Best Batteries for Solar PV System
Today’s solar batteries are better than ever. So are the devices that regulate and protect them. But you still need to do your homework to make sure you get the best solar battery storage solution for your needs.
There are two main kinds of deep cycle batteries: lead-acid and lithium. Lead-acid batteries have a lower upfront cost, while lithium batteries have the longest lifespan. Flooded lead-acid batteries require maintenance, and more expensive sealed lead acid batteries are maintenance-free.
Batteries are the primary storage source for off-grid systems, but they also work as an emergency backup power source for grid-tied systems. Installing a grid-tied system with a solar battery backup also gives you the option to sell excess stored power back to the utility company at a later time.
In this article, we will list what is the best, the worst and most cost-effective battery options for solar or any other renewable energy storage system. Plus, we will introduce a brand new battery technology that is getting rave reviews. And we’re not talking about lithium-ion batteries. So stay tuned to the end to find out about this technology.
Lead-acid battery
So the question is what are the best batteries for solar? Well, contrary to popular belief, the flooded lead-acid batteries that are using cars are not the best option. In fact, they are one of the worst options. Unfortunately, in the developing world, mostly flooded lead-acid batteries are used because they’re cheap and easily available. These car or truck batteries are designed for providing high bursts of current for a short duration of time. So to run starting motor for the engine, and this is inverse to the requirements of the solar energy storage system, which requires the ability 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. The car cranking battery has smaller electrodes. For solar application. Deep cycle batteries are best suited. In construction, deep cycle batteries have longer electrode plates inside them. The lead-acid battery is a very established technology and within the lead-acid umbrella, There are different types of battery names of each other as follows. Flooded lead-acid battery, the AGM battery, and GEL battery. In flooded batteries, the electrolyte is in liquid form and can flow. Whereas in AGM and GEL battery, the electrolyte cannot flow. And therefore, these batteries can be used in any orientation. Both the AGM and GEL batteries are maintenance-free where in flooded batteries, the water for the electrolyte has to be topped up from time to time. Again, it is emphasized here that for solar applications, avoid using a car or even truck batteries, because on the outset they might be cheaper. But in the long run, they’ll turn out to be the more expensive option.
One should aim to acquire deep cycle batteries that are flooded AGM or GEL batteries. In terms of price, the deep-cycle flooded lead-acid batteries are the cheapest, whereas the AGM and GEL batteries are almost the same prices, but more expensive than flooded batteries. Their price ranges from $80 per kilowatt-hour to $150 per kilowatt-hour. GEL batteries are very similar to an AGM in terms of performance but have a slightly longer lifespan.
In addition, Lead Carbon battery is an evolution of the traditional, tried & tested VRLA AGM lead-acid technology. In a Lead Carbon battery, carbon is added to the negative plate which results in much longer life. In fact, the added carbon gives the battery electrode many of the properties of a super-capacitor, which improves charge and discharge performance.
Partial state of charge (PSoC) performance is also much improved, with almost no sulphation between 30 and 70% SoC. Sulphation is one of the primary causes of failure of traditional lead-acid batteries and is generally caused by partial charging and aging.
Advantages of Lead Carbon batteries versus Lithium batteries and Lead-Acid
- No BMS (Battery Management System) is needed to prevent over-charging and under-charging on a per cell basis.
- No thermal run-away risk of individual cells overheating, exploding, and burning.
- Much greater kW storage capacity per dollar compared with lithium. Approximately twice the storage capacity, or about half the price for the same.
Lithium-ion Battery
Next, 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. They also have a higher DoD and longer lifespan when compared to lead-acid batteries.
However, lithium-ion batteries are more expensive than their lead-acid counterparts. Again, within the lithium-ion umbrella, there are different types of batteries. The two main types that are used in solar energy systems are Lithium Ferro Phosphate and Lithium Cobalt Oxide.
Saltwater Battery
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 because of its price. It is one of the safest batteries on the planet. The saltwater battery can handle heat very well and is completely recyclable. It is a very stable battery with no maintenance. And it has a 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 of this battery is cheaper than lithium-ion but slightly more expensive than a lead-acid option. It should be understood that saltwater battery has many more charge cycles at a higher depth of discharge. And therefore it is a more cost-effective option than a lead-acid battery. Note that you can get 3500 charge cycles at 90% DoD.
However, the saltwater body has a couple of drawbacks. Firstly, it is slightly heavier than a lead-acid battery. And secondly, it can be charged and discharged at lower rates than other batteries. As noticed earlier. The saltwater battery is a cheaper alternative to lithium-ion, and the prices are expected to drop further with developing competition and economies of scale.
Battery Recap
So just to recap, the best option in terms of longevity is the lithium-ion battery if you can afford it, the next best option is the saltwater battery. Thirdly, the lead carbon battery. And lastly, we have the deep-cycle AGM or GEL batteries.
| 100Ah Batteries | Amp Hours Removed | Amp Hours Needed to Recharge | Efficiency |
|---|---|---|---|
| Saltwater | 100 | 120 - 130 | 70% - 80% |
| Flooded | 100 | 115 - 118 | 82% - 85% |
| AGM/GEL | 100 | 108 - 112 | 88% - 92% |
| Lead Carbon | 100 | 105 - 110 | 90% - 95% |
| Lithium-ion | 100 | 104 - 108 | 92% - 96% |
