Solar panel question

[KD3Y]

Hi fellas,

Anyone know stuff about solar panels?  I know enough about them to know I don't know much about them.   I have one I bought at a flea market.  I googled it to make sure I was getting a killer deal and it's sold as a 20 amp, 12 V polycrystalline panel.
Now when I got it home and put my meter on it, at night in the garage with two lightbulbs on the ceiling it measured 11 volts which is pretty darned good for just a couple of 60 watt bulbs 20 feet away.  When I checked in in the full sunlight today the meter read 21 volts.

I went online hunting a charge controller for it, and I see similar panels that are 20 amp/24 volts.  I just want to make sure it't actually a 12 volt panel so I don't ruin a battery or fry a 20 amp/12 v charge controller.   I don't understand all the tech stuff but the sticker on it says,

NOMINAL POWER: 20W
POWER OUTPUT TOLERANCE: -0/+3%
LSC: 1.30A
VOC: 21.7 V
IMPP: 1.20A
VMPP: 17.3V
MAXIMUM SYSTEM VOLTAGE: 600V
MAXIMUM SERIES FUSE RATING: 15 A
NORMAL OPERATING CELL TEMP: 45+/- *C

I don't know what any of those acronyms mean, but I see 20 amp charge controllers range in price from fifty bucks to a hundred and fifty bucks.  Am I right in thinking this is a "regular" solar panel similar to my little 8 watt panel that I can connect to a 20 amp charge controller like this one here https://www.renogy.com/new-edition-voyager-20a-pwm-waterproof-solar-charge-controller/ and charge a regular old 12VDC flooded deep cycle battery?  I'd rather ask VS buying a $100 charge controller just to connect it up and "poof" it in a cloud of white smoke.
 

 

[K3MRI]

Hi Antony. Lots to unpack here.

First the panel you bought. If P=VI, then the panel you bought is 240 watts. That's a big panel! That's the type of panel you would see on a house roof. (but as we will see below, your sticker tells another story).

Next the controller. A 20A/24V will definitely handle your panel.

The panel is not fixed at 12V. The VMPP rating is the Voltage and Maximum Power Point which means that your panel, in full, vertical sunlight, should deliver 17.3 V. Note that panels will often deliver even slightly higher peaks. Hence the need for a controller.

Now let's talk about the controller (and the panel's sticker). The sticker says 20W; that's actually a small panel. The IMPP and VMPP confirm this. If you multiply the two, so 1.20A X 17.3V, you get 20.76W. So in actual fact, the 20A, 12V rating you got when you googled it, does not match the sticker. As for your 21V measurement, like I said, the VMPP of 17.3V can sometimes be exceeded.

In short, the controller you will need is not that big. It needs to handle ±2A and 18V; those are fairly cheap and standard. What you will have to decide is whether you want a PWM or MPPT controller.

Now my advice. Get a bigger controller because you may end up getting more panels. Given the choice, get an MPPT controller but check out their RFI. Many solar controllers cause RFI, bad sometimes...

What follows is a more detailed technical description of what you've asked (sorry you asked?? 😎)

• NOMINAL POWER: This is also known as the power rating of the solar panel. In your case, it's 20W, meaning the panel should generate 20 watts of power under standard testing conditions.
• POWER OUTPUT TOLERANCE: This shows the variance in power that the panel could produce. In your case, it's -0/+3%, which means the panel could produce up to 3% more power than its nominal rating but will not produce less.
• LSC: This stands for Short Circuit Current. It's the maximum current that can flow through the solar panel when there is a short circuit. Your panel's LSC is 1.30A.
• VOC: This stands for Open Circuit Voltage. It's the maximum possible voltage across the solar panel when no current is flowing through it. Your panel's VOC is 21.7 volts.
• IMPP: This stands for Current at Maximum Power Point. It's the current at which the solar panel outputs the most power. Your panel's IMPP is 1.20A.
• VMPP: This stands for Voltage at Maximum Power Point. It's the voltage at which the solar panel outputs the most power. Your panel's VMPP is 17.3 volts.
• MAXIMUM SYSTEM VOLTAGE: This indicates the maximum voltage that can be safely handled by the solar panel's internal components. Your panel's maximum system voltage is 600 volts.
• MAXIMUM SERIES FUSE RATING: This is the maximum current that can pass through a fuse in the system without blowing. It's a safety feature to protect the system from excessive current. Your panel's maximum series fuse rating is 15 amps.
• NORMAL OPERATING CELL TEMP: This is the average temperature that the solar cells will operate at under normal conditions. Your panel's normal operating cell temperature is 45 degrees Celsius, plus or minus a certain amount that isn't specified here. 

Please note that all these values are typically measured under standard test conditions (STC) which include a solar irradiance of 1000 W/m², cell temperature of 25 °C, and air mass 1.5 spectrum. Real-world conditions can cause the performance of a solar panel to differ from its rated specifications.

Now let's look at the differences between PWC and MPPT.

Solar controllers, also known as solar charge controllers, are essential components in most solar power systems. They regulate the voltage and current coming from the solar panels going to the battery, preventing overcharging and ensuring the longevity and efficiency of the system. There are two main types of solar charge controllers: Pulse Width Modulation (PWM) controllers and Maximum Power Point Tracking (MPPT) controllers.

• Pulse Width Modulation (PWM) Controllers: PWM controllers are relatively simple and cost-effective. They match the solar panel voltage to the battery voltage by slowly reducing the amount of power applied to the batteries as they approach full charge. This is accomplished by "pulsing" the full charge on and off very rapidly. The downside of PWM controllers is that they do not optimize the power output from the solar panels as conditions change.
• Maximum Power Point Tracking (MPPT) Controllers: MPPT controllers are more advanced and efficient. They continually adjust the input voltage from the solar panels to find the maximum power point and convert the excess voltage into more current. This optimizes the performance of the solar array and can significantly improve the efficiency of the system, especially in colder temperatures. MPPT controllers are generally more expensive than PWM controllers but can provide up to 30% more power from the same solar panels under certain conditions.

It's worth noting that the best type of solar charge controller for a particular system depends on the specifics of the system, including the power of the solar array, the type of battery, and the climate and environment where the system is installed. But like I said Anthony, check the RFI!!!!

My final, final recommendation: I would suggest using an MPPT type controller for amateur radio applications due to their improved efficiency and advanced technology. However, I'll note that product availability and models may have changed since I bought my last controller, so I can't provide a specific product that's currently available.

That said, one brand known for their high-quality solar charge controllers is Victron Energy. They manufacture MPPT charge controllers which are reputed to have low radio frequency interference (RFI). You might look at a model like the Victron SmartSolar MPPT 75/15 which can handle up to 75 volts and 15 amps, that way you can grow with it. This model has Bluetooth built in for monitoring and configuration, and Victron has a strong reputation for quality. I'm not sure of the price difference, but you could also save a little and get a 75/10. Here is the link to both: https://www.victronenergy.com/solar-charge-controllers/smartsolar-mppt-75-10-75-15-100-15-100-20

Sorry for the lengthy reply to such a simple question. I was in the mood....  😁

Last point. Considering you bought the panel at a super cheap price and the controller is overkill, maybe look on Ebay or get something much smaller just to get your feet wet!!

[KD3Y]

Thanks for the detailed information answer Jim.  Makes it easy for me!
I googled the charge controller you posted.  Looks like there is a marina in Oriental that is a dealer and sells them. 
I might take the ferry across in the next few days.  I like seeing in person and handling things before buying VS dealing with the ordering online and delivery mess.

Anthony, KD3Y

[K3MRI]

8 hours ago, KD3Y said:

Thanks for the detailed information answer Jim.  Makes it easy for me!
I googled the charge controller you posted.  Looks like there is a marina in Oriental that is a dealer and sells them. 
I might take the ferry across in the next few days.  I like seeing in person and handling things before buying VS dealing with the ordering online and delivery mess.

Anthony, KD3Y

Anthony, before you actually buy it, do some more research on any RFI issues. They say that they have mostly worked them out, but you need to be sure. Another option that does not create RFI is the West Mountain Radio solution here: https://www.westmountainradio.com/product_info.php?products_id=epic-pwrgate

This is the one I have in the car (full disclosure, I have the Victron in my portable battery pack). If I get a chance, I'll take some photos. Actually, wait, I do have a picture handy.

**edit** I lied 😎 I have a picture of the battery pack, it's there on the floor in front of me, but the Victron is buried beneath the postcards, oh well 🤣

[AB3NA]

I learned, the hard way, that you must always, always connect the battery to the charge controller before connecting the solar panel to the charge controller, and disconnect the solar panel from the charge controller before disconnecting the battery from the charge controller.  (I'm sure that I could have said that it fewer words, but I want to be absolutely clear.)  The battery needs to power-up the charge controller before the charge controller can switch the solar current.  Does this mean that the battery must already be charged?  I'm not sure.  It may be that even a "really dead" battery would supply a low-resistance load to the panel to prevent it from going full open-circuit voltage and damaging the charge controller.  As you configure your system, I suggest a label: "connect panel last, disconnect panel first", because there will come a time when you want to take it apart, and the panel is "hot" whenever the sun shines on it.

I like the charge controller that charges two batteries, independently, so I can put my load on one battery, run until it's depleted, then switch to the other, and the charge controller will direct charge to the weaker battery as needed.

When you found the "20A, 12V" rating on the panel, I suspect that someone meant to write "20W, 10V".  Maybe it's just a typo, or maybe it's like the ingredient list at the restaurant that said the soup contained "crap".  "Ha!", I thought, they meant "crab"".  But, no, it was imitation crab meat.  If I had complained about that, the chef's defense was ready: "I never said that there was crab in the soup".  In your case, you might complain "20A? It's only 20W!"  "Oops.  Sorry about that; just a typo."

 

[KD3Y]

My typo.  20 watt panel not 20 amp.  🙂

Real convenient with my 16 ft mobile mast.

 

 

 

[KD3Y]

I made my battery box from a type 27 box.  It has the charge controller mounted on top.  The pigtail for the solar panel is on the left, a 6-foot cable for the go box on the right, and three 12 volt cigarette plugs on the left side .  The cigarette plugs are fused and turned on/off with the illuminated rocker switch on top.   With the bluetooth adapter I can control the solar charger and monitor the volts/amps/watts with the app on my phone.

 

 

 

[K3MRI]

Anthony, I'm assuming from the image that it is not water-resistant? If so, you might want to fashion an emergency cover for it. Obviously, if you do make one, remember the condensation!

Otherwise, as always, what an impressively clean job!!!

[KD3Y]

Hi Jim,

No not water resistant.  The panel is sealed and weather proof rated for outdoor use but the controller and box accessories arent.

But I'm already a step ahead of you.  I was thinking of one of those plastic tubs like they sell at WalMart with the snap-on lid to use as a storage box when not in use.  Especially since in the garage where my sanding and sawing and other work generates a lot of dust.  Then in the field I can just flip the plastic tub bottom upside down for an emergency cover.

Yes?  No?  Maybe?  I see no need to reinvent the wheel when a clear plastic tub would be cheaper than anything I could build and just as functional.