I'm not sure those conclusions can be drawn by that article. I mean, there was one solid regression in there which clearly showed a near perfect linearity between less gas-hours (that is more fossil free power) and lower electricity cost. And in that regression Sweden and norway was even omitted, had they not been the correlation would be even stronger.
As for the other regressions presented they were not apples to apples comparisons and no conclusions can be drawn because of bad methodology. Sure enough R-square was very low as well, but that would be expected.
The issues with the methodology are that A) the cost of electricity isnt decided by what is produced in a country, but by how much is in demand in neighboring electricity regions. For instance, the price of electricity in sweden is closely tied to demand in Germany. Thus will wind and solar in Sweden have very little explanative power on price. And B) the meassured price is t the true mean price as met by the consumers. If 5% of households has a solar installation it will skew the mean price by alot. Not only will their price of electricity inversely follow production as they will first use there own production, they will also see negative prices when the installation delivers more electricity than what is used by the household. Both mechanisms skew the price of the mean bought kwh electricity And neither is accounted for in this comparison.
But the main conclusion stands. Any reduction in gas-hours will lower the price of electricity.