Mixing different solar panels. How to connect.

[VIKINGBEAR]

I have two 12V, 75 Watt Siemens SP75 Solar Panels (in parallel) hooked up to a 30Amp Charge Controller.
I need about 100 Ah and am looking at adding one flexible panel of about 150-200 watt. Do not have space for more rigid panels without major modifications. Have been looking at Renogy 175 Watt?
Can I hook this flexible panel together with the two Siemens panels (parallel) and use the same charge controller or will I have to connect this flexible panel to a separate charge controller?
Additional info: My battery house bank consist of three 12V, 105 AH AGM. In addition, one similar 12V AGM starter battery. The starter battery is charged from the house bank via a Xantrex digital echo charger.
I have done a lot of searching and although there is much info about this subject, I have not found anything quite similar to my set up, or – in some cases- it was too complicated to fully understand.
Hopefully someone can give me good advise.
Thank you

[lmxr]

Yes, they can all go in parallel. It's usually preferred to add diodes to ensure power from one panel cannot flow into another panel. Without diodes, such a power flow can in some cases damage the other panel.


Here you find a brief discussion about this subject with some schematics.

[noelex 77]

The specifications of the panels are needed to answer the question properly, but it is likely that the new Renogy 175 Watt panel will have a significantly different Vmp from your existing Siemens SP75 so the new Renogy panel will need its own controller.

The specifications will be on a sticker fixed to the back of your existing 75w panels and available from the website selling the 175w panel. The maximum power point voltage (Vmp) is the most critical number when trying to match solar panels in parallel. Post these numbers and members of the forum will be able to provide a more definitive answer.

[wholybee]

You need to match the voltage of the new panel as closely as you can. The 75W panels are probably ~20V panels. The 175W might be ~20 or 40. If the 175W panels is ~40, then you can series the 75W panels to get to 40V, then parallel that to the 175.

[Jammer]

From what I could find ---


Vmp on the siemens SP75 is 17 volts (Innovationhouse.com - Siemens SP75/SP70 Solar Panel)


Vmp on the Renology panels is 19.5 volts (https://www.renogy.com/175-watt-12-v...e-solar-panel/)


--- you would want to confirm that for the specific panels you have and are looking at.


If you run them in parallel you will give up about 10% of the power from the Renology panels.


Best practice would be to install a second charge controller.

[VIKINGBEAR]

Thank you all.
Here is a picture of the label from the Siemens 75 Watt panels. Hope this help.
Appreciate your help.

[HeywoodJ]

To really answer we’ll also need to know what controller you have.

Based on the specs, the current panels probably operate at about 15V in Florida sun. A PWM controller wouldn’t lose you much. The new panel will likely want to operate around 17V, a PWM would bring that down to battery voltage, so 12.x to 14.x depending on state of charge.

What that all means, worst case, is that operating new and old in parallel your new panel would be effectively de-rated to something around 120W. If that’s enough then fine. If your controller is MPPT then the de-rating might be less, say 150W. A new, separate MPPT controller would allow to gather the full 175W (all values STC/nominal for comparison purposes).

[VIKINGBEAR]

Heywood J.
Thanks for your reply. I have a 30 Amp PWM charge controller, but am plan to replace that with MPPT due to new batteries. My old batteries which I am about to replace is Flooded Lead Acid and for that the PWM was ok. I stated in my first message that my battery bank is AGM. I thought i had a good deal on the AGM batteries but that fell through for various reasons. I am now looking at perhaps replacing old batteries with Lithium LifePo4, in which case i need new charge controller as well. They are a bit expensive but understand they will last much longer than AGM so maybe that will be the way to go. I could only get about 2 plus years out of the FLA batteries and understand the AGM may not last much longer....
However, regardless of which type batteries I end up with I will take your advise and hook up the new panel with a separate MPPT controller.
Again thank you, and thanks to all others as well for their replies. I have learned much.

[Adelie]

You can hook up the new panel in parallel but you would get better output by running separate controllers on each panel, when groups of panels share a controller shading on one panel drags down the output on all of them.
You will get better output from the MPPT.

AGMs are poor choice for house batteries maintained by solar unless you never discharge very deep and recharge them to full everyday.

In bulk charging they need to charged at 0.2C minimum, 0.3-0.4C is better. For a 200Ahr bank 0.2C is 40A which means you need to run the engine or have a huge solar array.
The only AGM that tolerate PSoC use are Fireflies.

I would get Trojan golfcart FLAs unless access was restricted or I didn’t think I would be good about checking water levels then I’d get Gels.

Or LFPs. Currently Trojans are cheaper over their lifetime unless you want to DIY LFPs.

[VIKINGBEAR]

Adelie.
Thank you for the very good info. From what you are saying then the AGM may not be for me.
Golfcart FLA will not fit in the compartment, too high. I have used most of today to study up on Lithium batteries here on this website, and do not feel comfortable installing them on the boat.
I guess I am back to my old type FLA’s and will just have to be better watching the water level. Over the past 16 or so years I get 2-3 years out of them, about the same as in our cars, but they will not break my bank when I replace them.
Again, thank you so much.

[Adelie]

What are the dimensions of the space where the batteries will be?

[VIKINGBEAR]

Adelie.
The problem is the height, the max height available is 9.5"
The 6V golf carts batteries with around 200 plus AH are very attractive to me (4 in paralell/series) but the height is the problem.

The Golf cart batteries i have looked at are all higher than 9.5", Trojans are around 11'.
There may be a possibility to modify the battery compartment to fit some of these golf cart batteries, but it is a difficult task and is also in a very tight work area making it hard to get to, and i am not quite up to it.

I am 76 and my body does not bend the way it used to :-)

Length and width in the compartment is not an issue and is ok for 4 or maybe 5 of most batteries, with some exceptions.
Again thanks for all your help and inputs.

[wholybee]

This is a perfect case for LiFePO4 batteries. They charge faster and make better use of available solar, so you get more Ah replaced each day. They prefer to NOT be charged fully, so better when you are just a tad shy on solar and can't fully charge every day. And you get more Ah in a smaller space, so better for tight/small spaces. You can easily get 2x the usable Ah in the same space, and up to 3x if you shop around. And that 3x usable capacity comes at half the weight.

[VIKINGBEAR]

Wholybee.
Thanks your response. Much appreciated.
As i mentioned in an earlier posting above, what i have read about Lithium batteries does not make me very confident in regards to safety and how I can manage these types of batteries properly. Its all so new to me.


However, based on your and Adelie's recommendations I will take another look at Lifepo4. Any particular brand you would recommend?

The size, weight and AH looks good although some Lifepo4 i have looked at are a bit pricey.

Again thank you.

[wholybee]

LiFePO4 is pricey. There is also some learning, and perhaps reconfiguration of other parts of your electrical system, so it isn't always straightforward. For safety, there is a lot of fear driven misinformation. Most Lithium batteries in the world are NOT LiFePO4, and dangers of those other Lithium batteries spill over. LiFePO4 is safer than a Lead Acid battery. LiFePO4 batteries are safer then charging a laptop or cell phone on your boat. Both of which use batteries that can spontaneously burst into flames, which LiFePO4 cannot.

My favorite of the "Drop-In" batteries (which is a misnomer, you still need to make some electrical changes in your boat) is Kilovault.

The most-simple way to Lithium is to give up Alternator charging of the Lithium battery and have the alternator connected to the start battery only. If you want to charge via alternator, there are multiple ways to accomplish it, with varying cost and complexity.

If you are interested in Lithium, you could start a thread, and get a lot of information. Just be aware than much of it will be how to do it the best of the best way, which is undoubtably great, but also very expensive and not necessary.