This was a frustrating stage for us with my younger daughter because my older daughter declared to me one day that she was ready to wear panties at night, and lo and behold she stayed dry from that day on. She did this at a younger age than my 3 year old now did. So when my now 3 year old said she wanted to wear panties at night I thought, ok here we go. But she didn't stay dry. and I was changing sheets and washing them every day for a week, until I decided she had to prove to me that she could stay dry in her pullup first.
So I took the advice of one of my friends. I backed this advice up by watching her pee habits at night. Since she stayed dry during the day and at naps I realized she could hold it for quite a while when she sleeps, then let loose when she was starting to come out of her deep sleep in the morning. So I go in about 11 every night, pick her up and take her to the potty. She goes right back to sleep. This drains her bladder so she won't go in the morning and it trains her body to wake up if it has to go. IF she had already peed by 11, I just left her. Then in the morning we talked about whether she was dry or not. I did this for a few weeks with her pullup on, and when it stayed dry for a few nights under this regimen then I kept her in panties. She was so happy! I also decreased her liquids before bed and had her go pee right before I turned out the lights.
Another of my friends who has done this said her daughter wakes up around 1030 now to take herself to pee, then goes right back to sleep. And using this method we have been dry for weeks, with 1 accident.