TechnoWeenie Educational Series - Solar Panels

[TechnoWeenie]

Intro ​

I'm going to cover some fundamentals of solar power including types of panels, safety equipment, and best practices when implementing a solar system. Electrical is an entirely different subject that I'll go into at a later date, and will discuss integration into an existing system, but you really need to match your electrical demands to your solar system, and vice-versa. I will go into more detail on general electrical in another thread, as this is focused on the solar aspect.


Solar panels are also known as Photovoltaic, or PV for short. If you see 'PV', I'm talking about a solar panel

Some of the topics discussed will be...

• Basics of solar panels
• Solar power generation
• Types of panels
• Charge controllers
• Wiring

The information provided is based on years of experience and training, and is designed to be a general overview. Please seek a qualified electrician or mobile installer if you need to. I'm not responsible if you burn your truck down or fall off your roof..

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Fundamentals​

Solar panels use the sun to generate electricity. Yeah. I know that's kind of a no-brainer, but we're starting off with the basics. Here's a general list of things to keep in mind...

• Solar panels don't like heat. I know, it's counterintuitive, but panels can overheat, and will produce less power in extreme temps (120*+)​
• Solar panels will work even on cloudy days, although generally only outputting 10-20% of their rated power.​
• Larger solar panel installations can produce dangerous voltages and high currents. If you're not sure what you're doing, consult a professional.​
• The average 100W consumer panel produces ~18V @ ~5.5A.​
• Solar panels work best when angled properly, HOWEVER, in mobile installations, it's probably gonna be laid flat. Just understand you will lose a little output in doing so.​

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Energy Production
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Solar panels aren't always the best answer in every situation. The use of solar really depends on your environment. Areas with lots of overcast days are not going to be great for producing a lot of power. Every area has calculated 'sun hours'.. Hours of full output from the solar panel, based on location, and time of year. Your panels will still produce output both before, and after, peak hours, but at lower rates.





Here is a general map of solar output based on location.





The above map shows an average of Peak Sun Hours, or Peak Solar Hours, for your PV system. Because this changes during the season, you will get less hours during the winter, and more hours in the summer.

Generally speaking, solar output is measured in watt hours or kilowatt hours. The amount of electricity generated can be guesstimated fairly easily, using the charts above. Again, this is averages, so individual days could be significantly lower, or higher.

A tale of two cities...

So, let's say you have 4 - 100w panels, for a total of 400W... Assuming full production for ONE hour, would be 400 watt hours, or 400 Wh..

Let's look at two cities, using solar peak hour averages, to figure out how much power we'd be making... This is assuming the panel is laying flat, and not angled.


Using Albuquerque as an example.

• Summer Peak Sun Hours (June): 7.18 hours per day (400 * 7.18 = 2,872 Wh, or 2.872 KWh)
• Winter Peak Sun Hours (Dec): 2.79 hours per day (400 * 2.79 = 1,116 Wh, or 1.116 KWh)

Some areas aren't so lucky....


Using Seattle as an example..

• Summer Peak Sun Hours (July): 5.88 hours per day (400 * 5.88 = 2,352 Wh, or 2.352 KWh)
• Winter Peak Sun Hours (Dec): .92 hours per day (400 * .92 = 368 Wh )

To put that in perspective... Let's say you have 3, 12V LED lamps, that consume 1/2 an amp, or 500mah, for a total of 1.5A...

V*A=W

12 * 1.5 = 18W...

So, NOT including losses in line, charge controller efficiency, battery efficiency, etc. and assuming that everything else is 100% efficient (which it most surely is not, and never will be)... In Albuquerque, in the winter, on ONE day of collection, you'd bring in enough juice to run the lights for 62 hours. In Seattle, you'd bring in enough juice to power those same lights for a little over 20 hours...

The ideal setup would be to have enough solar to provide for your needs during the day AND fully charge your battery bank from the usage of the night before. Sizing your battery bank is another topic I'll be discussing in another thread. Your solar setup will depend on your needs and battery capacity.

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Panel Types​

Solar panels come in 3 main varieties, Polycrystalline, Monocrystalline and amorphous (thin film). Because we're focusing on vehicle applications, I'm leaving out amorphous, as it's not rugged, and is very space inefficient compared to poly or mono panels, and is considerably more expensive.

Polycrystalline​

Polycrystalline panels tend to have a less uniform, bluish tint, and are easily distinguishable from Monocrystalline. Poly panels require a larger surface area in order to produce the same amount of power, but can be a little better at producing power in adverse conditions,

PROS:

• Less expensive

CONS:

• Less efficient
• Not a uniform appearance

Monocrystalline
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Mono panels are made from larger wafers of silicon, and have a uniform black appearance to their cells. They are also more efficient, and can produce more power from a smaller sized panel than an equivalent sized poly panel...


PROS:

• More efficient​
• Smaller size​
• Uniform appearance​

Cons:

• More expensive

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Charge controllers and wiring coming up next....

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[TechnoWeenie]

Wiring​

So, awesome, I got these panels.. .... What the #%(&# DO I DO WITH THEM?!

I'll go into more detail on the charge controllers in a bit, but first, let's talk about panel layout.

Panels are just like batteries in terms of being able to be put in parallel, or series, configuration, just like the stock battery system in M35s, M939s, and FMTVs, which uses 4 12v batteries in a serial-parallel configuration, to produce 2 banks of 24V...

Putting a panel in series, will increase the voltage, but amperage will be the same.
Putting a panel in parallel, will increase the amperage, but voltage will be the same.

Series Connection




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A series connection will DOUBLE the voltage, while keeping the amperage the same. The big advantage to this setup is you can reach higher voltages, which keep wire size down, and is generally more efficient. The problem with this setup, is if one of your panels gets damaged, or is shaded, it can bring your power collection to a halt.

PROS:

• Can use smaller wire, for longer runs.
• Generally more efficient

CONS:

• A shaded or broken panel can seriously impact your collection performance
• Larger systems can produce high enough voltage to be dangerous/lethal

Parrallel Connection




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A parallel connection will DOUBLE amperage, but keep voltage the same. The big advantage to this setup, is if a panel is shaded, or fails, it won't generally impact the production of the other panels. The disadvantage is, due to the higher amperage, larger wires are required, and losses can add up quickly in larger systems if inadequate wire size is used.

​

PROS:

• More reliable, less impact from damaged or shaded panel

CONS:

• Requires larger wires
• Can be less efficient if not wired correctly

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For the above reasons, I usually suggest a parallel/series hybrid connection, similar to the battery layout....

It allows for smaller wires, but also allows for redundancy in case of a failure. It comes with some pluses, and some minuses, of both systems...

 

[wheelspinner]

Loving this!

 

[TechnoWeenie]

Charge Controllers​

So, above we talked about how to wire panels, and parallel vs series, and how that impacts voltage and amperage...


Now comes the part where that juice gets converted into something you can use... This is where the charge controller comes into play.


There are some important things you need to look for, on any charge controller, regardless of which type you decide to get...

• Input voltage​
• Output voltage (adjustable?)​
• Battery chemistry (Sealed Lead Acid (SLA)? AGM? Li-ION? Li-Po?)​
• Input Amperage​
• Output Amperage​

Input voltage - What can the charge controller handle? Do you wanna put 4 panels in series? Well, it better be able to handle that high of a voltage.

Output Voltage - Are you running a 12V battery bank? What about a 24V battery bank? What are the output requirements? Can you charge a 24V battery bank with a 18V panel input (Boost charging)?

Battery Chemistry - Can the charge controller support the type of battery you have? Trying to charge a Li-Ion battery with a charger designed for SLA is a really bad idea.

Input Amperage - How much juice can it take in before it decides to let out the magic smoke?


Output Amperage - How much juice can it dump into your batteries?


The above questions will be easy to answer, when you know how many solar panels you need, and the size of the battery bank you have. It's just a matter of finding the charge controller that meets your needs...

Now, onto the controllers themselves...

Charge Controller Types​

There are generally 2 different types of charge controller.... PWM, and MPPT.. MPPT is far superior, and more efficient, but PWM is cheap. I'll go over how these work in detail. Keep in mind I'm explaining these in general terms, and I'm trying to keep it as least technical as possible so anyone can understand it. There are factors in operation of the controller, wiring, etc. that are not factored into, for ease of explanation.


PWM - Pulse Width Modulation

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A PWM controller, is very simple, very inexpensive, and very inefficient. Essentially, what a PWM controller does, is lower the voltage to what the battery can accept, while maintaining the amperage.

So, as our continued example.. We have a ~18.5V panel that puts out ~5.5A... 101.75 Watts

So, this controller, knows that the battery needs 13.8V..So it regulates that 18.5V down to 13.8V, and continues to put out 5.5A... Do you see the problem?

Let's do that math again.. 13.8V, at 5.5A = 75.9 watts... What the?! Where'd our power go?! It's dissipated as heat, basically.

All a PWM controller is, is a glorified voltage converter with a switch that turns power on/off to the battery. It's about 30% LESS efficient than MPPT.. Further, generally speaking, with PWM, you MUST match your input and output voltages. You can't use a single 18.5V panel set up to charge a 24V bank... You'd have to run 2 panels in series (37V) which would be dropped down to the 24V...


So, to summarize a PWM controller...


PROS:

• Inexpensive​
• Smaller/easier to manage​

CONS:

• Very inefficient​
• Not versatile​

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MPPT - Maximum Power Point Tracking

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An MPPT controller, as its name suggest, tracks multiple points of data, and constantly adjusts itself to maximize the power output.

Because the MPPT controller can adjust its voltage, AND current, it can retain the power coming in.

So, whereas the PWM controller went from 18.5V to 13.8V but maintained 5.5A, leading to an almost 25W LOSS, the MPPT maintains the power coming in...

So, the MPPT looks more like 101.75W = 13.8V * 7.37A - So, we're now pushing 7.37A into the battery, instead of just 5.5A.... You've just gained almost 2A over a PWM charger, and those gains increase the larger your system is.. This example shows just ONE panel.

So, to summarize MPPT controllers..


PROS:

• Much more versatile, able to handle more complex configurations
• Very efficient

CONS:

• More expensive than PWM controllers
• Bulkier, taking up more room than PWM controllers

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For the above reasons mentioned, for efficiency, I suggest the MPPT controller type. Yes, they're more expensive, but they are a lot more efficient, and are flexible enough that you can buy a larger one than you need, and add to it later, whereas PWM controllers tend to be pretty limited and designed for small, simpler installations.

Also, be aware that a ton of fake Chinese stuff is out there on Amazon and *bay....Saying it's MPPT when it's really just a cheap PWM model. I suggest buying from a known and reputable company, like Renogy.

 

[TechnoWeenie]

- Errata/Misc -​

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There are some flexible, thin panels, instead of the more rigid framed panels.

The downside with the flexible thin panels is they tend to be less durable, and more prone to heat stress/cracking. I do not suggest them unless they're a temporary solution.

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Panels do require maintenance, but it's usually nothing more than wiping them off occasionally, clearing them of any dust, leaves, etc.

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[DieselAddict]

TechnoWeenie, I hope yo don't mind if I expand on your explanation of PWM vs MPPT charge controllers a little bit.

A PWM charge controller doesn't actually convert any power. What it is in effect is an electronic switch that connects and disconnects the solar panels from the battery depending on the voltage of the battery. Where the PWM comes in is that it uses a PWM scheme to limit the power coming from the solar panels once the battery is coming up to the cut--off voltage programmed in the controller. This method is simple, cheap, and inefficient if the solar panels are not properly configured to the battery from a voltage standpoint.

A MPPT controller in comparison allows the battery and the solar panels to operate at different voltages while passing current from the solar panels to the battery. By definition, these DO convert power. Breaking the link between the battery voltage and panel voltage has an important benefit, it allows the panel to operate at its maximum power point, meaning that combination of voltage and current that extracts the most POWER. This voltage could be much different than the voltage the battery. Another way to think of MPPT is as a transmission between the solar panel and the battery. They each "spin" at the range that makes them happiest. MPPT makes enough of a difference in extracting best power from the panels that even with the higher losses from the internal circuitry it will still outperform a PWM charge controller in most conditions.

TechnoWeenie, this may be a good point to go into more detail about how a PV panel generates energy and what MPPT means in context to the panel. Including a good rundown of that info will make the differences between a PWM and MPPT charge controller much more clear.

 

[TechnoWeenie]

TechnoWeenie, I hope yo don't mind if I expand on your explanation of PWM vs MPPT charge controllers a little bit.

A PWM charge controller doesn't actually convert any power. What it is in effect is an electronic switch that connects and disconnects the solar panels from the battery depending on the voltage of the battery. Where the PWM comes in is that it uses a PWM scheme to limit the power coming from the solar panels once the battery is coming up to the cut--off voltage programmed in the controller. This method is simple, cheap, and inefficient if the solar panels are not properly configured to the battery from a voltage standpoint.

A MPPT controller in comparison allows the battery and the solar panels to operate at different voltages while passing current from the solar panels to the battery. By definition, these DO convert power. Breaking the link between the battery voltage and panel voltage has an important benefit, it allows the panel to operate at its maximum power point, meaning that combination of voltage and current that extracts the most POWER. This voltage could be much different than the voltage the battery. Another way to think of MPPT is as a transmission between the solar panel and the battery. They each "spin" at the range that makes them happiest. MPPT makes enough of a difference in extracting best power from the panels that even with the higher losses from the internal circuitry it will still outperform a PWM charge controller in most conditions.

TechnoWeenie, this may be a good point to go into more detail about how a PV panel generates energy and what MPPT means in context to the panel. Including a good rundown of that info will make the differences between a PWM and MPPT charge controller much more clear.

Yup.

That's why I put a disclaimer in my post saying that I am making my description as simple as possible, so people with zero experience or electrical knowledge can understand it

I've found that giving too much info just leaves people not caring. It's easier to give a brief synopsis that anyone can follow, instead of wading in too deep to find that most people got stuck in the mud behind you and end up turning back instead of pressing on

 

[TechnoWeenie]

Each one of these takes a couple hours to put together, so I can't do them all at once, but my next one will be on battery systems, which will cover charge rates, losses, load distribution, etc and will hopefully create a better picture on how solar integrates into the electrical system.