Battery energy storage systems (BESS) are the best way to store any excess power generated by solar panels. Integrating solar panels with storage technologies will enhance the reliability and robustness of solar energy systems. The stored energy can be utilized in case of a power shutdown or on cloudy days when solar panels are not generating enough power.
Solar systems coupled with BESS work effectively and provide steady-state power backup throughout the year. However, sometimes the solar system is not able to store enough energy which can power up your appliances. This article has covered strategies and techniques implemented to fix a solar power system that is not storing enough energy.
Two Important Solar Battery Considerations & Suggestions
There are different types of storage systems available in the market that can be integrated with a solar system. The problem of low storage can occur due to the wrong battery type and size selection. Both considerations are covered below with their possible suggestions:
1. The Type of Battery Used
There are four different types of battery technologies available for a solar system which can affect the storage capability.
1. Lead Acid
2. Lithium-Ion
3. Nickel Cadmium
4. Flow
Nickel-cadmium and flow batteries are not primarily used in solar power systems. Lead acid and Lithium-Ion batteries are most commonly deployed in solar systems within residential and commercial settings.
Lead acid batteries are a reliable and low-cost storage option for solar power systems. But due to a lower depth of discharge and lesser energy density lead acid batteries can’t store more energy as compared to Li-Ion batteries.
Contrary to the above, Lithium-Ion batteries have higher energy density with longer life spans. Li-Ion batteries have a higher depth of discharge, thus they can hold more energy as compared to Lead acid batteries.
Therefore, whether it’s an off-grid solar system or a hybrid solar system, Lithium-Ion (Li-Ion) batteries should be installed to increase energy storage for a longer time. “How long do solar batteries last?” is the question that comes to the mind of every solar system user. When it comes to Li-Ion batteries, the simple answer is “They last much longer”.
2. Size of The Battery Used
Solar batteries come in a variety of sizes and designs. The Ampere Hour, or Ah, is the most common measurement of battery current storage capacity, and Kilo-Watt Hour is the most widely used measurement of battery energy storage capacity. Single solar batteries may vary in size from less than 100 Ah to more than 1,000 Ah. This corresponds to solar batteries having an energy storage capacity of less than 1.2 kWh to more than 12 kWh. The energy storage capacity of small residential batteries usually ranges from around 2.5 to 5 kWh and for larger commercial systems batteries from around 13 to 15 kWh.
The battery size problems that correspond to low energy storage are fixed by following the approaches:
1) For cost-effective storage, the ideal solar battery size for off-grid and hybrid solar systems will be the one that will cover the backup for the whole evening and nighttime usage. Therefore, in the worst case scenario when a power breakdown is faced by your home or office, then the solar system will be able to provide continuous power in the evening and night time. The following day, the solar system will recharge the batteries from sunshine or grid power.
2) Afterward, check this storage capacity against the size of your solar power system in kW and its charger capacity in Ampere. If the size of the solar system is small then, there is no need to deploy a bigger rating battery.
3) The ideal size of solar batteries should be the one that provides backup in the worst-case scenario with litter extra space.
Other Common Solar Energy Storage Problems & Solutions
The most common questions asked by off-grid & hybrid solar system users are “how long do solar batteries last?”, and “why my solar system is not storing enough energy? To answer these questions we have discussed some problems which can happen with the battery storage system that should be fixed to enhance solar energy storage and are covered below:
1. Faulty or Dead Battery
Solar batteries have a limited life span i.e. their life depends on the number of charge/discharge cycles used. Therefore after completing these cycles, solar batteries come to an end-of-life period and replacement is the only option. The charge/discharge cycles of typical solar batteries are given below:
1) A standard Lithium-Ion battery delivers 6000 cycles at 90% depth of discharge or 8000 cycles at 80% depth of discharge. Therefore, 90% of discharge with 6000 cycles would approximately become 16.43 years based on one cycle a day, or 8.2 years at 2 cycles a day.
2) A typical VRLA battery usually has less than 1200 cycles at 80% depth of discharge, or 2500 cycles at 50% depth of discharge. Therefore, 80% discharge with 1200 cycles would approximately become 3.28 years based on a single cycle a day, or 1.64 years at 2 cycles a day.
3) Lithium-Ion Batteries have more cycles as compared to VRLA batteries at the same depth of discharge. After this given timeline, the battery should be replaced with a new one.
2. Overcharge & Overdischarge Battery
When a load is connected to an off-grid or hybrid solar power system, the batteries are discharged and the load draws the current from the batteries. Therefore, battery discharge happens when the battery is depleted of charge. When a greater amount of current is drawn from the solar battery, it will be an over-discharge condition and should be avoided to increase battery life. Similarly, overcharging a battery will also reduce its charge-retaining capability. Below is the standard voltage range for solar batteries:
1) Standby use charge voltage at 25 °C: 13.5V-13.8V
2) Cycle use charge voltage at 25 °C: 14.1V-14.4V
Overcharging & Over Discharging both conditions can be avoided by using good quality solar power inverters having smart solar charge controllers. Discharges of a solar battery deeper than 50% (below 12.0V) significantly shorten the Cycle Life of a battery.
3. High Battery Temperature
Solar batteries are sensitive to changes in temperature. The solar batteries should be kept between 50°F and 85°F for optimal performance. The optimal temperature is 70°C, although 50°F to 85°F is an acceptable range. If solar batteries are kept below or above this temperature range, then their energy-storing capability reduces. Therefore, for the efficient working of a solar system and handling enough storage, its batteries should be kept in the mentioned temperature range.
Conclusion
Whether it be an off-grid solar system or a hybrid solar system, adding a battery energy storage will enhance its reliability performance. Batteries will not only provide backup power in electricity breakdown but also helps to manage costs associated with peak factor charges. Batteries can get some problems and don’t provide enough energy, if not properly utilized and maintained.
This article has covered all the factors and aspects that should be considered when designing a solar power backup. The article also provides simple fixations to common problems that can occur during their usage. It is recommended to always read the manufacturer’s user manual that comes with the components of a solar system before doing troubleshooting tasks. Contact your solar service provider in case of any technical assistance.
