How Home Batteries Work: A Beginner's Guide

If you're thinking of buying a solar battery, don't go in blind. There are some fundamentals that you must understand. Firstly, the difference between battery power and battery energy. Think of a battery as a tank being filled with electricity. Imagine the size of the pipe into the tank determines how fast you can fill or empty that tank with electricity. A tank with a small pipe can only fill or empty slowly. It is a low power battery. A tank with a big pipe can fill and empty quickly. It is a high power battery. A battery's power determines how quickly it can fill an empty, and it's measured in kilowatt. If I tell you a battery is 10 kW, that only tells you how quickly it can charge and discharge. It doesn't tell you how big the battery is. The bigger the battery, the more electricity it can store. We call the size of the battery its energy capacity or energy for short. We measure the energy capacity in kilowatt hours. Note the hours at the end. That distinguishes energy from power. If we say a battery is 15 kW hours, that tells us how much electricity it can store. To make sure we get the battery we need, we need to specify both its power and energy. For example, a Tesla Power Wall 3. It's a 13 12 kWh 10 kW battery. It stores 13 1. 5 kW hours of energy and can discharge that energy at a rate of 10 kW. I've got a sauna. It draws 7 kW when it's cranking. My home battery can only dish out 5 kW. So, I will always be pulling 2 kW from the grid if I use my sauna at night. Yes, that's a first world problem, but it illustrates that if your aim is not to pull from the grid, you need to think about battery power, not just battery energy capacity. Now, let's talk battery chemistry. Before 2015, if you wanted home batteries, you were looking at lead acid batteries. Imagine rows of traditional car batteries in their own shed requiring routine maintenance, mostly owned by off-grids in the sticks. But in 2015, big lithium ion home batteries arrived and changed everything. Why? Because they have better performance. They need zero maintenance. They're set and forget apart from an electrical checkup every 5 years or so. They last longer. They're cheaper for kilowatth discharge. And they don't need their own shed. No wonder everyone apart from the diehard preers are going lithium ion these days. Now, there's two main flavors of lithium battery. You'll hear about NMC and lithium ion phosphate, otherwise known as a lifo. Both NMC and lithium ion phosphate are types of lithium ion batteries. Yes, I know it's confusing. People always ask me about other battery types. Flow batteries, nickel ion, you name it. But here's the truth. Nothing right now is beating lithium ion on performance and price. But keep an eye on sodium ion batteries. They might just might shake up things in the next few years. So, what should you get? Unless you've got a really unique setup at your place, lithium ion is your best bet. From a safety perspective, lithium iron phosphate batteries have a lower risk of thermal runaway, aka catching fire, than NMC batteries. Though, I will stress any well-installed battery from a major manufacturer is safe. I've got NMC batteries on my house, and I sleep fine at night. Now, let's talk about connecting a battery to your home and your solar. Batteries use DC electricity. Solar panels produce DC electricity. So, the cheapest, simplest way to connect a home battery to a home solar system is by keeping everything DC. We call this DC coupling. In my opinion, the biggest advantage of DC coupling is that you only need one inverter to convert both the solar and the batteries DC electricity into the 230 volt AC electricity compatible with your house. The do-it- all inverter is called a hybrid inverter. And it's cheaper to buy an install than a separate inverter for your solar and your battery. So, why doesn't everyone get a hybrid inverter? Because you're generally locked into whatever batteries the hybrid inverter is compatible with. If you want to keep your battery options open, you can add batteries to your home solar with AC coupling. That requires separate battery and solar inverters. So, what's better? DC coupling is cheaper, but it ties you into a particular battery brand and model. AC coupling is thousands of dollars more expensive, but lets you add whatever battery you like at a later date. So, it's your call. Let's finish by talking money. How do batteries reduce your bills? If you're on an old school flat electricity tariff where you pay the same price per kilowatt hour from the grid 24 hours a day, the battery simply charges up from solar during the day, then it's used instead of grid power overnight until the battery is discharged. If you're on a time of use plan where grid electricity is typically most expensive from 400 p. m. to midnight, a battery works slightly

differently. It will still charge from the solar during the day, but it can also charge from cheap daytime electricity when there's not enough solar to fill the battery. Think winter or overcast days or days when you all your solar was needed to charge your EV instead of your home battery. The battery can even charge up again after midnight to get you through breakfast. But this behavior is dependent on good battery control software. Watch out for cheap, dumb batteries that don't have the software to do this. And watch out for inexperienced installers who won't configure your battery to save you the most money, even if the battery is capable. If you're ready to get battery quotes for good batteries, properly installed, and configured by installers who care, just visit solarquot. com. au, pop your postcode in the box, fill out the form, and we'll organize up to three battery installers to give you great quotes on a kick-ass system.