Amp Hour @ 20 Hours
Friday, June 23, 2017
Solar Science 101: Comparing Batteries
Shopping for a portable solar generator + storage system? Feeling a bit overwhelmed by the jargon? You know all these technical specs are being thrown at you for a reason, but how do you compare apples to apples? Where do you even begin?
You’ve come to the right place. SunRunr is nationally recognized for our commitment to educate the public and promote preparedness. We want to put the power in your hands to choose the portable solar system that’s best for you and your family.
“What can I run on this thing?”
We’re all familiar with the basic idea of batteries – they store power that we can then use when we’re mobile. Whether it’s a flashlight, a smartphone, or a circular saw, batteries allow us to stay unplugged from a wall outlet (off-the-grid). “What can this solar generator really do for me?” That’s what we all want to know, right? “How long can this battery run my lights and my circular saw and my freezer and my coffee maker and my…?”
The road to that answer gets twisty quickly. Near the end of this article we’ll list some resources that can help you zero in on the answer for your specific power requirements. What we want to do here at the Science 101 level is to familiarize you with the common terms and designations you’ll run across so you can begin to consider your energy needs and your battery storage options.
Watts: your speed of consumption
Let’s say you have a flashlight that’s labeled “10W” (10 Watts). And to keep things simple, we’ll say your desktop computer is listed at 100 Watts. Watts are used to measure the rate at which energy is produced or consumed. If you think of watts as speed, the wattage is how fast you’re driving at a moment in time. Your computer is consuming energy faster than your flashlight – currently clocking in at 100 miles per hour whereas your flashlight in this moment in time is tootling along at 10 miles per hour.
Watt-hours: the amount you drive
In our analogy, Watt-hours (Wh) is the distance or amount you drive over a period of time. If you drive at a constant 100 miles per hour for 3 hours, you will have traveled 300 miles. So if your 100 Watt desktop is on for 3 hours, then your computer will have used 300 Watt-hours of energy. A more energy-efficient computer might only require 50 Watts and therefore if you left it on for the same amount of time, it would only use 150 Watt-hours of energy.
To give you some perspective, a typical house in the U.S. uses an average of 30,000 Watts per day. To see how your usage stacks up, take a look at your latest utility bill. Your energy usage will likely be listed in kilowatt-hours (kWh). As a reminder, “kilo” means “1000”, so 1 kilowatt hour is 1,000 Watt-hours. Are you using more or less than the average 30 kWh per day?
Amp Hour: “How many cars can I drive at once?”
When shopping batteries, comparing their Amp Hour specifications can give you an indication of what a battery’s storage capacity is and serve as a baseline for relative comparisons. Amp Hour attempts to answer the question, “How many tools can be running at the same time and continuously for 20 hours?”
In the case of the SunRunr:
Amp Hour capacity @ 20 hr rate = 245 Ah
245 AH@20 HR
As we mentioned above, Watts are used to measure the rate at which energy is produced or consumed. Your battery is “producing” as your computer is “consuming.” To determine the Watt-hours of a particular battery, multiple the Amp Hour times the Voltage. In the case of the SunRunr, the system uses a 12 Volt DC battery.
245 Amp Hour x 12 Volts DC = 2940 Watt-hours
It’s also important to learn from the manufacturer what the “usable storage” is for a particular battery. The battery in the SunRunr offers 2000 Watt-hours of usable stored power before recharge is required.
Because Amp Hour specifications are most often a 20 Hour rating, we have to keep that in mind when thinking about Watt-hours. With some simple math we can determine that SunRunr owners get 100 Watt-hours for 20 hours (2000 Watt-hours divided by 20 hours). Keep in mind that some solar generators, like the SunRunr, can be storing additional energy even while you’re consuming energy, allowing you to have sustainable daily power.
In a power outage, what electronics would you want to use? This energy calculator can give you a sense of how many Watts some common appliances consume. How many hours per day do you think you’d use each of them? With these Watt-hours in mind, you can play around with different scenarios to see how far 100 Watt-hours can take you. On our website, we’ve got some practical examples of what that power can do for you in an emergency, on the farm, or at a job site.
Apples to Apples
So, when it comes time to shop solar generators, look for these two battery specifications:
Amp Hour and Usable Watt-hours. With these numbers in hand, you now have the power to see how batteries stack up.
To dive in further, head over to our website where you can find more juicy technical specs plus other general FAQ about portable solar + storage.