The trust already has 150 individual renewables schemes, but the new document projects how fossil fuel will be reduced across its properties.
It aspires to set an example to others by integrating renewable energy into sensitive landscapes.
The organisation has been criticised for its chairman’s vociferous campaign against wind power.
This is considered as the renewable source with most potential in the UK.
Under its new plan, the trust’s main renewables by 2020 will be hydro (27%) and biomass (21%); augmented by heat pumps (1%) and solar (0.5%).
Grid electricity will supply 26% of its power, gas 15% and LPG 6%. Oil - currently a major cost and carbon source for the trust’s rural properties - will be reduced to just 3%.
There are also plans to cut energy consumption by 20%. Wind power will play no part, because the trust’s historic landscapes are deemed too sensitive.
Patrick Begg, rural enterprise director for the trust, which aims to preserve historic buildings and land for the enjoyment of the public, told BBC News: “We’ve put all our effort to make the big leap in generating renewable energy from all our properties. Our new programme will get us to (50% of energy) by 2020.”
The subsidised renewables will save the organisation money, he said, producing an expected return on capital of 10% - much better than traditional investments.