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4 Incredibly Useful Battery Tips for Your Solar Street Lights

04 August 2017
 
One of the main reasons why solar powered street lights have bad reputation is due to the fact that certain solar producers are deceiving potential buyers when it comes to solar rechargeable battery models, battery management and life cycle. In this blog, we will share our experience on this topic so that next time when you consider buying solar street lights (or any other solar system), you are fully prepared to save money, time and resources.
 
Every off-grid system has a battery bank for storing energy which is generated from the solar panels - if you would like to know more about how solar panels work, check out this link. However, not all solar batteries are the same and following specific parameters before making a purchasing decision will significantly improve the work of your solar outdoor lighting system. Cheap and inefficient battery models will incur high maintenance costs and will never deliver the performance of a reliable solar system. That is why you should have all the answers to the following crucial questions before getting your solar battery model:
 
  • Which battery models should I consider for my solar outdoor lighting system?
  • What is the expected battery life cycle in solar street light applications?
  • What is the price of each solar battery type under consideration?
  • What is the battery maintenance cost and how frequently it should be monitored?

 

By the end of this blog post, you will have all the necessary information about choosing the perfect battery type for your solar street lights. Next time when you talk to a solar company sales representative, you will be able to minimize your chances of making a mistake or being deceived. Let's find out how you can do this... 
 

Question 1: Which battery models should I consider for my solar street lights? 

Let's first define each type of solar battery in order to better understand the concept behind this technology. As some of you may already know, there are several types of solar batteries to consider when choosing a battery bank for solar outdoor lighting. We will only mention the three types of batteries that are most frequently used by solar street lights manufacturers in order to keep things straightforward and up to the point. 
  • Flooded lead acid battery
  • Sealed lead acid battery
  • Lithium-ion

AGM Battery for solar street lights.jpg

Flooded lead acid battery was first developed in 1859 by the French physicist Gaston Planté. It is the oldest type of rechargeable batteryThe flooded battery contains liquid electrolytes and is quite cheap when compared to newly developed battery technologies. Flooded lead-acid batteries are commonly used when surge current is not of high importance, as they are designed to provide higher energy densities. They are usually used for energy storage and UPS systems in cell phone towers, hospitals and other stand-alone power systems. 
 
Sealed lead acid battery has many names and industry professionals usually refer to it as AGM Battery or Valve Regulated Battery (do not get confused, the technology is the same). These solar batteries are made of Absorbed Glass Mat (AGM). They are designed for deep cycling and are maintenance free. Due to their inner structure, which contains no liquid materials, they can be positioned in any direction without worrying about possible spill out. 
 
Lithium-ion battery is the most common battery model. Its applications vary from cell phones to electric vehicles. They have low density, high charge and discharge efficiencies and high number of life cycles. 
 
Now that we know what type of batteries are out there, we need to compare them and see which one will be the winner in terms of solar street light performance and cost efficiency ratios. 
 
 
Question 2: What is the expected battery life cycle in solar street light applications?
 
In terms of expected life cycle, we have to say that Lithium-ion batteries should be the primary choice for consideration since on average they have greater life cycles than both flooded or AGM batteries. However, the main disadvantages of this battery model is the enormous market price tag and its unstable structure (easily exploding due to overcharging). On the other hand, if you buy AGM batteries from a verified supplier and you take care to properly manage, optimize and configure them, they can last up to 10 years. In fact, AGM batteries are quite competitive in the market and can be a very efficient alternative to Lithium-ion batteries. Now, that's something! However, you will usually hear that AGM batteries last up to 5 years and the warranty is up to 2 years. If you ask me, it all depends on the battery management steps you undertake to prolong your solar battery life cycle.
 
LIFE CYCLE VS. DEPTH OF DISCHARGE
 
Battery lifecycles for solar street light.jpg
 
Our company Lightinus is experienced in using smart off-grid solar controllers which are able to adapt the charging and discharging of solar batteries in real-time, including temperature compensation. Smart technology and system optimization are quite suitable for optimizing AGM battery models (you pay lower price than for Lithium-ion batteries and make sure that you get greater value in terms of life cycles). As the number of life cycles is greatly dependent on the depth of discharge (DOD), we always optimize our smart solar street lights for minimal DOD - between 10%-20%. To read more on the most important system components of smart solar street lights, click here.
 
Finally, the expected life of flooded batteries is the same as AGM batteries. However, high maintenance cost and ventilation limitations (which prevent burying them underground during installation of the pole) exclude flooded batteries from being the best fit for solar outdoor lighting applications.
 
Important Note: Placing batteries underground improves solar battery life cycles due to lower temperature variations. 
 
Solar Battery Placement underground battery box.jpg
 

To conclude, the winner in this category is the AGM battery model, but only if connected to a smart solar charge controller which can optimize its performance and prolong its life cycle. If you want to find out more about this topic, check out this blog: How to increase solar street light performance and reliability?

 

Question 3: What is the price of each solar battery type under consideration? 

 

In terms of solar battery price, Lithium-ion batteries are the most expensive of all battery models. Let's put it this way, if you want to properly size your solar street light performance, you would need to invest around $1000 just for Lithium-ion batteries alone. However, the advancement in wireless communication technologies and software applications gives you the ability to remotely control battery performance (in terms of charging, discharging, temperature compensation and proper configuration). With such monitoring tools in your hands, AGM batteries, which can cost as much as $500, can deliver the same results (if not better) as Lithium-ion batteries. Flooded batteries on the other hand, are the cheapest of all categories. But, they ask for constant maintenance and ventilation, which eliminates them from usage in solar street lights projects.
 
To make your life easier when comparing these three solar battery models, I am listing below the most important categories for calculating the total cost of a solar battery over its lifetime. 
 
  1. Price: We know that low price always sounds good. However, when you buy cheap solar battery you will have to replace it after 2 to 3 years, which will drastically increase the cost of your initial investment. That is why you should always try to find the right balance between pricing, performance and solar technology that is available in the market.
  2. Capacity: If you want your solar battery to last longer, you need to make proper configuration of your solar off-grid lighting system. The following article will give you insights on how to configure your solar LED street lights: WHAT'S IN YOUR SMART SOLAR STREET LIGHT: SYSTEM DESIGN AND COMPONENTS
  3. Voltage: Battery voltage needs to be aligned with the rest of the solar outdoor lighting system. For example, if your loads (LED lights) are 24 Volts, you will need to go either with two serially connected batteries (2x12 Volts) or with one solar battery (1x24 Volts).

All of the aforementioned tips have to be considered when purchasing a certain type of solar battery since these costs will add up to your initial investment calculations. For a smart solar outdoor lighting system to function over a 25 year period, my estimation of the total cost of an AGM battery model is up to 1000 USD (including replenishment costs). 

 

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Question 4: What is the solar battery maintenance cost and how frequently it should be monitored?

Both AGM and Lithium-ion batteries do not need to be refilled and significantly maintained in the long run, which puts them at advantage when compared to the flooded battery model. When you have solar street lights projects with solar batteries buried underground during installation (if the solar companies tell you differently, please ask them how do they protect the batteries against extreme temperatures), then you are not going to be able to maintain them much. As we have explained previously, the solution in this case is to have a smart off-grid controller as part of your solar LED street light system. This smart device will provide you with the ability to remotely control your solar battery performance and even predict how long the battery will last.  

 

Remote Monitoring for solar street lights.jpg

 

Final Advice: If you are not able to monitor and adapt battery charging according to your current energy consumption and external temperatures, your solar battery life span will be around 3 years. This means that if you go with AGM batteries without remote control features, you will end up paying every 3 years for a new battery set.

To conclude, flooded batteries may be a suitable solution for certain solar system applications. However, we have seen that they are not the right choice to make when implementing solar outdoor lighting projects. Lithium-ion batteries may have the longest battery life (the most life cycles), but the pricing tag that comes with them is still not competitive enough to generate a positive ROI from your solar street light project. 

AGM (VRLA) seems to be the best choice at the moment, with one caveat in mind: they need to be accompanied by smart technology which will enable the user to remotely control and monitor the battery to ensure longer life and high performance. 

CTA for Ebook: Ultimate guide for solar street lights

Looking forward to your comments, let's discuss and make some progress!

Source: Smart Solar Street Light, Solar Street Lights, Remote Control, smart solar LED lights, solar battery, battery models, battery price, battery maintenance, solar powered street lights, solar outdoor lighting, battery life cycle

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Andrej Gjokik

Business development

andrej.gjokikj@lightinus.com+38971368839
Technical Guide for Smart Solar Street Lights