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

or

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.

SunRunr’s Watt-hours:

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.

	SunRunr’s Battery	Battery B	Battery C
Amp Hour @ 20 Hours	245 Ah
Usable Watt-hours	2000 Wh

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.

Need help determining your power solution?  Let us know or contact one of our certified dealers!

SUNRNR OF VIRGINIA, INC. JOINS TRADE MISSION TO CANARY ISLANDS

Harrisonburg, VA. SUNRNR of Virginia, Inc. is one of nine U.S. companies in the Canary Islands this week on a trade mission exploring opportunities on the Islands as well as West Africa. Companies from four states and Washington, D.C. are participating in the mission.

“Africa presents an incredible opportunity for the entire U.S. business community,” said Deputy Assistant Secretary of Commerce Antwaun Griffin. “The economic growth and market diversity on the continent mean there are opportunities for companies in just about any sector, and I’m glad to see such a strong delegation of businesses participating in this mission.”

The mission is organized by the Virginia and Washington, D.C. District Export Council, and certified by the U.S. Department of Commerce. It will connect companies to government decision-makers from eight West African markets, facilitate business-to-business appointments with pre-screened potential partners in the region, and include technical site visits across the Canary Islands.

SUNRNR is a Shenandoah Valley based solar generator manufacturer. The SUNRNR line of products facilitates collection and storage of over 2,000 watts of solar, wind, or water energy that can be used for supplemental, remote, or off grid power in a wide-range of business and residential applications. The products’ durability, long life span, and low maintenance requirements make them particularly suitable for grid outages, disaster relief, rural electrification, and stand-alone power.

“Bringing SUNRNR to more markets that can truly benefit from access to portable power generated from available resources is not just a smart business move, it’s an important contribution to humanitarian and disaster relief efforts worldwide,” said SUNRNR principal Jenny French. “The Canary Islands is an excellent avenue for introducing more people to a renewable power option that not only has a multitude of commercial and personal energy applications, but that can run water pumps, refrigeration, and support medical operations during times of emergency.”
SUNRNR is also participating in the Africagua Conference, an event for renewable energy and water firms connecting to development opportunities in the region.

West Africa had the strongest economic growth on the continent in 2014, and the Canary Islands’ network of ports makes it an excellent launching point for entering multiple West African markets. The Canaries also boast a stable legal framework under the EU, and a low four percent corporate tax rate.

This trade mission is an important part of the United States’ Doing Business in Africa campaign, and comes two months after the U.S. Commercial Service led Trade Winds—Africa, the largest-ever U.S. trade mission to the continent. The U.S. government has committed billions of dollars to development initiatives in Africa, and has facilitated billions more in U.S.-Africa business deals since the start of the Doing Business in Africa campaign.

Portable Solar Generator (PSG) Differences

Accomplishing an Apple-to-Apple Comparison in the Apple-to-Orange World of PSGs

When choosing any piece of equipment, many variables come into play.  When that piece of equipment is a generator or power supply system, the variables may include intended use, size, output power, noise, energy source, and endurance.  Rather than buying a generator then determining what it will run, defining the equipment’s application first (its purpose and how you plan to use it) can be helpful in defining those variables, simplifying the choices, and making the most of your investment.

Wide range of solar products

• Want to run air conditioning or a food truck grill?  Better off with grid or fossil fuel as energy source.
• Want to run an electric water heater or halogen lighting?  Try solar thermal or again, gas or grid.
• Is the goal to run your house?  You’ll need a full residential installation, hopefully with batteries.  Check your monthly utility bill - the average US household consumes over 24kW per day.
• Need “portable” kW or MW arrays?  They make trailer- and container-sized units.
• Want to carry it into the woods?  Don’t plan on powering much.

But if you just want a reasonable amount of power, e.g. to offset grid usage and be available during power outages, to sustainably run your well pump, or to have power where there is none, keep reading.  (And by “reasonable”, I mean capable of running home appliances and tools, even several at once, not just charging a phone or keeping a light on.)  Generators in this arena will be compared below.

If you are new to or unclear on basic electricity concepts, such as W = V x a, and their associated numbers, please see the Electricity Refresher link.  An inverter must be rated for 1800W continuous or greater (120V x 15A = 1800W) to ensure it can power anything a standard household receptacle could power.  A 2013 SolSolutions article, “What to Look For In Solar Generators”, infers that an inverter with a rating larger than battery storage capacity is an injustice to the customer.  I beg to differ.  You do not need to use full inverter output, dumping the entire battery’s stored energy in less than an hour like you would by running an air conditioner, but it means the system is capable if needed.  Realistic examples: A well pump may require 20amps to start, but only 4 amps after and only minutes every hour – but you can’t run it if you can’t start it.  Two 10amp tools could each run 6 min/hour (e.g. air compressor one cycle/hour and 600+ cuts by table saw) for a full day’s work at a construction site.  Those tools could not run simultaneously with a 1500W inverter.  The same is true for say a refrigerator, microwave, fan, and light.

As for storage, the article accurately states “usable watt-hours” as being 2/3 battery capacity since battery life is extended by only using the top 50-66%.  And if the system is designed correctly, batteries can easily handle surge loads without degradation.  Of course, recharging when possible and at the correct rate (about 10% total storage per hour) will do the most toward extending battery life.  In the product examples below, you will notice two models offer solar input of about 5% battery capacity which means you better not use up what you’ve stored or it will take forever to recover via solar.  Another offers charging at almost 20% which is not good for an AGM battery.

Other options, characteristics, specifications, preferences, cautions to consider in the planning stages:

• What are your portability requirements or weight limitations?  Hand-carried, wheeled unit, use from pickup truck, semi-permanent location, …?  Greater storage = greater weight.  (Lithium-Ion is lighter, but 3-4 times the cost.)
•  Do you want energy generation options other than solar, such as wind, kinetic (bicycle), water, grid, …?
•  If solar, distance desired between unit and panels (some are combined/inseparable).  Cabled panels are often preferred since where the sun is shining may not be the same place as where power is required.  Seems silly to ask, but you would be surprised at the answers … If planning for solar, do you have good, direct sunshine?
•  What is the voltage of the equipment to be powered? (110V/60Hz, 220V/50Hz, 240V/60Hz, or 12VDC)
•  Is 12VDC output also available and at what amp limit?
•  Modified sine wave inverters are most common, least expensive, and work perfectly for most equipment.
•  Preference in country of manufacture - Chinese or American?
•  Electricity should always be treated with respect.  A plug and play system in a steel enclosure providing no access to the “pointy end” (potentially dangerous parts like battery, wiring) is safer compared to a kit, a non-steel/plastic enclosure, or a batteries-sold-separately unit.
•  The magic “sustainable” number (how many Watts you may use daily) is 75% of useable storage, based on reasonable sunshine daily.

As an engineer, I am reticent to mix units, but I am going to blend apples and oranges into an oran-apple smoothie by ADDING an inverter rating factor, sustainable storage capacity, solar input, bonus points, and even gasoline, all in some semblance of “Watts”, to rate each standard system vs cost.  Think of it as a point system for specifications and investment.  Data is taken from current product websites.  And here is a similar, interesting comparison table, although the data is over a year old.  Please also note, there are dozens of other similar products that could be in this comparison, but they would likely follow these trends.

Various Portable Generator Models and Basic Specifications

(least to most expensive, left to right)

	Wagan Power Cube, $1099	MySolar Backup, $1797	GoalZero Yeti1250, $1800	Xantrex/ MSB PowerHub, $3997	JASPak300, $4299	SUNRNR, $4350	Honda3000, $2330 + 600 gallons gas = $4580	Sol-Solutions SolMan, $4995
Inverter*,  W cont (surge~2x)	1500	1800	1200	1440	1100	3500	2800	1500
Battery Storage, Whr	660	720	1200	2400	1800	2940	**	3600
Useable Storage = 2/3 total (calculated)	440	480	800	1600	1200	2000	**	2400
Sustainable Storage Available = 3/4 useable (calculated)	330	360	600	1200	900	1500	1500**	1800
Solar Input, W	80	90	60	300	300	280	**	140
Bonus Points: High-load inverter? Other than solar? Expandable system? Pure sine or 240V option? Made in USA?	-- -- -- -- --	-- -- -- -- 200	-- -- -- 200 --	-- -- -- -- --	-- -- 200 200 200	200* 200 200 200 200	200* <-200> -- -- --	-- -- -- 200 200
Total “Watts”	410	650	860	1500	1800	2780	1500**	2340
Total “Watts” divided by Cost	0.37	0.36	0.48	0.38	0.42	0.64	0.33**	0.47

Grey = not included in total Green = higher total “Watts”-to-cost ratio; best value proposition, at least if the specifications meet your bottom line needs in the first place.  (A 1200W inverter most likely cannot power an 1100W microwave, much less run anything else at the same time.) Yellow = see * and ** notes to right Red = not so much.

*  I would like to have used these inverter output numbers since one stands out, but in the spirit of apples and oranges, I decided to deny full credit inverter capability points and just give bonus points for being able to run two 10-amp appliances/tools simultaneously (inverter >2400W).  **  A comparable gas generator was included for fair comparison to Traditional Territory.  With no gas, thus no power output, its Total Watts/Cost is 0.  Let’s call the following a cran-apple comparison to allow the Honda to compete.  Six hundred gallons of gas at $3.75/gal makes its cost roughly equal to the three highest-price models and able to output 1500W daily for almost five years.

One spec that stands out in the table above is that the gas generator is the only comparable system to even approach SUNRNR’s inverter output capability.  There is a reason for that … it is tricky to ask a lead acid AGM battery to give up that amount of power, at least safely.  SUNRNR solved that issue in its proprietary design and its proven and patented system.  Also note the bonus points for accepting alternative renewable energy sources such as a wind turbine.  (The Honda lost points for being carbon-based.)

Here is the comparison in a visual format:

Knowing your requirements and expectations is the key to investing in the right portable solar generator for your home or business. Once you have identified your applications, take the time to compare product specifications and value to help you choose the most appropriate PSG for your needs.

Comments welcome.  Also, I’d be very interested in seeing a Consumer Reports analysis of PSG products.  Please let them know if you are interested, too.