We are pleased to bring you a second instalment in a series of articles by Eshel Lipman, our Israeli Electrical Engineer who has been working at Nulux throughout 2017 – Tony
In my last blog, I finished with the promise to provide more guidelines to consider when implementing any energy saving action. But to understands those tips better, a brief introduction is required for the complementary component to the renewable energy sources.
Yes- I am talking about the recent years’ renewable energy ‘rising-star’ or the ‘the future (or passing trend…) The Battery. Hold your horses, don’t run to the nearest battery shop. Read this first…
But Hi! Batteries? What so new and innovative about them? They existed for more years then I can recall. In fact the technology dates back into the late 1700’s. They are an integral part of our daily activities without us even noticing for most of the time. Batteries are one of the largest growing field for start-ups, researches and initiatives, and is a big source of media buzz. So what has happened in the recent years to have turned this fairly mature technology, based on simple concept, into a centre of interest?
The answer is simple: The smartphone (and everything it represents).
Why? New, large-screen, smarter-than-you phones, require energy to operate, probably more energy than those ‘heavy blocks’ which we used to carry in our pockets roughly 10-15 years ago (remember the time phone could last for days or weeks!). The massive consumption of social media, texting and other endless activities these devices allow us to do require long-lasting batteries. To keep the device up and running for a long time between charges, we need a battery that can store a lot of energy. The smartphone is the perfect example of the orientation our society is taking. We strive to have energy available to us where ever we go, so we can do more and longer out of our appliances whenever we desire. Thus, always available energy which is also portable means more batteries, and preferably better ones. In addition, in the future, we will likely be charging our own smartphones with energy that originates from renewables – or from large-scale storage batteries (in case the renewable source is unavailable) .
What is a good battery? I will not go into details of how batteries work (try here), but the key parameter for comparing the performance of different is their capacity– or the amount of energy they can store.
The capacity of the battery is generally derived from two things: the physical size, and the energy density. In simple words, energy density is the amount of charge (or energy) a battery can store per unit volume.
For example, while a lithium-ion (Li-ion) battery has an energy density of 250 – 620 Wh\L (watt-hour per liter), your common car starter battery (based on lead-acid technology) has ‘only’ an energy density of 60–75 Wh\L. If we only compare the two battery technologies this metric, we would conclude a Li-ion battery can store at least 3x more energy than a lead acid one. For example, a common car battery has a volume of roughly 6 liters – If we were to manufacture a Li-ion battery of the same volume it will be able to store more than 5.4 Megajoules of energy (250 wH\L * 6 L * 3600 sec) – in contrast to the 2 Megajoules most car batteries can store.
*note, on most batteries you will usually find the capacitance in aH (which is Ampere hours, per the whole battery. If you would like to know the total energy, just multiply by the unit voltage)
Interestingly enough, we don’t see today wide-spread implementation of Li-ion car starter batteries. So how come we still manufacture batteries according to the ‘less’ efficient methods, when seemingly better technologies exist? The answer is complex, and I hope the next parts will give you a hint. However, bear in mind that there is no such thing as ‘old’ battery technology, thanks to several breakthroughs in the research of both common and new batteries chemistries.
In the meanwhile, here is a (partial) list of most of the important characteristics to consider when choosing a battery:
Rechargeable – there are two majors 2 different categories of batteries: Primary batteries which are not rechargeable (unless there is a mechanical/chemical process involved, for instance like the case of metal air battery) just like most of the coin batteries you see in your watches. Secondary batteries, which can be charged by with electrical current only, which are the most common batteries today that surround us.
Non-rechargeable Vs the rechargeable ones, manufactured by Energizer. See how from the outside, due to the standard container they look exactly the same, while the chemistry inside is totally different
Capacity – as explained before, the capacity is determined by the energy density and the physical size of the battery. In addition, it can be influenced by many other factors (temperature, humidity) one of the crucial factors is the Depth-of-discharge (DOD).
DOD is basically the percentage of current available charge within a battery cell out of all the total charge given out of its nominal capacity. For example, I am using a battery which is in a depth of discharge of 90%, the meaning is I already used 90% of the energy which was stored inside it, and I only have 10% left. This is important criteria to examine when comparing between batteries, because not all batteries has the capability to swing between 100%-0% of DOD. If one will not maintain his battery within the recommended DOD boundaries, he might cause irregularities in the battery’s desired operating regime (flat V-I curve fo) or even create irreversible damage to the battery itself . Li-ion batteries are capable of functioning well even if the battery is almost empty (capable of swinging between 0% to 100% of DOD) while lead-acid batteries stop working after few drops underneath with existing charge of 50% or less their charged capacitances.
Another two-key factors are the instantaneous charge/discharge current that the battery can tolerate, and the self-discharge characteristics of a battery. Lead-acid batteries are capable of supplying the extremely high (but quite short) discharge currents required to start an internal combustion engine, currents that would severely damage most Li-ion batteries.
Lifetime – What is the expected shelf-life (years) when the battery stays idle? How many cycles of charging and discharging is the battery capable of undergoing before losing certain amount of its capacity?
For example, early generations of Li-ion batteries experienced severe problems, caused by multiple Recharging cycle. The cycles were causing lithium metal tree-shaped growths on the battery anode called dendrites. In some cases these dendrites could eventually grown large enough to cause fatal short circuits in the batteries, leading to “concerning” results (does anyone remember exploding hoverboards?).
Efficiency – The process of charging battery includes electrical current, which always generates in undesired heat and EM emissions. This is the capability of battery to transform electrical energy to chemical energy and back, during a round trip, with less losses as possible. See this film for the more common definition.
Safety & Maintenance – Both the materials which consist the battery itself, as well as the battery packaging should be safe and non-toxic. The adaptation of each device to its’ different use cases has to be taken into consideration when engineering it, especially when batteries are involved. A good example is the infamous case of the Samsung Note 7, where negligence of their engineers allowed, in certain conditions, the anode and cathode to short circuit inside the battery (some attribute this issue to the formation of dendrites).
One of the problems with Li-ion battery technology is the flammability of the electrolyte inside the battery, which in the case of the Note 7 turned into a ticking bomb. The great documentary movie ‘the chase after the super battery’ (here, highly recommended!) shows some of the surprising behaviour of Li-ion batteries under certain external conditions, and what risks these batteries concealed inside them. Maybe now it is more understandable why we are not using Li-ion car starter batteries (Telsa’s cars however, have the floor of their car made of Li-ion batteries.)
Faulty batteries, looks fun (but don’t try this at home).
Price no need to elaborate here, however, the average $ per kWh of Li-ion batteries in Australia is currently between $400-$600. Not cheap at all.
Have in mind, that there are even more factors to take into consideration such as: the maturity of the technology, is it proven under the specific application you are planning to use it? What are the ancillary devices one needs to consider when design a system (Inverters, charging controllers and monitoring techniques) and even the electrical topology which dictates the cabling and arrangement of batteries in one big array.
To conclude the last chapter, I believe that there is no such thing as perfect battery. The engineering process of each application will have to take into consideration many different limitations and constrains.
As one already knows, there are many reasons to use batteries. Storing energy for later use is the simplest one, but the fact that we have available storage capabilities gives us some additional benefits:
I spoke about that a bit in the last blog, but it is important to understand some additional reasons to get some storage capabilities- For instance, off-grid and remote micro-grids approaches are now possible thanks to growing popularity of renewables and batteries. The battery role in the process is both to ‘smooth’ the unexpected behaviour of the renewable energy source (cloudy day has excessive effect on PV panel input, same as the fluctuating intensity of the wind which blowing a turbine). After the harvesting of the energy, the battery will be the reservoir where the energy will be stored for later use.
Another form of non-chemical energy reservoir, in some places around the world, when there is excess electricity generation, water is pumped up and stored. The same water is streamed back down during peak demand time.
Moreover, another good reason to have battery is the redundancy it gives to the user (both for the household level and the energy companies). A blackout (SA..) is not science fiction, the usage of energy is growing all around the country, but more and more ‘dirty’ power plants are shutting down for good. This generates some headaches for energy companies because they have less variety of available solutions to supply those peak demands. In the next event of very high demand, an initiated blackout is anticipated. It is even more probable that the same thing might happen in the case of any failure with the grid infrastructure. You can use a home generator as backup for energy sources, however the advantage of a battery over home diesel generator is that the battery has no emissions and it is ready to used always (if it is charged) with negligible lean time (frequency response). Try to take this concept and understand how it can be applied to larger scale of energy storage, managed by the network/grid companies.
Can you guess which state is currently out of the NEM?
To conclude, A good battery is the result of a long engineering process, started by recognizing the need, then choosing chemistry and housing, and eventually the right method to assumable it into a full size working application. The key is to understand the functionality the battery must comply with, while making sure it is will be efficient as possible. We should let the market show us how much greater and better batteries can become.
P.S I didn’t elaborate here about the different types of batteries that exist (See here for really good comparison chart) but I do want to mention few technologies and companies which are doing some current promising research. Interesting players in the energy market will be not only the companies/universities with the most unique battery chemistry: it could be breakthrough in the way the battery is manufactured (Tesla’s Gigafactory…) or innovative ways to monitor and control the battery.
• Solid state batteries – the quest to make the battery a safer for use, by changing Li-ion flammable electrolyte with safer Solid like material which allow Ion to flow
• Metal – air Batteries -Project like Storedot with it’s Aluminium battery or Fluidic energy with the Zinc-air battery, are two interesting approaches of harnessing the chemical energy stored in the metal itself. With a very common electrolyte (water) those batteries are providing promising results and surprising capacity
• Flow batteries – In contradiction to the other two batteries above, flow battery is actually the only proven example for a technology with vast commercial installations and the capability to store large scale of charge (up to 250 kWh per cell, size of a container). The most significant down side of the battery is the fact the it includes moving parts (pumps that moves liquid) and require constant maintenance. Some examples will be the CELLCUBE or Vanadiumcorp.
Check also – Ultrabattery, Sakti and many others… just google ‘ new battery technology’ and you will realize how this market is fast developing..
Ok, that is All for now. Until the next time…