Electricity
Photo Voltaic
Photo Voltaic, commonly referred to as PV or Solar Electric, is a process in which solar cells convert sunlight into electricity. Photo Voltaic systems convert sunlight into electricity without any moving parts or harmful emissions, which qualifies it as a clean, renewable energy source for the planet.
Solar radiation will allow the PV cells to generate a direct current through semiconductors mounted on or underneath the cell. In the case of SunPower, the manufacturer Sun Metrics prefers to use in its designs and installations, the cells are back mounted, meaning the entire surface of the Mono Crystalline cell is available to absorb maximum solar radiation from the sun. This results in record-breaking conversion efficiencies and minimizes the amount of space needed to garner a specific amount of solar specified in the design of a PV system.
Photo Voltaic systems are most commonly comprised of solar modules containing rows of sequential cells primarily consisting of Poly or Mono Crystalline silicon wafers. The wafers are treated, or doped with Boron, Phosphorous, or other agents to provide a high electricity output value. Certain doping agents work better to create a robust energy yield than others. Sun Metrics prefers to specify products that are the highest rated in performance, and exhibit the most minimal amount of degradation possible.
Efficiency
Efficiency is defined as the ratio of solar module energy produced vs. the available irradiance of sunlight. To calculate the efficiency of a solar cell divide the power output in watts by the available light and the area of the cell itself. A general guideline for efficiency output in the Northern California area is 20% efficiency equals 200 watts per square meter.
Does Efficiency matter?
That depends on many variables and project-specific considerations. For instance, if there is a finite area of roof available, say 300 sq ft, and the homeowner requires 7000 DC Watts of power, a very power-dense module such as the SunPower X-21 would be the only product available to meet the homeowner’s needs. If the roof area has an available space of 600 sq ft, then the module efficiency could be 50% less than the SunPower X-21 specified for the 300 sq ft area. This would mean that a less efficient module could be installed and still meet the 7000 DC Watts desired by the homeowner.
How efficient can solar be?
How efficient can solar be?
How efficient can solar cell be?
Solar cells are governed by the Thermodynamic Efficiency Limit. This is the maximum possible conversion efficiency of the suns light that can be turned into electricity. Currently the value is just under 87%. Due to the temperature of the photons released by the sun itself, light efficiencies reach a maximum point less than the amount of light actually measured. The efficiencies gathered by photo voltaic modules are substantially less than the theoretical thermodynamic efficiency potential due to very real world problems such as manufacturing capabilities and economic considerations such as cost and potential supply and demand.
Efficiency Examples
Sharp manufactures a solar cell that is 44.4% efficient. These cells are built in such a way that they have concentrator triple-junction solar cells. These are typically used in space and science applications.
SunPower manufactures 20%-24.2% efficient solar modules that are available today. Due to patented manufacturing techniques and designs SunPower modules have the gridlines commonly seen on the surface of other modules mounted on the back side of each cell. Boasting a solid copper foundation, mirror-backed Maxeon cell technology, and durable connection points, SunPower garners 44% more power per sq ft than other solar modules on the market.
Durability
Although modules available in the United States have a 25-year warranty mandate, SunPower expects its modules to have a useful life of more than 40 years. 99% of modules produced by SunPower are expected to produce at least 70% of their original output by year 40. Several design advantages result in SunPower’s cell manufacturing superiority. SunPower has no metal on the front of the cell, and the entire back of the cell is covered with a tin-plated copper foundation. The tin-plated copper is extremely resistant to corrosion, and the amount of metal is enough that even high amounts of corrosion stress cause little to no change in the resistance level of the circuit providing a healthy buffer against the damage caused by moisture.
Shading
It is a fairly common understanding that shade can cause efficiency loss to occur with solar panels. The very fact that light being obstructed from the solar cell reduces energy is indisputable. There are technologies employed that can drastically reduce the effects obstruction of light can inflict on a solar array. While many solar integrators rely on small micro-inverters to sidestep shading conditions, SunPower takes the extra step of creating bypass diode-enabled modules that can shut off cells in which light has become obstructed from reaching the surface. Specifically in a reverse bias condition (shaded) thermal runway is mitigated by the fact that SunPower’s Maxeon cells have a low breakdown voltage which occurs uniformly across the cell. Because of these characteristics, SunPower has the most shade-tolerant module available on the market.
Warranty
SunPower has a unique, industry-leading warranty. 25 years from the start date (The date at which the system is ignited and commissioned) SunPower warrants that the module will be free from defects in materials and workmanship and the power output of the PV modules will be at least 95% of the minimum peak power output for the first 5 years, and declining no more than 0.4% per year for the following 20 years. So the power output of the modules by the end of the 25th year will be 87% of the original minimum peak power level. SunPower’s warranty is unique in the fact that SunPower will cover transportation costs, reshipment costs, and costs associated with installation, removal, and reinstallation of the PV modules deemed to be defective. With over 7 million panels shipped and installed, less than 180 panels have proven to be defective.