It seems that in terms of the total amount of energy coming from the sun there is only a very small variation due to the changing level of solar activity during a single cycle. (newclimatemodel.com)
We know that there are significant changes of much longer term in the overall level of solar activity. (gcrio.org)
High levels of solar activity enhance radiation in UV and X-ray wavelengths, and in radio wavelengths, far more than in the visible portion of the spectrum. (gcrio.org)