Electricity rates in Ontario are set to rise on May 1. (CBC)

A hydro bill hike of $350 a year is in store for the average Ontario household, critics said Thursday as they warned that figure could double once the province's green energy subsidies are rolled out.

An eight per cent increase in domestic electricity costs announced Thursday is the latest in a series of fees that will drive up costs, and that's before the subsidies, the opposition said.

"It is reaching the point — not all at once but incrementally, just like a leaking faucet — that the sink is going to overflow," said Progressive Conservative energy critic John Yakabuski.

"People in this province are seeing increases that are putting them at the point where they can no longer cope with the prices of energy, and we haven't seen them all. "It's going to get worse."

The Ontario Energy Board said the new prices, which amount to about $7.60 a month and take effect May 1, apply to homes that don't have so-called smart meters, devices that record time-of-day usage.

Cheaper with smart meters

Those with the meters will see a more modest increase of 5.8 per cent, or about $5.79 per month. It's the latest in a series of hikes that include an additional $5 per month on hydro bills by 2012 as part of an $8-billion plan to create more renewable energy in Ontario.

There is also a new charge to help cover $53 million of the Liberal government's conservation and green-energy program. That fee was introduced three weeks ago, and is expected to add about $4 a year to the average electricity bill. That's on top of the extra eight per cent consumers will have to pay when the 13 per cent HST takes effect in July.

Energy Minister Brad Duguid said the price of electricity is going up everywhere, and he argued that some increases are warranted as the province moves toward greener, cleaner power.

It's still too early to say what the total increases will eventually amount to, Duguid said, since there are still too many green energy and nuclear projects being developed to nail down specific numbers.

Upgrades, green energy come at a cost

"We're modernizing our nuclear fleet, we're in the process of negotiating two new nuclear units, [and] we haven't even arrived at a price or a cost yet, so it's premature to be speculating on those kinds of costs," Duguid said.

"Those cost estimates have been rolled out as best as possible."

Yakabuski said the government's energy plans are inflating electricity bills by $350 a year — a figure that could double as more green energy subsidies are doled out.

Taxpayers may be willing to pay more for cleaner energy, Yakabuski said, but they need to know what types of increases they're being asked to agree to.

"The problem is, what's going to come in the energy bills in the future that this government doesn't want to talk about?" he said.

"They're selling the effects of [green energy] as being huge but not talking about the effect on price, and they need to be honest about that."