Friday, August 1, 2014

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.
solar gadget generator trailer installation
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?


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--

200


--

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200

--


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--

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--

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--

--

200


200

200


200*

200

200


200

200


200*

<-200>

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--


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:
visual comparison of portable solar generators
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.



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