The diagram shows the consumption of renewable energy in the USA from 1949-2008. Write a 150-word report for a university lecturer identifying the main trends and making comparisons where relevant.

Sample Answer 1:
The line graph shows growth in the consumption of renewable energy during the period 1949-2008 in the USA. The results are also broken down by source.The first thing to note is that renewable energy use more than doubled over the period, with particularly strong growth in biofuels. This sector did not exist in 1980 but experienced a steep rise during the 2000s to over one quadrillion Btu per year. This made biofuels a serious challenger to both wood and hydroelectric power, which both saw only limited growth overall. The former grew steadily between 1975 and 1985, but then slipped back to around its original level of 1.8 quadrillion Btu. The latter began the period at the same level as wood but experienced more substantial growth. However, it also fell back to around 2 quadrillion Btu, with a particularly sharp drop in the late 1990s.Finally, wind power emerged late in the period but showed a gradual rise to around 0.5 quadrillion Btu, suggesting that it, along with biofuels, will replace wood and hydroelectricity as the main sources of renewable every in the future.
(184 words, IELTS 8.0

Why does this Task 1 answer get an IELTS Band 8 score?
Task achievement: The model answer describes the overall trend first, followed by an analysis of the different energy sources. Numerical evidence is used sparingly to illustrate the trends. The main trends are used as the basis of a prediction in the final sentence.
Coherence and cohesion: Trends are explained in general terms first, followed by supporting figures. Some energy sources are grouped together for ease of understanding. It and this are used throughout as cohesive devices, and the writer uses the former and the latter to refer back to information in a previous sentence.
Lexical resource: The writer uses a wide range of vocabulary to describe change, including adjectives and adverbs such as limited, substantial and particularly sharp, and verbs such as doubled, slipped andemerged.
Grammatical range and accuracy: The model answer is free from grammatical errors. Sentence forms are complex and include relative clauses and linking words such as with. The candidate makes use of past, present and future tenses. Punctuation is also used carefully and accurately throughout.