For beginner musicians or anyone who might be interested in doing some simple research
before making an expensive or long term commitment, online piano lessons might be a realistic option. However, before making any financial commitments make certain you understand exactly what to expect for what you are paying for.
There are a few online formats that might have value in the beginning. They are reasonably priced but shouldn't be relied on for long term. Videos can at least provide sound and can be repeated over and over. There are many online options that allow a teacher to offer classes with multiple students and everyone can still communicate with each other - something vital to the learning process.
Some online courses are nothing more than printed materials with some easy practice sheet music and information on how to learn and practice scales. This type of learning is all but useless in the scheme of things since you have no feedback from a teacher and no idea how you are progressing. You might be learning totally wrong and you have no idea.
However, without any type of keyboard to learn on, no online course is going to help. Before you run out to buy a full size piano, make sure you want to make this is a real commitment. Too many people find out they made expensive mistakes in buying pianos they can't really afford or even have the room for.
If you are considering buying some lessons, and if you don't have a piano or keyboard, check out the latest technology called the "roll up" keyboard. These are very affordable and are exactly what their name implies: you can roll them up and carry them anywhere.
Unlike electric keyboards that can't really be transported easily, these roll ups are popular now with beginner pianists and even experienced players who enjoy their flexibility. They can go to their regular lessons and then follow up with their online lessons - using the same instrument.