This Is What Happens to Solar Power When Batteries Are Full? – (FACTS)


Solar panels are an increasingly popular way to provide electricity to residential homes. These systems allow you to significantly reduce how much you rely on the grid, dropping your power bill and your carbon footprint.

Many of these systems send the electricity they generate to a battery so that it’s available for use later. But what about when the battery gets full? What happens to the excess energy?

What happens to solar power when batteries are full? When solar-powered batteries are full, any excess energy is wasted if it isn’t redirected somewhere else. A switch is usually installed either to direct the excess power to auxiliary sources or to simply ensure that the excess charge doesn’t damage the battery.

If you’re considering installing one of these systems (or even if you’ve already got one), you’ll want to understand exactly how the system works. There are a number of ways you can setup the system to maximize usage of the power generated.

Where Does Excess Battery Power Go?

Electricity needs to be stored or expended in order to be useful. In other words, if you do not use it, you will lose it. Once your battery is full, any additional production is wasted unless you can find something else to redirect it to.

It’s worth being aware that fully charging your batteries is not often a concern as most people’s load requirement will more than keep up with the array’s output.

However, if you’ve got rather small batteries, rather little electrical usage, and rather large outputs from your array, then you may have potentially wasted power.

solar panel for RV

In more technical terms, when sun is shining on your array, the controller will allow amperage to the batteries and on to the inverter.

If the array is producing enough power to meet the inverter’s load requirement, then the batteries will remain fully charged.

If the load requirement is greater than the array’s output, then the deficit will be made up by the batteries.

However, if the array’s output is greater than the inverter’s load requirement, then the battery will discharge the deficit.

This potentially wasted power is known as an opportunity load, and there are ways to ensure that it isn’t wasted.

Related reading: What is an Inverter in an RV and Why Do You Need it?

Where Can I Float Excess Energy?

The extra energy produced after the battery is fully charged, and the inverter’s load requirement is met is known as an opportunity load. This is because it represents an opportunity.

You could simply allow this excess to discharge from the battery, wasting the produced power and potentially damaging your battery over time—or you can find something useful to do with it.

What you need is a charge controller. This is a voltage-sensitive relay which activates only when the battery is fully charged. The additional power can then be floated to other areas.

These are generally power needs which are always active. What are some option for floating excess power? Let’s take a look.

1. Refrigeration

Your refrigerator is an electricity-hungry animal that’s never satiated. When you’ve got extra power, you can float it to the refrigerator.

Additionally, you can send this power to a freezer or icemaker. If the ice is stored with good insulation, it can be useful for several days.

2. Heating

If you’ve got a large enough additional output, you can use the extra energy to help with some of the heating. Heated air and heated water are both ways to take advantage of the extra energy and store it somewhere useful.

3. Air Compression

If you use the extra power to compress air, you can then potentially sell that compressed air at a profit. This option may be particularly appealing to commercial outfits, but it isn’t out of reach for the average homeowner either.

4. Flywheel Spinning

Another great option for commercial applications that may be impractical for the typical homeowner is using extra energy to spin up a flywheel.

For certain types of heavy machinery or energy generation, the equipment uses a large flywheel, which takes a large amount of energy to spin up but then little energy to keep spinning.

Maybe Batteries Aren’t Your Best Option

Look, big batteries for extra solar power aren’t cheap. Depending on the size of your system, a battery can come close to doubling the cost of your solar setup.

If you’re generating more power than you can use, there’s an easier way to dump the extra energy.

The simplest way to use the extra energy you generate is just to have your system connected to the grid. This means that instead of storing extra energy you generate in a battery, you’ll simply send it off to the grid.

Your power company will usually pay you a small amount for the energy you export. When your system isn’t generating solar power, you’ll get your electricity from the grid.

A lot of people avoid this option because they’re turned off by the small amounts that power company pays for electricity pushed to the grid and that they’ll still have a power bill every month. In truth, this is the most economical way to run your solar setup.

You might not be thrilled with how much your power company gives you for the energy you send to the grid, but this represents a significant opportunity cost.

Combined with how expensive batteries can be, don’t turn your nose up at this option too quickly.

Sending power to the grid also makes your system that much more environmentally friendly.

Every bit of electricity sent to the grid from your solar panels is electricity that the electric company doesn’t have to generate by burning fossil fuels.

Related reading: This Is Why Your RV Battery Is Overheating? (Read This First)

Your System May Need Some Refinement

If you’re consistently filling your batteries to bursting, then there may be something in your setup that just isn’t lining up. Essentially you want to be generating close to the amount of power you use.

You could be generating too much or not able to store enough. Let’s take a look at a few elements to take a closer look at if you’ve got lots of extra power production.

Too Many Solar Panels

You may be generating too much power. If you never use all the power you generate, you have purchased more solar panels than you need. There is a secondary market for solar equipment out there.

You could try to sell off a panel or two to get your production more in line with your usage requirements.

Too Small Battery

It’s also possible that your battery isn’t big enough to suit your needs. If your battery generally stays topped off, then this probably isn’t the case, and you’ve got more of a production issue.

But, if your battery is constantly swinging from full to empty, then maybe you just need more capacity.

The idea of the battery is to provide power for your home when the sun isn’t shining—or when the panels aren’t producing.

If you can’t last a few cloudy days without running the tank to empty, then you probably didn’t dish out enough on your battery.

A larger battery will prevent you from generating a surplus and give you a bigger buffer when power generation is low.

Related reading: 4 Essential Reasons Travel Trailers Have Batteries [Must-read]

Can I Leave A Solar Trickle Charger On All The Time?

Can I leave a solar trickle charger on all the time? Yes, you may leave a solar trickle charger indefinitely if you ensure that your charger has the float method of recharging.

Some earlier models of solar trickle car battery chargers continue to charge even after your battery is full and could cause damage to your car battery if left on for long periods.

Solar batteries use the trickle effect to match a car battery’s energy discharge rate, generally the power a battery loses when it stands idle.

The float method of trickle recharge engages circuitry, which prevents the battery from overcharging. The charger senses when the battery is nearing the ‘float level’ and temporarily stops charging. 

Charging will only resume when the float level lowers again, ensuring that your battery will not overcharge. This means that you may leave your trickle charger connected for as long as you want, without fear of overcharging.

Alternatively, you may use a solar charge controller, which regulates the voltage with pulse width modulation. This system can also be left safely for more extended periods. 

What is a Solar Charge Controller? >> Check Out the video below:

How Do I Know When My Solar Batteries Are Fully Charged?

If your solar battery does not have a controller or an LED light indication of battery levels, you might find a voltmeter or multimeter handy. A voltmeter measures either DC or AC voltage in a scale of millivolts, volts, or kilovolts.

How do I know when my solar batteries are fully charged? To measure if your solar battery is full with a voltmeter or multimeter, you should:

  1. Set the multimeter/voltmeter to 10-15 volts
  2. Connect the negative terminal of the meter to the negative terminal of your battery
  3. Connect the positive terminal of the meter to the positive terminal of your battery
  4. Check the voltage measurement on the tool of the meter
  5. If the voltage reading is within 2% of your maximum battery voltage, your solar battery is full.

Solar charge controllers also prevent night battery drainage by ensuring that the batteries are not overcharged in the day.

Likewise, the power doesn’t run backward into the solar panels overnight and drain your batteries.

What Can a 300-watt Solar Panel Run?

300 watts is a standard power rating for a solar panel, and the number of panels would determine what electrical appliances it would run.

What can a 300-Watt solar panel run? A 300-watt panel produces roughly 300 watts of electricity if the panel has been exposed to direct sunlight for an hour. After about three hours of charge, your battery could charge appliances such as TV, fans, Led lights, etc.

The best battery to store power from a 300-watt solar panel would be a 12-volt battery.

I have recently written an article in which I describe how a TV can run on a 12V Battery in more detail, read this article here: Can a TV Run on a 12V Battery? [This Is How]

If you use a single device, your runtime would be longer, and the simultaneous running of varied appliances will consume the electricity according to their ratings.

What Happens To Solar Panels With No Load?

What happens to solar panels with no load? When a solar panel has no load, it is in an open circuit condition. Since there is no flow of electrons when the circuit is disconnected, there is only a small leakage current from internal cell resistance, which should not damage the cells.

A disconnected solar panel should not suffer any damage by being exposed without a load beyond the usual damage incurred when operating. 

However, you should cover your panels when not in use over a long period as they will degrade at the same rate as an operating panel with none of the benefits.

The one exception is some CdTe (cadmium-telluride) panels that suffer damage without a load.

Which Solar Batteries Last longest?

Which Solar batteries last longest? Lithium-ion batteries are the longest-lasting solar batteries because they have the highest depth of discharge (DoD) at 80%-90%, which means you can use more of your battery’s charge to power your loads.

With a lifetime of 10,000 cycles or ten years average, their high cost may be offset their initial cash outlay. 

Lead-based batteries may sometimes have to be replaced three times in ten years (based on the average 3-year warranty offered with lead-acid batteries.)

So ultimately, the high cost of lithium batteries that last an average of 10 years is offset by the lead batteries’ multiple replacement costs.

Frequently Asked Questions

Here are a few common questions people often have about Solar Panel and battery:

How Many Years Does A Solar Battery Last?

How many years does a solar battery last? A solar battery’s general lifespan is between 5-15 years, depending on the intensity of use, maintenance, type of battery, and proper charging practices. The most significant drain to your solar battery is improper amps to capacity usage, where the amps are too high for your battery.

Although higher amps may charge your battery more quickly, your battery’s lifespan will ultimately be halved.

Resting your unused batteries for long term storage also speeds the degradation as does exposing your batteries to temperature extremes.

Can Solar Panels Drain Batteries At Night?

Can solar panels drain batteries at night? No, If your solar panel system is correctly designed, your solar panels shouldn’t drain the batteries at night. During the night, when the panel has low potential (not producing electricity) and the battery at a higher potential, there is a chance that the current will flow from the battery to the solar panel.

That is why a blocking diode is usually installed to allow current to pass from the panel to the battery and prevent backflow from the battery to the panels.

Do Solar Panels Work At Night?

Do solar panels work at night? No, solar panels do not generate electricity at night, but they can still provide solar energy through net metering and solar battery storage.

The solar panels require photovoltaic energy to convert to direct current power. This DC power is sent through a converter to deliver the AC that most of us use in our homes.

When your solar panels are dormant during the night, you may use net metering and solar plus storage systems to access electricity produced by your solar panel at night.

Net metering allows you to use the excess power produced by your solar panels when you are outside of sunlight hours. However, net metering is not available everywhere in the US, and then your best option is storing your solar energy in battery form.


When solar batteries are full, you need to find a way to use the excess power, or it will go to waste. There are a number of ways to utilize excess power.

You may even want to look into whether your system is running optimally or if a battery is even your best option.


Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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