Dump Load Needed For PV?

[markpj23]

Been trying to read everything prior to getting to the detailed design phase. Planning to run a PV array to power a swimming pool variable speed AC motor through a Growatt solar pump inverter. I know best practice (and preference) requires a DC breaker to disconnect the PV array from the inverter. I also read where leaving the panels exposed to the sun w/o a load for long periods can damage the panel due to excess heat.
If my pool pump is not run for a few hours during sunlight, there will of course be no load on the PV array. Likewise when the DC breaker is open for system maintenance, etc.
Do I need to design a dump load into the system or not?

 

[TomC4306]

Do I need to design a dump load into the system or not?

No.

 

[chrisski]

I also read where leaving the panels exposed to the sun w/o a load for long periods can damage the panel due to excess heat.

I’m curious where you read this. I google questions like this and often times Quora or a similar site pops up with answers. These sites are open sites which anyone can answer a question and can be wrong.

I don’t see how this could be true, and if it is, the panels are cheaper to replace than building a system to make they are never idle.

The one exception to this would be a flexible panel. Those have a limited life of 1 to 5 years and keeping them in a closet would let them work forever, but a glass panel is in excess of 20 years with a loss of 1% a year.

 

[markpj23]

Thanks. The google search results are all over the place.... yes, no, yes, no .....

 

[OzSolar]

Planning to run a PV array to power a swimming pool variable speed AC motor through a Growatt solar pump inverter.

Are you using batteries also?

I also read where leaving the panels exposed to the sun w/o a load for long periods can damage the panel due to excess heat.

This does not apply to PV panels.

One does need to be careful with solar water heating panels and not let them remain filled with water and not pumping. They can generate steam and self destruct.

edit to fix typo.

 

[HRTKD]

This does apply to PV panels.

Does or does NOT apply to PV panels?

Panels left in the sun will certainly age, whether they're used or not. Panels left in a warehouse aren't going to age much.

 

[OzSolar]

Does or does NOT apply to PV panels?

Panels left in the sun will certainly age, whether they're used or not. Panels left in a warehouse aren't going to age much.

Oops... "Does not" will edit to correct. Thanks! Side note: that used to be my stock joke when teaching solar PV classes. "leave them inside to protect them"

 

[Rednecktek]

I like to tell people that solar panels don't PUSH power, the battery ASKS for power and the panels GIVE power to the batteries as best they can.

 

[peakbagger]

BTW Solar Hot Water Panels do not typically boil over and produce steam. A standard flat plate panel will only raise the temperature of the water by 80 degrees F. Water boils at atmospheric pressure at 212 F and not many roofs hot enough to get things to boil. What usually happens is that the antifreeze goes stagnant and overheats turning acidic. On the other hand Evacuated tubes while they are working can heat the water to much higher temp causing boiling. They need fool proof temperature protection.

 

[markpj23]

No batteries planned for this system. Even though not part of my original question, the comments about pool solar water heater panels are interesting. The system my pump will supply does have the vacuum valve at the high point and thus water drains back down into the pool once the pump shuts down.

 

[JRH]

I’m curious where you read this. I google questions like this and often times Quora or a similar site pops up with answers. These sites are open sites which anyone can answer a question and can be wrong.

I don’t see how this could be true, and if it is, the panels are cheaper to replace than building a system to make they are never idle.

The one exception to this would be a flexible panel. Those have a limited life of 1 to 5 years and keeping them in a closet would let them work forever, but a glass panel is in excess of 20 years with a loss of 1% a year.

some are good and some are way off… you have to know enough to know which is what…

 

[OzSolar]

BTW Solar Hot Water Panels do not typically boil over and produce steam. A standard flat plate panel will only raise the temperature of the water by 80 degrees F. Water boils at atmospheric pressure at 212 F and not many roofs hot enough to get things to boil. What usually happens is that the antifreeze goes stagnant and overheats turning acidic. On the other hand Evacuated tubes while they are working can heat the water to much higher temp causing boiling. They need fool proof temperature protection.

None of this has to do with the OP's questions about PV.

However, If the pump stops and there's no way for the system to relieve the pressure a solar water panel has a very high chance to self destruct. Is it producing steam, maybe not?? All I know is that I've seen many flat plates with ruptured capillaries inside the collectors and fittings just outside the collectors in systems that had been poorly designed or with isolation valves that had been closed thus isolating the the collectors from pressure relief valves so when the power failed or the storage was satisfied bad things were going to happen.

At the end of the day it doesn't matter if it's a flat plate, an evacuated tube or a 2 liter plastic bottle. If you've fill something full of water and leave in the sun for too long with no way for it to get rid of the pressure it will self destruct. Again.... none of this has to do with PV.

 

[OzSolar]

No batteries planned for this system. Even though not part of my original question, the comments about pool solar water heater panels are interesting. The system my pump will supply does have the vacuum valve at the high point and thus water drains back down into the pool once the pump shuts down.

No batteries and a variable load to tied to an inverter will be problematic. Now I think I see why you asked the original question which is why I asked about batteries.

You are good on the drain back part of your solar water heating system though!

 

[markpj23]

No batteries and a variable load to tied to an inverter will be problematic. Now I think I see why you asked the original question which is why I asked about batteries.

You are good on the drain back part of your solar water heating system though!

Growatt makes a unit specifically for this:

Growatt 2.2kW 3HP Solar Pump Inverter l Water Pump Inverter | Grid-Assisted | SPI 2200TL2-HV​

 

[OzSolar]

Growatt makes a unit specifically for this:

Growatt 2.2kW 3HP Solar Pump Inverter l Water Pump Inverter | Grid-Assisted | SPI 2200TL2-HV​

What happens when the clouds come out? Does it switch back to the grid? Flawlessly? Not sure I'd want to risk a fancy variable speed pump to that. These battery-less inverters that can support AC loads when the sun is shining have been discussed before and people had plenty of concerns but I don't think anyone with hands on experience has chimed in. Hopefully someone will.

 

[GXMnow]

I’m curious where you read this. I google questions like this and often times Quora or a similar site pops up with answers. These sites are open sites which anyone can answer a question and can be wrong.

I don’t see how this could be true, and if it is, the panels are cheaper to replace than building a system to make they are never idle.

The one exception to this would be a flexible panel. Those have a limited life of 1 to 5 years and keeping them in a closet would let them work forever, but a glass panel is in excess of 20 years with a loss of 1% a year.

This question has come up a number of times.

"Does a PV solar panel actually get hotter if you are not using the electrical output?"

My thinking as an electrical engineer says that it should not get any hotter. I think of the PV Solar panel as a battery, but sunlight replaces the electrolyte. If it is not being loaded, the voltage does rise a bit, but I can't see it getting hotter than when it is loaded to hold the voltage down. In my mind, the internal resistance combined with the current flow would cause more heat when there is a load on the panel. The counter point is the conservation of energy view. The electricity going out is taking energy from the system, and therefore will reduce the expelled heat. I don't buy it. I think of it more like a battery. A higher charged battery has a higher voltage, and lower state battey has a lower voltage, but without a load on them, neither one makes heat when it is sitting.

Who on this forum has a decent thermal camera and a pair (or 3) matching PV solar panels? I propose a simple test. Leave one panel open circuit, connect one panel into a dead short, and have the third panel running an MPPT into a battery. Have them all in equal sun and check it with a thermal camera. Is anyone equipped and up to do this test? To be totally fair, maybe repeat it a few times, switching which panels are open, connected to MPPT, or shorted.

We should also take a pole on what people think will be the hottest and coldest panels. Here is my educated total guess. Open circuit panel will be the coldest, shorted would be hottest, and MPPT in the middle. My assumption is that the solar thermal heating will be the same, and the current flow will cause a little more temp rise. The shorted panel will be the highest current, so hottest panel.

 

[efficientPV]

Conservation of energy. A panel sending current to an outside load will be slightly cooler. Shorting a panel will have the same temperature as one open circuit. No need to poll, this is science.

 

[GXMnow]

I still want to see the science tested. I don't see how an unloaded panel can be hotter. Have you actually observed this with a thermal camera?

 

[RCinFLA]

Panels have in the ballpark of 20% efficiency. This means if you don't pull output from panels they will absorb that power in their inherent shunt diode of each cell in the panel.

20% extra heating is not going to damage panel.

 

[chrisski]

Conservation of energy. A panel sending current to an outside load will be slightly cooler. Shorting a panel will have the same temperature as one open circuit. No need to poll, this is science.

I still want to see the science tested. I don't see how an unloaded panel can be hotter. Have you actually observed this with a thermal camera?

I’d like to see a test. I could easily put panels out and take temp readings on 300 watts of panels maxed out and the same 300 watt panels set up next to it with no load.

I would like to see some math first. My numbers for amount of energy the sun puts out is 1370 meters per square meter, while my panels can harvest 180 watts per square meter. You might be able to say

180
===. Equals 13 %
1370

so the outside temp is 100 degrees F 37 C with that being 312 Kelvin

but noone would believe that the temperature would drop 13% because that is the amount of energy harvested.

On a hot day, my panels reach 135 F to 155 F, but I’ve never tested powered and unpowered side by side.