Renewable sources, including wind for generating electricity, are delivering net savings of €260m per year to Ireland between fossil fuel and carbon emission savings.
The information is contained in a report by the Sustainable Energy Authority of Ireland.
The fossil fuel that is saved would be enough to provide electricity for 780,000 Irish households.
Incorporating electricity generated from renewable sources, particularly wind, onto the country's electricity grid is a complicated business, It requires changes in the way the more traditional power plants - which use coal and gas - are operated.
This reduces the efficiency of individual fossil fuel generators by up to 7%.
However, this is more than compensated for by substantial gains in the overall system efficiency due to the displacement of fossil fuel generators by wind turbines and other renewable sources.
The report says total electricity system efficiency would actually be 18% lower if these renewable sources of electricity were removed from the system.
The SEAI report is the first time that the hidden costs and constraining factors have been incorporated.
It finds that when everything is accounted for, Ireland would need to burn 26% more fossil fuels if it did not have wind and other renewables.
The bottom line cost would be €245m per year, plus an extra €15m for carbon emissions.
Ireland is currently fourth in the world for the proportion of wind generation on its electricity system.
Overall, 20% of its electricity comes from renewables. The plan is to increase that to 40% by 2020.