Why Hot Spots are a Problem
Abstract - "Hot spotting is a problem in photovoltaic (PV) systems that reduces panel power performance and accelerates cell degradation. In present day systems, bypass diodes are used to mitigate hot spotting, but it does not prevent hot spotting or the damage it causes." From - IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 31, NO. 2, FEBRUARY 2016: Photovoltaic Hot-Spot Detection for Solar Panel Substrings
Definition of Hot Spots (for the geeks) Photovoltaic (PV) hot spotting is a temporary fault condition that occurs in series-connected PV cells. Ideally, the electrical characteristics of all cells in the string are identical and the string operates at the maximum power point (MPP) current to achieve each cell’s optimal output. However, when there is mismatch among the cell electrical characteristics, the single string current is unable to operate at every cell’s MPP, which leads to suboptimal performance. There are many factors that can create mismatch, such as manufacturing error tolerance, partial shading, and degradation. When there are only a few underperforming cells (e.g., due to heavy shading) in a string of normal cells, the imposed string current tends to reverse bias the compromised cells. The string can settle to a current that is greater than the weakened cell’s short-circuit current, causing the weakened cell’s voltage to become reverse biased. Because voltage is negative but current is flowing, the shaded cell sinks power rather than sources power. If the cell sinks significant power, the generated heat drastically increases the localized cell temperature, which can damage the cell; this is commonly known as hot spotting. Hot spotting is a temperature increase of a PV cell or a portion of the cell above the temperature of its surroundings due to reverse-bias power dissipation. Hot-spot damage refers to permanent damage or degradation of a PV cell caused by hot spotting.
PROF. RICHARD HASKELL, WHY HOT SPOTS ARE A PROBLEM
CHERP has partnered with idealPV and licensed their technology that eliminates Hot Spots in solar PV panels called FOZHS (Forward Only Zero Hot Spots) CHERP will be deploying idealPV’s patented technology that completely eliminates hot spots from occurring in our solar panels. This key technology:
Simplifies manufacturing complexities so that panels can be made in local factories. Since no cell will ever overheat due to reverse bias, the soldering and assembly tolerances are greatly relaxed.
Reduces costs by eliminating by-pass diodes, sub-strings and wiring size.
Allows use of rejected/donated materials. Solar Cell manufacturers are in pursuit of the highest purity and quality of cells to help avoid hot spots due to impurities, micro-cracks, and subtle variations in cell efficiencies. In pursuit of the highest quality A-grade cells, many millions are rejected each year as B and C-grade cells. With FOZHS technology, we are not concerned about hot spots, and can use less than perfect cells. So, manufacturers can donate them to us at the charitable deduction rate that is much higher than selling the imperfect cells on the secondary market at 5 or 10 cents on the dollar.
Dramatically improves energy output of each panel. Early reporting data from the Harvey Mudd Clinic test trials shows a 24.66% increase in energy from the idealPV panels compared to Tier 1 conventional panels.
Increases panel durability and longevity due to absence of hot spot heat cycling.
CONSEQUENCES OF HOT SPOTS
For technical references from comprehensive literature search go HERE.