the answers above are all valid, but there is another point to note: even though Sweden does not have gas, its prices are still influenced by fossil fuel generation thanks to the NordPool, is the joint electricity market of Scandinavia, which includes also Danish coal-fired plants and gas-fired plants, as well as Norwegian hydro.

It's increasingly influenced by links to the main continental market (via Germany) so gas-prices get expressed via these exchanges.

Wind power