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I hate to be the seller who ate the loss for a customer's fault.

Very high PV-battery voltage differentials bring about another problem. The DC-DC conversion process gets less efficient, esp. at high currents. There's another disadvantage of most installations with MPPT controllers that is not well recognized, esp. in the boondocking context. Since the...

Hi Abby, most of us here are geeks & we would like to see #"s, lots of it. Instead of posting relative figures like 25% less, etc, how about posting actual volts, amps, etc? Since you have two similarly rated panels, you may use one as a reference. Prop up both panels in the same orientation...

The panels were in series for the MPPT and so, there was sufficient headroom. I didn't measure each panel's output voltage, but the string's voltage a little over 75V. so the individual panel voltages must have been around 15V. I used 5 panels simply to max out each controller. With four (or...

Higher temperatures reduce a panel's Voc & Vmp and therefore, the power. There's no way around this fact. In parallel wired systems, if the panels' voltage drops too low, it may not have the 'oompf' to drive a current thru the batteries.

Interesting timing - I just finished a test of 30A MPPT & a 30A PWM close to their rated capacities - five 100 Watt panels in series for the MPPT & parallel for the PWM. The MPPT delivered 28.5 Amps to a 12V battery (battery voltage 13.5V) and the PWM delivered 30-31 Amps. This result is what I...

There's a lot of misconception expressed in this thread as to what MPPT & PWM controllers are. MPPT controllers do use a PWM circuit block but not in the simpler way that a PWM controller uses. The PWM circuit in an MPPT controller changes the duty cycle of the buck converter switches, which...

Ampacity does not scale linearly with the cross-sectional area at large current magnitudes. The reason is that the magnetic field induced by the current flow pushes the electrons away from the core of the conductor - in other words, the current density (Amps/cm^2) is not the same across the...

Flooded cell type batteries are the "proper" batteries for off-grid - very simple & straight forward. Most of us have a lot of solar panels for the very reason you cite - winter time. Once in a while, we run the generator to bulk charge & let solar finish off the process. Living off-grid...

Well, we have five ambulance conversions that were done 4-5 years ago with flex panels glued to the box. The panels are still putting out close to their specs. These vehicles are used up & down the US West coast, summer & winter. Our anecdotal examples are not going to prove anything. I'm...

You're correct. A workaround is to measure the level of sunlight and the Isc at that light level and see if that is close to what the panels should produce at that light level. @Abby Smith, download a couple of pyranometer apps to your phone and measure the light level around noon on a crisp...

Be careful if/when you try charging at very low temps. Lithium plating often leads to the formation of dendrites which can puncture the separator & cause an internal short. Do it in an explosion proof freezer that is placed outside. I wouldn't trust the datasheets claiming sub-zero charging...

If your goal is warm (45-60 C) water, your best bet is a solar thermal system. Even simple solar thermal heaters are 50-60% efficient, with some designs exceeding 80% efficiency. You may combine the solar thermal with a small PV to run a pump. Heating water from PV energy is at most 20%...

I'm not commenting on painting the aluminum framework black. I'm referring to painting the white backing sheet black (OP had done that). I really hope he did not paint the front of the panel black:-) Despite the fact it looks white (in the visible spectrum), and hence, should reflect heat, the...

Then there's no issue at all! The controller is actively hunting for the sweet spot on the solar side so that it can deliver the most power to the batteries. If the panels are not very close in their individual specs, there can be multiple max power points - pseudo max power points - and the...

Discharging lead acid batteries below 50% will not kill them. Leaving them in a discharged state - 25% or 75% - for longer than a few days will cause hard-to-reverse sulfation. If lead acid batteries are used in an application, there must adequate charging capacity available - enough capacity...

An option - a Bogart Trimetric & its WiFi Module. The WiFi range is 300+ ft in unobstructed settings. The battery info is presented on a local web page the module serves, so OS agnostic. It can also join your starlink router & be accessible remotely.

Under the ambient conditions of the test today, yes, a MPPT performed slightly worse than the PWM. As I explained earlier, the panels were at 55C. This alone causes a 15% drop in their Vmp. The Epever MPPT was not mis-configured. There are some factors to consider in the MPPT vs PWM debate. In...

Flexible panels lose heat thru the front (Sun) side and not the rear. Gluing them to a rigid surface is acceptable and should not compromise heat dissipation. What kills flex panels is repeated flexing. It leads to micro-cracks in the silicon cell, causing a mono crystalline to become a...

AGM's are compromise. Most, if not all, that are off-grid and rely on batteries don't use AGMs. My comments about exceeding the 50% discharge limit are for flooded cell batteries. These batteries can be charged at higher rates. Besides, there are several tricks for pushing the rate even...

A PWM controller switches on/off (modulates) the ungrounded connection between the solar panel(s) (+ in a negative ground system and or - in a positive ground system) and the battery. The electronics required for switching on the positive side is a little more complicated (& hence more...

The voltage you see when a battery is under (heavy) load has no relation to the voltage vs state of charge curve. In the latter, the voltage refers to the "resting" voltage - no charging or discharging for a few hours. It is perfectly normal/acceptable for the battery voltage to sag by 0.5 to...

You're referring up Joule heating (I squared R) that happens when a current flows thru a resistive material. In a solar panel, the unharvested electron-hole pairs have a finite lifetime. If not collected & transported away quickly, they recombine with the silicon lattice, giving up their...

this is wrong in so many ways! A 400 Ah battery has 400 Ah of usable charge. Most lead acid batteries will give 300-500 cycles of full (100%) discharge before they are dead. At 50% DOD, one can expect a little more than 2X cycles (800-1100); at 25% DOD, batteries will last 4X+ cycles. In the...

The backing sheet in most panels is PVF, with Tedlar being the most popular brand. In the IR, almost all plastics are"black" - that is their emissivity is close to 1. Painting it black is not going to improve radiative heat transfer to its surrounding, the rooftop.

Since I commented on @MBR's post, I want to add something about lead acid batteries. What a LA battery manufacturer guarantees is the lifetime amp-hrs one can expect from the battery. If a hypothetical battery is rated at 100 Ah & 500 charge cycles, you can expect to get 50000 Amp-hrs from it...

Only conductive heat transfer is proportional to the deltaT between the two bodies. Radiative heat transfer is proportional to the differences in the 4th power of temperature of the two bodies. The best way to cool solar panels mounted on RV rooftops is attach a coil of thin-walled copper...

Think of Amps as gallons/min flow rate. One Amp is equal to 1 Coulomb of charge flow per second. In your case, the MPPT controller sends 100 Amps to the battery thru the positive cable and 100 Amps comes out of the battery thru the negative cable and goes back to the controller. In that process...

A 500 Amp-50 mV shunt will dissipate 4 Watts @ 200 Amps ((200/500)*.05V times 200A).

The way this thread is going, I predict a new thread soon, titled "Should I protect the breaker with another fuse or a breaker? If so, do I put it in parallel or series with the 1st breaker?":)