What Happens to Solar Power When Batteries Are Full?
Whether living off-grid or as a full-time RV camper, a renewable energy source makes life easier. It’s an excellent option for environmentalists, survivalists, and pragmatists who know that having an alternative power source isn’t just a luxury—it’s a necessity.
Solar power generators use batteries to store the electricity they generate for later use. But what happens to that power when the batteries are full? Does it go to waste?
Here, we look at how solar power systems work and the critical role that their batteries play in storing power. Whether you keep that power on standby, sell it to the grid, or float it to other devices, here’s what you can do when your battery is at maximum capacity.
What Happens When Solar Power Batteries Are Full?
Solar power systems use batteries to store solar energy. However, if the power generated exceeds the solar battery’s capacity, it can overcharge the system. An overcharged solar system can severely damage a battery’s life.
As soon as a solar battery reaches full charge, the inverter and charge controller must step in to mitigate risks by handling excess power. They can do this in three ways: push it back into the panels for power loss, back into the grid for credits, or force a dump load.
Off-grid systems typically include solar panels, charge controllers, battery monitoring systems, and batteries. Solar panels collect energy, which passes through a charge controller to batteries. Battery monitoring displays the battery bank’s charge level.
The charge controller protects batteries and solar panels by managing the energy flow. Battery charge controllers stop electricity flow when they signal that batteries are full.
Many solar power systems incorporate inverters and charge controllers to ensure trickle charging and redistribute excess charges. However, you can also return power to the grid. Surplus energy fed back into the grid is available for use by community members who cannot access solar panels or other renewable energy sources.
A New Way to Stay Charged—EcoFlow DELTA Pro Smart Battery
The DELTA Pro Smart Battery from EcoFlow mitigates the risks outlined above by giving you control of your battery charge levels and recharge rate. With this extra Smart battery, not only can you double the capacity of your DELTA Pro Solar Generator from 3600Wh to 7200Wh, but you can also prevent overcharging issues.
The DELTA Pro Smart battery connects to the DELTA Pro portable power station or solar generator. Connect two, and you can achieve up to 10.8kWh for a robust off-grid home backup or full-time RV living. A sleek LCD screen lets you check the battery’s charge percentage, recharge time, and more. Plus, you can use the EcoFlow app to check the battery’s status, no matter where you are. Once you charge it to maximum capacity, the battery will hold its charge for up to one year after a full charge. Power doesn’t get more convenient or reliable.
How to Know When Your Solar Batteries Are Fully Charged
Several options are available to check the charge level of a battery within a solar energy system.
Intelligent energy storage solutions like the EcoFlow Smart Battery feature display screens that indicate the battery’s charge based on its voltage.
Some inverters display the battery’s charge level on their screen, so you can tell if it’s charging or full. Inverters without display screens may have a warning or indicator system to tell you the battery status.
You can also purchase meters to check the charge level. Look for a voltmeter, hydrometer, and multimeter.
- Voltmeters are instruments that measure electric potential. To check the charge of a battery, connect your voltmeter to the red and black ports. If you want an accurate reading, the battery shouldn’t have delivered electricity for the last few hours.
- Hydrometers are only used for flooded lead-acid batteries since it requires measurements from the liquid inside.
- A multimeter can measure voltage, current, resistance, and many other things about your battery’s condition.
What to Do if Your Batteries Regularly Become Full
If you find that your solar batteries are regularly becoming full, you can offset that extra power and put it to good use.
Sell One of Your Panels
You may be connecting too many solar panels for your energy needs. You can sell excess panels in many marketplaces and local swap pages. There is no doubt that solar panels hold their value well, and you might be surprised at how quickly people will snatch them up. In many cases, worn or outdated solar panels can be recycled or reused.
Purchase Additional Batteries or a Higher Capacity Solar Generator
Purchasing a higher storage capacity solar generator will also help store more power. For example, EcoFlow’s DELTA Pro Solar Generator stores significantly more energy than the generators from EcoFlow’s River 2 series. The River 2 series is intended for camping and other off-grid activities where portability is crucial, while the DELTA Pro is an ideal home backup power solution.
Many solar generators also allow you to purchase extra batteries to increase your solar power storage capacity.
It’s possible to do nothing with your full battery until you need the extra power. Downsizing or upsizing may not be worthwhile if excess power is only available during the sunniest days.
Compare your power usage with the capacity of your battery bank. It may be best to keep the setup unchanged if they are well-matched. On rainy or overcast days, you may need that extra energy.
You can use extra power for future needs, such as:
- Charging tools
- Cooking food
- Refrigerating food
- Dehydrate food for storage
- Run an AC unit for longer
Where Does Excess Solar Power Go When Batteries Are Full?
The direction of the power depends on your setup and whether you have a grid or an off-grid system.
An on-grid solar system sends AC power to your appliances first. If the home doesn’t have enough load to use all the electricity, it’ll feed the remaining power back into the grid.
In off-grid applications, the inverter receives extra electricity and converts DC into AC power. Any appliance connected to the circuit can then use this power. With EcoFlow solar generators, the battery will stop absorbing energy once the battery has reached full capacity to prevent any possible damage.
Where Can I Float Excess Energy?
There are two ways to handle excess power. You can let it discharge from your battery, wasting the power and potentially damaging your battery in the long run, or you can float it to appliances and devices to reduce your on-grid power consumption.
Typically, solar panels generate power for devices and appliances that require electricity immediately but not continuously. If you’re generating enough solar power that your battery consistently reaches capacity, consider using the excess energy to run ice and refrigeration systems.
The Electrical Grid
With many fixed solar power systems, you can send excess energy to the electrical grid if your solar panels have collected enough energy to power your home and charge your battery. For many people, this is a significant reason they use solar energy.
The electrical grid distributes electricity to homes and businesses. Without solar panels, your home depends on the electrical grid.
Owning portable solar panels and a solar generator allows you to live on or off the grid. You don’t have to worry about running out of solar power while on the grid. Electrical grids serve as backups when an on-grid solar system fails.
You can install a net meter on the grid to record your solar energy use. Excess solar energy is directed back to the grid through this meter. Homeowners can earn credits for the extra energy they generate, which can be used on a future bill, saving them some money.
Air compression machines are the next dump load for an excess charge. Intelligent on-grid solar panel systems will send excess power to air compression devices to store energy for later use.
Depending on how much additional energy your solar system generates, you can use it to assist with home heating. Both heated air and heated water are ways to expend extra energy. For example, you’ll want to use the heater more frequently in the winter to keep the home warm and cozy.
Some solar batteries are at risk of igniting and overheating — or at the very least reducing their lifespan — when overcharged.
Select a solar system that takes the hard work out of monitoring battery performance, adding additional capacity, and efficiently handling excess energy. Shop EcoFlow today for solar energy that’s Smart and efficient.
EcoFlow is a portable power and renewable energy solutions company. Since its founding in 2017, EcoFlow has provided peace-of-mind power to customers in over 85 markets through its DELTA and RIVER product lines of portable power stations and eco-friendly accessories.
Can a Solar Charge Controller Work with a Wind Turbine?
Solar and wind are two popular clean energy sources that are gaining traction with the world working into uses environmental-friendly energy sources. And, of course, many devices are set to improve the services people get. For this article, we FOCUS on solar charge controllers. Generally, it is a device that connects the solar panel to the battery, ensuring that your device isn’t overcharged, which can lead to more problems. Solar charge controllers significantly limit the solar power that goes to your battery keeping your devices safe. Since solar and wind FOCUS on clean energy, can wind turbines use solar charge controllers? We FOCUS on this question as we try to define the possible relationship between solar charge controllers and wind turbines. Check it out!
Can I Use a Solar Charge Controller for A Wind Turbine?
Using solar and wind energy is the sure bet to a greener life that doesn’t use fossil fuels. But how connected are the two sources when charging your batteries? Having a charge controller when using solar or wind is vital. Of course, many assume the two can use the same charge controller, which isn’t the case. Can I use a solar charge controller for a wind turbine? No! We have solar and wind charge controllers that protect batteries from overcharging and permanent damage. However, the way the two controllers work is different.
The wind charge controllers must eliminate the excess load, but for solar charge controllers, this issue isn’t a problem for them. Whether you are using wind or solar sources, having a charge controller in your system is crucial. The device works between the battery and the energy sources. But you must realize that you can’t use a solar charge controller for a wind turbine. There are a few differences between a wind controller and solar charge controllers that make it impossible to use the two interchangeably, including:
The Variation Between Solar and Wind Charge Controllers
The primary function of a charge controller is to protect the device’s battery, whether using wind or solar sources. It works on disconnecting your battery automatically after it entirely blocks the flow of charge to prevent battery damage. It also ensures that your fully-charged battery won’t recharge the sources after they are complete, ensuring that the charge flow back is impossible. However, despite the two controllers doing the same job, using solar charge controllers for wind turbines is impossible. The reason is the difference in how the two deliver their electricity. With that, the two require different things from their charge controllers. Wind charge controllers require different things compared to solar charge controllers. A solar charge controller mainly focuses on disconnecting the electricity from your battery after it is full. The controller joins the float mode, ensuring no more charge flows into the battery, and the latter can’t recharge the solar panel. If you start using the battery, the charge controller will terminate the float mode and recharge the battery again.
A wind charge controller protects both the battery and the wind turbine. It works by sensing the battery’s voltage. After the battery is full, the electricity will divert instead of powering off, which protects your battery and keeps control of the wind turbine. With that, it prevents the wind turbine from spinning and losing control.
How Can You Use a Charge Controller for Wind Turbines And Solar Panels?
The definition above explains why you can’t use a solar charge controller for a wind turbine. After all, the solar charge controller doesn’t account for the wind turbine like the wind charge controllers. So, is there a way to get a controller that works for both sides? It is possible, but you must invest in hybrid charge controllers. This controller is set to account for the needs of solar panels and wind turbines. It is a good and reliable investment, especially for people who use the two sources. Having a hybrid controller would mean you can use them interchangeably when one source is more powerful.
Is Wind Turbine Charge Controller the Same as Solar?
Wind and solar sources are popular sources of clean energy; by definition, charge controllers do the same job. Thus, the question of whether these controllers are similar is quite popular. Plus, the clean energy industry is relatively new, and there are many details people are learning about it. So, is a wind turbine charge controller the same as solar? No! Wind turbine charge controllers and solar charge controllers are different. The main difference is how they work and protect the batteries. Solar charge controllers disconnect the solar panel from your battery, popularly known as opening the circuit.
For wind charge controllers, the work on diverting the power when the battery is full to something popular as the dump load. The latter means that all the excess energy is dissipated into the air instead of letting it back into the wind turbines so that they can stay safe.
What Would Happen If You Used a Solar Charge Controller for A Wind Turbine?
The explanations above have focused on why you mustn’t use the solar charge controller for a wind turbine. Research shows that you mustn’t use solar controllers on wind turbines due to the difference in how they do their job. But what would happen if you ignored the warning and used solar charge controllers for wind turbines? What are the risks? The wind turbines need a charge controller with a dump load feature to keep off excess electricity from the turbines. The normal dump loads are devices like filament light bulbs, radiators and fans. If you use solar charge controllers with wind turbines, things will work the same after connecting. But, after a full battery and disconnection of the battery, there won’t be a dump load hence no resistance. With that, the turbine’s spin would be as fast as the wind drives, destroying the motor. But, if you use the solar charge controllers on the solar panels, things aren’t bad. In that case, solar charge controllers in wind turbines are bad and would damage the motor. So, please don’t use them.
Dump Loads for Solar, Wind and Microhydro
Dump loads a.k.a. diversion loads are are an important part of the off grid electric system.
Most wind and water turbine installations will require them and most solar installations will benefit from a dump load.
As we discussed in the dump load intro, a dump load is simply an electrical device (load) to send electricity to when the batteries are full or the extra power is not required.
Solar panels are unique in that they can be short circuited and disconnected without any issue. If your batteries are full and the solar modules are still making power, you can simply short circuit (not so common) or disconnect the solar modules from your batteries with a charge controller.
Wind turbines and water turbines generate electricity by rotating and need to have a load on them at all time. Without a load (such as a battery or a dump load) they will over-speed and possibly be damaged. Water turbines will generally turn 3 to 4 times as fast without a load while it can vary greatly with wind turbines as the wind speed changes.
The best dump loads are made from resistive loads such as air heaters or water heater elements. Resistive loads like previously mentioned are:
- Durable and long lasting
- Can accept AC or DC current
- Not polarity specific ( or – is irrelevant)
- Useful for heating water or space heating
Incandescent light bulbs are not suitable for dump/diversion loads. Although you may have seen them used in the past think about this. Your system is working smoothly and you have 10 x 100 watt light bulbs as a dump load. On a bright sunny day your system is dumping 1000 watts into your light bulbs and one of them burns out. Oh no, now your dump load is only 900 watts and the voltage starts to climb.
As the voltage starts to climb, the bulbs will actually consume the 1000 watts or more. When the bulb went out, the resistance dropped. Now the bulbs are operating above their rating and the second one burns out. Within minutes they will all burn out leaving your battery bank at the mercy of your system.
You can use an AC air heater or water heating element for your DC dump load but the element will not dump as much power as you might think. Click here to learn about using off the shelf AC elements as a dump load.
In the past the normal way of installing a dump load was to use a voltage controlled switch. This switch would turn the dump load on at a specific voltage (maybe 14.6 in a 12 volt system) and off at a specific voltage (maybe 14.0 in a 12 volt systems). The larger the dump load, the larger the difference between the on and off set points. This larger voltage difference was to prevent cycling of the dump circuit.
This on/off dump load system worked but it was not the best. Batteries work best (and last the longest) if the bulk/absorption voltage is steady instead of cycling up and down. When you purchased your batteries you were told to set the bulk/absorption voltage to 14.6 volts (just an example voltage), not somewhere between 14.0 and 14.6 volts.
DC current is very difficult to regulate. You can change the power out easily in AC current by using something as simple as a dimmer switch. DC is not that simple. It can only be on full or off full without expensive equipment.
Then how can we regulate (and hold the voltage steady) DC current for our dump load?
The answer is pulse width modulation or PWM. Don’t worry PWM is not really that complicated.
Let’s pretend we have a 200 watt air heater but we only want to dump watt 100 watts. All we need to do is make sure the 200 watt dump load is only connected 50% of the time. If we connected the load for one second and disconnected it for one second it would only use half of the 200 watts (100 watts). This is all PWM is. Pulse width modulation turns the load on and off many times per second. The more power that needs to be dumped, the more on cycles there are. The less power that needs to be dumped the less “on” cycles there. Of course these cycles are so fast you will be able to keep track or count.
Below you will see the most common way to install a PWM dump load.
The above system uses a PWM Morningstar Tristar TS60 charge controller/diversion controller. The TS60 monitors the battery voltage and only dumps what is necessary to hold the voltage steady at the bulk/absorption voltage. The TS60 either works as a 60 amp solar charge controller or a 60 amp diversion controller. It does not do both.
We do not show the solar panels, micro hydro turbine or wind turbine on purpose. You need to treat the dump load circuit as a completely independent system. Every item you add to your system should be treated independently. It can be very confusing if you start thinking about installing a wind turbine, a solar array and a water turbine on the same battery bank. But, if you treat each as an independent system you can just think about one step at a time.
The solar/wind/microhydro connect directly to the batteries and stay connected to the batteries. Every watt hour they produced goes to the batteries. Every extra watt hour produced goes to the batteries first and then out to the dump load.
If you are using a dump load you do not need a charge controller on the solar array. The only exception would be using an MPPT solar charge controller to get the most out of your panels. In that case you would set the MPPT controller to disconnect the solar array at a volt or two above what the dump load is set to turn on. You do not want the solar charge controller disconnecting the array as you want to use the excess power to operate your dump load. However if the dump load were to fail, the MPPT controller will disconnect at a volt or two higher than usual to protect your batteries from over voltage.
Another option for a dump load circuit is to use one of the programmable auxiliary outputs from either your inverter, charge controller or battery monitoring system. Here is an example below:
Most of the high end inverters and charge controllers made by Outback, Xantrex, Midnite Solar and Magnum Energy include an AUX OUTPUT relay driver. This relay driver is a programmable 12 volt circuit. You can tell it what voltage to dump and it sends a 12 volt output to operate a solid state relay which turns the dump load on and off.
You MUST use a solid state relay if you want to use the PWM dump mode. A standard relay will not handle the many on and off cycles per second. Make sure you take advantage of the PWM setting on your AUX OUTPUT relay driver. Some are labeled “dump load using SSR” and some are labeled “Pulse Width Modulated” in the menu of the charge controller.
There are many other ways to make your diversion load circuit. The one’s listed above are the common methods. If there is a method we have missed and you think we should add it, let us know in the comment section below.
You can make your dump load to divert AC current instead of DC and use a standard AC heating element. The only problem with dumping AC current is if there was an inverter failure. If the inverter were to shut down for any reason, your dump load would not work. It can done, but it is more risky than using DC.
Things to Remember:
- AC heating elements make good DC diversion loads.
- Polarity does not matter with any resistive load such as a heating element.
- Heating elements work the same with AC and DC current.
- Pulse width modulated dump loads always work better than simple on/off.
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Dump loads with MPP Solar
I’ve been wrapping my head around MPP Solar gear and found the community here seem to have a solid grasp on the subject.
I am considering using 2x MPP Solar 8000W units in parallel, to manage a 16kW array. Providing I don’t get a knock-off, these inverters tend to get pretty good reviews. Running without batteries is an impressive feature.
We’re at a 58° northerly latitude. 16kW will see us through the short winter days for our basic needs. but kicks out a huge amount in summer.
The plan is to dump summer excess into heating elements. a large hot water thermal store. and a Rayburn range I’m converting; it has a bank of heat storage bricks that can hit 700°C.
I had been looking at keeping everything DC, but using AC from the inverter makes a few things simpler. in terms of selecting standard elements and off the shelf thermostats.
My head gets fuzzy when trying to figure out what size elements to install. and how I might program an inverter to dump to these when the batteries are charged.
For instance, if I attempt to power 16kW of elements (3.3Ω at 230v). the theoretical maximum of the system. but the PV array is only kicking out 8kW. what happens? I imagine this all depends on the specific inverter. From what I see if the load is too big for the inverter. the inverter shuts down.
These are very cool and might be good to throw into the mix. MPPT controllers for connecting PV direct to heating elements: https://www.polskieprzetwornice.pl/skle3500w-pro
Wondering how best to achieve this goal and perhaps overwhelmed by the number of options I could take.
Just seen this in the manual. Could it be used to operate a relay (SSR or similar) when the battery is full. switching the PV to the MPPT heater controllers?
My system is a bit complicated, but really good IMHO:
On my grid tied system, I use a Raspberry Pi to log the battery charge status and grid feedback (ie. excess PV production). I have a script that monitor the data and decide when to switch On/Off various Wi-Fi Smartplugs (eg. https://www.amazon.com/TP-LINK-HS103P2-Required-Google-Assistant/dp/B07B8W2KHZ ).
One logic looks just at excess PV power available, and turns on an additional higher priority load, such as my PHEV chargers (ea 200V8A), pond ump, etc. When not enough power is available, one device at a time is turned off.
Another logic looks at the battery charge state, charge rate, and time of day, using is all to estimate whether the battery is likely to get full by the end of the day. If so, it turns on the low priority dump loads, such as my future hot water pre-heater.
PROs: Wi-Fi Smartplugs are easy to use all over the house and garden can start dumping before batteries are full multiple smaller loads to optimize usage of excess energy
CONs:. SmartPlugs can switch only ~10A, so need to use relays for bigger loads. A lot of thought and work to configure everything just right
The inverter cant do what you want. You need external logic. Element is on/off so you need to have many elements or never start it until you have full sun. Like ajw22 wrote.
Like for instance the sun outputs 5kw and you can then have 4kw of elements active. and so forth. Unless you bypass the inverter its AC that is going to be used and when having 8kw sun expect only to get 7kw out at MOST. Also note that running those inverters without battery will work like crap. They are not ment to run full load from sun to a device without battery. Sun fluctuates alot and it relies on using the battery/sun as primary to run the device to. So just a slight Cloud and its dead unless you have a battery. Many people have seen this so dont expect it to work off-grid without a battery with only sun.
To me it sounds like you want grid-tie system where you use some of the power to elements? If so look at my bypass video where i forward energy when i have excess around. Here is one of the videos:
I have later on even done even better ones just using esp8266 controlling it.
Though this require that you can connect it to grid and use it that way but to be honest if you dont plan to have a battery connected this is the only way to go if you want it to work as you think.
And if you ONLY plan to heat water the best option is solar-water heaters instead. Dont even consider going electric because its so inefficient comparing to area vs solar panels for electricity
Note going Solar. Electricity. heating water with elements is one of the worst ways doing and should only be done with the rest of the energy so dont design your system to have that as a main thing. If you need heat its better doing that with other sources and cheaper
Now im eager to hear your actual thougths. Why 16kWp? Why no Battery? Grid-Tie?
Is it you plan that you have max 16kW needed in the house? or other?
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