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The best battery for solar energy storage


The solar energy battery storage is still the number one problem for the future development of solar projects. In this blog we will discuss the use of lithium iron phosphate (LiFePO4) battery for stand-alone solar photovoltaic (PV) applications. There are many advantages of this battery, such as: they are environmentally-friendly, much safer than other lithium batteries, have long cycle life and comparing to other solar batteries relatively low lifetime costs.

solar battery energy storage

Different characteristics of batteries from various manufacturers have been studied in several battery tests. Among the examined properties are the relations of capacity, state of charge (SOC) and end-of-charge voltage as well as different charge-discharge durations. Differences between the capacities specified by manufacturers and the ones reached in experiments are reported. The tests show that LiFePO4 batteries are an ideal choice for stand-alone Solar (PV) systems due to their high efficiencies and long cycle life, if they are operated with a charge controller specifically designed for a long charge duration as they are typical in solar PV applications.

Introduction

Stand-alone solar photovoltaic (PV) applications provide an enormous benefit to places where no grid is nearby, and the cost of solar systems must be compared with those of bringing the grid to that location, which could be up to several thousands of US dollars per kilometer. In many remote areas, they also compete with gasoline or diesel-powered generators that often use subsidized fuel and for which users are charged on a “pay-as-you-use” base. Apart from the much higher environmental benefits compared to diesel generators or individual kerosene lamps, the large-scale dissemination of stand-alone solar systems heavily depends on the lifecycle cost of the systems, which are mainly driven by the cost and the frequency of exchanging the batteries. This is addressed here by proposing a new type of battery for solar PV application: Lithium-iron-phosphate, LiFePO4 battery.

smart solar battery lithium lifepo4

In developing countries, a small solar panel and a battery to run a few lights and a radio can change people’s life. The charge and discharge rates in these systems are typically very low, ranging from 10 hours to 100 hours for a full cycle. With the significantly decreasing costs for solar panels in the past few years, batteries are playing cost wise a more important role. Their limited lifespan compared to solar modules (20+ years) increases the total cost of the whole system correspondingly. That is why it is so critical to choose wisely the right battery for your solar application.

Lead acid batteries, such as AGM and GEL, have been usually used for stand-alone systems and of course for solar applications, though they have many disadvantages, such as possible leakage of acid due to damage or spillage, noxious fumes given off during the charging process and their heavy weight-almost three times more than LiFePO4 battery. Also, the disposal of lead acid batteries often does not happen in a very environmentally friendly way, especially in remote areas, threatening the local people’s life for a long time. Another significant problem of lead acid battery is the fact that they age faster when kept in a low state of charge. Lead acid batteries need therefore to be frequently replaced due to this aging effect, which leads to additional system cost over time. Alternatively, in stand-alone system design, lead acid batteries can be over-sized compared to their nominal capacity, which then, however, increases the initial capital cost of the batteries significantly. LiFePO4 batteries are widely used in electrical mobility applications, due to their advantages over other kinds of battery types: one key feature is its superior thermal and chemical stability, which provides better safety characteristics than lithium-ion batteries with other cathode materials. Due to significantly stronger bonds between the oxygen atoms in the phosphate (compared to cobalt, for example), oxygen is not easily released and as a result, lithium iron phosphate cells are virtually incombustible in the event of mishandling and can survive high temperatures up to 85°C without decomposing. The LiFePO4 battery is environmentally friendly, there is no hazardous or noxious substance inside the battery, which is also an excellent feature for stand-alone solar system application, because most of the end users are in remote areas, where safety awareness is very low. The specific volume of a LiFePO4 battery is 65% of lead-acid batteries and the weight is 1/3 of that of a lead-acid battery, which also makes the battery more portable. The total lifespan (cycles) is about 2000 cycles with the capacity still reaching 80%, which is 6-7 times higher compared to lead acid batteries over the entire lifetime. Moreover, it is maintenance free and does not get affected by longer duration in low states of charge, which allows for a higher utilization of its capacity.

A comparison between various types of lead acid batteries, Li-Mg/Co batteries and LiFePO4 batteries for stand-alone solar system. It indicates that LiFePO4 batteries have a higher initial investment cost, but the