Choosing the Right Solar Charge Controller/Regulator
A solar charge controller (frequently called a regulator) is similar to a regular battery charger, i.e. it regulates the current flowing from the solar panel into the battery bank to avoid overcharging the batteries. (If you don’t need to understand the why’s, scroll to the end for a simple flow chart). As with a regular quality battery charger, various battery types are accommodated, the absorption voltage, float voltage can be selectable, and sometimes the time periods and/or the tail current are also selectable. They are especially suited for lithium-iron-phosphate batteries as once fully charged the controller then stays at the set float or holding voltage of around 13.6V (3.4V per cell) for the remainder of the day.
The most common charge profile is the same basic sequence used on a quality mains charger, i.e. bulk mode absorption mode float mode. Entry into bulk charge mode occurs at:
- sunrise in the morning
- if the battery voltage drops below a defined voltage for more than a set time period, e.g. 5 seconds (re-entry)
This re-entry into bulk mode works well with lead-acid batteries as the voltage drop and droop is worse than it is for lithium-based batteries which maintain a higher more stable voltage throughout the majority of the discharge cycle.
Lithium batteries
Lithium batteries (LiFePO4) do not benefit from re-entry into a bulk mode during the day as the internal impedance of the lithium batteries increases at high (and low) states of charge as indicated by the orange vertical lines in the chart below and it is only necessary to occasionally balance the cells which can only be done around the absorption voltage. A related reason is to avoid the Rapid and large variation in voltage that will occur in these regions as large loads are switched on and off.
Lithium batteries do not have a defined “float voltage”, and therefore the “float voltage” of the controller should be set to be at or just below the “charge knee voltage” (as indicated in the chart below) of the LiFePO4 charge profile, i.e. 3.4V per cell or 13.6V for a 12V battery. The controller should hold this voltage for the remainder of the day after bulk charging the battery.
The Difference Between PWM and MPPT Solar Charge Controllers
The crux of the difference is:
- With a PWM controller, the current is drawn out of the panel at just above the battery voltage, whereas
- With an MPPT solar charge controller the current is drawn out of the panel at the panel “maximum power voltage” (think of an MPPT controller as being a “Smart DC-DC converter”)
You often see slogans such as “you will get 20% or more energy harvesting from an MPPT controller”. This extra actually varies significantly and the following is a comparison assuming the panel is in full sun and the controller is in bulk charge mode. Ignoring voltage drops and using a simple panel and simple math as an example:
Battery voltage = 13V (battery voltage can vary between say 10.8V fully discharged and 14.4V during absorption charge mode). At 13V the panel amps will be slightly higher than the maximum power amps, say 5.2A
With a PWM controller, the power drawn from the panel is 5.2A 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.
With an MPPT controller the power from the panel is 5.0A 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.
In summary, there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.
PWM:
A PWM (pulse width modulation) controller can be thought of as an (electronic) switch between the solar panels and the battery:
- The switch is ON when the charger mode is in bulk charge mode
- The switch is “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the absorption voltage
- The switch is OFF at the end of absorption while the battery voltage drops to the float voltage
- The switch is once again “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the float voltage
Note that when the switch is OFF the panel voltage will be at the open-circuit voltage (Voc) and when the switch is ON the panel voltage will be at the battery voltage voltage drops between the panel and the controller.
The best panel match for a PWM controller:
The best panel match for a PWM controller is a panel with a voltage that is just sufficiently above that required for charging the battery and taking temperature into account, typically, a panel with a Vmp (maximum power voltage) of around 18V to charge a 12V battery. These are frequently referred to as a 12V panel even though they have a Vmp of around 18V.
MPPT:
The MPPT controller could be considered to be a “Smart DC-DC converter”, i.e. it drops the panel voltage (hence “house panels” could be used) down to the voltage required to charge the battery. The current is increased in the same ratio as the voltage is dropped (ignoring heating losses in the electronics), just like a conventional step-down DC-DC converter.
The “Smart” element in the DC-DC converter is the monitoring of the maximum power point of the panel which will vary during the day with the sun strength and angle, panel temperature, shading, and panel(s) health. The “smarts” then adjust the input voltage of the DC-DC converter – in “engineering speak” it provides a matched load to the panel.
The best panel match for an MPPT controller:
- The panel open circuit voltage (Voc) must be under the permitted voltage.
- The VOC must be above the “start voltage” for the controller to “kick in”
- The maximum panel short circuit current (Isc) must be within the range specified
- The maximum array wattage. some controllers allow this to be “over-sized”, e.g the Redarc Manager 30 is permitted to have up to 520W attached
Choosing the Right Solar Controller/Regulator
The PWM is a Good Low-Cost Option:
f or solar panels with a maximum power voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc).
When the solar array voltage is substantially higher than the battery voltage e.g. using house panels, for charging 12V batteries
An MPPT controller will yield higher returns compared with a PWM controller as the panel voltage increases. I.e. a 160W panel using 36 conventional monocrystalline cells with a maximum power amp of 8.4A will provide around 8.6A at 12V; while the 180W panel having 4 more cells will provide the same amperage but 4 additional cells increases the panel voltage by 2V. A PWM controller will not harvest any additional energy, but an MPPT controller will harvest an additional 11.1% (4 / 36) from the 180W panel.
For the same principle, all panels using SunPower cells with more than 32 cells require an MPPT charge controller otherwise a PWM controller will harvest the same energy from 36, 40, 44 cell panels as it does from a 32 cell panel.
Solar Charge Controller Features and Options
Boost MPPT Controllers
“Boost” MPPT charge controllers allow batteries to be charged that has a higher voltage than the panel.
Combined MPPT and DC-DC Chargers
The MPPT function is a natural adjunct to the DC-DC charger function and there are several quality brands that provide this with more under development. A single unit can be used by itself, as it automatically switches between alternator charging and solar charging. For larger systems, our favoured arrangement is to use a separate MPPT controller for the fixed roof-mounted panels and use the combined MPPT/DC-DC with portable panels. In this case, an Anderson connector is placed on the exterior of an RV which is then wired to the solar input of the MPPT/DC-DC unit.
Note that the battery capacity must be sufficient so that the combined charging current from simultaneous charging from the alternator and the roof solar panels does not exceed the manufacturer’s recommended maximum charging current.
Cheaper Options
Cheap controllers may be marked as an MPPT but testing has shown that some are in fact PWM controllers. Cheap controllers may not have the over-voltage battery protection which could result in the battery being overcharged with potential damage to the battery; caution is recommended. Normally, due to the increased circuitry, MPPT solar charge controllers will be physically larger than PWM solar charge controllers.
Multiple Solar Chargers
Properly wired, it is possible to add multiple solar chargers (any combination of type and rating) to charge a battery. Proper wiring means that each solar charger is wired separately and directly to the battery terminals. This ideal case means that each controller will “see” the battery voltage and is unaffected by the current flow coming from other charge controllers. This situation is no different from charging a battery from the grid/generator at the same time as charging from solar. With modern controllers, the current will not flow backwards from the battery to the controller (excepting a very small quiescent current).
DIY Solar Battery Charger for 18650 Li-Ion Batteries
In this DIY project, I will show you how to design and build a simple but effective Solar Battery Charger for 18650 batteries. Using this project, you can charge two 18650 Li-Ion batteries directly from solar without any wall adapter.
Introduction
The need for sustainable living has led to the increased usage of renewable energy. Keeping aside the efficiency numbers, Solar Energy is one of the convenient alternatives (when compared to other renewable energy sources such as wind) to the grid supply.
Now-a-days, large Solar Farms are being setup in acres of barren lands in many countries. But small-scale solar plants like on independent building rooftops and near small home communities are also becoming popular.
The setup of a Solar Power Plant. whether large or small, is fairly simple. Setup an array of Solar Panels on rooftop, connect them to a Solar Charge Controller and charge the batteries. From the batteries, you can run any mains appliances using appropriate inverters.
As a beginner’s solar project, I have designed a very simple Solar Battery Charger to charge 18650 Li-Ion batteries. Using these batteries, you can charge your mobile phones, tablets or use the batteries in LED Lamps, emergency lights etc.
Circuit Diagram
Let us dive into the project by taking a look at the circuit diagram or rather the connection diagram of this DIY Solar Battery Charger for 18650. All the components, which I will list out in the next section, are very easy to acquire and are easily available in local electronics stores (you can get them online as well).
Components Required
- 6V – 100mA Mini Solar Panel
- 2 x 18650 Li-Ion Batteries
- 18650 Battery Holders
- TP4056 Li-Ion Battery Charger Module with protection
- 1V to 5V Input to 5V Output Step-up Converter (Boost Converter)
- 1N4007 PN Junction Diode
- Switch (Push to ON and Push to OFF)
- Connecting Wires
How to Setup DIY Solar Battery Charger for 18650?
First, I will explain the connections and the step by step setup of the Solar Battery Charger for 18650. Then we will understand the principle of operation.
Coming to the connections, the Mini Solar Panel has two wires coming from it. One is Red, which is the positive wire and the other is black (or brown in my case), which is the negative wire.
Now, take the TP4056 Li-Ion Battery Charger Module with battery protection. At the input side, it has two connections named IN and IN-. Take the Red wire from the solar panel and connect it to the anode of 1N4007 Diode.
Connect the cathode of the diode to the IN terminal of the TP4056 Module and directly connect the black wire of the solar panel to the IN- terminal of TP4056. This completes the input section.
On the output side of the TP4056, there are four connections named B, B-, OUT and OUT-. Take two 18650 Li-Ion batteries with holders and connect them in parallel i.e. both positive terminals of the batteries are common and both negative terminals are common.
Connect the common positive terminal of the batteries to B of TP4056. You may have to solder the wires on to the Li-Ion Charger board. Similarly, connect the common negative terminal of the batteries to the B- of TP4056.
The final step of the constriction is to connect the output of the TP4056 to the 5V Boost Converter Module. The Step-up converter module has two input terminals named IN and IN-. Connect the OUT of TP4056 to IN of Boost Converter module and OUT- to IN- respectively.
You can use a switch between TP4056 and Boost converter so that you can turn ON or OFF the output. I have glued the entire setup on to the battery holder case with a switch in the center and the USB port on the edge.
Principle of DIY Solar Battery Charger for 18650
The solar panel used in this project is small 6V panel with a small output of 100mA. The output of this solar panel will not be a constant 6V but it might fluctuate between 5V and 7.5V (as per its data sheet).
This voltage is given as input to the TP4056 Li-Ion Battery Charging Module, which in this scenario, acts as a Solar Charge Controller. The input to TP4056 can be in the range of 4V to 8V (which is the range of the output of the solar panel).
TP4056 then charges the battery from the solar power itself. If you only want to charge the batteries, then this is sufficient. But since our project also needs to charge a Mobile Phone, we need to have a 5V output and the output of the 18650 Li-Ion batteries is only 3.7V.
Here comes the Boost Converter to the rescue. The boost converter I have used is a 1V-5V input to 5V output step-up converter i.e. it takes an input anywhere between 1V and 5V and produces a constant 5V output. Also, this boost converter can support a current up to 1A, so the charging of mobile phone will not be that slow.
I have used the project to charge my mobile phone as well as to power up an Arduino board.
Everything You Need To Know About Solar Batteries
Samantha covers all topics home-related including home improvement and repair. She previously edited home repair and design content at The Spruce and HomeAdvisor. She also has hosted videos on DIY home tips and solutions and launched multiple home improvement review boards staffed with licensed pros.
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Table of Contents
Whether you’re new to the world of solar power and searching for the best system for your building or have had your home bedecked with solar panels for years, a solar battery can make a tremendous difference in the efficiency and versatility of your solar setup. Solar batteries store the excess energy generated by your solar panels, which can then be used to power your home during gloomy, rainy days, or after the sun sets.
Our guide to solar batteries can help answer your questions about solar batteries and assist in selecting the best option to meet the needs of your facility or household. But note not all solar installation or sales companies offer solar panels.
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What Are Solar Batteries, and How Do They Work?
Without somewhere to send energy produced by your solar panels, solar would be fairly inefficient—your appliances would only work when the sun is shining and your panels are working. If you don’t use the energy, it’d be wasted—and you wouldn’t be able to use it at night. Enter solar batteries, which store energy generated by your panels for use when you actually need it. Solar batteries are an alternative (or addition to) feeding energy back to the grid and can help you make your house or facility somewhat immune from power outages and even help take it off-grid entirely.
Solar Battery Types
The four main types of batteries used in the world of solar power are lead-acid, lithium ion, nickel cadmium and flow batteries.
Lead-Acid
Lead-acid batteries have been in use for decades and are one of the most common types of battery used in automotive and industrial applications. They have a low energy density (meaning they cannot hold much energy per kg of weight), but remain both cost-effective and reliable and thus have become a common choice for use in a home solar setup.
Lead-acid batteries come in both flooded and sealed varieties and can be classified as either shallow cycle or deep cycle depending on the intended function and safe depth of discharge (DOD). Recent technological advancements have improved the lifespan of these batteries and lead-acid continues to be a viable option for many homeowners.
Lithium-Ion
The technology behind lithium-ion batteries is much newer than that of other battery types. Lithium-ion batteries have a high energy density and offer a smaller, lighter and more efficient option. They allow the user to access more of the energy stored within the battery before needing to be recharged, making them great for use in laptops and phones—and in your home.
The major drawback of lithium-ion batteries is the significantly higher cost to the consumer. If improperly installed lithium-ion batteries also have the potential to catch fire due to an effect called thermal runaway.
Nickel-Cadmium
Nickel-cadmium batteries are rarely used in residential settings and are most popular in airline and industrial applications due to their high durability and unique ability to function at extreme temperatures. Nickel-cadmium batteries also require relatively low amounts of maintenance when compared to other battery types.
Unfortunately, cadmium is a highly toxic element that, if not disposed of properly, can have a significant negative impact on our environment.
Flow
Flow batteries depend on chemical reactions. Energy is reproduced by liquid-containing electrolytes flowing between two chambers within the battery. Though flow batteries offer high efficiency, with a depth of discharge of 100%, they have a low energy density, meaning the tanks containing the electrolyte liquid must be quite large in order to store a significant amount of energy. This size makes them a costly and impractical option for most household use. Flow batteries are much better suited to larger spaces and applications.
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Solar Battery Costs
The cost of a solar battery or battery system will depend on the type and size of the battery chosen. Generally, lead-acid batteries will incur a lower up-front cost to the consumer than lithium-ion batteries, but depending on how the batteries are used, investing in a lithium-ion battery could save money long-term.
A single lead-acid battery can cost between 200 and 800 or even more depending on the size/power of the battery. Multiple lead-acid batteries may be needed to keep a household powered completely. The average cost of a residential lithium-ion solar battery system with installation falls in the 7,000 to 14,000 range.
The of nickel-cadmium and flow batteries vary widely and depend on the size and scale of the installation. These batteries are not commonly used in residential dwellings and are better suited to commercial/industrial settings due to cost, durability, size, stability in extreme temperatures and requirements for disposal upon replacement.
Things to Look for When You’re Picking a Solar Battery
Several factors contribute to the performance of your solar battery. Before choosing your battery system, consider the following:
Type or Material
Among the types of batteries to choose from, each type offers a different major advantage. Weighing these pros and cons can help you decide which style is right for you. If you’re looking for something compact and longer-lasting, lithium-ion may be right for you. Lead-acid might be better for those conscious of more immediate budget constraints.
Battery Life
The “lifespan” of any battery is multifaceted; the age, type, quality and depth of discharge of the battery all contribute to its longevity. Referring to the manufacturer’s specifications for a battery can help you determine how long it’s likely to last.
In general, lead-acid batteries can last anywhere from one to 10 years depending on how they’re used. Lithium-ion batteries typically last seven to 15 years.
Depth of Discharge
Depth of discharge refers to how much of a battery’s stored energy is used before the battery is recharged. Typically, the deeper the battery is discharged, the shorter its lifespan will be. Batteries often come with both a cycle life estimate (indicating how many cycles it will last given a particular depth of discharge) and a recommended maximum depth of discharge.
Both lead-acid batteries and lithium-ion batteries will decay more quickly when deeply discharged, but lead-acid batteries tend to offer a lower tolerance for deep discharges than lithium-ion batteries, significantly reducing life expectancy if deeply discharged on a regular basis.
Efficiency
Solar systems and batteries are not 100% efficient when transferring and storing the collected solar energy from panels to batteries, as some amount of energy is lost in the process. Depending on the amount of energy you’re able to generate from your panels and how your system is configured, it may be worth investing in a more expensive, more efficient battery. This can help save money long-term. Your solar panel efficiency and battery capacities will be calculated and your system explained to you by any competent sales and installation team, but our solar resources can help you understand exactly how your system works, too.
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How to Select the Best Solar Battery for Your Needs
When selecting a solar battery for your setup, you may want to consider how you’ll use the batteries and what your need actually is, how safe each system might be and the overall cost of the system.
Use and Need Considerations
Do you need the battery or battery bank to provide only short bursts of emergency power when the power goes out, or do you need it to maintain the combined electrical needs of your entire household/facility for extended periods of time? How much sun exposure do you expect to have on a daily basis? Consider the recommended depth of discharge for your batteries and how this will affect their lifespans.
Safety Considerations
How does the battery need to be stored to maintain it safely? What kind of maintenance does the battery require? What is the safe temperature range for your battery and is the storage location going to maintain that temperature? When the time comes, how do you plan to dispose of/recycle the battery?
Cost
Does it make more sense for you to spend less up front for lead-acid batteries, or invest in the efficiency and longevity of lithium-ion batteries? How many batteries will you need to purchase to provide for your needs? What’s the expected lifespan of the battery and will you be prepared to replace it when it dies?
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Benefits of Using A Solar Battery
The best thing about solar battery storage is that it lets you store the excess energy you produce. One of the most important benefits of solar batteries is that they don’t just provide backup power; they also produce energy after hours when you don’t want to send excess solar electricity back to your local utility company.
Energy Independence
A solar battery is an essential component of a home reliant entirely on solar power. The battery can store power during the day, so it’s available at night to keep the lights on for an entire evening. A solar battery system can also turn your off-grid solar system into an emergency backup during power outages.
Electric Bill Savings
Solar power batteries can help consumers power their homes by harnessing the sun. This will allow them to purchase less from the grid and save money on their electric bill.
Reduce Carbon Footprint
Solar energy can minimize our use of fossil fuels and protect our environment. Solar batteries generate solar energy when exposed to sunlight, which can then be used to power devices or recharge a laptop or phone battery.
Are Solar Batteries Worth It?
Solar batteries represent a significant upfront financial investment, but can ultimately help save you money on energy costs after sundown or during an emergency. If you’re living off-grid, they may be critical components of your energy system.
Solar batteries provide your home with clean, fairly green, renewable energy that would otherwise need to come from an outside source. Some areas also provide incentives or rebates to help mitigate the costs of adding a solar battery to your system and it’s possible to receive up to 30% off of your battery installation if you qualify for the federal solar tax credit.
Ultimately, only you can decide if the investment in a solar battery and its rewards is worth the cost and upkeep requirements.
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Frequently Asked Questions (FAQs)
How long do solar batteries last?
Solar batteries last for about 5 to 15 years. The life of the solar battery depends on its type, how well it’s maintained and how frequently it gets used.
What are the disadvantages of using solar batteries?
Cost: Solar batteries can cost anywhere from several hundred to several thousand dollars to purchase and install. Batteries also offer a limited lifespan and will eventually need to be replaced.
Maintenance: Different batteries maintain different maintenance requirements in order to operate safely. Proper maintenance can be both costly and time-consuming.
Space: Batteries take up space and, depending on the size of your system as well as the type of battery you choose, the amount of space needed to store and adequately ventilate your batteries may be significant.
Safety: There are inherent risks associated with operating any batteries (overheating, leaking, etc.), especially if products are not installed and maintained properly.
Complexity: Adding batteries to your system will create additional complexity with regard to wiring and setup. Depending on your level of electrical expertise, you may wish to consider consulting or hiring a professional when installing solar batteries.
How many batteries does it take to power a house with solar?
The quantity of batteries you will need depends upon the type of battery, the storage capacity of the battery, the size of your solar system, the energy requirements of the circuits and appliances you wish to power and the amount of time you wish to provide power to your circuits/appliances.
The best way to estimate your energy needs is to figure out the kilowatt-hours you would require in the event of a power outage and compare that to the capabilities and specifications of the batteries and systems you consider.
How long do solar batteries hold charge?
The length of time your solar battery will hold a charge depends on the battery and the amount of energy being stored. A standard solar battery will store energy for one to five days.
What solar batteries are the best?
The best type of battery for one system may not be the best for another. For a home solar system, an adequately sized battery bank of sealed lead-acid batteries or a lithium-ion battery system will likely fit the bill, depending on the intended use (daily, short/long duration, etc.)
Some common brands for solar batteries include: Tesla, Panasonic, LG Chem, Electriq Power, Enphase, Generac, Sunpower, Solar Edge, SunVault and Renogy.
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How Does A Solar Battery Work? | Energy Storage Explained
A solar battery can be an important addition to your solar power system. It helps you store excess electricity that you can use when your solar panels aren’t generating enough energy, and gives you more options for how to power your home.
If you’re looking for the answer to, “How do solar batteries work?”, this article will explain what a solar battery is, solar battery science, how solar batteries work with a solar power system, and the overall benefits of using solar battery storage.
What is a Solar Battery?
Let’s start with a simple answer to the question, “What is a solar battery?”:
A solar battery is a device that you can add to your solar power system to store the excess electricity generated by your solar panels.
You can then use that stored energy to power your home at times when your solar panels don’t generate enough electricity, including nights, cloudy days, and during power outages.
The point of a solar battery is to help you use more of the solar energy you’re creating. If you don’t have battery storage, any excess electricity from solar power goes to the grid, which means you’re generating power and providing it to other people without taking full advantage of the electricity your panels create first.
For more information, check out our Solar Battery Guide: Benefits, Features, and Cost
The Science of Solar Batteries
Lithium-ion batteries are the most popular form of solar batteries currently on the market. This is the same technology used for smartphones and other high-tech batteries.
Lithium-ion batteries work through a chemical reaction that stores chemical energy before converting it to electrical energy. The reaction occurs when lithium ions release free electrons, and those electrons flow from the negatively-charged anode to the positively-charged cathode.
This movement is encouraged and enhanced by lithium-salt electrolyte, a liquid inside the battery that balances the reaction by providing the necessary positive ions. This flow of free electrons creates the current necessary for people to use electricity.
When you draw electricity from the battery, the lithium ions flow back across the electrolyte to the positive electrode. At the same time, electrons move from the negative electrode to the positive electrode via the outer circuit, powering the plugged-in device.
Home solar power storage batteries combine multiple ion battery cells with sophisticated electronics that regulate the performance and safety of the whole solar battery system. Thus, solar batteries function as rechargeable batteries that use the power of the sun as the initial input that kickstarts the whole process of creating an electrical current.
Comparing Battery Storage Technologies
When it comes to solar battery types, there are two common options: lithium-ion and lead-acid. Solar panel companies prefer lithium-ion batteries because they can store more energy, hold that energy longer than other batteries, and have a higher Depth of Discharge.
Also known as DoD, Depth of Discharge is the percentage to which a battery can be used, related to its total capacity. For example, if a battery has a DoD of 95%, it can safely use up to 95% of the battery’s capacity before it needs to be recharged.
Lithium-Ion Battery
As mentioned earlier, battery manufacturers prefer lithium-ion battery technology for its higher DoD, reliable lifespan, ability to hold more energy for longer, and a more compact size. However, because of these numerous benefits, lithium-ion batteries are also more expensive compared to lead-acid batteries.
Lead-Acid Battery
Lead-acid batteries (the same technology as most car batteries) have been around for years, and have been used widely as in-home energy storage systems for off-grid power options. While they are still on the market at.friendly prices, their popularity is fading due to low DoD and shorter lifespan.
AC Coupled Storage vs. DC Coupled Storage
Coupling refers to how your solar panels are wired to your battery storage system, and the options are either direct current (DC) coupling or alternating current (AC) coupling. The main difference between the two lies in the path taken by the electricity that the solar panels create.
Solar cells create DC electricity, and that DC electricity must be converted into AC electricity before it can be used by your home. However, solar batteries can only store DC electricity, so there are different ways of connecting a solar battery into your solar power system.
DC Coupled Storage
With DC coupling, the DC electricity created by solar panels flows through a charge controller and then directly into the solar battery. There is no current change before storage, and conversion from DC to AC only occurs when the battery sends electricity to your home, or back out into the grid.
A DC-coupled storage battery is more efficient, because the electricity only needs to change from DC to AC once. However, DC-coupled storage typically requires a more complex installation, which can increase the initial cost and lengthen the overall installation timeline.
AC Coupled Storage
With AC coupling, DC electricity generated by your solar panels goes through an inverter first to be converted into AC electricity for everyday use by appliances in your home. That AC current can also be sent to a separate inverter to be converted back to DC current for storage in the solar battery. When it’s time to use the stored energy, the electricity flows out of the battery and back into an inverter to be converted back into AC electricity for your home.
With AC-coupled storage, electricity is inverted three separate times: once when going from your solar panels into the house, another when going from the home into battery storage, and a third time when going from battery storage back into the house. Each inversion does result in some efficiency losses, so AC coupled storage is slightly less efficient than a DC coupled system.
Unlike DC-coupled storage that only stores energy from solar panels, one of the big advantages of AC coupled storage is that it can store energy from both solar panels and the grid. This means that even if your solar panels aren’t generating enough electricity to fully charge your battery, you can still fill the battery with electricity from the grid to provide you with backup power, or to take advantage of electricity rate arbitrage.
It’s also easier to upgrade your existing solar power system with AC-coupled battery storage, because it can just be added on top of an existing system design, instead of needing to be integrated into it. This makes AC coupled battery storage a more popular option for retrofit installations.
How Solar Batteries Work with a Solar Power System
This entire process starts with the solar panels on the roof generating power. Here is a step-by-step breakdown of what happens with a DC-coupled system:
- Sunlight hits the solar panels and the energy is converted to DC electricity.
- The electricity enters the battery and is stored as DC electricity.
- The DC electricity then leaves the battery and enters an inverter to be converted into AC electricity the home can use.
The process is slightly different with an AC-coupled system.
- Sunlight hits the solar panels and the energy is converted to DC electricity.
- The electricity enters the inverter to be converted into AC electricity the home can use.
- Excess electricity then flows through another inverter to change back into DC electricity that can be stored for later.
- If the house needs to use the energy stored in the battery, that electricity must flow through the inverter again to become AC electricity.
How Solar Batteries Work with a Hybrid Inverter
If you have a hybrid inverter, a single device can convert DC electricity into AC electricity and can also convert AC electricity into DC electricity. As a result, you don’t need two inverters in your photovoltaic (PV) system: one to convert electricity from your solar panels (solar inverter) and another to convert electricity from the solar battery (battery inverter).
Also known as a battery-based inverter or hybrid grid-tied inverter, the hybrid inverter combines a battery inverter and solar inverter into a single piece of equipment. It eliminates the need to have two separate inverters in the same setup by functioning as an inverter for both the electricity from your solar battery and the electricity from your solar panels.
Hybrid inverters are growing in popularity because they work with and without battery storage. You can install a hybrid inverter into your battery-less solar power system during the initial installation, giving you the option of adding solar energy storage down the line.
Benefits of Solar Battery Storage
Adding battery backup for solar panels is a great way of ensuring you get the most out of your solar power system. Here are some of the main benefits of a home solar battery storage system:
Stores Excess Electricity Generation
Your solar panel system can often produce more power than you need, especially on sunny days when no one is at home. If you don’t have solar energy battery storage, the extra energy will be sent to the grid. If you participate in a net metering program, you can earn credit for that extra generation, but it’s usually not a 1:1 ratio for the electricity you generate.
With battery storage, the extra electricity charges up your battery for later use, instead of going to the grid. You can use the stored energy during times of lower generation, which reduces your reliance upon the grid for electricity.
Provides Relief from Power Outages
Since your batteries can store the excess energy created by your solar panels, your home will have electricity available during power outages and other times when the grid goes down.
Reduces Your Carbon Footprint
With solar panel battery storage, you can go green by making the most of the clean energy produced by your solar panel system. If that energy isn’t stored, you will rely on the grid when your solar panels don’t generate enough for your needs. However, most grid electricity is produced using fossil fuels, so you will likely be running on dirty energy when drawing from the grid.
Provides Electricity Even After the Sun Goes Down
When the sun goes down and solar panels aren’t generating electricity, the grid steps in to provide much-needed power if you don’t have any battery storage. With a solar battery, you’ll use more of your own solar electricity at night, giving you more energy independence and helping you keep your electric bill low.
A Quiet Solution to Backup Power Needs
A solar power battery is a 100% noiseless backup power storage option. You get to benefit from maintenance free clean energy, and don’t have to deal with the noise that comes from a gas-powered backup generator.
Key Takeaways
Understanding how a solar battery works is important if you’re thinking about adding solar panel energy storage to your solar power system. Because it operates like a large rechargeable battery for your home, you can take advantage of any excess solar energy your solar panels create, giving you more control over when and how you use solar energy.
Lithium-ion batteries are the most popular type of solar battery, and work through a chemical reaction that stores energy, and then releases it as electrical energy for use in your home. Whether you choose a DC-coupled, AC-coupled, or hybrid system, you may be able to increase the return on investment of your solar power system and reduce your reliance on the grid.
Having the right system design is vital to making the most of your solar panels. At Palmetto, we have the expertise and experience to guide you on your clean energy journey. From solar power installation and service to system maintenance and monitoring, our solar professionals are here to help you take advantage of clean energy.