Solar storage batteries are the newest component of a solar power system. As they become increasingly cost-effective, more and more systems include them. This article breaks down what to expect and what to look out for when selecting a storage battery for your solar power system.
Price should always remain relative to quality, and with solar batteries the old saying “ you get what you pay for” holds true. In other words, buying the cheapest battery available to you has very little chance of saving you the most money in the long run.
So how do you find the sweet spot between long term value and initial upfront cost?
Your budget is obviously a factor. You might not purchase the best solar battery on the market for the same reason you would not purchase a ferrari…you can’t afford it. More importantly, you don’t need it either. There are many mid-range options that can suit your purposes and save you money on your electricity bills.
A metric that is often more useful than price is “price per warranted kWh” which gives a better idea of the long term cost value of the system (this is explained below).
Capacity & Power Output
The capacity refers to the maximum amount of electricity that a solar battery is able to store. This figure is measured in kilowatt-hours (kWh).
The majority of residential solar batteries are stackable, this means they can be combined in a series – or stacked – allowing you to create extra capacity for your system. This option requires you to buy more than one battery but means you can upgrade your system over time if desired.
Where capacity is a measure of much your battery can store, power is a measure of how much electricity it will give you when it is in operation. A battery’s power output tells you how much electricity is being delivered through your house to run your appliances.
A battery could have a very high capacity but if its power output is low then it is delivering a low amount of electricity to your house. On the other hand, a battery that has a low capacity but a high power output can deliver a lot of electricity to your home but for a shorter amount of time. In an ideal circumstance, both capacity and power output will be sufficiently high but this will push you towards the more expensive end of the market.
The average home should operate well with any storage battery that falls between with 3 – 7kWh power output, and 7 – 14 kWh capacity. Anything above this is going towards an industrial level.
Depth of Discharge
This metric refers to how much of a battery’s capacity empties during use before it requires recharging. The charging and discharging process takes a toll on a battery and regular deep discharge adds to this wear and tear. This is why most solar batteries try and operate at around a 50% depth of discharge.
Depth of discharge such as 80% gives you more capacity before a recharge is necessary but it will also mean you will need to replace your battery sooner than if it has a lower depth of discharge.
For example, a battery may have 3,000 cycles at 50% DoD but only 1,000 cycles at 80% DoD. meaning, in the long run, you get more use out of the 50% DoD battery.
Price per warrantied kWh
This figure is calculated by dividing the cost of the battery by the number of battery cycles included in the warranty. This is useful for deciphering long term value because it offers a good idea of how far your money will go.
For example, imagine two different batteries:
The first has a price of $10,000. It has a 6kWh capacity and a 5-year warranty. This means its price per warrantied kWh is 0.91cents.
The second battery – is more expensive at $12,000 – however, it has a 10kWh capacity and a 10-year warranty. Therefore, this battery has a price per warrantied kWh of 0.32cents.
The second battery cost more initially but will prove better value for money in the long run.
The $12,000 battery gives you more power in one cycle (10kWh beats 6kWh), and it comes with a larger warranty than its counterpart (10 years beats 5 years).
This is why you should pay attention to the price per warrantied kWh when evaluating battery prices.
There are several types of battery you can find in the solar industry, the main two being Lead-acid and lithium-ion.
Lead-acid batteries have been a part of off-grid energy systems for decades. They have a shorter lifespan, and a lower depth of discharge than a lithium-ion battery but they are also less expensive. Ultimately, it looks like the lead-acid battery will be completely phased out of all-in-one solar power system packages. However, it is still useful for those who would like to customize their own power system and add extra batteries.
The majority of new solar storage batteries use some form of lithium-ion composition. Due to their compact size and lightweight, they are much better for home installations. On top of that, they also boast longer lifespan and a higher DoD then lead-acid batteries. As a result, lithium-ion batteries cost more than their lead-acid counterparts.
Saltwater batteries are new to the solar energy scene. Unlike other batteries, they don’t contain heavy metals replacing them with saltwater electrolytes. This makes them easily recyclable and better on the environment. However, they remain untested as compared to the other batteries.
The industry standard for a solar power system battery is 10 years. Some companies slip just below that and even fewer go above it. A solar battery should last between 5-15 years. However, due to constant charging and discharging, it will lose some of its performance capability and by the end of its life cycle will not be working as efficiently as it did in the beginning.
Size & Weight
The average battery needs 1.5m² wall space and can weigh anything from 30 to 300 KG. The smaller batteries tend to be less powerful which could require purchasing two or three of them.
Often the first thing you will need to know is whether or not the battery is compatible with your existing system. Certain batteries only work with certain panels and inverters. If you are retrofitting a battery you have to make sure it is compatible with your system. If you are buying a whole system new this shouldn’t be a problem. However, the battery fails before the panels do so it is an issue that can arise.
Solar batteries are here to stay, and as the technology develops the time will soon arrive when no solar power system comes without one. The information here should prove useful when selecting a solar power system for your home.
If you have any comments or questions regarding solar power please contact us or leave your comments below.