been increasingly at risk of deterioration from flooding and damp at the 16th century farmhouse Ty Mawr Wybrnant, near Betws-y-Coed, Snowdonia, where it is on display.
But now the Trust, which cares for the property, says it has found a sustainable solution by installing a "pico" or small scale hydroelectric turbine to use water from the nearby stream to help power the heating system to prevent damp.
It means the bible is being protected by the very thing, water, that is also putting it at risk through increasingly heavy and persistent rainfall, flooding and damp, as the climate changes.
The book, on display with more than 200 other bibles in different languages, is one of only 24 known copies of the first bible translated into Welsh.
The translation was undertaken by Bishop William Morgan, who was born at Ty Mawr Wybrnant, and printed in 1588.
Experts say it helped standardise the Welsh language and is considered to be the single most significant step in ensuring the survival of the language today.
But the bible, along with the rest of the collection, is susceptible to moisture in the air.
Now the hydroelectric turbine will generate power for the electric radiators that control levels of humidity in the Grade II listed farmhouse, with the switch to renewable energy protecting the books in a sustainable way, the Trust said.
It will only take a proportion of water from the stream to drive the turbine when water levels rise to a certain point - likely to be just when the electricity is most needed, as the air is full of moisture after rainfall.
The turbine, discreetly housed in a larch-clad shed, is expected to cut the property's carbon dioxide emissions by 5.2 tonnes a year.
Keith Jones, the National Trust's climate change adviser, said: "Earlier this year we experienced the worst flood at Ty Mawr Wybrnant in living memory and that extra moisture meant we needed to use more heating to ensure the humidity levels didn't get too high.
"Climate predictions indicate likely increases in the severity and frequency of rainfall in the area.
"This small-scale technology is allowing us to adapt to future changes more sustainably."
He added: "The energy is consumed directly on-site, solely for the conservation of this priceless bible collection.
"We must reduce our impact on the climate, but we can harness the tools nature gives us to adapt to the challenges we are facing."
It is the first time the National Trust has used hydroelectric power for the primary aim of protecting a historic collection.
Mr Jones said the organisation would be looking at how the approach, developed with the help of the Dwr Uisce Project which includes researchers from Bangor University and Trinity College, Dublin, could be used where other collections may also be at risk.
Tim Pye, the National Trust's libraries curator, said: "Extreme weather is one of the threats to our collections, with sensitive and fragile objects like books, manuscripts and other documents especially susceptible to conditions such as damp.
"The energy-efficient and sustainable pico hydro solution for Ty Mawr Wybrnant will help greatly in its efforts to safeguard the Bible collection for today's and future generations to enjoy."
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