Editor’s Note: This is Part IV of a series. To see all parts, click here.
Have you ever wondered why you don’t see many electrically powered motor vehicles on the roads, despite all the recent hype? Well, it’s because electricity has a dirty little secret: We have the technology to generate massive amounts of electricity, however storing those massive amounts of electricity for later use has been something of a problem that hasn’t yet been solved.
The two main ways our society currently stores electricity for later use are batteries and hydro-electric facilities. I’m not suggesting that anyone construct a hydro-electric dam and generator in their backyard because it would require a huge volume of water to generate useful amounts of electricity, so instead I’ll discuss batteries and what they are all about.
You might not know it, but batteries are quite an old technology. At home I use lead acid batteries, a technology which was invented back in 1857. They produce electricity through a chemical reaction between the two metals lead and lead oxide with an electrolyte of sulphuric acid. As the amount of electricity stored in the battery decreases, the metals change to lead sulphate and the electrolyte becomes water. As the battery is charged, the chemical reaction reverses to its previous state. Fortunately, you don’t have to understand the chemistry behind a battery to be able to use one, however it is useful to remember that a battery is really a chemical reactor, which gives it odd quirks and limitations which we’ll discuss later.
There are alternatives to lead acid batteries such as: Nickel Metal Hydride batteries; Lithium Ion batteries; and fuel cells – just for some examples. Most of these examples would probably work far better than a typical lead acid battery of the same capacity. They may even weigh less than the equivalent lead acid battery. However, none of these alternative batteries are commercially available on the scale that you would require for a home solar power system. Even if they were, they’d be hideously expensive because of their use of exotic materials and low production volumes so they aren’t worth considering here.
Lead acid batteries are both a simple and reliable technology. They are also relatively cheap to manufacture. Therefore, if you looked at most off-grid solar power systems, they’d be using lead acid batteries.
Aliens and acid: More alert readers will notice that I’ve now used the word acid eight times so far. Way back in 1979, I went to the cinema and watched the science fiction film Alien as a young child, which left me with nightmares for weeks. One scene showed acid from the Alien‘s fluids dripping through several floors of the spaceship. Needless to say I’ve been left with an unnatural respect for the powers of acid (even though an acid couldn’t really reproduce the affect in the film — the effect was pure artistic licence, even for Alien acid). Batteries really do contain sulphuric acid though, which is corrosive.
Lead acid batteries come in two types: flooded; or sealed. The difference between flooded and sealed batteries is that the sulphuric acid is accessible for flooded batteries, whilst sealed batteries, as their name implies, are sealed. This doesn’t sound like much of a difference, but in flooded batteries, the acid can escape from the battery through evaporation or boiling off (if they are overcharged) so you have to keep any eye on the quantity and quality of the acid. Also, with a flooded battery, to stop the acid eating through the floor of your spaceship should it get knocked over, the battery has to sit in a drip tray. Other than that either type of battery has about the same amount of electrical capacity for its size, but sealed batteries are more complex to manufacture, so they cost a whole lot more.
Sealed batteries suit me and I use gel type sealed batteries in my solar power system. Many more people use the flooded lead acid batteries though because they are cheaper to manufacture, so they are cheaper to buy.
You might not think about it much, but there are lead acid batteries literally all over the place. Every time you see a motor vehicle, you can be pretty sure that somewhere in that vehicle there’ll be a lead acid battery. Given that there are so many of them kicking around people often ask me the question:
Can you use the batteries ordinarily found in a motor vehicle in a home solar setup? The simple answer is, yes, but the long term practical answer is no.
Anyone who has ever run out of petrol or diesel in a motor vehicle and tried to continue driving using the electrically powered starter motor knows that the battery goes flat pretty quickly. The batteries that are put into motor vehicles are manufactured so that they deliver a large amount of power quickly for the purposes of starting, lighting and ignition, but they won’t provide that power for very long. The batteries used in solar power systems are referred to as deep cycle batteries because they are manufactured to have a longer life, deliver a smaller amount of power over a longer period of time, and, more importantly, they can be charged and completely discharged many more times than a motor vehicle battery ever could.
Getting back to the dirty little secret. Existing and commercially available batteries simply can’t store that much electrical energy. If you wanted to run a 2,400Wh fan heater for an hour, the lead acid battery would weigh about 70kg! This shows the simple rule relating to lead acid batteries. Generally, the larger and heavier the lead acid battery, the more electrical energy that that battery can deliver. It may surprise some people to find that the lead acid batteries that I use in my house weigh in excess of 1,000kg. This weighs as much as a small car and their total electrical storage capacity when 100% full is only around 30kWh which an average household may use in about 1 to 2 days.
A Tesla Roadster (an electric vehicle recently released in Australia at a drive away price of over $200,000) according to Wikipedia will use about 17.4kWh to travel 100km. Admittedly, the vehicle uses advanced Lithium Polymer batteries, however this is almost half the storage capacity of my own system. If you think about how far you drive your own vehicle in a day, try and take this information and work out how much electrical energy you would require (174Wh per km). Then, have a second look at A Solar Powered Life – Part III and try and calculate how many solar panels you would require to power just your daily requirements. You can quickly see why oil derived products became the choice of fuels in motorised vehicles.
If anyone wanted a guaranteed way to make a fortune, it would be through developing a cheap and lightweight way to store large quantities of electrical energy.
In the next article, I’ll discuss how batteries work in the real world and more importantly what batteries, the space shuttle and airship disasters have in common.
Continue on to read Part V