Solar Panel Voltage Drops Under Load (Problem + Solutions)

Are you concerned that the solar panel voltage drops under a load?

Unfortunately, it is not an uncommon problem with solar arrays, and inside we go through some troubleshooting options that explain why the voltage on solar panels can drop.

Is your solar array losing voltage while under load?

If so, the cause may be natural degradation or one of a few easy-to-fix issues. However, the problem can also be something more ominous. 

In this blog, we discuss the following:

  • Common problems that cause the low voltage from solar panels
  • Whether it is the panel that is the problem
  • How temperature plays a role in solar power efficiency
  • Errors in testing that can cause a false reading
  • Connections and exposure reasons solar panels have low output. 

Keep reading If you want to know what you can do to regain voltage from your solar array when it is under load. 

What is Degradation in Solar? 

Degradation is the decrease in peak performance over some time. With solar panels, there is a natural degradation loss of about 0.50 percent per year.

Unfortunately, there is not much you can do about fixing this issue. That process is part of the natural lifecycle of solar panels. 

While there is not much you can do to fix the degradation of solar panels, your only option is to replace the panel if the degradation becomes too large of an issue. 

Also, remember that voltage loss may have nothing to do with the solar panel. 

Is the Panel Operating at Full Capacity? 

Whether using a single solar panel to power a small device or an entire array, the voltage may drop when engaged if the solar panels are not fully charged and producing power at their peak capacity. 

Issues that can cause a solar panel to not perform at peak capacity include:

  • Shading
  • Fluctuations in lighting to the panel, such as dawn and dusk, cloud cover, storms, and debris. 
  • Corroded connections between the panel and the inverter.
  • Age — panels only last for so long before they naturally degrade. 

See also: Solar Panels Maintenance: Essential Tips for Optimizing Efficiency and Longevity

What is Shading 

Shading is a term that we hear a lot about in solar. Shading occurs when something, usually a tree or shadow of a building, blocks the sunlight that would otherwise strike the solar panel.

Without full sunlight, the panel cannot produce energy at the peak of its performance.

When shading occurs under load, the power produced by the solar panel drops because the panel cannot produce its total energy capacity.

The load has little to do with the decline because the power level from the panel was already low. 

Charge controller mounted on the wall

Is the Temperature Playing a role in Load Capacity?

If the solar panels become overheated, it causes them to decrease the amount of energy they produce.

For example, if the panels are lying on blacktop as the blacktop warms up during the day, it heats the panels and causes them to drop efficiency.

The same is true for panels situated close to objects that heat up during the day. 

In this case, if the panel temperature rises too high, it will not be able to recharge batteries fully. Can you overcome this issue? Yes, you can. 

Solutions to prevent solar panel overheating

  1. Move the panel to a location where it receives full sun but is not gaining heat from its environment. (portable panels)
  2. Elevate the panels so they do not lie directly on the hot surface. 
  3. Measure the drop in energy and use solar panels that have a higher energy rating. When the drop occurs, it will bring the energy panel output down to what you need. 
  4. Is Something Else Stealing the Power?

The issue may be with other solar components if the voltage drops while under load. The control is a good bet as it is a connection that blocks energy via a transistor.

You can test the control to see if it is faulty by bypassing the controller and connecting the panel directly to the batter for testing. 

What Does A Solar Controller Do?

You can think of a solar controller like the gas pedal on a vehicle. It reduces or increases the amount of power that reaches the battery.

A gas pedal, when not depressed, allows the car’s engine to idle. A controller that is closed decreases the amount of energy the battery receives.

Press the gas pedal to the floor, and the car engine races. Bypass the solar controller, and the batter gets the total amount of energy.

Without the controller, the batter would burn out quickly. So, A solar controller controls the amount of energy that a battery receives. 

Note: the controller is there to prevent overcharging of the battery. Overcharging can permanently damage the batter, cause it to overheat, explode, or even catch fire. 

Are Bad Connections the Problem?

When we measure energy, the outcomes can be iridic. Be sure that you measure the voltage output with solid connections so that the results are consistent.

If you have a low output reading under load, be sure the connections you use are not the issue. 

The same advice is true of connections along the circuit.

If there is a poor connection at the inverter, controller, or batter, the result can show as a drop in voltage.

Check all the connections and make sure they are solid. If the connections are good and the decline continues, look at the components that make up the circuit.

Again, the problem can be the controller, inverter, or panel. 

Do You Need to Determine the Source of a Drop-in Voltage from a Solar Panel?

If your solar panel or array drops volts when under a load, the problem may be any number of issues. The best place to start is as follows:

  1. Start with your testing equipment. Make sure it is working correctly and that the connections during testing are good.
  2. Test the output at the solar panel and make sure that the panel is at peak capacity. Eliminate issues such as shading or corroded connections. 
  3. Test the solar components between the solar panel and the battery. If needed, bypass the solar regulator or controller to make sure it is not the problem. Remember that a solar regulator is essential to the array and will protect the battery from overcharging. 


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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