The short answer is yes, you will still be exposed to price volatility. Even if you have a fixed-rate contract there are two risks you are exposed to:
Market timing risk at contract expiration.
You will be subject to the prices available in the market when your current supply contract expires — either higher or lower. The price with your new agreement can be substantially higher or lower than what you originally budgeted. Consumption variance risk is usually the result of a change in operations or weather anomalies.
Consumption variance risk to the extent your energy consumption falls outside of the parameters established in your supply agreement.
Most supply contracts contain consumption tolerances (or bands) around specified monthly consumption levels. If your consumption exceeds the tolerance, you will pay the market rate, which can be quite punitive because there is no incentive for the supplier to purchase the excess energy at the lowest rate possible. If your consumption is beneath the tolerance, the supplier will sell the difference into the market to maximize their revenues. If they do not get at least the rate for energy indicated in your supply contract, you will be liable for the difference, so you are still subject to the market prices.