Why should I invest in lithium iron phosphate batteries (LiFePO4)?

With the current energy and environmental crises, now more than ever it is time to invest in LFPs. Perfect for your home, boat, caravan, and campervan, they are unrivalled in terms of efficiency, safety, and life-span. Cost effectiveness has doubled since the energy crisis, with payback on solar panel installations averaging at 12 years now averaging at 6! Beginning to invest in renewable energy systems now seems extremely worthwhile, not to mention an excellent return for those already invested. Read ahead if you are interested in finding out why LFPs and solar panels are the future and how to install them.

What are the main advantages of lithiums over other batteries such as lead acids?

More efficient charge and discharge

LFPs lead the way in maximising the amount of energy stored, being almost 100% efficienct in comparision to 60% for lead acids.

Higher cycle life

A battery ‘cycles’ when it charges to its maximum voltage and discharges to its minimum this is referred to as 100% depth of discharge (DOD). However, this applies stress at the battery’s extremities and we recommend 85% DOD (explained later)

Lead acid batteries

There are many different versions of lead acid leisure batteries, classified as type A, B or C. However, the class you purchase is usually undisclosed, and thus the quality. The number of cycles will vary between 50 and 250 and will be largely dependent on the price.

An LFP has the potential for thousands of cycles (approximately 2500). The steeper price upfront is paid back in just 125 cycles, giving them a huge advantage over lead acids. Overall, LFPs are more cost effective for long-term use.

How many times will my LFP battery cycle per day?

With a solar installation, your battery will usually cycle once per day, depending on patterns of use. For example, in summer, the battery will charge fully. Using electricity during peak daylight hours will be most efficient as it will be taken directly from the panels without needing to be stored. Using electricity at night will likely discharge the battery completely, resulting in one cycle for that day. However, cruising on a boat in the morning, using appliances at lunch, and then cruising again at night would result in the battery cycling twice per day (as it completely charges from the alternator on the engine, twice).

What depth of discharge should I choose?

As previously mentioned, a battery has undergone a cycle when it charges to its maximum voltage and discharges to its minimum. At 100% DOD, the maximum will be set to 100% and the minimum to 0%. You will receive the maximum energy during a cycle, but your potential number of cycles is significantly reduced to approximately 600 due to added stress on the battery at the top and bottom of its range. We recommend using 85% DOD as a long-term solution.

 

Our LFP batteries are programmed by Battery Management Systems (BMSs) to set the maximum at 92.5% and the minimum at 7.5%, where you lose 15% of your capacity during each cycle. Operating at 85% means your potential number of cycles reaches over 2500 as the battery is no longer being stressed. The choice is yours to make but consider the trade-off carefully. It is also possible to change your mind at any point and alter the DOD in the app. Click here for instructions on installing and using the app - coming soon!

How long will my battery last?

This is solely dependent on your choice of DOD. At 85%, cycling once EVERY DAY your LFP battery should last around 7 years. At 100%, cycling EVERY DAY your LFP battery should last around 2 years. Moreover, your battery will usually only cycle during spring and summer, meaning these figures will double! The larger the battery, the less it cycles, which greatly boosts its longevity.

In addition, after this time frame the battery will still be completely usable, it simply loses 20% of its capacity. For example, a 100Ah battery will decrease to an 80Ah battery. This will occur after 600 cycles for a battery operating at 100% DOD, and after 2500 cycles for a battery operating at 85% DOD. It will result in a barely noticeable change in everyday power use but will impact the distance (not speed) you’re able to travel in an electric boat for instance. The battery still holds a phenomenal amount of power and should not be discarded or replaced at this point. If you do require more energy, then investing in another LFP is the most plausible solution.

What are the differences between the 3 main types of batteries?

Lead acid

Distributors usually fail to mention that to reach the number of cycles advertised, lead acid batteries must be operating at 50% DOD. For example, if you would like your 100Ah battery to last the advertised 200 cycles, you will only be able to use 50Ah from it.

 

NMC (Nickel Manganese Cobalt) Li-ion

Known for their light weight and use in cars and bicycles, NMCs are however unsuitable for renewable energy systems. Their disadvantages are outlined below:

  • Expensive

  • Highly flammable (insurance will not cover them in your home)

  • Low thermal runaway temperature* (once hot enough it will self-ignite and begin generating its own heat)

  • Cycle life half that of LFPs (300 at 100% DOD, 1250 at 85% DOD)

  • Made with cobalt (scarce and generally not responsibly sourced)

LFP

Advantages

  • Higher cycle life

  • Made with iron and phosphate (abundant resources)

  • Safer (higher thermal runaway temperature*)

Disadvantages

  • Heavier

  • Life expectancy diminishes if charged below 0°C

Note: lithium itself is not a scarce resource

*For further insight including the battery chemistries, please visit Powertech Systems

and Battery university

How safe are LFPs?

Some LFP battery suppliers do not offer Battery Management Systems (BMS), but we value them, knowing they are crucial in protecting the battery. A BMS ensures it is impossible to flatten/destroy it, damage it through temperature, overcharge, or draw too much current from it.

Our cells will never reach thermal runaway, both intrinsically (as they are too small at 6Ah to self-ignite) and if artificially triggered by an eternal source heat source or hammering a nail into them for instance. Any cell larger than this will be dangerous in your home and should be avoided at all costs.

Cells operate best at 24°C, any higher or lower and your 100Ah battery will stop giving out 100Ah. The cells have a default ‘workable’ range set at -10°C and 75°C but charging the battery at these extremes damages it and reduces the number of potential cycles. Fortunately, our BMSs can be easily programmed by an app to any range you wish. We recommend setting the limits at 0°C and 40°C through the app, meaning the battery will stop charging once they are reached, protecting it in the long-run as well as in emergencies like electrical fires. The heat of a fire would cause the BMS to shutdown the battery and save the cells from self-igniting and further fuelling the fire.

Some ways in which you can avoid your batteries reaching these extreme temperatures is through thermal insulation (we recommend 25-50mm PIR insulation board) or painting your battery enclosure white if it sits in the sun.

How do LFP batteries and solar panels work for caravans/campers and
motorhomes?

Charging from the car's engine via the alternator.

With fuel and energy economy in mind, new vehicles are fitted with smart alternators, which affects the type of charging required for your vehicle. If you are unsure about which form of alternator your vehicles has, visit autoelectro and enter your details under the ‘vehicle search’ tab. It is important to know how much current you can take from your alternator without damaging it. The smart alternators will draw larger currents from the alternator when you are decelerating or braking, thus assisting breaking and conserving energy.

Replacing lead acid leisure with an LFP battery.

The issues lie more in charging an LFP than discharging one. Lead acid batteries have a high resistance to charge, making them difficult to charge quickly (5-10A is a rough guide for a 100Ah battery,as they recommend 14 hours for a full charge.) LFPs are well known for fast charging and can exceed 200A on a charge for a similar size battery. This would put a strain on the alternator/cables and split charger if you have one. When fitted correctly, charge times can be considerably shortened thereby saving energy. The most popular charging methods are vehicle charging/solar charging and mains charging.

Suplementing an existing lead acid leisure with a lithium.

It is possible to fit an LFP battery as a leisure battery to co-exist with your pre-existing lead acid, however you need to isolate them from each other. Having a DC-DC converter on the input of the Lithium battery will isolate the inputs and a battery change over switch on the output will isolate the outputs. This does mean you have to manually switch the power from Lead Acid to Lithium and vice versa. If you try to parallel the batteries, then the high energy efficiency of the lithium will be lost, and a lithiums charged voltage can be high enough to drain wastefully into the lead acid.

​Charging from an alternator

With the shorter charge time of Lithiums over lead acids, there is a chance this greater power will overload and burn out your vehicle alternator. To overcome this, it is best to use a DC-DC converter which will regulate the charge current, we recommend one here.

Vehicles with a smart charge alternator will be able to charge at higher currents and more efficiently.

Charging from solar panels

You will receive approx 30% more power from your solar panel system with a lithium battery, rather than a lead acid. Your solar charger should have mppt and the ability to charge lithiums, if not it is important to replace it with one that can. MPPT (Max Power Point Tracking) is the ability of the regulator to allow the output of the solar panel voltage to stay at it's most efficient. It should be shown on the label of the solar panel. For a 12V solar panel, the Vmpp is approximately 18V.

Charging from the mains or generator (240V)

Your vehicle/caravan/boat/motorhome may have a built in 240V charger

Problem solving a lithium battery

The most common issue with lithiums is the very thing that protects it, the BMS (Battery Mangement Sytem), we humans are not used to a battery than can protect itself, the issue is not really a problem with lithium batteries as such it is more to do with the installer and the cheap products used to charge them with. If a charge system, say a solar regulator has the high voltage setting incorrectly set, then the battery will switch off to protect itself, but then the regulator which may be an auto detect voltage will show and alarm. The user may well blame a faulty battery. To solve this problem, it is best to set the battery at 100% DOD and all other chargers and inverters to 85% DOD, this way the battery will never switch off to protect itself.

What do I need to know about solar panels?

We advise using monocrystalline instead of polycrystalline or amorphous panels as they are the most cost effective with the longest lifetime and highest efficiency.

Solar panels can interfere with wind drag on your roof. It is best to place them as far back and low as possible. There is a trade off when it comes to choosing the best solar panels for you. We recommend using solid glass panels however some choose to opt for flexible ones:

Advantages

  • Slimline fit (better for wind drag and aesthetics)

Disadvantages

  • Technology optimised for flexibility of the solar cell and optimised for the efficiency and lifespan of the solar cell

  • Have a misleading ‘15-year warranty’ but come with a sticky back plastic, thus removing them would destroy it meaning you can’t send it back.

  • Compromised on using silicon chips (solid and brittle)??

 

The back of a solar panel will show several pieces of data

  • Power

  • Maximum current

  • Open circuit voltage – the voltage the panel sits at when you are not drawing any current

Test by putting a voltmeter across the positive and negative (with solar panel under bright sunlight)

  • Short circuit current

Test by putting an ammeter across the positive and negative (with solar panel under bright sunlight)

  • Maximum Power Point Tracking (MPPT) voltage – turns solar into battery voltage

 

The MPPT of your solar panel must be greater than the fully charged voltage of your battery (100% DOD).

12V battery – max voltage: 14.6 (round to 15)

24V battery – max voltage: 29.2 (round to 30)

48V battery – max voltage: 58.4 (round to 59)

In addition, the regulator will take around 2V.

Therefore, the MPPT for your solar panels should be:

12V battery: MPPT > 17V

24V battery: MPPT > 32V

48V battery: MPPT > 61V

You must have a regulator with an MPPT to maintain the maximum power point. For every amp hour that is drawn, the voltage decreases, so a regulator ensures you do not draw too much or too little and lose out on achieving maximum power. The regulator then converts the MPPT down to the voltage of the battery. For example, with a 12V battery, your solar panel should have an open circuit voltage of 24V and an MPPT voltage of 18V ± 1V because it pulls down the voltage and varies depending on where the power point of the solar panel is. The regulator then converts the 18V down to 12V.

How should I install my solar panels, battery, and inverter charger regulator system?

Firstly, always attempt to install them yourself, you can only learn from mistakes, just stay safe 😊

Secondly, it is important to note that if there is a substantial distance between your solar panels and your inverter charger regulator system (which should be as close to your battery as possible) it is more advantageous to have panels with a higher voltage.

Power can be delivered with either a high voltage and a low current, or a high current and a low voltage. For example, 100W can be delivered with 100A at 1V or 100V at 1A, it’s identical. However, wires heat up with current not voltage, so a higher voltage is preferable in order to keep the current low.  

Thirdly, shading on your panels could significantly decrease their power.

Wired in parallel

  • Each panel is independent so if one panel is shaded, you only lose one panel’s worth of power, with all the others at maximum power

  • The current will increase, wires will heat up, and power will be lost

 

Wired in series

  • Preferable when there is substantial distance between your panels and your inverter/charger/regulator system

  • Gives the same power but delivers a higher voltage (you can reduce the thickness of your cables and your losses)

  • The MPPT voltage will have to compromise if any panels are shaded (unless you have an inverter/charger/regulator system with 2 solar inputs)

 

Method

Lay your panels out and watch them throughout the day. Work out which are shaded at similar times and wire those together in series. Finally wire all the groups together in parallel to create a grid of series parallel connections and plug into your single solar input. If you have 2 solar inputs, keep them separate and plug both groups into your system separately. They will be independently tracked, so your MPPT will show 2 different voltages on each input, giving you a higher MPPT overall than if you had 1 solar input where the MPPT would have to compromise to the lower voltages.

Top tip: if you need an inverter (turns battery voltage into mains voltage), charger (turns mains voltage into battery voltage), and a regulator with an MPPT, it is cheaper to buy a unit with all three combined.

How do I calculate which batteries and solar panels to invest in?

Attach an energy meter to your consumer unit (electricity input). This will measure your maximum and daily energy use.

  • Daily energy use tells you the size of the battery and number of solar panels needed

  • Maximum energy use tells you the size of the inverter needed

 

Batteries

Many appliances when initially turned on may require surges of power. This is accommodated for in your inverter, as it can take surges of up to double the rated power for a few seconds. However, your battery must be capable of accommodating such surges, so it may have to be larger than you think.  

 

For example, if you have an inverter with a rated power of 1.2kW, you know it can take surges of up to 2.4kW and thus your battery (with a standard 200Ah BMS) must have a 2.4kW capability. 2.4kW/200Ah = 12V, and therefore purchasing a 12V battery would be appropriate.

If you want a more powerful inverter (be capable of running more/more powerful appliances), you need to put more batteries together in parallel. However, it is cheaper to invest in a larger pack than many small ones. You suffer losses in your cables and lose money on additional BMSs. Maintaining the same amount of power and increasing the voltage is better for your inverter and your battery.

 

You are advised to upgrade to:

24V battery to accommodate a 2.4kW inverter (4.8kW/200Ah = 24V)

48V battery to accommodate a 4.8kW inverter (9.6kW/200Ah = 48V)

If your electronics are at 12V and you have upgraded to a 48V battery, simply use a power supply to convert 48V to 12V. However, you will have to invest in a 48V alternator for your engine. In terms of your solar panels, if their open circuit voltages sum to 48V it is possible to arrange them in series parallel and upgrade this way (see figures below).

 

Solar Panels

You want to invest in solar panels that serve your energy needs for the greatest number of months in the year. Therefore, we usually look at perfectly matching power to consumption during spring and autumn, with a little wastage in summer and a little scarcity in winter. However, if you have (or plan to have) an EV in the future, investing in more/larger solar panels will guarantee sufficient energy in winter and prevent wastage in summer as you can use any excess to charge your car battery.

What do I do if the system fails?

If there is a fault with the cells, the BMS will alert you, indicating which ones are damaged. Batteries from other manufacturers are generally delivered in sealed cases and therefore irreparable if a fault occurs. Our cells however are completely accessible, easy to replace and therefore the battery can be repaired rather than discarded. Please contact us for advice on this.

If there is a fault with the BMS, the battery will stop working and the BMS will not illustrate any faulty cells. As with the cells, the BMS can also be replaced, and the battery repaired rather than discarded. Again, please contact us for advice on this.  

If you’re interested in a system, please contact us for a quote, and tell us the size of your solar installation, your maximum and daily energy use, the size of your inverter, and whether you have (or plan to have) an EV. If you live locally (in and around Suffolk), please let us now if you’re also interested in a solar installation.