For Lampiris's co-founder and chairman Bruno Vanderschueren, its growth is testimony to its environmental credentials as well as the ability of customers to easily switch accounts in a relatively liberalised market.
"People come to us because we are one of the cheapest suppliers and our power is green," he said, adding that the fact that Lampiris is the only locally-owned energy retailer also helps.
The EU's liberalisation of energy markets in 2007 was meant to make it easier for utility customers to switch supplier. Results have been most marked in liberalised markets, such as Belgium, Britain and Sweden, where rates range from 10 to 15% of residential customers per year.
Elsewhere rates are less than 5% in countries like France, Austria and most of eastern Europe, data from utility consultancy VaasaETT show.
In Belgium, the energy market is dominated by foreign companies, so authorities – free from bias for national players – have embraced competition to lower prices, even providing official price comparisons between suppliers.
Customers are therefore leaving once-dominant Electrabel, a unit of French utility GDF Suez, in droves, forcing it to lower prices.
Last year, Electrabel's market share fell to 57.2%, from 66.4% in 2011, while competitors like Italy's Eni and Essent Belgium, owned by Germany's RWE, gained ground.
Lampiris, Belgium's only independent energy retailer, has grabbed 3.5% of the market by volume of electricity sold, but 8.5% in terms of number of households served, since it does not sell power to corporate clients.
Founded in 2003 by two individuals with €30,000 of their savings each, Lampiris last year had turnover of 695 million and expects sales of more than 800 million this year.
Lampiris has no generation assets of its own and buys half of its electricity from renewable sources, as well as on the spot markets. Its 600 to 800 megawatt hour output is nearly equivalent to the capacity of one nuclear plant.
Last week, regional state investment funds GIMV and SIRW each paid €20 million for a combined 33% stake in the firm, giving it the financial firepower to grow and allowing Vanderschueren to considering acquisitions.
In 2011, Lampiris lost a bid for Nuon Belgium to Eni, which paid Vattenfall €157 million for the group. "If Essent Belgium were to come up for sale, we would be interested," Vanderschueren told Reuters.
He said there were important economies of scale to be had from taking over a competitor. And he saw further options if the company gets bigger.
Vanderschueren did not rule out an IPO, although Lampiris is too small to go public for now. "An IPO would make sense, but first we need to become two to three times bigger," he said.
Like all independents, Lampiris takes advantage of big utilities' inertia to win business. The firm got its first break by buying up electricity from small-scale solar installations.
"Electrabel preferred to sell its own electricity and was not interested in buying solar power from its customers, so they offered bad prices," Vanderschueren said.
Lampiris built a network of 1,300 solar plants and sold the power to environmentally conscious customers.
Later, it bought natural gas on spot and forward markets, instead of through oil-indexed long term contracts, and built up a 9% market share in gas retail.
Switching is a double-edged sword though, as only the most price-conscious customers change suppliers, and those clients will readily change to another utility a few years later.
VaasaETT director Philip Lewis said utilities typically make little or no money on new customers and will lose money if they switch again two to three years' later.
"There is nothing more expensive than volatility in your customer base," Vanderschueren said.