Here is how solar works. I could have started my RV solar series with this article or I could have avoided it entirely. Some of you might just trust the rest of us who say it works and leave it to that. I find it interesting to know how things work. I hope this article will take some of the mystery out of how solar works in solar photovoltaic panels.
Not about me
I am anticipating, because of the number of questions I get on the subject, you might be thinking that I am writing about how my Zamp solar array is working. It works quite well, thank you. I will be gathering more data and reporting on that subject soon. This article however is about how solar works and it gets way into the weeds. I promise everyone can understand it easily. Not once will I mention the weights of atoms — I promise. Well, I guess that was once, but from now on no more atomic weights.
Science content warning
Science tells us that light is energy composed (partly) of photons. On the earth, the sun is bombarding us with a tremendous amount of energy in the form of photons. The sun delivers on a daily basis more energy in terms of photons than energy in all forms consumed by all the people in the world. A solar panel (photovoltaic panel also known as a PV panel) is designed to allow these photons to increase the energy state of the electrons which causes them to move. The more direct the bombardment the better the solar panel will work.
The displacement of an electron caused by a photon hitting it is called the photoelectric effect. When this happens the newly displaced electron is called a photon-electron. A solar photovoltaic panel captures the moving electron and puts it to work. This bombardment of photons is how solar works.
Direct light and indirect light
The clear blue sky has light. So even solar panels that do not have direct exposure to sunlight still work. A solar panel can work both with and without direct shadow-casting sunlight. This is the reason that a solar panel will work under a cloudy sky. Some panel designs work better in poor light but all panels work in all light. The question about how solar works is if it has sufficient extra energy to achieve a usable energy state.
If the light is intense enough then the electron energy state will be sufficiently increased to move enough to be captured as useful work. If the light intensity is insufficient, then they will not have a sufficient increase in energy state to create the desired current, and thus even though photons are influencing the electrons, no useful work will be accomplished. Direct bombardment of the panel, perfectly facing the sun, is far better than any other orientation. Obviously, solar panels exposed to direct radiation from the sun work far better than panels that do not have direct radiation.
Silicon not silicone
Silicone is a sealant, a very good sealant. Silicone spray is a very slippery liquid. Silicon (without the hanging e) is an element that is a semiconductor. The words silicone and silicon are often confused. Silicon is a semiconductor used in computer chips. Semiconductors are elements that sometimes conduct and sometimes do not conduct electricity. This means that they will occasionally allow the movement of electrons. Conductors (like copper) willingly allow the movement of electricity. Insulators inhibit the movement of electricity.
The silicon crystals in a solar panel are not uniform nor are they pure silicon. Impurities are carefully chosen and added to the nearly pure silicone. These different elements have slightly different compositions of electrons that when influenced by sufficient sunlight create the ability of the electrons to move in a specific direction. The makeup of the silicon creates the ability for incoming photons to cause some of the electrons to gain energy when they are affected by bright enough light sources. The incoming light, if it is bright enough, will increase the energy state of the electrons sufficiently to influence the electrons and nearby conductors. This increased energy state caused by the photons then “pushes” the electron flow at the small conductor then causing the current in the conductors all the way to the wires and eventually the solar controller. This increased energy state is how solar works.
Sunlight converted into electricity
This is a common statement among solar salesmen and given the source of the sales talk it is a great simplification, just as my description above is a huge simplification. The sunlight does not turn into electricity, but rather the sunlight effect on the solar cell increases the ability of the electrons to move.
The smallest conductors are called fingers. These fingers attach to bigger conductors called bus bars. An important design decision is made to make sure the fingers are short and thin. They need to be short so that the electrons don’t have far to move. They need to be thin to increase the amount of exposed silicon. When shopping for good solar panels you should note how close the fingers are to each other and how far the electrons have to travel to get to the bus bar. Areas not covered by silicon are not producing electricity. A short distance for the electrons to travel and sufficient photon energy is how solar works.
The reason for the fingers to be short is to enable them to move easily without losing energy by creating unnecessary heat. If unnecessary heat is created this is wasted work that could have been done by the electron.
Since these finger conductors are very small, any crack in these conductors will cause a stop to the movement and thus that conductor will not transmit the electrons to the bus bar. Break enough of these conductors (or silicon wafers) and you will destroy the electrical output of the panel. Please treat your panels carefully. Don’t bend them or walk on them.
Really you don’t have to worry about the length or thickness of the fingers. The cell designer has already done this for you and will be represented in the efficiency of the panel. In a dramatic difference, one panel may be 20% larger than another panel of the same rating. This is a representation of efficiency. The smaller panel is more efficient than the larger panel. If space is a concern when installing your array using panels with higher efficiency makes more energy from a smaller area.
Fingers attach to bus bars. Bus bars attach to wires. (All three are conductors.) From the bus bars, the electrons then travel through the wires to the solar controller. Then the electrons travel back to silicon crystals ready to start the process over again.
Each solar cell is very low voltage and very low current. It takes the combination of multiple solar cells together in a panel all tied together to create a significant current. Generally the more solar cells you have on a panel, the higher the output of the panel. Fewer cells = lower output.
Cells in series (one after the other)
In the solar panel design cells are arranged in series, one after the other. Each cell in the series adds to the voltage of the previous cell. When one cell produces (let us say for simple math — these numbers are high) two volts and a current of five amperes then two cells in series will produce four volts and five amps, and three cells in series will produce six volts at five amps. To have a panel out of 12 volts then you need six 2-volt cells in series. To charge at more than fourteen volts you need more than seven cells in series. The problem arises when one of the cells is broken or shaded. This causes a break in the increased voltage in the series string and thus previous cell energy production is halted. The energy production of the entire series string is wasted.
A solar cell’s effectiveness is measured by having a very bright light flashed on the panel. This light is at a right angle to the panel and at the surface of the cell, it is at 1000 watts per square meter. The temperature is also controlled precisely at 25 degrees Celsius.
If the sunlight on your solar panel is brighter than 1000 watts per square meter they will work better. Panels installed at higher elevations with low humidity have this advantage. Panels here will perform better than panels at lower elevations with more moisture in the air. Same for panels with cooler surface temperatures. Cooler panels work better than warmer panels. However rated output is unlikely to be achieved consistently and panels are rarely exposed to perfect orientation. Plus you have to account for energy drops in the wires, charge controller, and resistance in the battery. This is how solar electricity works; you have to keep the losses low. Putting any restriction in the way will cause a drop in the delivered energy.
Decreased performance with age
New solar panels work better than old solar panels. Most of this decreased performance will happen in the first year of use. This is caused by repeated heating and cooling while they are sitting in the sun. Poorly designed panels will have lower performance in the long term than the best panel designs. All solar panels should have an air gap behind the panel to provide for shaded cooling air.
Thus the typical output of a solar panel at the point of energy entering the battery at best is around 80% of the rated output of the panel. Sorry to note that rarely you will achieve 100% rated energy from a solar panel. Again this is how solar works.
What can you do with this information?
I was going to say not much, but that is really not true. The answer to the question of how solar works isn’t hard to understand. To give your solar photovoltaic panels the best chance at meeting your needs you need to point them at the sun without shading. Don’t cause unnecessary restrictions by using small wires. Don’t waste electricity at the controller by using the least expensive controller you can find. Last on the list (but first for most of us), don’t buy the least expensive panel you can find.
I purchased used solar panels for my first RV and honestly, I got away with it. Used panels are available for less than half the price of new panels. Some of the used panels are really good deals. Some of them are just hazardous waste looking for a new home. If you are going to buy a used panel then you run the risk of buying junk and until they are installed, and charging a battery then they are not truly measurable in terms of performance. I measured both the voltage and the short circuit current of my used panels as a test prior to purchase. I also did a visual inspection of the cells. How do I know that I got a panel without hot spots? I didn’t measure them “under load” while sitting in the sun for an extended period with a thermal camera.
You have to ask yourself the question, “why were perfectly good panels removed and then sold at a big discount?” Since solar panel prices are quite low, is buying used panels worth the risk?
Refer also to the paragraph above about solar panel performance decreasing with age.
Shadows can inhibit the transmission of electrons from one solar cell to the next solar cell. Each cell on the panel acts to give the electrons on the bus bar a little push along the conductor on its way to the connecting wire. A shadow on an individual cell can destroy the output of the entire string of cells. Each cell in a string adds a little more to the flow. This photo shows the classic mistake of one set of panels shadowing the second row. This will completely destroy the output of the entire array. Solar electricity works by direct exposure without shading.
In this photo, assuming the five panels in the front row were 100 watts each and 20 volts (I don’t know the real numbers) each could produce five amps per hour. Thus the front row would produce 25 amps at 20 volts or would produce five amps at 100 volts. The panels in the aft rows, depending on how the cells inside the panels were wired, may produce about 10-25% of the production of the front row. Shade destroys a solar panel’s ability to create useful work.
Panels in series
Just like the discussion of cells in series, panels can be wired in series to create higher voltages and thus lower voltage drops (wasted energy) in the wires on the way to the controller. I wired some of my panels in series (sets of three) just for this reason. However, if one of the panels of the series arrangement is shaded, or even part of one panel in the series is shaded, then the voltage will drop for this entire string, and the output of the series string will be much lower than its full potential. If you are going to use series wiring then you should group each panel in the string in about the same location so that they might get about the same sunlight (or shadowing).
On an RV news, you can use
I considered big panels and decided to use more expensive small panels for one reason. Bigger panels didn’t fit as well on my roof as the smaller panels. Bigger panels would have increased my RV height at the wrong locations at the edge of the RV. Taller RVs will hit more branches, especially on the passenger side. I wanted to keep the height as low as reasonable while still covering much of my roof with panels.
Design your RV solar array without shading from other components on your roof or by shading from other panels.
One other thing you might consider on an RV is getting mono-crystalline solar panels because these cells in a quality panel will deliver more energy per square foot than other types of panels. I also suggest making sure to install the panels with a good air gap behind the panel to at least try and keep them cool. Even if you get flexible panels, don’t flex them and expect them to work as well as rigid panels. Don’t ever walk or sit on the panels during installation, regardless of the type of panels you choose.
Lastly, I would try to buy a panel made in the U.S.A. from a company with a good reputation and the ability to stand behind its product.
Measuring the electricity produced
If we didn’t measure the electricity produced and more importantly how much electricity we already drained from our battery then living on solar power would be folly. This one device made our electricity manageable. Here is a link to what I consider the critical component. Battery Monitor
This article is a prelude to the RV Solar Series. Here is a link. RV Solar Series
Here is a link to our Zamp solar array install. Zamp Obsidian Solar Install
Here is a link to the Zamp website explaining the Zamp Obsidian solar panel. Zamp
Components we used
As you know, our blog income is zero – this allows us to be independent and just tell the truth. We do not get income or commissions. No, we don’t make paid endorsements. We don’t make recommendations but instead, we will tell you what we like (or dislike). The links are only provided as a quick reference to help our readers.
Lion Energy UT1300 Lithium Iron Phosphate Batteries we also have other batteries in addition to the Lion UT1300 but I mention them specifically because they are currently on sale at Costco.
BMV-712 Victron Battery Monitor w/shunt & temp sensor
Zamp Obsidian solar panel. Zamp