Best Batteries for Solar PV system

In this article we will list what are the best, the worst and the most cost effective battery options for Solar or any other renewable energy storage. Plus a brand new battery technology will also be introduced that is getting rave reviews and its not Lithium Ion batteries.

What are the best batteries for solar?

Contrary to the popular belief, the flooded lead acid batteries that are used in cars are not the best option. In fact it is one of the worst options. Unfortunately, in the developing countries mostly flooded lead acid car batteries are used because they are cheap and easily available.

Gel batteries, better than flooded Lead Acid battery

Gel batteries, better than flooded Lead Acid battery

These car or even truck batteries are designed for providing high burst of current for a short amount of time (i.e. to run the starting motor for the engine). This is inverse to the requirements for the Solar energy storage system, which require the battery to provide relatively less current but for a longer duration of time.

The problem is not the lead acid chemistry but the design of the battery. Car cranking battery has smaller electrodes. For solar application deep cycle batteries are the best option. In construction, deep-cycle batteries have longer electrode plates inside.

Lead Acid is a very established technology and within the Lead Acid umbrella, there are different types of battery. They are as follows:

In flooded batteries, electrolyte is in liquid form and can flow. Whereas in AGM and Gel batteries, the electrolyte cannot flow and therefore these batteries can be place in any orientation. Both AGM and Gel batteries are maintenance free, where as in flooded batteries; the electrolyte has to be topped up from time to time. Again it is emphasized here that for Solar application, avoid using car or even truck batteries because on the outset they might be cheaper in the long run, they will turn out to be more expansive option. One should aim to acquire deep cycle batteries be it flooded, AGM or Gel.

In terms of price, the deep cycle flooded lead acid batteries are the cheapest (only about $70-80 /kWh), whereas AGM and Gel batteries are almost the same price but more expensive than flooded battery. Their price ranging from $260 per Kwh to $330 per kilowatt hour.

Next up we have Lithium Ion batteries. They are long lasting, robust and durable. They are also much lighter and smaller than Lead Acid batteries of equivalent capacity. The prices for Lithium Ion batteries are dropping by almost 8% per year. Again within Lithium Ion, there are different types of batteries. Two main types that are used at Li-Ferro Phosphate and Lithium Cobalt Oxide.

The Cheapest Lithium option is the Tesla Power wall which comes out to be $505 / Kwh. Other Lithium batteries such as Simpliphi batteries range between $900 – 1100/Kwh. There are many Chinese brands which do provide lithium batteries at a considerably low price but they are not renowned brands in the western world. The video link is present below which will provide you with the prices.
And lastly we have the latest commercialized technology in the battery world and that is the Saltwater battery, also called the Sodium Ion battery. This battery is very exciting not only because of its performance but also for its price.

It is the safest of the batteries on the planet. Saltwater battery can handle heat well and is completely recyclable. It is a very stable battery with no maintenance and high amount of charge cycles. Even if this battery is discharged deeply, it doesn’t make much of an impact on its health. The price for this battery is around $400-$500 / kilowatt hour which makes it cheaper than Lithium Ion but only slightly more expensive than lead acid.

It has a couple of drawbacks. First it slightly heavier than Lead Acid and secondly it can be charged and discharged at slower rates than other batteries.
Currently there is just one company Aquion Energy that is commercially producing it. As noticed earlier the saltwater battery is a cheaper alternative to lithium ion, the prices are expected to drop further with the developing competition and economy of scales.
So to recap again, the best option in terms of longevity is lithium ion, if you can afford it. Next best option is the saltwater battery and lastly we have the Deep-cycle AGM or Deep-cycle Gel batteries.

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