Do you think manufacturing improvements were government subsidised? Does China (the solar powerhouse @78% of the world's supply) get a direct kickback from your government? Perhaps it's market based.
Could you provide a reference? The only $818B I can find.. is a purchase of $818B of renewables, not just solar and not a subsidy/tax break. Perhaps you have a better source. Their 887GW of solar capacity alone costs $887B at current market rates.