Over the last 150 years the total amount of energy people use has increased. The population has grown, living standards have risen and homes and businesses now have far more electrical appliances. All of this pushes up the demand for electricity.
The mix of resources used to meet that demand has changed over time. Coal supplied most electricity in the UK for a long time. Nuclear power stations were added from the 1950s. From the 1990s gas replaced coal in many power stations, because gas stations were cheaper to build and produced less carbon dioxide. Use of coal for electricity in the UK has fallen sharply in recent years.
Renewable sources such as wind and solar have grown quickly, especially in the last 20 years. Two reasons are that governments set targets to cut carbon dioxide and slow climate change, and that the technology has become cheaper. Other things that change a trend are the cost of fuel, how reliable a supply is, and public concern about pollution.
To explain a trend in data, first describe the trend, then give a reason, and quote figures from the data to back up your point.