Anyone familiar with using Renogy Solar Kits?

[Debrajoy54]

<takes sip of coffee>




Combining panels with disparate specs on the same controller typically results in lower power harvest than with separate controllers.




They aren't. MPPT is negatively affected by inefficiencies that generally do not apply to PWM systems: buck conversion losses, cell temperature derating, wiring losses, etc.

Sometimes these inefficiencies stack up so much that, in edge cases, PWM can make more power than MPPT.



You won't.

Average daily increase from MPPT is typically closer to 15%. The +30%-40% numbers are real, but only occur in circumstances when local panel/string Vmp is significantly higher than Vbatt (battery voltage) and the system can take advantage of it. Bulk stage, for example. In float or late absorption there may be no MPPT advantage at all.

Whether or not +15% is worth 2x-3x the price is a matter for the consumer. Horses for courses. (I use MPPT, PWM, and shunt controllers for different purposes).




They can.

The PWM controller will have an input voltage max just like MPPT. You can charge a 48v battery from a 48v solar config with PWM for example.





Panel voltage can be much higher than that. Mine are running at 30.8v right now.




Doesn't work that way. Voltage is quite stable above 20% insolation (like shortly after daybreak). Current will vary based on conditions.




Depends on battery chemistry and number of cells.



? This is a controller spec. Mine goes to 150v, and some go higher. Some are as low as 23v.




When I blew a controller in the summer I put my 24v panels in parallel on a spare PWM to charge my 12v bank. The PWM ran the panels at Vbatt, which is effectively how PWM works.





Cloudy weather generally does not alter the voltage of solar panels.* In early morning or late evening insolation can drop below ~20% and voltage can crash, but so little power is available at those times that it is not a compelling argument for series arrangements. (I use series but not for that purpose).

MPPT is typically most efficient (lowest buck losses) when panel voltage (Vpanel) is about 2x battery voltage. Check your MPPT manuals for the relevant efficiency curves.




Section of a panel is correct; that is the bypass diode's job. Around any panel is incorrect, but it can be accomplished with external bypasses. Some controllers will also reduce overall string voltage to deal with shaded panels but that is a different (and more complex) topic.

---

For anyone who's read this far, I have attempted a rubric for choosing between MPPT and PWM in this RVwiki article.

* it may affect the voltage at which MPPT runs the panels

I know this is days later, but I have been trying to wrap my head around all this stuff and all I have gotten is a big headache and a wish for tons of money just to pay someone to do what needs to be done! And I have a question that you will either laugh your butt off about or slap your forehead or probably both. I don't know how to work this forum stuff. Back in 2016 when I had my camper van I did get some advice, but that was a long time ago.

 

[Calaverasgrande]

Just want to mention, don't fixate only on volts.
Ohms law is a three legged stool with Volts, Amps and Resistance all forming equally important legs.
So in the previous example of parallel vs series connection of panels, series is not better because it increases volts output. Depending on your charging controller specs and the capabilities of your battery bank to be charged, it may be better to parallel to increase amps while holding volts the same.
My charge controller doesn't want to exceed 20V but can handle up to 50 amps. So I'm best off paralleling my panels to exploit the capacity to handle current (amps) when it has a low capacity for volts.
Your mileage may vary, check the published specs of your panels and charging unit.

Also, something I've noticed about MPPT vs PWM;
some but not all PWM chargers have different profiles for battery types. All MPPT chargers I've looked at have battery profiles per type.
Also, almost all MPPT chargers I've looked at have temp probe and many also have voltage sensor inputs to keep track of the battery bank.
PWM chargers can have these, but since they have become the budget option you are often going to see such added frills deleted to keep manufacturing costs down.

Frankly, now that I've lived with my Renogy charger for a a while, I wish I'd spent more on a more premium brand. The wiring connections could be more robust, and the lack of any information display is annoying. It's kept my battery bank charged fine. But I have to go into the app that talks to my batteries via bluetooth to see the status. And it tells me nothing about the rest of the system. Only what is happening around the bank.
I've no idea if the charger is unhappy about it's load or temperature. If there is any fault I won't know until I notice stuff not charging. Spending $50 on a grey LCD screen seems a bit much.

 

[WanderingRose]

And for people like me, for whom this technical stuff is like a foreign language I can’t wrap my head around and don’t want to learn, folks who do electrical work on autos and RV’s can cut to the chase for you.

I have a 100 watt Renogy suitcase, and for a very nominal fee had a local shop hook a 6’ extension cord to my coach battery, so that all I had to do was hook the suitcase cord to it, set it in the sun and I was ready to go.

 

[frater secessus]

I know this is days later, but I have been trying to wrap my head around all this stuff and all I have gotten is a big headache

My wording in that post was more formal than usual; I apologize for the headache.

When I work on articles like A Gentle Introduction To Solar for the RVwiki I try to use more everyday language and broader concepts.

And I have a question that you will either laugh your butt off about or slap your forehead or probably both.

If you mentioned the question here I didn't see it. If it's about this topic (connecting multiple charging sources to the same battery) go ahead and ask.

If it's not related it would be traditional to start a new thread for your question by clicking the red Post Thread button in the most fitting area of the forum. Folks will find it and chime in.