About a decade ago, a solar battery was a remarkably premium item with very few customers - something like a $8 popcorn bucket that most of us just roll our eyes at. However, plunging prices and increasing benefits have boosted the popularity of solar batteries.
Thanks to benefits such as backup energy and resilience against blackouts, an increasing number of Kiwi homeowners are seriously considering installing a solar battery - both with or without solar panels. If you are contemplating buying a battery storage system, here are a few things to consider.
1. Battery Chemistry
Humans learnt how to harness energy thousands of years ago, but it was just recently that we figured out how to ‘store’ energy. For a long time, heavy, bulky and somewhat ugly-looking lead-acid batteries were the most common type of batteries used for energy storage.
Fortunately, lithium-based batteries have risen as the most desired and the highest-selling battery type in recent years. Lithium batteries are significantly lighter and more efficient than older technologies. Plus, they also last longer and require little to no maintenance over their lifespan.
Among lithium-based batteries, there are two main types - the NMC chemistry (Nickel Manganese Cobalt) and the LFP chemistry (lithium iron phosphate). NMC batteries have been the most common type of lithium batteries for many years now. They have higher energy density and versatility, making them suitable for a variety of applications.
However, if you aren’t too short on space and just need to power your home, LFP batteries offer remarkable advantages over NMC - they last longer and have much better thermal resistance, meaning you won’t have to worry about fires.
Some popular examples of NMC batteries are the Tesla Powerwall 2 or the Enphase IQ battery. On the other hand, the Tesla Powerwall 3 and the BYD battery models come with LFP chemistry.
2. Energy Capacity and Power Rating
One of the key factors to consider when choosing a solar battery is its main set of technical specifications - its energy storage capacity and power rating. The energy capacity will decide how many kilowatt-hours (kWh) of energy you can store in it, while the power rating decides how much power in kilowatts (kW) you can draw from the battery at any given moment.
Most solar batteries today come with an energy storage capacity of 10-15 kWh. However, you can easily find models with higher or lower capacities. In most cases, you can increase your storage capacity by connecting multiple batteries together. Several battery models today also come with a modular design, allowing you to increase capacity by just stacking another module on top of your existing battery.
As a rule of thumb, it’s a good idea to choose a battery capacity that is similar to your daily energy requirement. If you live in an area with frequent blackouts, getting a larger battery also makes sense. As for power rating, choose a model with a continuous power output that can handle most or all of your home’s appliances - especially the power hungry ones.
3. Roundtrip Efficiency and Depth of Discharge
Roundtrip efficiency is a somewhat fancy name for your battery’s generosity. In other words, it is the amount of energy that can be retrieved from the amount of energy that was previously stored in a battery. For example, if a battery is charged with 10 kWh of energy and it discharges to produce only 9 kWh, it has a roundtrip efficiency of 90%.
Needless to say, you should look for a model with roundtrip efficiency that’s as high as possible. The good news is that while older batteries offered disappointing efficiencies of 60-70%, modern lithium batteries offer roundtrip efficiencies of over 90%, and some models even hit the 100% mark!
Besides efficiency, there’s another percentage value that you need to look at - the depth of discharge. As the name suggests, it is the amount of energy that just remains in the battery and cannot be extracted. Think of the last few drops of juice in a box - those that you can never get out but just make slurpy noise and embarrass you around people.
Older batteries had low depths of discharge, meaning that with a 10 kWh battery, the usable capacity was just 7 or 8 kWh. Thankfully, modern batteries excel here too, regularly offering a 100% depth of discharge.
4. Battery Life and Warranty
When you are spending thousands of dollars on something, you typically have two worries - how long will it really last, and what if it breaks down? Once again, lithium batteries beat older technologies by offering long lifespans of 10 or more years. Most lithium batteries even come with a notable 10-year warranty.
The only catch is that the battery’s efficiency and capacity will drop slightly over time. Thankfully, your battery manufacturer will also offer a warranty for how much degradation the machine will undergo over the decade.
5. Cost For Solar Batteries
Probably the most obvious item on this list is considering the pricing of your battery options. Typically, a solar battery will cost anywhere between $10,000-$15,000 with installation, but these numbers can vary widely based on size, brand, features, etc.
A more useful number would be the price per kWh, which allows for a better comparison of different models. Currently, home solar batteries cost somewhere around $1000-$1500/kWh with installation.
6. Battery Grid Charging Capability
Although it is called a ‘solar battery’, your battery doesn’t have to charge from solar power alone. Many battery models today come with grid charging capability. While the primary goal of a solar battery is to store excess solar energy and supply it later, grid charging offers significant flexibility, especially during cloudy, rainy days when our solar panels are as unproductive as us.
Some energy retailers also offer cheap or free power at certain times of the day or week, such as Contact’s Good Nights plan which offers free electricity between 9 pm and midnight every day, or Z’s EV charging plan which offers free power from 3-6 am and half rates between 9 pm and 7 am. You can charge your battery during hours of free or cheap power and use the energy during peak hours such as mornings or evenings - effectively enjoying free power at whatever time of the day you want.
7. Solar Battery Brands
There are dozens of solar battery brands in the market today, and not all of them are equally reliable for product quality and/or customer support. Some of the brands that are highest-rated across all categories are Tesla, Enphase, Sonnen, Sungrow and BYD. Check out our battery product comparison page to compare numerous reputable solar battery brands and models.
8. Smart Functionality and Other Features
From watches and cars to refrigerators and TVs, every commodity is becoming ‘smart’ in one way or another, which is why it would only be a surprise if batteries remain ‘dumb’. Modern batteries are a lot more than just energy storage devices. They come loaded with several sensors and other electronic stuff that make them more usable.
For instance, nearly every modern solar battery comes with Wi-Fi connectivity. You can connect your smartphone to the battery even remotely and monitor several parameters such as state of charge, solar charging power, discharging power, and more. The Tesla Powerwall can even connect to a weather station and keep an eye out for potential storms, in which case it can reduce discharging and charge fully to prepare for a possible blackout.
Final Thoughts
Solar batteries have come a long way in terms of technology, cost and features. When paired with solar panels, they offer a complete home solution - one that brings you energy independence and electricity bill savings.
However, with the huge variety of battery brands and models available today, choosing the most suitable option for your needs will take some work. It’s always a great idea to consult a reputable solar installer to calculate your required battery size and figure out what features you need. And don’t forget - we can help you get multiple free quotes from vetted solar installers.