Solar energy is a prevalent green energy source nowadays. And it’s getting more popular day by day. So besides solar panels, solar batteries are also getting popular. But solar batteries are more popular among individual homeowners than grid users. As we all know, batteries are nothing but energy storage. Also, it’s true that we can’t harness solar energy production. It solely depends on the weather, geographical position, daylight, etc.
But our demand for energy doesn’t vary for one particular household or system. Batteries are essential to match this demand and supply of energy. They store the excess energy produced and ensure to keep the energy supply intact during short energy production. For stand-alone solar systems, batteries are a must-have thing. Batteries are directly connected to inverters. It changes the DC electricity into chemical energy and stores it within it. Now, how many batteries you need to run your system correctly depends mainly upon your energy needs, i.e., how large your system is.
The number of batteries you need can be determined by considering several factors. It depends on the energy production capacity of your system and how much energy you need to run your household properly. On the other hand, it also depends on the climate of the region you belong to. You also need to know how much the demand and supply can differ in the worst possible case. If you intend to save money, you’ll need enough batteries to cover your extra energy production (It’s somewhat like 2-3 batteries for a 10 kWh system). But if you intend to keep the supply intact when the grid is down, only one battery is enough to serve that purpose. For a completely stand-alone system, you’ll need much more than that. It generally takes 8-12 batteries for one 10 kWh system to run smoothly.
How to determine your energy consumption?
Let’s check first how to determine your total energy consumption. The standard unit of measuring energy is Joule. But when it comes to commercial purposes, we don’t talk about energy in Joule. We use KiloWatt-hour instead. That’s more convenient as the electrical appliances we use have a definite power consumption (in units of Watt or kiloWatt), and we can check their usage time in “hours.” We know that energy is nothing but power times and time of usage. So kilowatt-hour is simply kilowatt times hour (Joule is Watt times second).
Hence, the Energy consumption of one appliance in Watt-hours = Power rating in Wattage x Time in hours.
To convert it to a commercial unit of electricity which is kWh (1 unit of electricity consumption), you need to divide it by 1000.
Hence, Energy in kWh = (Power rating in wattage x time in hours)/ 1000.
Now, to estimate the total energy consumption of your whole household, you have to calculate the same thing for every electrical appliance and device you are using in a day and add them. And if you repeat the same for each day of a month, you can determine your whole month’s energy consumption. If you track this for several months, you can know about your household’s average monthly energy consumption. You can also calculate the average daily consumption. If the energy consumption is more or less the same each day, then you can multiply it by 30 (whatever the number of days in that month is) to get the monthly consumption.
Knowing the monthly consumption, you can estimate how large a solar panel you need to power up your household. But over the year, the weather varies. We all know that weather has a significant impact on the production of solar energy. So, it’s also essential to know the yearly energy demand of your household to run the system smoothly throughout the year. By estimating that, you can understand how much energy you need to store for the less-energy-production days of the year. That will tell you how many batteries you’ll need.
How much is solar power needed for a home?
A generalized estimation
In a general household, some equipment needs very low power to run while others have high power ratings. Televisions, fans, computers, chargers for chargeable electronic gadgets, etc., and even refrigerators are low-power equipment (less or equal to 0.3 kW). High power equipment includes a water heater (2-3 kW), electric iron (1.2-1.5 kW), air conditioner (2 kw+), microwave oven (~1 kW), mixer grinder (~1kW), etc.
The overall power consumption of lighting, fans, TV, computer, and chargers doesn’t exceed 1-1.5 kW. Instead of being a low power rating equipment, the refrigerator runs almost the whole day long with intermittent rest. So it consumes a large part of the energy demand of the house. Generally, AC, water heaters, etc., don’t run on solar power (I mean, people don’t prefer to connect them to solar panels, but it’s all about choice). But if you want to power them with solar panels, you need additional solar panels to cover the energy need of those high-rating gadgets.
How many solar panels do you need?
Once you have a clear idea of your household energy consumption, it’s time to know how much one solar panel can serve on average. Well, it depends pretty much on the country (the climate) you belong to. The average power generation varies from 80 kWh to 150 kWh in one month. If your solar panel receives almost similar sunlight throughout the year, then you can safely assume that it will be able to generate nearly 115 kWh on average in a month.
In countries having cold climates, the average monthly power generation can be assumed to be more or less 100 kWh. Still, when considering installing solar panels, you need to know how much power a solar panel can generate in your locality. You can google it, mentioning your country and the state you belong to.
Determining the perfect battery size for your system to meet your daily energy needs is essential. You will not get a continuous, steady power supply if you have undersized batteries as they cannot fulfill the demand. We’ll need other backups to get your home going.
Also, if you install too many batteries, i.e., large batteries, that’ll put unnecessary pressure on your pocket. The more the apparatus of the system, the more it gets complicated and hard to maintain. Especially for an off-grid system, the need for perfect battery storage is absolute.
So, you need a precise calculation of how many batteries we need.
How to calculate the number of batteries needed to cover your monthly consumption?
Solar sizing, better known as battery bank sizing, can calculate the number of batteries needed to cover your monthly energy consumption. For exact battery sizing for your system, you need to consider daily power usage and battery type in the first place.
• For on grid
For your on-grid solar system, installing battery storage is always worth it. If you have battery storage, your solar system can provide you with energy under any condition. To calculate the needed number of batteries to cover up your consumption, you have to determine your energy usage on a day-to-day basis. Keep reading to know how to size your solar in detail.
• For off-grid
If your solar system is off-grid or stand-alone, batteries become an integral part of your system. As for off-grid systems, we get the power from the battery only when panels are not active. So, batteries are essential. You need to know the perfect battery sizing for your solar to get an uninterrupted supply.
If you’re unfamiliar with the terms and workings of a solar system, you may get a headache doing the math to know the proper battery sizing! But wait! Don’t worry about that. There are some easy steps to deciding the best battery size for your solar system. Following those steps, you can determine your battery bank’s size without getting into trouble.
Determine your kW usage:
Obviously, when you intend to install battery storage, you first need to calculate your energy usage. For that, you need to determine the size of the solar array, i.e., the average monthly consumption in Kilowatt-hour (kW-h).
Maximum and minimum sun hours:
To size your battery bank properly, you have to do it according to the time when your panels get the least amount of sunlight; by doing that, you can have ample energy throughout the year.
Also, you must keep track of peak sun hours in your locality. The intensity, as well as the peak sunlight hours, varies mainly depending upon the locality. So, it is important to know how much time your panels are getting the most sunlight in a day.
Know your perfect battery bank size:
As soon as you know your daily kWh usage and your peak sunlight hours, you can calculate how many batteries you need. A standard battery is considered to have 600-800 amp hours of capacity. Battery banks are wired for either 12 volts, 24 volts, or 48 volts, depending on the size of the system.
In lead-acid batteries, 24kWh is obtained by 2,000 amp hours at 12 volts, 1,000 amp hours at 24 volts, and 500 amp hours at 48 volts.
For Lithium-ion batteries, 12.6 kWh is obtained by 1,050 amp hours at 12 volts, 525 amp hours at 24 volts, and 262.5 amp hours at 48 volts.
Now let’s clarify some frequently asked questions you might be thinking of!
We need batteries with different capacities for systems with different wattages. These questions surely show up in your mind. Like how do we need to size a battery bank for specific power output? Let’s check them out.
Number of batteries we need for a 10 KW solar system
A 10kW solar system is a huge energy source and probably the largest possible home solar system. We need a 600ah, 48V steady system in this case. For that, we’ll need 16 batteries of 12V. Each set of 4 batteries is connected in series, and we’ll get 4 such sets and need to connect them parallelly to get the desired 48 volts, 600ah.
Number of batteries we need for a 5 KW solar system
A typical 5kW system will need a 500 ampere-hour 12V battery. If you want to use two batteries, you can use 210 ah 12V batteries for your system, which can power your system for 40 mins on average. But to run the system for up to 1 hour, you’ll need 750ah 12V batteries.
For extended hours, a 2500ah battery can run a 5kWh system for up to 4 hours.
Number of batteries we need for a 4 KW solar system
For a 4kWh system probably, you’ll require it to work at 48 volts. 4 batteries of 12 volts connected in series can help you. If you somehow need 12V or 24V, you can lower the battery number, and that will be fine.
Number of batteries we need for a 2 KW solar system
At 12 Volts, 200ah energy of 2.4 kWh is generated by your battery if your system has a load of 1200W. This energy can power your appliances for an hour. If the inverter input of your system is 12 Volts, you will require two or more parallel connected batteries to cope with the loads to the electronic devices. If the batteries are working in 24 VDC, you’ll require two batteries of 12V with an input DC voltage of 12 Volts, or you can use two sets of a total of 4 batteries.
The simple formula for calculating the required no of batteries is Hours needed× wattage= battery amps.
Knowing the battery’s ampere capacity makes it easy to calculate the battery sizing.
Factors impacting the solar sizing
Well, a solar power system’s efficiency depends on some dynamic factors. So does the solar sizing or battery bank sizing. Let me elaborate to you:
1. Maximum and minimum system voltage:
Solar cells have a specific voltage range at which they operate. Generally, they need to be energized at 2V to 2.25V to be fully charged. The maximum and minimum system voltage vary for different batteries. For lead acid, it has a range of 96-128 Volts. So we must choose batteries that keep up the maximum and minimum system voltage.
2. Correction factor:
Battery capacity changes with temperature, and you have to keep this factor in mind while sizing your battery bank. Batteries also age with time, so we need to add a margin of 25% for that factor. So these are collectively known as correction factors. We need to consider regular derating factors while sizing our solar.
3. Duty cycle:
However, the abovementioned factors are filled with more electrical information than practical understanding. Some of the practical factors that anyone without having any scientific background can also understand are-
4. Seasonal factors:
Solar panels effectively vary with seasons noticeably. This is because the amount and intensity of solar irradiance change with seasons. So, at specific times of the year, we depend more on the battery than anytime else, and we need to size the batteries thinking about that time.
5. Ambient temperature:
The battery capacity and functionality drastically change with temperature. Some batteries are also not compatible with extreme temperatures (Nickel-cadmium batteries are primarily known for their tolerance). Most solar batteries work efficiently at a certain temperature.
Solar batteries come in different price ranges, and you can choose the one that suits you. Before battery bank sizing, you need to set up your budget and find the best suit for your needs.
Factors to keep in mind while considering the combination of Solar Batteries
A single battery can’t provide enough storage for most applications or a whole household PV system. So the user needs to connect multiple batteries. While connecting numerous batteries, we can connect them in series or parallel.
In a series connection, we need to connect the positive end of one battery to the negative end of the other and so on. In a parallel connection, we need to connect all the positive ends of the batteries together and all the negative ends of the batteries together. When we connect them in series, voltages are added up.
When we make parallel connections, amperes are added up. So before making the connection, we have to be sure about our requirements. One can also adjust their voltage and ampere requirements by connecting them accordingly. The users mostly demand parallel connection, as high voltage requirement isn’t very common. Rather high amperage is on demand.
Why is battery backup an essential factor when calculating the number of batteries?
In solar sizing, we should consider the factor of battery backup for future benefits. A solar system is never self-sustaining without a battery backup, as off-grid systems will die at night, and your home will be in the dark without a backup power supply.
Also, on on-grid or hybrid systems, the power grid can sometimes break down. At times of blackout, backup energy storage keeps your home going. So, battery backup is very important in all kinds of solar systems. We need to consider that our battery bank must be able to provide the required backup power at times of need. So, we choose batteries accordingly.
Things to consider for your solar battery system
There are different types of solar batteries to suit other purposes. There can be several potential decision-making criteria, and we’ll talk about some very common criteria to best suit them.
- There are batteries with high power ratings. You are looking for these if you want to use many appliances at once (that will draw more power).
- High instantaneous power rating batteries may fulfill your need to power one more energy-intensive appliance.
- If your requirement is extended, you should look for high-capacity batteries that will light up your house for a long time.
- A battery with higher round trip efficiency will help you to get the most out of every kilowatt hour.
- If you are looking for a battery that needs less space but still has excellent storage, there are lithium-ion nickel manganese cobalt (NMC) solar batteries for you.
- If the battery’s lifetime is your first priority, you should use lithium iron phosphate batteries.
- And there are many more, and you need to check your priority list before choosing the correct battery for your household.
How to choose the best battery on the market?
1. Power Rating
The power rating of a battery tells you how much energy it can provide at once. So from the battery’s power rating, you can know which appliances in your house can be powered up simultaneously by the battery. Solar batteries generally have two power ratings.
One is how much energy they can provide at once (as I said earlier), and the other is instantaneous power rating that tells you how much power it can provide in one short burst. Some appliances need a high burst of power to start but then run smoothly with lesser power. To connect that equipment, you must ensure your battery provides a high instantaneous power rating.
2. Battery Capacity
Battery capacity is the size of the battery, and it determines how much energy it can “store” within itself. The more storage, the longer you can access energy from the battery, and the capacity is expressed in kWh. Also, the fewer appliances are connected to it, the longer it can serve.
So if you need to run (or backup) only a few low-power rating appliances, smaller batteries can serve your purpose pretty well. When you’re checking on your battery storage requirement, you need to remember that how long it will perform depends on how much energy it has been fed and how much power is being drawn from it.
3. Round Trip Efficiency
Like every other system, batteries can not provide every unit of energy it has been fed. There is energy loss in the process of converting DC to AC electricity. So you’ll lose some kWhs you have put in the battery while you’re taking it out.
Round Trip efficiency tells you how much, and greater roundtrip efficiency implies lesser loss. That means losing energy is inevitable, but still, you can minimize the loss by choosing the right battery.
Battery lifetime depends on two factors, i.e., throughput and cycles. Throughput estimates how much energy the user can pass through the battery over its lifetime. Cycles are the expected number of times you can fully charge or discharge it.
If you divide the warranted number of cycles by the number of days in one year, then you can get the expected years of operation for the battery. For example, a 4000 cycles warranty implies 11 years of warranted operation.
5. Chemical Components
Batteries are made up of chemical components where the energy of sunlight is converted to chemical energy to store within the battery. There can be different components in different batteries. And some are just a bit safer than others, and some can have more energy density than others.
You can find different types of batteries in both lithium-ion and lead-acid components and both high and low-energy dense batteries with lithium-ion components. There are vanadium flow batteries too. The price of the battery also depends much on its chemistry of it.
List of some popular solar batteries
Goodwe Lynx U-Series
Goodwe has earned the reputation of one of the best Chinese inverter manufacturers over the last decade. This company also offers various lithium battery systems for residential and small commercial applications. They are available in high and low voltage and use Lithium Iron Phosphate cell chemistry in their batteries.
These batteries are most popular because of their reliability, long lifespan, great performance, and high safety (low risk of damage due to overheating). The Lynx U-Series batteries are particularly low voltage 5.4kWh battery scalable up to 32.4 kWh (using several batteries in parallel). 90% of its capacity is useable. It costs $3100 per battery and comes with a 10-year warranty and min 70% capacity after the warranty period.
BYD LVL & LVS
BYD is the largest Chinese manufacturer of rechargeable lithium batteries. Here BYD stands for Build Your Dreams. Their LVS series is a low voltage modular battery system. They also use Lithium Iron Phosphate cells to provide low voltage. It provides a nominal voltage of 51.2 V. They require a battery monitoring unit to manage and control the individual modules.
Each module is 4.0 kWh, and up to 6 modules can be installed in one tower. 100% of its capacity is usable. Round Trip efficiency is 95%. It’s scalable from 4kWh to 256kWh. It costs $3000 per battery box and comes with 10 years to 60% retained capacity.
The LVL series is just an updated version of the previous. They are very similar to the previous and have increased capacity to 15.4kWh along with some technical improvements. Each module of this series is 15.36kWh and 100% usable.
They are scalable up to 983kWh. They can be operated within a temperature range of -10 degrees C to 50 degrees C. It costs $10500 per battery box and comes with 10 years to 60% retained capacity.
This battery carries the advanced signature features of Huawei and module-level optimization. Huawei has over 10 years of experience in this field. An energy optimizer carries out the charge and discharge of each module of a 5kWh LUNA2000 battery. The Huawei LUNA2000 battery comes with a claim of generating 10% more usable energy and has high voltage lithium (LEP) modules with a 100% depth of discharge (DoD).
LEP or Lithium iron phosphate batteries are famous for their stable chemical substances and are regarded as the safest battery. You will be amazed to know that these batteries have AI-powered internal cell short circuit diagnosis facilities which can avoid catching fire in any situation.
LUNA2000 also can detect overheating or thermal runaway by cell level temperature control. A 5kWh LUNA2000 is the minimum size of this kind of battery, and it has an output power of 2.5kWh. A 5kWh battery is enough for most households.
Also, this battery seems to be the lowest battery cost per kWh basis. A 10kWh LUNA2000 battery along with two 5kWh batteries and a power module costs around $5,400 without installation.
The second generation Tesla Powerwall 2 was released in 2016. In May 2021, Tesla Powerwall+ (plus) was launched with the same Powerwall 2 battery system with an integrated solar inverter. The Powerwall+ is a complete all-in-one solar storage system.
The Tesla Powerwall 2 comes with a 13.5kWh usable storage capacity and a continuous power rating of 5kW.
This battery has a 5.8 kW on-grid power rating and a 7kW off-grid power rating with advanced thermal management. But Tesla Powerwall 2 is mainly available in the USA with a price tag of $11,000.
PowerPlus Life Premium
This battery is considered the best battery for an off-grid or stand-alone battery system. These are self-management Lithium batteries of high quality.
They have great compatibility with off-grid inverters. These flexible, modular batteries can be transformed into large-capacity storage. Generally, this battery has a 100% usable capacity with 80% DoD (Depth of Discharge). A 3.5kW PowerPlus Life Premium battery will cost you about $4,000 on an average of $1000 per kWh. Also, the company provides you a warranty of 10 years to 70% minimum retained capacity.
Redback Tech Smart Hybrid
The manufacturer is an Australia-based company who has collaborated with Chinese inverter manufacturer Goodwe to deliver a smart, integrated, featureful energy storage system for your house and work. Redback Tech Smart Hybrid battery comes with a ten years warranty and 60% minimum retained capacity. It has a cycle life of approximately 3500, and this battery comes with a price tag of nearly $10,000.
The best feature of Redback Tech Smart Hybrid is its pass-through power ability, which allows it to handle high loads in all kinds of solar systems, off-grid or on-grid.