The line graph represents the amount of electricity generated in France by four forms of sources

electricity production (in terawatt hours) in France between 1980 and 2012

The line graph represents the amount of electricity generated in France by four forms of sources during the period of 32 years, starting from 1980.
Overall,electrcity produced by nuclear station accounted for the highest amount over the period shown, as the primary source of electricity. By contrast, this figure for the remaining means of electricity generation leveled off.

In 1980, It is clear that thermal power was used to produce well over 100 terawatt hours of electricity. At the same time, hydroelectric and nuclear station just generated about 75 terawatt hours of electricty, but there was no electricity produced by renewables power.

Between 1980 and 2005, the amount of electricity generated by nuclear station rose drammatically by nearly 300 terawatt hours and reached the peak of under 450 in 2005. However, there was a negligible rise of 25 terawatt hours of electricty produced by renewables power from 2000 to 2012. Even though thermal power overtook nuclear power in the year of 1980, that statistics remained stable for the rest of period.

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The measurement reference should have been mentioned in the summary overview. It was, afterall, mentioned specifically in the report title and above the live graph in the image presentation. It is considered the default reference for all 4 power sources. Always double check the image data. A highlighted representation must always be included in the summary report to add accuracy to the short form presentation.

Review conjunction usage rules. "But" is a conjunction used to contrast a related discussion topic. Since a new electricity source is mentioned in the second paragraph towards the end, a conjunction cannot be used. A new sentence would have worked better.