How do Photovoltaic Panels work and are there any that work at night?
A PV panel is a set of modules and each module is simply a piece of silicon (the most common are silicon panels) which, when hit with a photon (it’s a particle of light that physicists sometimes say exists and sometimes argue that it doesn’t), gives up an electron and the electron is knocked out of the structure the electron travels to the surface of the mosule and is caught there by the so-called busbar and sent to the PV installation (usually to the inverter) for forced work. Interestingly, after ejection of an electron, a so-called hole with a positive charge is created, which goes to the bottom of the panel and is collected by the lower conductive layer.
As you can see, the panel does not produce anything, it is simply a kind of solar sail that captures photons sent by the sun.
The more photons from the sun, the more electrons released and put to work. So we have a lot of energy on a sunny day, less energy on a cloudy day and less at night??? and at night nothing. What do you mean nothing? after all, the moon, black matter and infrared!
The panel achieves its nominal power at a radiation intensity of 100oW for each square meter of its surface. And unfortunately, if we measure the radiation, both visible and beyond the range of our vision, these values are at the level of single watts per m2, which means a thousand times less energy reaches the panel at night. Which confirms the very fact of the existence of seasons. When the sun shines only 12 hours or less for every 24 hours, the temperature drops very quickly. and when it shines longer each day, the temperature is higher, and temperature is a measure of the amount of internal energy of a given substance, in this case air.
Therefore, it does not matter what frequency of radiation we choose (although blue light carries more energy, and the closer to red, the less), whether it will be infrared or gamma or whatever. If this value per m2 is too low, there will not be enough energy from the panel to activate the inverter.
Which type to choose? which is the best
as we said earlier, the panels are made of modules, EACH MODULE GENERATES A VOLTAGE OF 0.5V.
EVERYONE!
Small modules will give less current (A), larger ones will give more current, but the module voltage is always 0.5V. And these modules are connected + to – to obtain the desired panel voltage.
for the smallest panels it is 36 modules in series, i.e. about 18Vmpp, for the largest even 96 modules in series.
So now you know how to calculate panel voltage without even having to ask for data sheets or specifications. you simply count the modules on the panel and divide by half.
And why do the panels have these modules of different colors and shapes? And which ones are better?
Black octagonal panels are monocrystalline, blue rectangular panels are polycrystalline.
When creating silicon crystals, we can obtain a beautiful uniform cylinder. It is not easy, which is why such panels are more expensive, but they have higher efficiency. A single module of such a panel is simply a slice of silicon salami. And to save space, he has an octagonal haircut. But despite this, when we put them together in a system of 36 or more pieces, we have gaps between them. So, despite the theoretically higher efficiency of 500W, monocrystalline panels are not much smaller than polycrystalline ones.
If we have waste, e.g. cuttings from the processing of monocrystalline panels, we can press them together and obtain polycrystalline modules. Any shape, including a rectangle, so these modules do not glow intermittently from a distance, but look like blue sheets of opalescent glass. Polycrystalline modules have slightly lower efficiency, but in today’s technology it will be below 1% or there will be no difference at all.
THE MOST IMPORTANT PARAMETER!!!
That is, the temperature coefficient of the power of photovoltaic panels. And this is the most important not only for power but also for the safety and durability of the panels.
What is this magic factor? How much power do you lose for each degree of panel temperature above 25 degrees Celsius? it is around 0.3%, but even the differences in the second decimal place are important. Why? Let’s count
Panels on the roof can reach 40 degrees above ambient temperature, i.e
for 400W panels with a coefficient of 0.25%/degree we have a 10% loss, i.e. the panel actually gives us only 360W despite full sun
For the same 400W but panels with a coefficient of 0.35%, it means 14%, i.e. the panel gives us only 344W but…
That is not the most important . The most important thing is where this power goes. Because the panel does not reflect sunlight more on a warm day than on a cold day, so the same amount of photons, i.e. energy from the sun, enters the module and… this energy stays there. The panel is simply heating up. As if each panel had a heater with a power of 40W or 56W, depending on this factor.
And this, in turn, again raises the temperature of the panel with a higher coefficient by an additional few and sometimes even more than 10 degrees, i.e. an additional 3% of power is stolen and pushed into heating.
Due to this heating, not only do we have less energy, but our panels wear out more than twice as fast, even with such a small difference.
And the possibility of failure or even fire is, of course, greater with a hotter panel.
So don’t listen to whether it’s PERC or BiFacial, just ask about the TEMPERATURE POWER COEFFICIENT!
Whether the 400W panel is PERC Multijunction, Bifacial, monocrystal or polycrystalline, it will still have the same 400W of power, neither more nor less.
Don’t fall for it! This is marketing for the unaware, but we know how to count.
That is why, as you can see, the installation is oversized because the panels have a nominal power at 25 degrees and in July on the roof at 60 degrees there will be 10-15% less.
Voltage and current of the panels
The panel documentation and rating plates provide two voltage values and two current (current) values.
Tension
Voc is the open-circuit voltage of the circuit, i.e. when no current flows, it is the DC voltage which we can measure when we buy a panel by inserting the meter leads into the terminals of the panel cables.
Vmpp, i.e. the maximum power voltage of the panel – this is the voltage at which we can obtain the maximum power from the panel
Current(A)
Isc short-circuit current, i.e. the current at which the voltage on the panel drops to zero. This is the current that we can measure when buying a panel if the given value is less than the maximum measurement value of the ammeter of our meter. As in the case of the previous measurement, connect the meter to the panel wires. Connecting an ammeter to the +i- panel will short circuit it, so we will read the short circuit current
Impp is the current at which the panel will obtain maximum power.
Note that some inverters have a limited operating current of 13A, so for example 400W 29V panels are not suitable for use with such an inverter and you need to look for panels with a higher voltage Vmpp
But about the power/current/voltage characteristics and methods of controlling energy production from photovoltaic panels in the next episode