The top 7 considerations when looking to purchase battery storage backup. Today I will only focus on Lithium Iron Phosphate batteries as they are very common in the market today.
1. Is your inverter capable of utilizing battery backup? Like I wrote in a past article, not all inverters are the same. Some are able to be paired with battery backup and some are not. If you are not sure then ask an expert. They can let you know.
2. If your inverter is capable of battery storage then the next consideration is what is the nominal voltage needed for your inverter? Some common nominal voltages of battery storage are 48 Vdc and 300-400 Vdc. Ask an installer or an expert to walk you through the differences.
3. Once you know what voltage is needed, you need to consider what size of battery do you want or require. This is where it gets a little more involved. Talking to an expert can help you through this portion of the process. Let’s start with the basics. Are you looking to be able to supply energy to your house to just ride through the frequent short power outages in your area or are you looking to use battery storage to supply the energy for your house during the entire evening (12 hrs)? There are differences in choosing the right battery for this application. For example if your inverter was capable of using the LG RESU battery then you have a limit of 2 batteries in parallel, per inverter totalling approx 20 Kwh of storage per inverter. If you don’t want to buy additional inverters but want high levels of storage then choose a different battery or inverter if you were still in the planning phase of purchasing a solar system. Other batteries on the market allow much higher storage capacities that can be paralleled together up to 15- 5.12 kwh batteries. Thats a whopping 76.8 Kwh’s of storage. This is important to understand when choosing a battery backup system, it is also important to understand when choosing an inverter. Some inverters are limited to certain battery options. Know the difference before purchasing a system. Ask an expert.
4. Common Battery types and sizes. This is a huge topic in itself, so I will only generalize specific points. As stated there are different nominal voltages but there are also different styles of mounting or racking. These two generalized types are network rack mounted batteries or wall mount batteries. They are self explanatory as one comes with a cabinet to mount the batteries together, similar to a network cabinet and the other has its own mounting bracket that fastens to the wall. Network batteries are typically 5.12 Kwh batteries with some manufacturers making 4.8 kwh batteries of a similar size. Wall mount batteries tend to be larger in size, weight and capacity. All batteries are heavy as it’s just the way they are made.
5. Discharge rates. Each battery has a specific discharge rate. This is listed in the spec sheets as current or Kw’s. For example the LG RESU battery is limited to a 5 Kw discharge rate where as the EG4 PowerPro can discharge at a rate of 10 Kw’s. That’s a big difference when you are running larger loads in your home. This is why experts ask you questions regarding your energy consumption and what electrical appliances you have in your home. They want to match up the best inverter and battery system for your application.
6. Battery Cycles rating, what does that mean? We all understand 5 years or 10 years warranty. But battery cycles are a little different. First let’s explain what a cycle is. A typical cycle is from 100% charge to 20% charge. So when you see a statement saying that the battery is good for 6000 cycles, its referring that you can safely cycle your battery 6000 times from 100%-20% which is known as the DOD or depth of discharge in this case its 80%. All batteries lose storage capacity over time. With 6000 cycles at a DOD of 80% most batteries will retain a specific storage amount in that battery after the 6000 cycles is up. Usually that is between 70% and 80% of the batteries original capacity. This doesn’t mean that the battery is no good after 6000 cycles, it means that it has lost some storage capacity. Most batteries today list 6000 cycles. I use one battery manufacturer that boasts 8000 cycles and I use this battery in my quotations to clients. That’s 21.91 years of cycling 100%-20%, that’s great value for the clients system. Typically there is one cycle per day if your inverter is set up to supply energy to your home during the evening. The inverter will utilize the battery energy instead of the grid energy up to the 20% discharge setting. If you had a large battery capacity then it’s possible that you would not reach the battery cut off of 20% so you could be dealing with half cycles which I will not cover in this article. These cut off points are programmable and can be changed in the set up of most inverter. Some batteries also have this cut off set up function in their BMS.
7. Closed loop communications, what does that mean for a battery? Closed loop communications means that the battery sends information to the inverter so that the inverter doesn’t overcharge the battery and destroy it. This is 1 level of safety that is built into the battery and inverter system. Overcharging will kill a battery and in some cases it can actually cause the lithium battery to catch fire. These days most quality batteries have a built in BMS, Battery Management System that can shut itself off if the inverter keeps charging. There are 3 levels of safety that I will discuss in more detail in a separate article. Stay tuned. In this article I will only discuss the closed loop communication between the inverter and battery. The short explanation for this safety feature is that the battery sends information to the inverter; the inverter monitors that information and adjusts the charging output accordingly. That information is the state of charge, battery voltage, current levels being discharged or charged, battery temperature etc etc. It’s simple and straight forward and in my opinion it should be a part of all solar system designs. When purchasing a solar system, ask if there is closed loop communication between the battery and the inverter. It’s worth it.
Well there are many more features that we could discuss regarding batteries, but in an effort to keep this article short, I think I will break those up into individual topics for later. I hope this was helpful and that it gave you a better understanding about battery storage and what to look for. As always, if you want more information I am happy to help, please contact me at sunnysidesolarcr@gmail.com or 506 6330-5137 what’s app. Till next time everyone. You can also follow me at Sunny Side Solar Solutions facebook page to read my weekly articles on many different solar topics. These same topics can be read at my facebook group at Costa Rica Solar Installation Reviews along with other important information related to solar.
