What are solar panels made of and how do they work?
Solar cells are made primarily from silicon, a chemical element with conductive properties. Exposure to light changes silicon’s electrical characteristics, which generates an electric current.
A cell is a small square of silicon (about 6” x 6” or 5" x 5") with electrical contact plates on the face.
Solar panels are made by laying out a grid of these cells on a protective back-sheet and covering them with glass on the front.
It takes multiple panels to provide power to a typical home or office. A collection of panels in your system is called an array. Panels wired into the same inverter are known collectively as a string of panels. (Inverters have a maximum string size, an upper limit to the number of panels they can support.)
For example, you may have a system with three inverters supporting three strings of 10 panels each, which comes together to make a 30-panel array.
How long do solar panels last?
Based on different manufacturers, they provide guarantee at least 80% efficiency for 20-25 years under that warranty of solar panels.
Even the warranty is up, the panels simply keep working at a reduced output. A panel that is rated at 320 watts, for example, would still produce 256 watts of output at the 25-year mark.
Panels tend to be extremely reliable. A study by NREL (National Renewable Energy Laboratory) showed that over 75% of panels outperformed their warranty. However, other parts like inverters and batteries have a shorter lifespan. These parts at least once should be replaced over the life of ownership, and those replacements should factor into total costs over the life of the system.
Inverters are warranted for 5-10 years based on different manufacturers. So, it is safe to say, need to replace the inverter once or twice in the system's lifespan. Lead-acid batteries typically last 3-7 years depending on how well they have maintained. Lithium batteries are warranted for 3-10 years.
How big are solar panels?
Panels come in two standard configurations: 60-cell or 72-cell. 60-cell panels measure 39” by 65”, while 72-cell panels are 39” by 77”. In reality, these dimensions can fluctuate by up to an inch because manufacturers use different frame sizes. But the 60 and 72 cell layouts are standardized across the industry. There are also smaller options for RV / mobile use, and some companies are experimenting with larger 96-cell panels, but these sizes aren’t common enough to be standardized at the moment.
What are the types of solar panels on the market?
There are two established cell technologies that dominate the market: monocrystalline and polycrystalline solar cells (mono and poly, for short).
Mono cells are cut from a single source of silicon, while poly cells are made by blending multiple bits of silicon into a single cell.
Since the composition of poly cells is less “pure,” they tend to be slightly less efficient on average. However, this isn’t a hard and fast rule, since other factors affect solar cell efficiency as well.
How is solar panel efficiency measured?
The concept of solar panel efficiency is often misunderstood. Most panels have an efficiency rating in the range of 15-25%, which sounds really low without context.
Some people hear this and think, they are getting only 20% of the production from the panel? "That sounds like a waste.” The assumption is a 100-watt panel would only produce 20 watts of power. But that’s not what we mean when we talk about efficiency.
In reality, the efficiency rating measures how much of the sun’s potential energy is converted to solar power. Using the same example, a 100-watt panel with a 20% efficiency rating will absorb 20% of the potential 500 watts of continuous power coming from the sun.
Don’t sweat too much about panel efficiency. The only real benefit to more efficient panels is that they fit more solar in less space. High-efficiency panels matter if the system is trying to build in a tight space, but there’s nothing wrong with building a larger array with less efficient panels. The latter option typically reduces the overall cost of the system (because less efficient panels have a lower cost-per-watt, all other things being equal).
