There has been work done reconstructing the solar irradiance record over the last century, before satellites were available. According to the Max Planck Institute, where this work is being done, there has been
no increase in solar irradiance since around 1940
This reconstruction does show an increase in the first part of the 20th century, which coincides with the warming from around 1900 until the 1940s. It's not enough to explain all the warming from those years, but it is responsible for a large portion. See this chart of observed temperature, modelled temperature, and variations in the major forcings that contributed to 20th century climate.
The most popular theory (other than CO2) for why weather has been warm recently does not rely on solar irradiance, but instead on cloud cover which interacts with the sun's magnetic field.
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