solar backup – batteries 101

basics on how a battery works

The workings of a battery are really quite simple. There are little leprechauns inside each one, and when needed, they do their little magic jig and things start to happen. 

Just kidding. Watch this, then read on. 

Essentially, batteries have two “poles”, positive and negative. When a pathway (or circuit) is provided, connecting the two, energy flows through it. If that energy happens to run through a light bulb in the same circuit, the bulb will light up. If it runs through a motor, the motor will spin. 

Simple right?

And to charge it back up, electricity is applied, reversing the process and restoring power to the battery… keeping the leprechauns happy. 

Depending on the guts of the battery, this process may be repeated anywhere from several times up to several thousand times.

More on different battery technologies in a minute.

what do you need from your leprechauns?

In the realm of energy storage there are a googolplex (yup, that’s a thing) of considerations when looking for the best solution.  For the sake of this exercise, let’s keep things simple shall we? After all, life is complex enough as it is.

On a basic level, we need to consider three things. 

grid tied or off grid?

Storage is storage right?


There is a difference. You see, with a grid tied system, you will likely be utilizing a process called “net metering”.

grid tied

Simply put, it looks like this.

Though widely accessible, it is important to note that net metering is not available everywhere, nor with every power company within the same region. Is it available where you live?

Now, on a basic level, picture the entire grid as your personal bank. When your panels (or turbines) produce more power than you need, the excess goes into the grid for others to use. 

Awww… that’s kind of you to share. 

For helping them out, the utility company adds “credits” to your account. While your system is sleeping (and you still need the power), the grid then feeds your house and uses up whatever credits you’ve earned. 

24 hr power. No batteries required… until the grid goes down. 

In terms of financial gains, you pay (peak or off peak prices) what the utility company tells you to pay. 

backup battery power

This is the middle ground. Essentially a grid tie system “with benefits”. Ooh… so new age. 

The addition of a battery bank to your system can buffer things like frequent outages and fluctuating energy prices. Units like the Tesla Powerwall 2 come with a myriad of features that are used to optimize your energy position. 

For starters, it has the ability to store enough power to see the average home through the night. This theoretically means that you can run solely off of your own system. Panels throughout the day, battery throughout the night. 

Then there’s the “smart” aspect of it…

This Thing is hooked up to the internet. It will automatically reference the weather, building energy stores before storms are predicted, in case of outages. It’ll optimize energy going to and from the grid. It prioritizes its own energy usage during “peak” times when utility prices are higher.

 It will even assess and adjust its own optimal working temperatures.

All in the name of saving you money and reducing your dependence. And if all else fails… you’re still connected to the grid!

off grid

But what if you’re not connected? Well… that’s a different story. 

In an off grid situation, a larger capacity of storage is recommended. After all, 13.5 kWh (Tesla’s capacity) is a decent amount of power. However,  if bad weather significantly reduces your charging capacity, then it will only get you so far. Without the backing of the grid, a larger bank of stores should be considered. 

This can be done with either Lead Acid (PbAc) or Lithium-Ion (Li-ion) batteries, but the key take home point here is that the capacity should be increased to ensure that you have power for days, in the worst of weather. 

With this type of set up, you are your own boss, but the onus is all on you. 

battery jargon… what does it all mean?

Here are some terms and explanations to better arm you in finding the meaning to all of this. 


It’s just that. The amount of energy that a single battery can store. Luckily, most batteries are stackable, meaning you can upscale your bank to suit your requirements. This is measured in kilowatt hours, or kWh.


A kilowatt hour is a measurement of energy. It represents 1000 watts sustained for one hour. 

As a reference, this is the same amount of energy used by your 1000W microwave if you ran it on MAX for 1 hour. 

Power (or Power rating)

The deliverable amount of energy that your battery can provide at one time, measured in kilowatts (kW).

Depth of Discharge (DoD)

Measured as a percentage of the battery’s total capacity, depth of discharge refers to the amount of power that can be safely used before affecting the performance and lifespan of the battery. 

Round Trip Efficiency

Batteries lose energy through their cycle. Round trip efficiency is measured as a percentage. It represents the amount of energy retained from the amount of energy taken to store it.

For example, feeding 100 kWh into a battery may result in  80 kWh of usable energy. This would equate to a round trip efficiency of 80%.


The process of charging and draining a battery. 


The battery capacity will diminish over time. Warranties may be expressed as 7000 cycles or 7 years at 80% efficiency (referring to round trip efficiency).

With these terms under you belt, let’s take a look at the meat and potatoes of these units. 

battery technology

There are predominantly two types of batteries for you to choose from, with a third technology earning a notable mention. 

  • Lead Acid 
  • Lithium-ion
  • Sodium-ion (Salt Water)

lead acid 

Lead acid batteries have been around for a long time. Like 150+ years kind of long. They come in two styles:

Flooded Lead Acid – Requiring regular maintenance and regular charging 

Sealed Lead Acid – No maintenance required and won’t self discharge as quickly

First and foremost, while Lead Acid batteries do not perform at the level of their immediate rival, Lithium-ion, they are 99% recyclable.  Furthermore, brand new lead acid batteries contain 95% reclaimed and recycled lead. 

Them some pretty impressive numbers!

Lets face it. You’re exploring this avenue for a reason. You have a conscience. 

Lithium-ion batteries paint a very different picture. But we’ll get to that.

Cost is another win for the Lead Acid battery. They are significantly cheaper for their initial upfront cost, however will have to be replaced more often due to a faster depletion rate than their lithium counterparts. 

On top of that, they require more (but simple) maintenance and effectively hold less power. This is due to their depth of discharge being around 50%, whereas lithium batteries boast up to a 100% DoD. This of course can be worked around. By simply adding more batteries to your bank, you increase your capacity while maintaining your discharge ratios. 

Lead Acid batteries are also more susceptible to damage from temperature extremes. Alongside this, the flooded variety slightly offgasses, requiring them to be housed externally, adding complexity to keeping them within optimal operation ranges. 

Lastly, Lead Acid batteries run at around 80% efficiency, while lithium batteries clock in at around the 95% mark.


Lets start on a high. 

Higher efficiency. Higher energy density. Longer life. Deeper DoD meaning more usable power. Less maintenance. Cheaper in the long term. 

Heck, why wouldn’t you go for this? 

Well… from a spec’s perspective you should. But then again, there was that subtle hint of  lithium’s dirty little secret I mentioned earlier. 

It’s environmental impact.

While Lead Acid batteries (now) come from almost completely reclaimed and recycled sources, lithium, in all of it’s glory, is a mined raw material. Not only that, it’s mining process and the safety and environmental factors surrounding it are questionable. It has a current recycled rate of less than 5% worldwide. With demand set to increase massively in the next decade, we can start to see another side of this amazing technology. 

For all intents and purposes however, it is still the best commercially viable battery technology… for now.

and for the mystery guest…

Salt water batteries. 

Yup. Salt. Water. AKA Sodium-ion.

Ultra safe, easily sourceable and recyclable, long lifespans and very importantly, low impact. Ultra low. 

If this technology is sized correctly for your system, you will be employing the greenest battery technology available at present. 

These batteries perform at the level of lithium.  They are maintenance free, scalable up to the multiple MegaWatt range and have a 92% round trip efficiency. Not to mention a 100% DoD and a lifespan of 15 years at 70% usable capacity and 5000 cycles at 80% DoD.

All this, paired with an estimated cost of being 30% cheaper to produce than Lithium-ion batteries in the near future. 

Why the near future? 

Because these batteries are not yet widely available, they still cost more upfront than other available technologies. Two players, however, are producing them: Greenrock (Austria) and Faradion (UK). 

Worth mentioning, these units are large and heavy. Since these are currently only available in europe, shipping a potential half a metric ton of batteries to your door may prove to be a little out of your budget. 

Then again, if you’re a long term thinker, the true cost analysis may help you sleep a little better. 

Personally, it would be the clean factor that would ease my mind, but that’s just me. 

the final thought

While there are obviously a number of factors that go into choosing the right type of battery for your clean storage solutions, we can reduce the overwhelm by asking ourselves some fundamental questions. 

What exactly do I require?

How much maintenance am I realistically likely to perform?

How green do I really want to take this?


Happy futur-ing




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Hey folks, I'm mj. I live in a gorgeous inland temperate rainforest in BC, where i get to enjoy countless facets of nature on the daily. This setting allows me to play in the outdoors in every season with my beautiful family. I'm on a mission to play a role in helping preserve our natural world, so that our collective progeny may also enjoy it for years to come.