Recent records of the sun's activity show that solar radiation reaching Earth varies by about 0.1 percent over an 11-year solar cycle. The change is too small to explain documented warming over the past 50 years, and scientists haven't found any long-term trend in solar output that would explain it.
Two factors control how much energy Earth receives from the sun. First, subtle wobbles in our planet's orbit around the sun vary the amount of solar radiation received. These "Milankovitch Cycles" do affect Earth's seasonal cycles, but on timescales of thousands of years. Their impact on climate change is well understood. Second, the sun's energy output changes following the 11-year sunspot cycle, but also may vary gradually over longer periods of time.