- Written by: Garret Towne
There's more then one type of solar panel... How do you choose the right panel?
The short answer:
Forget all that stuff and just make sure your panels are compatible with your charge controller.
The long answer:
Most panels you will find on the consumer market are going to use conventional monocrystalline 6” cells. Fortunately, these are excellent for use on a skoolie.
Monocrystalline cells have a uniform crystalline structure that is made from taking very thin slices of an ingot that was grown around a small seed crystal. Because of the uniformity, electrons “flow easier” than they would in a polycrystalline cell.
Polycrystalline cells have an irregular crystalline structure that formed when molten silicon is cooled in a mold. The manufacturing process for polycrystalline cells is simpler and less expensive than that of monocrystalline, but polycrystalline solar panels will only produce about 95% of the output of an equally sized monocrystalline solar panel.
Thin film solar panels are made with a chemical process, and can usually be more flexible than crystalline cell solar panels. Currently, thin film solar panels are more expensive and only produce about 50% of the output of an equally sized monocrystalline solar panel. In ten years, this may change, and thin film may be the preferred technology.
Back contact mono solar panels use special monocrystalline cells made by SunPower. Their unique technology has the silver traces that are normally on the surface of a cell, moved to the back of the cell, allowing more photon collecting surface area. These panels are about 50% more expensive than conventional mono, but about 15% more efficient. Unfortunately, as I write this, import duties and changes in SunPower’s distribution channels are making it increasingly difficult to find glass and aluminum framed, RV size panels with back contact mono cells.
Flexible panels typically use the back contact mono cells, laminated in a thick plastic coating, giving them the rigidity of a truck’s mud flap. If you absolutely need a low profile and shatter resistant panel, these are the way to go. But, they only last about two years before the plastic starts breaking down, and the cells cup. These panels don’t collect off-angle light very well and they cost about twice as much as conventional mono solar panels. I have also seen them leave burn marks on vehicle roofs. I would avoid these.
How you should buy panels:
In most cases, the warranties on panels aren’t worth the paper they are printed on because solar panel manufacturers, especially those making small off-grid type panels, don’t stay in business long enough to back up their warranty. Or, the burden of proof for a malfunction (which would require a flash testing machine) and shipping costs are the responsibility of the end user. Either accept this as a fact of life, or buy panels from an established, reputable, American company. If you don’t want to pay for panels more than once, buy them from a company with good customer service and reputation to maintain.
The seller should be able to guide you and help you find the panel that is right for your application. In another article I can explain mixed panel compatibility and charge controller selection.
Garret Towne, President
A.M. Solar, Inc.
- Written by: Garret Towne
Does solar and electricity seem too daunting to understand?
Don’t be that guy that says “Amps per hour”. It’s like saying “miles per hour per hour” and it doesn’t make any sense. In order to talk like a solar expert, or to avoid confusing a solar expert you are seeking help from, it’s important to understand the terminology.
Guest article by: Garret Towne, President
A.M. Solar, Inc.
Let’s start with the basics and build from there:
Atoms – Atoms are the building blocks of matter, and an atom consists of a nucleus with positively charged protons and neutrally charged neutrons surrounded by negatively charged electrons. Different types of atoms have different numbers of protons in their nucleus. Think of an atom as a mini solar system, with the protons and neutrons being the sun and electrons being the planets. The wires in your electrical system are made of matter, which is made of atoms.
Electrons – Because opposite charges attract, electrons are drawn to the protons in the nucleus, similar to how gravity keeps planets in orbit around the sun. Unlike planets, with their slow elliptical orbits that create centrifugal force to keep the planets from crashing into the sun, electrons repel each other due to their charge, and they orbit the nucleus at the speed of light in a path that is best described as a “probability cloud”.
Voltage, Volts, V, Potential, Charge – Because like charges repel, and electrons all have negative charges, this repulsion force builds up as a "pressure" when electrons are in close proximity to each other. This “pressure” in the context of an electrical system is known as Voltage.
Amperage, Amperes, Amps, A, Current, I - When electrons flow from a high voltage (pressure) area to a low voltage area, the flow rate is measured in Amps. An Amp is one coulomb per second. A coulomb is 6.241 x 10^18 (or 6,241,000,000,000,000,000) electrons.
Resistance, Ohms, Ω - Along the path from high voltage to low voltage areas, electrons encounter resistance. This resistance controls the flow rate like a nozzle on a hose. This resistance is measured in Ohms.
Watts, Energy, W – When flowing electrons encounter resistance, work can be performed. This is what makes electricity do things. This work can be measured in Watts and is equal to Volts times Amps (Watts = Volts x Amps).
When sunlight hits a solar panel, voltage is created, which produces current. This current, pushed by voltage, flows through wires in an electrical system to perform work when it encounters resistance, which can be measured in terms of watts.
Now read this a couple more times and it might make sense.
Side note: Don’t be that guy who buys a solar charger system, installs it, complains it doesn’t work, sends pictures of the installation to tech support and quickly learns that mounting solar panels in the middle of his living room (in a house with a roof) is the cause of his problem. It has happened.