Please give me suggestions about how to improve this essay on energy efficiency.
The following house features discussed throughout this essay leads to a 5 star energy efficient house which will save $13 237 in 20 years compared to a base house with no insulation. In comparison, a 6 star energy efficient house saves only $11 332. This is due to the rise in insulation costs when aiming for a 6 star energy efficient house. However, it will save more money than a 5 star energy efficient house if examined in period of 40 years or more as it will pays off in the long run. Thus, by just looking at a period of 20 years, a 5 star energy efficient house pays off better. On the other hand, one suggested feature for future use is solar system which is reliable and effective. Solar system panels harness the sun’s rays converting sunlight photon energy into electrical currents which can be used directly in home to power light and appliances. Even though it may be expensive at the beginning, it will pay off in the long run.
The main problem with this paragraph is that it has two topics. First, it sets out to discuss 5 star versus 6 star ratings that are gained by insulating the house. Then it turns to solar panels. You need to have just one topic per paragraph.
You could simply delete the part about solar panels. Otherwise, you could try to make this a comparison between all three options. You could start by saying “The house features that have been discussed so far lead to a 5 star rating. But is this the best way to minimize costs? A homeowner could aim for a 6 star rating or could use solar panels to reduce costs.” Then you would talk about the benefits of 5 star, ratings, 6 star ratings, and solar panels. The paragraph as a whole would then have one clear point.