One of the most common terms you'll see when shopping for solar panels is efficiency. An efficiency rating is how well the panel can turn sunlight into usable energy (listed as a. Most solar panels on the market range in wattage from 250 to 400 watts. The higher the wattage, the higher the energy output. If you get a solar panel with high wattage but a low efficiency. What your solar panel is made of matters, and not all are created from the same materials. First, look for panels with cells made from silicon. Because solar panels should last for decades, it's important to only purchase from companies that back up their product with a warranty that.