The given diagram
This is a singular reference to an image. Yet, you describe 2 images in the summary, creating a an irregularity in the singular versus plural reference. Please note that you wrote:
shows how a wave-energy machine is designed and where it can be located
Therefore, the numerical reference of your opening sentence should be in plural form (diagrams) or in numerical form (2 differing images). You cannot open with a singular reference and close with a plural reference.
That said, you did an acceptable job of referencing a trend for both images though.
As can be seen from the diagram
Which diagram? This is precisely why you need to clearly identify the differences in image references and use these as a part of the anchor sentence of the reporting paragraph. This unclear reference will cause confusion for the reader who has to read further to get a clear idea of what you are speaking of. You could have said "
In relation to the procedular diagram (image 1)" and offered true clarity to your image reference.