Large energy users and residential customers on 'smart tariffs' will see higher electricity costs during the peak hours from 5pm to 7pm.

It follows a decision by the Commission for the Regulation of Utilities following a consultation period announced last month.

However, the 'smart tariff' customers will also see savings on off-peak rates.

Energy users on flat rate plans will not be affected.

Under the decision, peak time rates will be 10% higher than the day rate but during off-peak hours, the rate charged will be 10% lower.

For domestic customers, the prices they finally face will be set by their energy provider who may choose to follow through the directive from the CRU fully or in part, depending on the plan.

There are 38,000 residential customers with smart meters availing of 'smart tariffs' or 'time of use tariffs'.

The low take-up has prompted questions about the value of the plans.

The decision to broaden the differential between on and off-peak tariffs may encourage more customers to consider "time of use" offers.

There are approximately 950,000 smart meters installed around the country and around 100,000 customers have opted into receiving data on their energy use, according to a spokesman for the CRU.

The decision also details that the PSO levy, which subsidises renewable energy, will again be negative next year resulting in an annual saving of €89.10, or €140 when VAT is included, for residential customers.

An additional €40 annual saving for domestic customers will also be introduced following a change in how the network charges are distributed between households and large energy users.

However, this will be cancelled out due to an overall increase in transmission charges from inflation and the costs of maintaining the electricity supply through emergency generation which will add €41 annually to domestic bills.

The new charges will take effect from October.

Professor of Energy and Economics UCD Lisa Ryan said the CRU was trying to address high electricity costs as well as security of supply.

Speaking on RTÉ's Drivtime, she said the announcement "is really about reducing the price on the off-peak time, so this could be good news for consumers, actually.

"In that, if you can change your use of electricity so that you're using it off-peak, before 5pm or after 7pm, you'll face a lower price in your unit electricity price.

"So really it's going to encourage people to change their behaviour...I think that's more the focus of it and that's what the European Union has suggested countries do."

Prof Ryan added: "We're not talking about the full electricity prices - the CRU is just talking about our network tariffs which only make up 30% of our bills ... so it's not a huge differential either way."