See here for an article on the Reuters website on the impact that the upcoming EMIR rule on bank guarantees will have on the Nordic power market. Nasdaq Commodities own announcement can be found here.
EMIR will not permit bank guarantees to be used as collateral to meet margin requirements. The rules will be applicable from early next year after which market participants will need to post other forms of collateral, such as cash.
The ability to use bank guarantees has made it easier for smaller players to participate directly on the market which has led to a very high clearing rate in the region. Some alternative solutions have been put forward, such as going via financial clearing members. It remains to be seen how liquidity is impacted on the market once the rules come in.