20W. - I have tried it for the last 2 months... it seems to deliver what it promises. Good framework and it looks resistant.

The panel works fine and provides some charge even with a little sun, the only thing you need to know from the instructions is how to connect the contacts because it doesn't come with cables, but okay an electrician who is supposed to connect it knows.

edit
So, without looking at the sun at all, it faces east with a wall behind it towards the west side where the sun is in the afternoon at 6 o'clock in April with cloudy weather, it provides a charge of 12.6 volts and 0.07 amps, which is approximately 0.9 watts, so it has a small efficiency for even a little battery charging even in poor lighting conditions.

Take it without fear. It meets the specifications exactly. Very good and fast service from the store.