Solar power systems offer some real cost savings when used instead of or to supplement your existing energy supply. However they only work in daylight. More and more solar users are looking at solutions to help them to store the energy that their solar panels generate so that this electricity can be used later.
The only real means of storing this power is with batteries and the question of ‘what is the best battery for solar panels’ prevails.
When looking at batteries for a solar system there are certain things that we need to consider such as how long will the solar battery last and how much energy can it supply.
We’ll take a look at the various factors to help you to choose, as well as the different types of batteries that are available.
Making solar battery comparisons
A battery is a means of storing energy that can be accessed and used at a later time – generally they are charged with power that remains in situ until you access it.
As with many technical items though you’ll find some terms that you’ll need to be familiar with.
The main ones concern the battery’s capacity and power ratings, the level of discharge that it can sustain, how efficient the battery is and whether it comes with a warranty.
Battery Power and Capacity
The battery capacity refers to the total amount of solar batteries can be daisy chained which means that you can connect multiple batteries together into your solar system, this will provide you with more power, for longer periods of time.
Another important consideration while looking at the battery’s ability is to consider just how much power the battery can provide at any one point in time.
Ideally you need to source a battery that has a large enough capacity to serve your home for a long time and a power rating that will allow it to deliver large quantities of power for short periods, if and when such power delivery is needed.
If a battery has high capacity and low power rating then it can provide energy for a long period of time at low levels so perhaps to run a few appliances. On the other hand a battery with high power but low capacity could provide power for your entire home but only for a short period of time.
Level of discharge (known as DOD)
Every battery, regardless of type or purpose needs to retain some level of charge. To completely discharge a battery is to render it almost useless or at the very least, you’ll damage it and shorten it’s life.
Most battery manufacturers will tell you the optimum level that this is so that you do not over discharge the battery. So, for example if your battery has a total charge of 5kWh then it may have a discharge of 90% which would mean that you cannot use more than 4.5kWh of power before the battery needs a recharge.
In plain speaking the higher the discharge level the greater the level of battery power you can use.
Battery Efficiency – known as ’round trip efficiency’
The efficiency of the battery is important and this is really important when looking at the amount of energy that you can use as a percentage of the energy taken to charge it up.
So for example, if you feed 2 Kwh into your battery but can only get 1kWh out of it then the battery is 50% efficient.
It goes without saying that the higher the efficiency rating, the better the battery.
Lifetime and Warranty
As a battery goes through the motions it charges, then discharges, then charges again, then discharges etc etc etc.
This activity (which is normal and is known as ‘cycling’ ) gradually reduces the ability of the battery to hold charge and the ability of the battery will gradually decrease as time goes on.
This is true of all batteries, the battery in your car gradually decreases in ability as does the one in your mobile phone.
Most battery warranties will provide you with an indication of the number of ‘cycles’ that they will warranty the battery for. So for example they might provide a warranty of 6,000 cycles or 10 years.
When we think about how long a solar battery will last the answer depends on the brand of the battery and the level of ‘cycle’ that it can sustain over it’s lifetime.
Which Brand is best?
That’s a difficult question to answer as many manufacturers produce great batteries and have been doing so for many years.
Battery technology is constantly improving and developing and as more and more products are unleashed that require batteries, such as electric cars and so forth, battery developments are constantly under review and progressing.
How long will the charge last on solar batteries?
This depends on the amount of electricity that your house uses and this is determined by what appliances you have and how long you use them for.
Houses and users vary but typically an average house uses about 30kWh worth of electricity daily. So, if your battery is rated at 10kWh then, if you have three batteries connected together, then, in theory, you would be able to power your house for a full day on battery power.
In practice it’s a bit different and you’d be advised to get more battery capacity to ensure that you have enough power.
How long do solar batteries last before they need replacing?
In general solar battery lifetime can be anything from 5 to 10 years.
If you install a solar battery at the same time as your solar panels then you can expect to change the battery at least once during the 25 year lifespan of the panels.
But, having said that, as battery technology improves then it’s very possible that their lifespan will increase and improve too.
What type of batteries are best for solar powered systems?
Batteries that are used for solar power systems are generally of three types and are made with one of three types of chemicals. These being lead acid, lithium, and saltwater.
Of the three the lithium batteries are the best choice, but the others may be more affordable.
One of the cheapest options available lead acid batteries have been around for a long time. They generally have shorter lifespan than other battery types but, if you need high levels of energy storage and need to buy lots of batteries then they can be a good choice.
These batteries are lighter and smaller than lead acid batteries. They have a longer lifespan and can generally supply more power for longer periods of time. The downside is cost they are more expensive.
Saltwater batteries are a new technology that remains primarily untested. Although they use little in the way of damaging pollutants, they are rare and difficult to source.
Their effectiveness is not fully known.
If you are looking at cheapest options and have high power needs then lead acid batteries could be a good choice for you.
If however, you want best performance for your buck, cleanliness and longer life batteries then Lithium Ion would be the way to go.