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  • Ian

Lead Acid to Lithium batteries for off grid

Updated: Feb 14, 2022

We woke up one day to find our power system completely failed. The inverter, which converts DC to 240V AC, has a low voltage light blinking. The voltage has dropped to a point where the system shut down. Our battery has failed. We knew it was coming since we had been testing the batteries but now we are confronted with the reality.

Living in the bush can often involve living without any connection to the electricity network, supplying your own power, running 'off grid'. It is a wonderful feeling to be independent and seemingly 'green' however the reality is you need to manage the power system yourself. One reality of living off grid is the eventual failure of the battery system. All batteries have a life span and will eventually fail.

Batteries

Our system is around 8 years old. The battery bank is made up of a bank of 12 flooded lead acid batteries or cells, which was the most common type of battery at that time. Each battery or cell has a voltage of a little over 2V, when combined makes up 24V (2V x 12). These cells are large, six pairs of these will fill an area of two washing machines with each pair weighing nearly 100kg, totaling almost 600kg.


We were always told if one cell fails you have to replace the all of the cells. This is not exactly correct as we found after contacting suppliers. It is not recommended as it may affect all the other batteries and so cause problems with these but it is possible. It may give you an additional few months or even years by replacing the individual cells but each cell retailed at about $1000 so this could get expensive as each of the other cells does eventually fail. Batteries have a definite life span, although no one will say how long that it. "It depends" is the usual answer from suppliers when you ask. If you treat them well maybe 10 years but cells fail for lots of seemingly unknown reasons.

Batteries are one of the most expensive and important parts of an off grid system. Our original battery bank cost over $8000 eight years ago. These were the flooded lead acid batteries where you have to top up the water level regularly. Later models of lead acid batteries are often gel and so have less maintenance.

Suppliers

We started our journey by getting quotes from several suppliers in our region, northern NSW.

The current system was supplied by a nearby supplier, Rainbow Power from Nimbin, so these people were the first we contacted. They confirmed that the batteries were failing and we talked about replacing the bank. They also did mention replacing the failing battery, which was a surprise to us given we had always been told you shouldn't do this, even by Rainbow Power years earlier.

When we got quotes we were surprised by the variation in amounts, ranging from $8000 to $14000 for essentially the same gel lead acid battery. Rainbow Power was the only supplier that had any other battery other than lead acid. They quoted $12000 for a lithium battery replacement, installed. The other suppliers either dismissed lithium or were honest enough to say they didn't know enough about them.

Time to look further afield by researching the internet. We started to learn lots about lithium batteries. No other supplier seemed to have a good understanding of them, especially for off grid applications. Any information found is filled with technical jargon making it really difficult to understand.

We did come across a great site Solar Quotes and submitted our requirements and received some excellent information including a referral to another site, Solar Batteries Online.

There is a lot to learn about lithium batteries but online supplier sites are essentially interested in selling an item rather than informing or educating, just as you would expect of an online site.

Learning about Lithium

Lithium batteries have a number of major advantages over lead acid or similar batteries. They are smaller and weigh less, that is not to say that they are small or light, they aren't, just relatively so.

Also lithium batteries can be discharged to 0%, although they have a longer life if they aren't completely. This is significant when calculating storage capacity. More about that later.

They also don't require any real maintenance, unlike flooded lead acid batteries which need to be regularly topped up with distilled water.

To understand lithium batteries you need to understand a little about batteries in general. It can get a little technical but understanding a few terms helps.

  • Battery cycles - this will tell you how long the battery should last. It is measured in the number of charge and discharges cycles. For house systems a cycle can be considered a day - day time charge and night time discharge.

  • Battery Management System - BMS is the internal management of the lithium battery to ensure the battery is not damaged during charge or discharge. A primary safety feature.

  • Storage Capacity - How much energy does the battery store and how much is available for use. This is measured in Amp hours or Watt hours.

  • Recharge cycles - How the battery is best charged.

Lithium battery types

There are a number of types of lithium battery. (Check out this site for more detail) Some are designed for smaller appliances, like phones, or different types of environments where temperature may be extreme. Some lithium batteries can cause a fire in some situations. The battery most recommended for homes is a lithium-iron phosphate (LiFePO4) battery being the most stable (no fire) while providing good storage in relatively smaller space.

These LiFePO4 also tend to behave in a similar manner to lead acid batteries so can replace the old lead acid batteries with a few adjustments to the solar charger.

Buying Batteries

We decided on LiFePO4 batteries as they are the most recommended for home use and won't cause a fire. The next is to identify the capacity required, given that these lithium batteries can be discharged to a fair greater degree than lead acid batteries. We calculated we needed around 6kW to get an equivalent amount of usable storage. See below for these calculations.

Lead acid batteries are big and heavy. Their shear bulk usually requires a supplier to install. Lithium however are considerably smaller and lighter so can be acquired and delivered via an online site. They can be installed relatively easily.

Lead acid batteries compared to lithium batteries

There are a variety of suppliers of these types of batteries. We need a battery that will replace our current batteries, with minimum additional equipment.

Most people have heard of the Tesla battery. This battery is actually a lithium cobalt battery and are really specifically designed for use on the grid. It and many of its competitors won't just plug into the system that we have.

We found one manufacturer, PowerPlus an Australian company, that did allow us to simply replace the old battery without additional equipment just a few changed settings to the charger/regulator. Their 24V product stores 3.3kW hrs and additional units can be added together to increase capacity now or later. The batteries are manufactured in Australia and surprisingly were the least expensive of all comparable batteries. We purchased 2 units for around $6700 including $200 delivery. Each battery is quite heavy, 35kg, but is about the size of a large computer, in fact it can be installed in a computer cabinet.

The order was placed and a few days later the batteries turned up at the depot.

Installing

The trick is to incorporate the new batteries into the old system with minimal disruption. The old batteries filled a large wooden box located on the verandah with the main cables running inside to the regulator and inverter. We needed to join the two batteries in parallel and connect these to the cables.

We acquired a sheet of bronze and cut to a couple of strips then drilled holes into each strip making two bus bars, connecting one to the positive and one to the negative. Each battery was connected to each bus bar then the cables running inside are added connecting the batteries to the main system.

NOTE: Always shut down the whole system before disconnecting or connecting anything.

The cables are connected to the battery using an easy clip connection, a ??????, making it easy to establish a secure and clean connection.

Once everything was connected it was time to turn on the system. We had already checked the voltage of each battery before connecting which showed a voltage of just over 27V each. The system turned on without an issue and showed a voltage of 26.5V once when the load was added.

Charge settings

The regulator, which manages the charging and load, needed some changes to accommodate the lithium batteries. The main differences between lead acid and lithium LiFEPO4 battery relate to the maximum voltage (max 29.2V) for charging and the different way the charging happens. Our regulator has a custom setting which allows all the values typically set for lead acid batteries to be changed. See here for details of the settings that we used.

Running Smoothly

Since our installation and commissioning of the batteries we have been pleased to find no issues.

The battery behaves differently to the lead acid batteries. Lead acid batteries have a more gradual reduction in voltage as they are used while lithium batteries tend to stay around 26-26.5 with 0 to 50% use. Lithium batteries charge time is less and the voltage rises to about 27Vs then when approaching full rises to your maximum voltage which we set to 28V. Lithium batteries don't have to be 100% full most of the time like is recommended by lead acid batteries.

Recommendations and Disclaimer

We don't recommend any particular regulator settings as these will vary from one system to another. Our only experience is with the PowerPlus battery so we can't recommend them yet, however we have had no problem since they were installed and commissioned. We will provide further updates if any issues arise over the years of use we hope to get from these batteries. Their modular form is great though and they are really easy to set up.

We used Solar Batteries Online to supply the batteries. The reason? They were the least expensive and they had them in stock. Technical support was pretty poor with sometime one word answers to complex questions. We also approached Energy Connections for a quote and their responses and information was far better but they were a little more expensive and quoted two weeks after paying to receive the batteries at that time.

There are a number of battery manufacturers around so it is worth checking what is out there.

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