Batteries 1/2

 About my battery choice 

The energy storage system for EV

Beforehand: all the information below represents my personal opinion, built after research over the content I consider a good and reliable information source 

 About batteries

One of the highest challenges in any electric vehicle is the batteries. They represent one of the highest costs in a conversion, but they are also challenging in terms of setup:

What kind of battery (chemistry)?

   - Lithium-ion (Li-ion)?

   - Lithium Iron Phosphate (LiFePO4) ?

   - Lead acid (regular cars battery) ?

   - NiMH (your usual AA and AAA rechargeable battery, the worst!)

 Each battery chemistry will have a different voltage per cell. To increase the voltage of your battery pack, you simply put the cells in series (the positive pole of one cell to the negative pole of the next one) 

For example

Car batteries are actually made of 6 lead-acid batteries cells connected in series: 6 X 2.1 volts = 12.6 volts 

 

 Things you have to consider before deciding on the energy storage system:

   - Space available

       If you have lots of space available in your project (e.g. a light truck), you may go for the bulkier battery chemistry that gives you more life cycles.

   - Final total weight of the vehicle

       The vehicle weight will impact mileage (distance per watts) and motor performance

    - Desired range   

That is an important thing. If you are building something to run around your farm, it will make 50km (31mi) per day max and will always be relatively close to a charging station, no need to go fancy with a LiFePO4 or Li 18650 cells. Probably the best solution will be the good old car (or truck) lead-acid batteries connected in series to reach the desired voltage.

   

Here goes a little research about current batteries and energy storage system:

At least from the point of view of physics and mechanical engineer, the best mobile energy carrier we have now liquid fuels. Gasoline (petrol) and Diesel have both very high energy density and specific energy. They are relatively safe, easy to transport and store. Seriously, it is not by chance that we rely more than 90% of our transportation sector on these fossil fuels. Unfortunately, they are destroying our planet. 

This paragraph is for you if you are a little more in a geek mode. Gasoline: The original feed-stock, or what was used to make the crude oil, was nothing but ancient microalgae. That's right! Microscopic plant-like organisms, many of them unicellular (just one cell big), that lived in our planet way before any animal or land plants. They flourished back then, to the point that they changed the planet's atmosphere (air composition), trapping CO2 (carbon dioxide) and releasing O2 (oxygen). But like all living things, they died and sunk, and their biomass accumulated in specific spots. These spots became what today are the crude oil fields. Before the microalgae, there was only a little oxygen in the atmosphere but a lot of CO2. Most of this CO2 was trapped in the microalgae biomass (and oil), which sunk into localized deposits. While they bloomed, they produced lots of oxygen. So, you can imagine how much CO2 was removed from the air: they built the 20% O2 that we currently have in our atmosphere! If we burn all the fossil fuels, we will bring our atmosphere back to the point before land animals and plants.

 

 

The EV is a big part of the solution to avoid circling the atmosphere back to the pre-historic era. Nevertheless, I find it extremely useful to always compare any alternative energy source to the conventional ones. From the science perspective (and I worked with biofuels), it gives an idea of the pros and cons of each alternative and the challenge of implementing them. For the specific case of this EV motorcycle, it helps determine what kind of battery, why, and how much space will be needed. Finding room for the battery could be a big issue here.

Batteries 2/2

About my Battery Choice 

Beforehand: all the information below represents my personal opinion, built after research over the content I consider a good and reliable information source 

So, here I'm going to compare some energy carriers (batteries and Gasoline) in terms of specific energy (watts per mass - or weight if you prefer, in kg) and energy density (watts per volume, e.g. litre). If space and weight are a problem, you want a carrier with high specific energy and energy density.

So, about the alternatives: 

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Gasoline (Petrol)

Total potential (*1)

Specific energy: 12 889 Wh/Kg

Energy density: 9 500 Wh/L

 

*1 = Average engine efficiency: Car engines = only 20% - 35%

Specific energy * 30% efficiency = 3 866 Wh/Kg

Energy Density * 30% efficiency - 2 850 Wh/L

————-

Lead-acid battery (regular car batteries)

Specific energy: 35-40 Wh/kg

Energy density: 80-90 Wh/L

Life expectancy: < 350 cycles

Pros - High power capability, can discharge a lot of energy in very short bursts

Cons - very heavy (like, really heavy!) and bulky!

———————

Lithium Iron Phosphate (LiFePO4)

Specific energy: 200Wh/kg

Energy density: 325 Wh/L

Life expectancy: 2 000 to 12 000 cycles (depending on the unit)

Cost: 3 to 24 Wh/U$

Pros: reasonable price for the lifespan of the battery. Many companies can build one for you, matching the space you have available, so, easy to fit in void spaces in your car or truck.

Cons: Bully. Less bulky than lead-acid space, but still very bulky! you will need 8.7 times the space of your gas tank for the same range

———————————-

Lithium-ion

Specific energy: 180 (+/- 40) Wh/Kg

Energy density: 500 (+/- 250) Wh/L

Cost:

Life expectancy: 400 to 1000 cycles

Pros: higher energy density and possibly specific energy, depending on the kind of li-ion cell you bought. 

Cons: li-ion has a relatively low lifespan. Tesla is known to, software-wise, avoid full recharge/discharge of their cars to decrease battery degradation and increase lifespan. Also way more complex to set up.

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In a nutshell:

LiFePO4 is the best choice by far if space is not a problem. Why? 1/5 of the weight of the lead-acid batteries and 10 to 40 times the lifespan. Way higher lifespan compared to Li-ion batteries as well. Depending on your setup, you may need to sacrifice some of the cycling capability (e.g. 12 000) for higher performance. Still, there will probably remain a lot of cycles.

However, my choice is:

I do have space constraints. Motorcycles don't have that much space available. So the higher energy density of the Li-ion may be a game-changer for me.