Solar panels or solar modules (which are normally installed on the roof) are made up of photovoltaic (PV) cells, and those cells convert sunlight into direct current power. The power then goes through an inverter to be flipped to Alternating Current (AC) power. From there, it goes into your main electrical panel and powers everything in your home.
If your solar power system is producing more than necessary, the meter will spin backward, which will allow you to accumulate credit with your utility company towards your next bill. Learn more about HOW SOLAR WORKS.
A solar panel is two sheets of silicon solar cells connected by bus bars encased in glass often surrounded by an aluminium frame, but that doesn’t mean all solar panels are created equal. The grade of the silicon and the wattage of the panels as well as how those cells are assembled all matter when it comes to lifetime power output and reliability.
Mono or polycrystalline
All solar panels are made from silicon crystals. In a polycrystalline panel, each of the wafers used to make the solar cells is composed of multiple silicon crystals. The process used to make the silicon ingots is a bit like the one used to make particle board in construction. A single crystal seed is placed in a vat with lots of chunks of silicon and it’s all melted together. Many crystals grow as it cools. It’s cheaper to make and creates less waste, but the borders where the crystals meet make for a slightly rougher surface which causes electricity to move around less efficiently. This type of panel has a 13-16% efficiency rating. It also has that typical blueish hue due to the composite nature.
For a monocrystalline panel, the silicon wafers are sliced from a single crystal, giving them a much more uniform surface which converts sunlight into power at a higher efficiency (15% to 22%+). Due to the purer nature of the silicon, monocrystalline panels have a dark black appearance. They are also perform better at higher temperatures – a big plus in our desert heat. Robco recommends high efficiency LG NeON 2 Mono Crystalline solar panels.
These days, most solar panels are at least 280 watts. That is the rated output of the panel under perfect test conditions. On your roof top though, the output will depend on which way the panels face, how much sun is hitting them, what angle they are tilted at, how much shade is present and how hot it is outside. When your solar installer is providing an annual power estimate, they are taking all these variables into account. Obviously higher wattage panels will produce more power over their lifetime then lower wattage panels even with these variables.
Silicon crystals break down over time. This is called degradation and it is a natural quality of the material so every single panel will lose a little bit of performance as it ages. It can be increased by environmental factors and stress to the module structure – like someone walking on your solar panels. Your power output in year 20 will be lower than it was in year 1. How much will it drop off and will you notice it? That really depends. Manufacturers guarantee that the typical solar panel will produce at least 80% of the day 1 power at Year 20, but manufacturers can reduce degradation in a number of ways from using more and thinner bus bars to the surface of the cells. Those technology advances mean that long term power production from panels is getting better and better and that you should not be concerned over degradation.