There is a difference in the manufacturing technique, and as a result monocrystalline cells are more efficient. The monocrystalline cells can produce more power in a smaller space. And monocrystalline panels have a darker blue color, almost appearing black, and are usually higher in price than the polycrystalline ones. While the polycrystalline panels are less efficient and take more room. However, the difference is size and efficiency do not impact power. A 100 Watt monocrystalline panel and a 100 Watt polycrystalline panel will both output 100 Watts, neglecting power loss in the system, but a monocrystalline panel will output 100 watts with a smaller surface area.