I decided to write this post as I was explaining how solar energy works to my friend Aaron.
He is diving into the nomad life and bought a Goal Zero Yeti 150 to power his devices.
The 150 in “Yeti 150” represents the watt hour capacity of the battery.
A watt is a measure of energy, the result of multiplying volts x amps.
For now let’s not worry about volts or amps, because if we speak in terms of watts, both volts and amps are accounted for.
One watt is enough energy to power this USB fan.
Our portable laser consumes 20 watts.
In this context we are consuming watts of energy.
The storage of watts is measured in Watt Hours.
One watt hour is the amount of energy it would take to power our fan for one hour.
With Aarons Yeti 150, he could power our 1w fan for 150 hours, or run our laser for 8.3 hours.
Aaron’s power will be collected via a Boulder 30 watt panel.
30 watts is the maximum output of this panel,
so in perfect conditions it could produce nearly 30 watts.
Generally, the bigger the surface area on the panel, the more watts it can produce.
In our experience, we generally get between 18 - 24 watts out of the Boulder 30.
So the panel is making about 60% of it’s maximum power intake.
This is something to keep in mind when looking at solar panels.
From our 30 watt panel, we can count on 20 watts of power output.
In the sun, the panel will push 20 watt hours of power into the batter over the course of an hour.
With this setup, we can harvest 100 watt hours of power in 5 hours,
20 watts coming in for 5 hours is 100 watt hours.
Aaron can bank on making around 100 watt hours of power per (5 hours of sun) day with his setup.
Powering a Laptop
Aaron’s MacBook Pro has a 63 watt hour battery, lets round to 60.
With the 100 watt hours of power Aaron makes in a day,
he could charge his laptop 0 to full once and still have 40 watt hours of additional power.
Laptops have variable energy consumption, meaning they consume different amounts of energy for different tasks.
A battery will last much longer when taking notes vs watching a movie.
This is because the processor and peripheral components use more power to do intense tasks.
Watching a movie is a complex task for the computer, so it uses more power.
This is important to keep in mind when deciding how much power you need for your laptop.
If you are doing complex things like rendering high resolution footage often,
you may need to charge your computer 0 to full several times throughout the day.
Charge During Sun
If Aaron’s Yeti 150 is full and it’s still sunny out, he needs to put store that extra power somewhere.
This is the best time to charge other devices, because the energy will otherwise be wasted.
Cumulative power bank
usb-c, iPad, electric blanket
MacBook, magic bullet
Since the laser uses 20 watts of power, for every hour the panel is in the sun, we store enough energy to power the laser for an hour.
Absorbent Glass Matt (AGM) vs Lithium
This is assuming that we could use the full storage capacity of the battery without harming it.
Which is not the case given that the 150 is an AGM battery.
AGM batteries can degrade if their capacity is dropped too low, it’s best to keep it above 50%.
If we can only use ~50% of the battery without harming it, our effective battery is about 75 watts,
half of the 150’s cumulative storage.