Some energy firms claiming to offer green power to Irish households are buying cheap renewable energy “credits” from abroad — a practice that campaigners claim is misleading consumers.

Irish firms brought in 9.6m of these credits, called “guarantees of origin” (GOs), from renewable-energy projects in the UK, Norway and Iceland in 2015.

Companies can buy enough guarantees of origin to cover a household’s entire electricity demand for a year for as little as €0.30, according to Bureau Européen des Unions de Consommateurs (BEUC), a coalition of European consumer-rights groups. It says the practice is legal but misleading.

Five of Ireland’s 10 electricity retailers now claim to supply 100% renewable power to their customers. The Commission for Energy Regulation certifies these green claims, which appear on customers’ bills, based on both companies’ supply contracts with renewables generators in Ireland, and on their use of guarantees of origin.

Jorg Muhlenhoff, renewables co-ordinator at BEUC, said: “The guarantees of origin are just a statistical value. It’s more or less virtual. It just states that, somewhere else in Europe, renewable electricity has been produced.

“The problem is that when consumers see nice advertising with ‘100% renewable’, or a pie chart on their bill saying the electricity comes from 100% renewables, they think [that’s what] they pay for,” he said.

The number of guarantees of origin imported by Irish power suppliers in 2015 was almost double that of 2014. Irish firms imported so many of the credits that, when all their claims for 2015 are added up, they equate to 41% of renewable-electricity “supply”. Actual renewable- electricity consumption in 2015 was 25%.

SSE Airtricity, which claims to be “Ireland’s largest supplier of 100% renewable energy”, is basing its claim in part on GOs from renewables in Britain. In Ireland, SSE operates four fossil-fuel power stations, as well as wind farms. SSE said it was Ireland’s largest generator of wind power.

Some Irish customers may be opting for a more expensive tariff with SSE because of its green claims, currently the subject of an extensive advertising campaign. A year’s electricity on a direct-debit contract with SSE is €68 more expensive than a similar contract with Bord Gais, which claimed only 20% renewable power in 2015.

Energia, which also claims to offer 100% renewable power, owns and operates a large gas-burning power station at Huntstown in north Dublin. Energia said Huntstown had “no bearing on [its] ability to offer customers 100% renewable energy” because power from Huntstown is “sold into the wholesale energy market . . . and is available for purchase by all Irish energy suppliers”.