The hotter the temperature, the lower a solar panel's voltage will be !
With lower voltage, you'll get less amperage into your batteries !
Many dealers won't tell you their solar panel's peak operating voltage. Some dealers will even hide this information by not posting it on their website !
The second most important question to ask when buying a solar panel is "what is the solar panel's peak operating voltage ?"
17 volts to 17.8 volts is the predominant voltage for a 12 volt panel and double that for a 24 volt panel.
Because of the current shortage of solar panels,
some dealers have begun selling lower voltage panels that do not perform
as well in hot weather as higher voltage panels.
You may come across these lower voltage panels at what appears to be a
pretty good price, but as the old saying goes, "You get what you pay for". Be
careful when shopping for panels, since we posted this notice, some dealers have
begun the practice of not posting their panels peak operating voltage in what
appears to be an effort to hide their panel's true performance.
If you come across a dealer that only posts their panels wattage and amperage and not the panel's peak operating voltage, be cautious, chances are that you've come across one of these lower voltage panels. In fact if you come across a dealer that only advertises a panel's wattage, ask that dealer why he doesn't post the panel's peak operating voltage.
The majority of name brand solar panels on the market operate at a peak voltage of 17 to 17.8 volts or higher or 34 to 35.6 volts or higher (12 or 24 volt mode respectively)
Voltage, also known as electromotive force can be compared to pressure in a water pipe. The more pressure in a water pipe, the more water flows per unit of time. The same situation exists when using a solar module to charge a battery. The greater the voltage, the greater the flow of available electrical current.
This is especially important in solar modules because contrary to popular belief, the hotter it is, the poorer a solar module will perform. In fact, solar modules perform best in the dead of winter in full sun, when it's nice and cold. Ironically, heat is actually a solar module's worst enemy. Solar modules operate from light not heat.
As the temperature rises, solar cell efficiency and voltage begins to drop. The lower the voltage, the less current is able to flow in a circuit. If a solar module is not rated at a high enough voltage, elevated temperatures could cause a state of equilibrium between the battery voltage and the solar module voltage and no current would flow at all. So a high current rating on a solar module is only half the story, there must also be a high enough Voltage rating or the Amperage rating is meaningless.
Imagine two tanks of water connected to each other through a pipe, with one tank filled to a higher level than the other tank.
As long as the pressure or voltage is higher in the solar module than in the battery, current will flow into the battery.
As the voltage or pressure in the solar module begins to fall due to increased air temperatures as illustrated in the above example, less current flows into the battery. For example, a typical 75 watt panel can drop to as low as 55 watts when the surface of the panel reaches 80 degree centigrade.
This is why it's important to start with a solar module that has a high enough voltage to compensate for the voltage drop that occurs when air temperatures rise. This is especially important if the solar system is being used in hot climates. Always check a panel's specification sheet for the panel's peak amps and peak volts. Be cautious when dealing with a website that only posts a solar panel's peak amperage without the panel's peak voltage.
Also don't let a dealer confuse you with a panel's open circuit voltage. An open circuit voltage is the voltage that a panel produces when it is not connected to a load. Be sure that you ask for the panel's peak voltage and not the open circuit voltage. Again, the majority of name brand solar panels on the market operate at a peak voltage of 17 to 17.8 volts or higher or 34 to 35.6 volts or higher (12 or 24 volt mode respectively)
Don't be penny wise and pound foolish !
Your making a big investment ! For a few pennies more per Watt, we can guaranty you higher voltage, higher performance, name brand solar panels from companies that have been in the business of manufacturing solar panels for many years not just a few months !
Please Note : The animated graphic used in this illustration is not meant to depict any solar panel's actual performance at any specific temperature. It is only being used to roughly illustrate the effect that increased temperature has on the photovoltaic principal.