Large volcanic eruptions cause temporary decreases in global temperature largely due to dispersal of sulfates in the upper atmosphere. The very large eruption of Tambora in 1815 caused global cooling of 0.53° C. The size of volcano eruptions is characterised by the Volcanic Explosivity Index (VEI) which is a logarithmic measure of the volume of ejecta from the eruption. Tambora was a VEI-7 event, and such events are estimated as occurring every 500 to 1000 years.
This eruption is estimated to be a high VEI-5 event, which category occurs around every 12 years (with most being toward the low end of VEI-5, however). That is the category of Mt. St. Helens. The last VEI-6 event was Pinatubo in 1991. Even a VEI-7 event, however, would not dramatically decrease the power generated by photovoltaic panels, although local disruption (comparable to thick cloud cover) would occur downwind of the eruption until the plume dispersed. Pinatubo caused global cooling of around 0.4° C and beautiful sunsets for months, but no obvious decrease in solar intensity. The Tonga eruption is substantially smaller.