DENVER -- If you're not already conserving energy, you may want to start now. Xcel Energy's new tiered-rate program began Tuesday.

Customers who use no more than 500 kilowatt-hours of electricity will be charged one rate: 4.6 cents, not including fees and adjustments. Customers who use more than 500 kWh in one month, will be charged 4.6 cents for the first 500 kWh. Then, for each kWh more than 500, they'll be charged a higher rate. nearly double: 9 cents, not including fees and adjustments.

Estimate your summer bills using this table provided by Xcel.

Customers whose lives depend on electricity aren't given an exception. Xcel users who need electricity 24 hours a day to power oxygen tanks or ventilators have to pay the same usage costs as someone who wastefully keeps on their air conditioning.

"That's what the problem is, it's basically a surcharge for disability," said Julie Reiskin, executive director of Colorado Cross Disability Coalition.

Reiskin told 7NEWS her organization was never notified by the Public Utilities Commission prior to the tiered-rate system decision. The PUC oversees Xcel.

"I was shocked we did not know about it," said Reiskin. "It's disturbing that the PUC saw fit to get input from Xcel, but not from the people who are directly affected by this."

"We asked the company to go look at that particular group of customers to determine what the impact of tiered-rates would be on them, and the company came back to us and told us a couple of things: One, the medical equipment that's being used is not a large electricity draw, it's not using a lot of electricity, compared to like an air conditioner. The second piece of it is, again, these customers' annual bills, there won't be a significant change," said Terry Bote, from the Colorado Public Utilities Commission.

Bote told 7NEWS that all Xcel customers received notices with previous bills, alerting them to public comment hearings prior to the PUC vote on tiered rates.

"The whole purpose of a tiered rate is to encourage energy efficiency," said Bote.

"There's disabled parking (and) wheelchair accessible sidewalks, why didn't the PUC demand some sort of medical exemption?" asked 7NEWS reporter Marshall Zelinger.

"The commission considered the exemption that was raised as an issue," said Bote.

"What would the PUC tell the customer that has to have a ventilator on 24 hours or oxygen on 24 hours a day?" asked Zelinger.

"Again, if this is an issue, they should first contact the company and the company will work with them," said Bote. "Xcel has committed to us that they will work with these customers, we expect them to honor that. If customers are calling us and saying Xcel won't work with them, we'll look at that issue."

Xcel sent some customers a notice regarding the tiered-rate increase and the effect on their use of electricity for medical equipment:

"Your special circumstance may make it difficult to significantly reduce your electricity use for medical equipment and for your comfort this summer. However, you may be able to conserve electricity in other ways. We have a variety of energy-saving tips, no-cost and low-cost solutions and rebate programs for you to choose from our web site … "

7NEWS profiled Jan Bach, who requires oxygen 24/7, and an electrical device to wear at night to deal with her sleep apnea. She called both Xcel and the PUC to find out about potential bill assistance programs.

"We understand where you're coming from, unfortunately, we don't have anything as of now," said one Xcel customer service representative. "What we can certainly help you out with, though, is trying to find other ways inside your home, you know, with other appliances and things that are plugged in to help you reduce your energy usage and that aspect versus cutting off your medical equipment."

"And there's nobody from your customer service department working to enact something to help these folks?" asked Bach.

"Like I said, unfortunately, at this point we don't have anything," said the Xcel representative.

"There haven't been any exceptions made at this point," said a customer service representative from the PUC. "Ultimately on a yearly basis, it's not supposed to be much of a difference."

"Well, you know, what you say and what is the reality for most of us, isn't true," said Bach.

According to both Xcel and the PUC, if the tiered-rate system weren't in effect, the base rate for each kilowatt-hour would be more than 4.6 cents -- 4.6 cents is the Tier I level and also the amount customers will pay for all electric use from October through May.

"If there was a discount for medical clients, who would pay for the difference?" asked Zelinger.

"It would be the rest of the rate payers who would have to make that up," said Bote.

Since fees and cost adjustments can change month-to-month, it's hard to predict your exact bill. To get an idea of what you may owe this summer, grab a bill from June, July, August or September last year and follow these steps:

Find your kilowatt-hour usage.

If you use less than 500 kWh in one month, multiply that value by .046 (4.6 cents).

If you use more than 500 kWh in one month, multiply 500 by .046 (4.6 cents). Then, take the difference (for example, if you use 687 kWh, the difference will be 187 kWh) and multiply that value by .09 (9 cents).

To get an accurate value for your total bill, you'll have to know your fee and cost adjustments and add that to the number you got from the steps above. (These fees and cost adjustment values may change month-to-month.)