Thinking about installing batteries to go with your solar panels? No matter if it’s an off-grid mountain cabin or a battery back-up for your grid-connected homes, the basic process for planning designing your own DIY battery bank is fairly straightforward, but can be a bit confusing your first time around.
Below are the basic steps to planning and designing your own DIY battery bank to complement your solar installation. To make the planning process a bit easier to understand, we’ve included a running example throughout the article. Simply find the italics throughout each section to follow-along!
Use the information below as a starting point, but when the time comes to really start planning your DIY battery bank, be sure to check out a few books on the subject at your local library, browse relevant online articles and videos, and join a couple online forums for guidance and help with any questions you have!
Calculate Your Load
The first step in designing your DIY battery bank is calculating how much electricity you typically use -known as your electricity load. There are two methods to calculate your load:
- First, you can look at your previous electricity usage. If you are already connected to the grid, simply look at your total electricity use for the last 12 months and divide by 365 to get your daily average.
- If you aren’t connected to the grid, you probably don’t have any data on your previous energy use. In this case, you’ll need to calculate how much electricity you need by adding up the wattage of all the electrical devices in the home and estimating how many hours you’ll use them each day.
For example:
- 5 LED light bulbs*8 watts (the wattage of each light bulb)*3 hours per day = 120 watt-hours/day
- 1500 watt blender*.05 hours per day = 75 watt-hours/day (I can’t go without my morning smoothies!)
- 50 watt laptop*6 hours per day = 300 watt-hours/day
As you can imagine, this process takes time and there are a lot of numbers to keep track of, so be sure not to rush this step! The size of your entire battery bank will be based on these calculations, so you need to make sure they are as accurate as possible!
To help you keep track, use a spreadsheet like Microsoft Excel or Google Spreadsheets (which is free with Gmail!). There are also many online tools to help you in this process, including calculators from websites like Wholesale Solar and Affordable Solar.
Example: Let’s say we have a small off-grid mountain cabin. The space heater, water heater, and stove are propane, so only a few key items need electricity. Along with the LEDs, blender, and laptop above, we’ll also have to power our cell phone, fans, TV, and clothes washer. Our usage probably looks something like this:
| Item | Amount of Items | Wattage | Hours per Day | Total Daily kWh Use |
| LED Light Bulbs | 5 | 8 | 3 | .12 |
| Blender | 1 | 1500 | .05 | .075 |
| Laptop | 1 | 50 | 6 | .30 |
| Cell Phone | 1 | 3.5 | 8 | .028 |
| Fans | 2 | 50 | 3 | .30 |
| TV | 1 | 100 | 1 | .10 |
| Clothes Washer | 1 | 600 | .50 | .30 |
| Total | 2,312 | 1.22 kWh |
Our total load for each day is 1.22 kWh and about 36.6 kWh a month. Just to note, this is a VERY small cabin with only a few electrical appliances! For reference, the average kWh usage per month for grid-connected homes in the US is 900 kWh!
Amount of Back-up Power and Depth of Discharge
Batteries allow you to store the electricity your solar installation generates for later use, and after you find your daily electrical load, you need to decide how many days of backup power you want. Most homeowners choose between 1 and 4 days, though this depends on your needs and weather.
Example: We’ll choose 3 days of back-up power, meaning our battery system needs to provide at least 3.66 kWh (1.22 kWh per day multiplied by 3 days) for those days when it’s rainy or cloudy.
To make the process a little more confusing: battery capacity is measured in amp-hours – not watt-hours or kilowatt-hours like the electricity generated by your solar installation. Lucky for us, finding amp-hours is easy! Simply divide watt-hours by the voltage of the solar installation. Off-grid solar installations can be 12 volt, 24 volt, or 48 volt – the voltage you choose depends on your installation’s size, location and layout, and needs.
Example: Our small installation will be 12 volts, meaning we need a battery with 305 amp-hours.
(3660 watt-hours/12 volts = 305 amp-hours)
305 amp-hours. Easy, right?
Hold on though, there’s one more step. If you discharge the batteries down to their full capacity, you can hinder their ability to fully charge in the future. Because of this, battery manufacturers recommend only using a portion of the available battery, usually only 25% to 50% for lead-acid batteries (the most common type of battery for solar). Of course, only using a small fraction of your batteries’ power is annoying, but just consider all the batteries an investment. If you only discharge your batteries down to 25% or 50%, they’ll provide you with years of reliable service.
Related: Tesla Powerwall II Battery Pack Review
We’ve decided that we’re only going to discharge about 40% of our batteries’ capacity, so we need to divide our battery size by .4 to account for this: 305 amp-hours*.4 = 763 amp-hours.
So, our batteries need to be 12 volts and have capacity of at least 763 amp-hours.
Connecting Batteries in Parallel vs in Series
Now that you know the voltage of your installation and the battery capacity you need, it’s almost time to start looking at batteries! In your battery system, there are two ways to connect multiple batteries together – in parallel or in series:
- In Parallel: Connecting batteries in parallel simply means that each battery’s positive terminal is connected to the next battery’s positive terminal (and each negative terminal is connected to the next negative terminal). Batteries that are connected in parallel add up all their amp-hours together, allowing you to increase the total capacity of your battery bank.
- In Series: Connecting batteries in series means connecting the positive terminal of the first battery to the negative terminal of the next, and so on. When connecting in series, amp-hours don’t increase, but voltage adds up amongst all the batteries. It’s also possible to create a system where batteries are connected both in parallel and in series to both increase voltage and amp-hours!
We need 768 amp-hours for our 12 volt solar installation. If we connect in parallel, we could have two 12-volt 400 amp-hour batteries, giving us 800 amp-hours but keeping our 12 volt system. If we connect in series, we could have 2 6-volt 800 amp-hour, giving us a 12 volt battery system with 800 amp-hour capacity. Whether to connect in series or in parallel is a matter of what batteries are available and the structure of your solar and storage installation.
All this can be confusing, but just remember: connecting in parallel adds amp-hours; connecting in series adds voltage! Knowing what options are available to you will help you build the most cost-effective installation that suits your needs.
Size Your Inverter
Inverters are an integral part of any solar and storage installation, as they convert the direct current (DC) electricity produced by your solar panels and housed in the batteries to alternating current (AC) required by all our electronic devices.
Inverters convert electricity from DC to AC in real time. Inverters have no storage capacity – as your devices use electricity, that electricity flows from the batteries through the inverter to the device. Because of this, your inverter needs to be large enough to handle the biggest load you’ll put on it at any single instance.
The easiest way to calculate this is to add up the wattage of all your devices that could be operating at the same time.
Let’s say we’re very busy in our cabin, so it’s possible that all our electrical devices could be going at the same time. As you can see from the table above, the total wattage for all my devices is 2,312 watts. So I need an inverter that can continuously handle at least 2,312 watts.
There’s one more critical step though to sizing your inverter. Some electric devices, especially motor-driven devices like refrigerators, power tools, and air conditioners, draw 2 to 8 times the amount of power they typically use just to turn on! This huge power draw is known as the surge load and you need to account for this when choosing an inverter.
Unlike a device’s typical wattage, which is printed on the back of a device, manufacturers don’t publish the surge load of their devices, so you either need to contact them directly or measure the electrical pull yourself for your motor-driven devices.
Fortunately for us, inverter manufacturers these days account for surge loads and most inverters can handle high spikes of electricity in short bursts. When choosing an inverter, be sure that they can handle the surge load for any of the electrical equipment you use.
We know that we need an inverter that can continuously handle at least 2,312 watts, but let’s say our clothes washer uses 3x the amount of power just to turn on, so our surge load is 3,512 watts. We could simply buy an inverter that can handle 4000 watts – but that’s expensive and unnecessary. It just so happens that there’s a 2500 watt inverter that can handle a surge load of 5000 watts – more than enough for our needs!
Photo Credits: Flickr vs CC License: 1, 2, 3, 4
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FAQs
How big a battery bank do I need for solar system? ›
Most residential batteries need at least 5kw or 6kW of solar panels to charge the battery. And if you're looking to the future (i.e., all-electric home, EV charging and energy trading , 10kW of solar panels is going to be much more suitable.
How to make a simple solar battery? ›- Step 1: Create a Template and Build a Frame. ...
- Step 2: Solar Cells. ...
- Step 3: Drilling Holes in Frame for Connection. ...
- Step 4: Gluing the Cells to the Frame. ...
- Step 5: Solder the Wire. ...
- Step 6: It's Electric. ...
- Step 7: Put Some Pressure on the Plexiglass. ...
- Step 8: Junction Box Installation.
If you want to save the most money possible, you'll need enough battery storage to cover your energy usage when your solar panels aren't producing – somewhere around 2-3 batteries. If you want to keep the power on when the grid is down, you'll usually just need one solar battery.
What is the best battery for off-grid solar? ›Lead acid or gel type batteries may work if you're looking to test a solar setup short-term to see if it's a right fit for you. But when you consider efficiency, reliability and lifetime cost, it's clear that lithium comes out on top as the best contender among all off grid solar batteries.
What is the best battery for solar power? ›What are the best batteries for solar? Batteries used in home energy storage typically are made with one of three chemical compositions: lead acid, lithium ion, and saltwater. In most cases, lithium ion batteries are the best option for a solar panel system, though other battery types can be more affordable.
Is it better to have more solar panels or more batteries? ›More panels means greater square footage of solar cells exposed to the sun, resulting in higher efficiency and longer runs times into the earlier morning and later evening when very little sun is available. If you're needing just an hour or two of longer run time, try adding another line of panels.
Can a solar battery be too big? ›An oversized solar battery could also lead to chronic undercharging and poor performance and lifespan. Search tool allows you to specify exactly what elements of a home should be powered by the battery.
How many solar batteries do I need to run a refrigerator? ›How many solar panels do I need to run a refrigerator? The average refrigerator takes about three or four average solar panels to run. The average refrigerator found in the United States uses approximately 57 kWh per month while the average freezer uses 58 kWh. Adding those together brings a combined total of 115 kWh.
How do you make a homemade power bank? ›1) Before building the battery pack check that voltage of both the battery it shall be same. 2) I used some hot glue the keep both batteries together you can even use tape or a heat shrinking tube. 3) Solder anode with anode and cathode with cathode of the batteries. 4) Battery pack is complete !
Can you use regular batteries instead of solar batteries? ›Regular alkaline rechargeable batteries can't usually hold enough energy collected by the solar panel and discharge power to the bulb in the way that NiCd and NiMH rechargeable batteries do.
Can you run solar panel straight to battery? ›
Don't connect a solar panel directly to a battery.
Doing so can damage the battery. Instead, connect both battery and solar panel to a solar charge controller.
A 100 watt panel receiving at least 8 hours of sunlight per day will produce almost 1 kilowatt-hours per day or 30 kWh per month. Divide that usage of the refrigerator (100kWh) by 30 kWh per month and you get 3.3 solar panels. This means you'll need four 100 watt solar panels to keep that refrigerator running.
How many batteries do I need for a 5000 watt solar system? ›Most 5kw solar system off grid contains an inverter that runs from 96 to 120 volts. You need a 6 x 200ah battery bank if your system generates 20 kilowatts daily. The necessary battery bank will be less as your daily energy usage increases. There are batteries to store any excess power that is not being used.
How long will a solar battery power a house? ›Home solar battery units last anywhere between 5 and 15 years. If you decide to install a solar battery today, it's almost certain you'll need a replacement in the future to match the 20- to 30-year lifespan of your solar power system.
How many batteries and solar do I need to go off-grid? ›The average off-grid home usually requires about 7 Kw (or 7000 Watts) of power to rely entirely on its own energy production. Solar panels come in various forms, shapes and sizes.
What happens when off-grid solar batteries are full? ›Should the battery bank become full, it will stop absorbing power from the solar system. The solar panels will continue to generate voltage, but that voltage will not be used or stored until there is available energy demand, or battery space.
How many batteries can a 400 watt solar panel charge? ›The number of photovoltaic cells in a solar panel varies depending on the wattage. A 100-watt solar panel uses 100 cells whereas a 400-watt solar panel has around 160-170 cells (typically 180 cells).
What are 3 drawbacks to storing solar energy in batteries? ›- Energy Storage is Expensive. The cost of energy storage is quite high and can quite easily increase the cost of your solar PV system substantially. ...
- Increased Complexity of Your Solar System. ...
- Increased Maintenance For Your Solar. ...
- Lifespan of Home Battery.
- Best Overall: Tesla Powerwall 2.
- Most Intelligent: Enphase IQ.
- Most Powerful: Generac PWRcell.
- Best Value: LG Chem RESU-10H.
- Most Versatile: BYD Battery-Box Premium HV.
If your solar array capacity is: < 1000W then 12V is Good. > 1000W and < 2000W then 24V is Better. > 2000W then 48V is Best.
Is it worth getting a storage battery for solar panels? ›
Solar batteries can be a handy add on to your solar panel set-up. Whilst you can still make full use of your solar panels without a solar battery; the benefits of having solar batteries means you might rely less on the grid and be able to store and use the electricity that your house generates.
What should you avoid with solar panels? ›- Worrying how your roof direction will affect your solar energy.
- Not identifying the best solar panel size for the home.
- Waiting in the expectation of obtaining reduced battery prices.
- Getting only a few quotes.
If your energy needs are around 1,000 to 5,000 watts, go for a 24 volt system. If you're looking to build a smaller, DIY system for your RV, van, or tiny home, go for a 12 volt system.
How do you keep a solar panel from overcharging a battery? ›Higher charging voltage from the solar panels leads to higher Ah being delivered to the battery and ultimately leading to overcharging. The easiest way to control over charging of the batteries is to control the output voltage of the solar panel. A hybrid inverter can do this.
What are the dangers of solar batteries? ›The batteries can overheat and catch fire, which could lead to serious injuries, death and property damage.
What angle should solar panel sun be? ›For most homeowners, the ideal angle for a solar panel installation is close to or equal to the latitude of your home. This angle is typically between 30 degrees and 45 degrees. Doing so ensures your home will get the maximum average output from your solar power system throughout the year.
Do solar panels generate electricity on cloudy days? ›Does a cloudy day affect solar energy generation? Anyone who's gotten sunburned on a cloudy day knows that solar radiation penetrates clouds. For that same reason, solar panels can still produce electricity on cloudy days.
How many 300-watt solar panels do I need to run a house? ›It is worth mentioning that you require nearly 20 panels to produce enough energy to sustain a decent-sized house.
How many solar panels do I need to run an air conditioner? ›Since most AC systems use around 1,200 watts, the required number of solar panels is 5.
What is the best battery for a home made power bank? ›18650 cells are, by far, the most common type of lithium-ion battery cell and they are the most common type of battery cell to use to build a power bank.
What makes a strong power bank? ›
Power bank capacity explained
Capacity, shown as milliamp hour (mAh), is a rough indication of the charging capabilities – the higher the number, the more power it can deliver to your device before the power bank also runs out of juice.
Avoid charging the power bank on places that build up heat, such as on your bed. Avoid short circuits: Keep your power bank away from metal objects such as coins, paper clips and keys. Do not insert any metal objects into the USB output port or joining terminals of the power bank.
Can I use any 12v battery for solar panel? ›Yes! Different batteries can have a huge impact on how your solar installation operates. There are three main types of deep cycle batteries used in solar systems: flooded lead acid, sealed lead acid, and lithium iron phosphate batteries. Each of these batteries vary in price, battery capacity, voltage, and cycle life.
Can I use solar battery without inverter? ›While a solar system can function without an inverter, different voltages depend on what the appliance needs, which can damage your gadget. For example, a grid-connected solar system without an inverter can power DC-current equipment such as lights and televisions, but it cannot do so efficiently.
Can you use old car batteries for solar? ›Lead-acid batteries can be used, but lithium-iron-phosphide batteries are better for solar systems. The biggest drawback of car batteries for solar power systems is that they are not designed to store solar energy or run continuously. They also do not have deep-discharge capabilities and are too heavy.
Can you connect 2 solar panels to 1 battery? ›What about connecting multiple solar panels to one battery? You can connect them in parallel, providing your battery management system can handle the maximum input power.
Do solar panels work at night without a battery? ›Yes, if you are connected to an electrical grid, you can use solar panels and inverters without battery storage. However, it's important to note that grid-tied solar systems are usually shutoff during power outages to prevent the backflow of electricity from harming utility workers.
Why my solar battery is draining fast? ›It may be that charging and discharging the batteries too quickly is a sign of inadequate battery sizing, improper IMEON settings, or the end of battery life.
How can I increase my solar panel output? ›- Buy one of the more efficient solar panel models. ...
- Buy panels with High Concentrated Photovoltaic (CPV) Cells. ...
- Avoid installing solar panels in shaded areas. ...
- Get an expert to install your solar panels. ...
- Clean your solar panels.
Costs and savings
With any domestic PV system, there will be times when the electricity you generate is more than you can use or store, so the surplus will be exported to the grid to be used by somebody else. If you want to be paid for exporting, you need to make sure you're getting an export payment.
Can I connect solar panel direct to fridge? ›
Short Answer Is Yes You Can Run A Fridge On Solar Power
Let's take a look. There are two situations where you would want to have a fridge run off solar power. The first is the fridge at home, running on-grid or off-grid power. The second is a portable fridge which stays cool being powered by the sun.
If you want to keep the power on when the grid is down, you'll usually just need one solar battery. If you want to go off-grid completely, you'll need far more storage capacity, more along the lines of 8-12 batteries.
How big a battery do I need for solar system? ›Most residential batteries need at least 5kw or 6kW of solar panels to charge the battery. And if you're looking to the future (i.e., all-electric home, EV charging and energy trading , 10kW of solar panels is going to be much more suitable.
What type of battery is best for solar system? ›What are the best batteries for solar? Batteries used in home energy storage typically are made with one of three chemical compositions: lead acid, lithium ion, and saltwater. In most cases, lithium ion batteries are the best option for a solar panel system, though other battery types can be more affordable.
What are the best batteries for solar off-grid? ›Lead acid or gel type batteries may work if you're looking to test a solar setup short-term to see if it's a right fit for you. But when you consider efficiency, reliability and lifetime cost, it's clear that lithium comes out on top as the best contender among all off grid solar batteries.
Will my solar battery charge during a power outage? ›Solar panels alone won't work during a power outage—but when paired with solar battery storage, they can. See how solar battery storage keeps your solar systems working during an outage with reliable, renewable solar power, and why we need clean energy now more than ever.
How do you charge a solar battery bank without a sun? ›Use Artificial Lighting Bulb to Charge Solar Lights
You need to place the solar panels underneath a household light to charge them rapidly. Furthermore, you can place solar lights close to the light bulb. The closer the solar light to the bulb, the less time it will take your solar panel to charge.
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.
How do I know if my solar bank is charging? ›The power bank can be recharged by solar energy when it's under the sun rays or in the environment with light strong enough. The green LED light is on when the power bank is being charged by solar energy.
Is a solar battery bank worth it? ›Solar batteries are also great if your main reasons for going solar are environmental, as it maximizes the amount of renewable energy your home uses. However, if you're only looking to save extra money, a solar battery might not be worth it for you.
Do solar panels charge on cloudy days? ›
Yes, solar panels still work in cloudy weather — they just might generate less power, depending upon the quality and efficiency of your panels.
Can solar panels work with moonlight? ›Electricity Generated by Your Solar Panels at Night Is Minimal. Seeing as moonlight is just sunlight reflected off of the moon, you will be happy to hear that the answer is yes: solar panels do technically work with moonlight.
Can I use solar panel directly without battery? ›Absolutely! In fact, most home solar systems are currently operating without battery storage. If you're fine with drawing from the grid and not particularly worried about power outages, you might not need a battery. However, there are benefits to having battery storage for your solar panels.
How long will a solar battery last during a power outage? ›“An average homeowner typically will draw 2 kilowatts maximum during an outage, and an average of 750 to 1,000 watts during the course of the outage," he said. "This means a Brightbox will last for 10 to 12 hours, while a Powerwall will last for 12 to 15 hours.”
How long can solar energy be stored in a battery? ›Generally, a standard solar battery will hold a charge for 1-5 days.
What is the disadvantage of solar power bank? ›High initial costs for material and installation and long ROI (however, with the reduction in the cost of solar over the last 10 years, solar is becoming more cost feasible every day) Needs lots of space as efficiency is not 100% yet. No solar power at night so there is a need for a large battery bank.
What should I look for in a solar battery bank? ›- Size and weight.
- Charging capacity.
- Charging speed.
- Battery charging time.
- Resistance.
- Number of connections.
Here's why a charge controller is so critical: most 12-volt solar panels output anywhere from 16 to 20 volts, so it's very easy for the batteries to overcharge without any regulation. Most 12-volt solar batteries require 14-14.5 volts to reach a full charge, so you can see how quickly an overcharging issue could occur.
Can I use car battery as solar bank? ›While car batteries are a perfectly fine source of power for a solar power system, they do have their limitations. The most obvious limitation is that car batteries are not designed for sustained deep discharge. solar power system, on the other hand, require a slow, steady release of energy.
What is the problem with solar batteries? ›In the short term, one of the biggest challenges with solar power storage is simply that the batteries used for this application are still quite costly, and they are large. The more power you need, the larger your battery will need to be.
How many solar batteries are needed to power a house? ›
If you want to keep the power on when the grid is down, you'll usually just need one solar battery. If you want to go off-grid completely, you'll need far more storage capacity, more along the lines of 8-12 batteries.