A Lithium battery is often the most expensive element in a solar installation, and as a battery is a long term investment, it is important to take into account all aspects of a battery before buying. There are a number of parameters that are important to consider when buying batteries, for example:
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Voltage and Capacity
The Voltage of a battery will have to match the Voltage of your inverter. These days, most home solar or backup installations are 48 Volts (V). The higher the voltage, the less energy losses take place inside the system.
The Capacity of a battery is the total amount of electricity that it can store, measured in kilowatt-hours (kWh) or Ampere-hour (Ah). If the battery capacity is measured in Ah, just multiply the Voltage of the battery with the Ah rating:
Wh = Ah x V
To calculate how long a battery will last, for your intended use, you can multiply the loads you want to connect, by the duration you want to run the loads for. For example, your load is 1 kW (1,000 Watts); a battery with a useable capacity of 4 kWh will run this load for 4 hours.
Time (hours) x kW = kWh
C-rate
While capacity tells you how big your battery is, the C rate tells you how much power a battery can provide at a given moment, or how quickly the battery can be charged or discharged.
A battery with a high capacity and a low C rate would deliver a low amount of electricity (enough to run a few crucial appliances) for a long time. A battery with low capacity and a high C rate could run your entire home, but only for a few hours. The C-rate is relative to the capacity of the battery, e.g.:
In summary, 1C means that the battery is fully charged and discharged within one hour, 2C is 30 minutes, and 0.5 C means 2 hours.
Example: a Pylontech USC will have a C-rate of 0.5, while some other batteries have a 1 C-rate. To be sure that a 5 kVA / 4 kW inverter can run at its full potential, you would need at least 3 of these Pylontech batteries.
Depth of discharge (DoD)
The Depth of Discharge (DoD) of a battery refers to the amount of a battery&#;s capacity that has been used. Most battery manufacturers will specify a maximum DoD for optimal performance. For example, if a 10 kWh battery has a maximum DoD of 90 percent, you shouldn&#;t use more than 9 kWh of the battery before recharging it.
In theory, all Lithium batteries can be discharged at 100%, but this will shorten its cycle life and might affect warranties. The stated DoD in battery specifications should therefore always be considered together with the life span (see below).
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Life span, warranty and back-up support
In general, most Lithium batteries will have an expected life-span of somewhere between 8 and 16 years. In most home solar systems, your battery will &#;cycle&#; (charge and discharge) daily. Over time, your battery will lose some of the charge.
This is similar to the battery in your &#; you are charging your each night, and as your gets older, the battery doesn&#;t last as long as it did when it was new. Extreme temperatures can affect the life span of a battery. The life-span of a battery is often stated in number of cycles, e.g. 4,000 cycles.
Your battery will have a warranty that guarantees a certain number of cycles and/or years of useful life, often for a certain maximum DoD. Warranty often states for example &#;10 years at a maximum (or average) DoD of 80%&#;, and that after 10 years &#;60% of the battery&#;s capacity&#; will remain. Always try to check for this statement in a battery&#;s specification, the DoD in combination with life span and remaining capacity.
Another aspect to consider is back-up support, and whether this support can be provided locally as well. For example, if a battery is assembled locally, and there is a specific battery cell that happens to be faulty, the manufacturer can come and simply swap out that cell. However, for many imported batteries, the unit has to be sent back to its origin for repairs, and you might have to wait for a long time to get your battery back once it is repaired.
Expandability
Most batteries are designed to be &#;expandable,&#; which means that you can add multiple batteries to your solar system to get extra capacity. Check for this option to make sure you can expand your system in the future.
Mounting
Some batteries can be wall-mounted, others have to be placed on the ground, and sometimes you need to buy specific cabinets. If, for example, you have limited space in your garage next to the DB board, the mounting system is something to consider as well.
Other considerations
Other aspects to consider are, whether you need extra specific battery cables, whether the battery is compatible with your brand of inverter and whether the battery is able to communicate with the inverter, and last but not least of course the what the total price is, compared to the quality of the battery. Price per kWh would be useful for comparison, taking into account, warranty, number of cycles etc; in short considering all the issues discussed above.
I just had a chat with DHL about this as I'm curious about this myself.They told me that this:... only applies to international postage and not UK postage. They said I cannot post any lithium cells internationally but I can send them within the UK and asked how many I wanted to send, so I looked at the international guidance and said between one and eight (based on what it said).The guidance linked above says that I need to put a certain comment in the handling instructions, however when you go to book delivery there is nowhere to put that information. I originally asked for some clarification on this and the answer was "that document is for international postage" and "we have customers sending batteries in the UK". I asked for some documents/guidance to support this but most of my questions were deflected or walked around by repeating that they have customers sending lithium cells within the UK.I even plainly asked for the steps I'd need to carry out in order to go about sending lithium cells within the UK and I couldn't get anything other than "we have customers sending lithium cells in the UK".They say that they can't provide any guidance on sending lithium batteries within the UK, other than "it depends on how big they are, small mobile batteries are OK". I asked for specifics but couldn't get anything.I went back and asked why they wanted to know how many cells I wanted to send, and was told that it depends on how many I wanted to send. So I asked how many mobile batteries I could send since they mentioned those specifically themselves, and the answer was two. They couldn't provide any documentation to back this up. I asked how many s I could send and couldn't even get an answer, no documentation, no guidance.I asked about how I'd have to package them, how I'd have to label the box, basically everything in the linked document above, nothing.They then told me to go to FedEx.It's all a bit of a shambles and to be honest I find it all quite strange like something's not quite right. The law says that you pretty much cannot send lithium batteries in the post unless it's with original equipment. So then how do you buy lithium cells, which is something that I can do even from RS and the like?
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