Episode3 – The differences that affect off-grid living
In episode 1 and episode 2 of this series we looked at the different types and characteristics of Lead-Acid and Lithium-Ion batteries. In this episode, we will compare them directly and how they affect your planning for your battery-powered home and business. In this episode, we’ll compare deep cycle Lead-Acid Batteries and Revov Lithium Ion Phosphate (LiFeP04) batteries
Choosing Lead Acid or Lithium-ion batteries has practical implications for you, your family and employees. We’ll consider how that choice will impact you over the years in the following main areas:
- How much of the charge your battery stores will you actually be able to use without damaging them.
- the cost of charging to use them (or recharging your batteries after using them)
- how much space you have to set aside
- the special ventilation you might have to install
- How long your batteries will last
- The amount of work involved in looking after your lead-acid batteries
How much of the charge your batteries hold will you be able to use? (Usable capacity)
Your batteries will come with a rated capacity or nominal capacity (see our article on Battery Measurements Episode 1 -Size for further explanation of capacity). This capacity rating tells you how much electrical charge the battery can store. It does not tell you how much of that storage you will actually be able to use.
In order to avoid damage, you can only use 30% of the electrical energy your Lead-Acid batteries can store before you recharge them, or deep-cycle batteries allow you to use 50-60% of the energy they store. You can never regularly use more than 50% of the energy that you paid for. If you drain lead-acid batteries more than this even occasionally their life will be drastically cut short
Revov LiFePO4 (lithium ion phosphate) batteries allow you to use 90% of the energy they store every single day of their lives without damaging them. That means to get the same output you will need to buy and install and maintain more Lead-acid batteries than Lithium-ion ones, (probably 3 times as many).
Don’t try to drain you Lead-Acid Batteries ”too fast” or they’ll give you even less usable capacity.
The faster that you discharge a lead-acid battery of any type, the less energy you can get out of it. This effect can be calculated by applying Peukert’s Law.
Once you have decided on your plans to stop depending totally on the power company delivering electricity to you, you must decide if you want to support some power-hungry items. Some items want lots of power and they want it in a hurry, this would include things like a geyser or pool pump so the kids can bath or swim, or the aircon or heater so the office is comfortable, or the microwave or stove.
When you really need to draw the charge out of the battery fast lead-acid compares very badly with Lithium-ion. Under these conditions, Lithium-ion batteries deliver their power and you can access pretty much the same amount out of the battery as you can when you draw power slowly. Lead-Acid batteries can only deliver 50% of their rated capacity, to begin with, but under these fast discharge conditions, they are further limited in their ability to deliver. Lead-acid batteries discharged are unable to deliver around 40% of their power, a whole bunch of the power they are rated for, that you paid for, cannot be reached.
Battery performance at different discharge rates
At the end of the day, an AGM battery rated for 100Ah at C/20 will provide a 30Ah usable capacity when discharged in one hour as 30Ah = 100Ah x 50% DoD x 60% (Peukert losses).
|Lead-acid usable capacity at C/20|
(20 hours discharge)
|Lead-acid usable capacity at C/1|
That means if you have some power-hungry items and you want to set up a battery pack to support them you will need around 6 times more lead-acid batteries than you would if you were using Lithium-ion to achieve your goal.
Lithium-ion saves you money and time when re-charging
The slow 20% – speed of re-charge
Lead-acid batteries present you with a conundrum. The last 20% of a Lead-Acid battery is relatively difficult to charge, but if you don’t fully recharge lead-acid batteries you damage them, and they don’t last as long as they would otherwise.
The first 80% of lead-acid batteries can be fast-charged if you have an intelligent 3 stage charger that understands lead-acid batteries. at final 20% of lead-acid battery capacity cannot be “fast” charged. Just like a home or office move or renovation or software development project, the final 20% of the work can end up taking 80% of the time.
This can really be a pain if your batteries aren’t full when you need it for your night-time power just because they are slow (remember lead-acid batteries can only give you 50% of their capacity any-way). If you’re grid attached and using cheaper night time to recharge this may not be an issue but if you’re depending on a solar system, you may be forced to add in a generator that’s messy, expensive to run and noisy to make sure they don’t get damaged by chronically being undercharged.
Wasted Energy – internal resistance
In addition to the slow last 20%, lead-acid batteries inefficient because they have higher internal resistance than Lithium-ion batteries. Lead-acid batteries require about an extra 15% of the energy put into them when compared to Lithium-ion. So, for every 100 Amps -hours of power you pay for that goes through your charger lead-acid batteries throw away 15 Amps-hours and only keep (store) 85 Amps-hours.
This means you need to buy a bigger solar system to charge them than you would need for lithium-ion batteries and once again they take even longer to re-charger. If you’re using solar they throw away 15% of all the hard work your solar system does to charge them before the clouds come or night falls and if your grid attached you pay for 115% of what you would pay to fill your equivalent Lithium-ion battery pack.
Too much of a good thing- overcharge damage
Not only do Lead-acid batteries throw away 15% of your hard-earned recharge power and slow to a crawl when refilling the last half of their usable capacity, if you send them more charge than they can store they get damaged.
Lithium-ion batteries are resilient in the face of “abuse”. If you keep recharging them when they are full, they just shrug it off and it has no appreciable effect on their performance or how long they last.
How long will your batteries last?
There are different terms used to talk about how long batteries last, you’ll see them mentioned on spec sheets and advertising. Battery geeks talk of “Cycle Life”, “Calendar Life” and “Service Life” (for more information we dealt with this in more detail in our article Understanding Battery Measurements – Power and Lifespan)
Calendar life – measured in the number of years the battery will last if you just leave it alone and don’t use it. (Sometimes called “Float-Life”)
Cycle Life – measured by the “number of times” you can use the battery before it is used up. One “use” of a battery is thought of as one session of partially draining it to run some of your home or business and then recharging it. Each “use”, drain/discharge and re-charge is called a cycle. Battery life is often reported in the number of cycles it will deliver.
Service Life – the length of time that the battery will last while doing what you want it to do and still be reliable. (meet the requirements of a specific application). If you use it only once every year and maintain it well it will last more years than if you use it every day and don’t maintain it.
The limits of Cycle Life
Deep cycle lead-acid batteries that are used gently and well maintained are certified for 500-1000 cycles. Lithium Iron Phosphate batteries are a lot less fussy about how you treat and maintain them and last at least 3500 cycles. So, you’d need to be replacing your lead-acid battery pack around every two to three years if you use them every day. Your Lithium-ion pack will last three times that long.
Lead-acid (AGM) Expected Life Cycles vs DOD
Big, Heavy and dangerous?
When you’re planning to move to a battery-powered home or business you must consider where to house your new power source. You’ll need to consider safety and finding a big enough space for them where it’ll be easy to get to them for any maintenance that may be needed.
How much floor or room space will you need? Can you put the batteries on shelves above each other to save floor area?
You will need at least 3 times the number of lead-acid batteries to give you the same output as your Lithium-ion battery pack. So that will need a space at least 3 times as large to accommodate your lead-acid pack. Lead-acid batteries are heavier than the Lithium-ion batteries of equivalent output as well.
You will need stronger shelves and walls if you’re going to place your Lead Acid batteries on shelves. (not to mention the effort required to lift them into place safely or move them for maintenance or replacement).
Do batteries present any safety hazards to your family, employees, building or equipment?
All batteries are intended to deliver electricity and like electrical power source should be treated with proper respect.
Flooded lead-acid batteries release noxious acidic gas while they are charging and must be contained in a sealed battery box that is vented to the outside. They also must be stored upright, to avoid battery acid spills. AGM batteries do not have these constraints and can be placed in unventilated areas.
Lithium-ion batteries can be installed unventilated in your living and working space (as long as people don’t fiddle with them). They are lighter and smaller than the equivalent lead-acid batteries and that can have real practical implications for you. If you are a 4×4 or RV enthusiast or you’re running your food truck, and have to take your battery power with you, you will definitely want to save on space and the weight you’re carting around to reduce the impact on a workspace and your fuel economy. Even in your home or business, it’s great if the batteries that power the place do not use up half of the garage or office and can be put on shelves without re-enforcing the wall.
You’ll need to add a set of chores to your daily routine with lead-acid batteries or write yourself a checklist to follow every time you use them if it’s not every day.
You’ll need to top off any flooded lead-acid batteries with distilled water periodically while ensuring you don’t get sulphuric acid solution spilling everywhere, and keep the terminals free of corrosion Sealed Lead-acid batteries don’t require that periodic work but are often permanently damaged by overcharging so you need to keep a close eye on them whenever you’re charging them.
When you’re recharging remember you will need to plan for properly topping up your lead-acid batteries. That last 20% is probably the most important 20% of the battery’s capacity -it’s half of all the power that the battery can deliver. You want to make sure you don’t run out of sun or wind or generator fuel before they’re fully re-charged. Remember if you’re grid attached, you’ll pay more for the recharging of your lead acid than you will for your Lithium-ion batteries and if you’re not you’ll need more solar or generator capacity with lead-acid.
Lead-acid basically requires more knowledgeable design and maintenance to keep it working well, and doesn’t last as long as the equivalent Lithium-ion battery pack. Recharging will be a slow drag over hours and hours rather than the quick 1-2hour process with Lithium-ion, while about 15% of the energy you give your lead-acid it will throw away- at your expense.
Lithium-ion is just a more convenient and safer alternative to lead-acid. It’s much more of an “install and forget” solution as you move off-grid and look to stop trying to depend on an unstable national grid power provider.