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Solar Generator

What to Look For in Solar Generators

Considerations before you buy
Friday, July 12, 2013, 11:25 AM
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Solar generators capture the sun’s energy via solar panels, store that energy in a battery bank, and release it through an inverter to be used for standard AC power. That is the standard definition of a solar generator.

Based on this definition, the key elements to look for in solar generators are:

  • Battery storage capacity
  • Solar PV input
  • Inverter rating
  • Component quality
  • Portability
  • Balanced system design

In this article, we will explore these key elements and hopefully give you a better understanding of each element, how is fits into the overall performance of your system, and what to watch out for in the plethora of systems and choices out in the solar generator market these days.

Battery Storage Capacity

The most important aspect of a solar generator’s actual usability is its battery storage capacity. Battery storage allows you to use the generator at night, in periods of limited sun, and when your energy needs exceed the amount of solar input coming in.

Batteries are rated in terms of amp hours (amp/hr). For example, a 12-volt 100 amp/hr battery. However, because most power applications (electronics, appliances, and tools) are measured by their wattage draw, estimating usage times becomes a bit problematic.

Therefore, by converting amp hours to watt-hours, we get a more convenient battery rating. To calculate watt-hours from amp hours, multiply amps times volts. For example, the watt-hour rating of the above 12-volt 100 amp/hr battery is 1200 (12*100).

Unfortunately, not all of the rated watt-hours should be used. Battery manufacturers recommend only using 2/3 of the full capacity in traditional lead-acid batteries in order to preserve life span and reduce failures. Draining batteries fully will effectively destroy them.

Lithium batteries, lighter and more power dense, are the exception to this, as they can be drained to 10% capacity. However, lithium’s developing nature and price limits its prevalence for the current solar generators on the market.

Following battery recommendations, the usable watt-hours of a system’s battery storage become clear. In the above example, the 100 amp/hr battery actually has 800 usable watt-hours of storage capacity (1200*2/3).

By knowing a solar generator’s usable watt-hours, you can determine how long it will run specific applications. In this manner, a solar generator with one 100 amp/hr battery could run a laptop with a 100 watt draw for 8 hours (800/100) before it would need to be recharged.

What to Watch Out For
  • Solar generators with limited or no battery storage capacity

    Without decent (1000+ usable watt-hours) storage capacity, reliability and usability are severely affected. Without batteries at all (batteries not included), a solar generator is pretty worthless.

  • Solar generators with overstated battery storage capacity

    Usable watt-hours is the real measurement, not the total battery rating.

Solar PV Input

Solar PV input (solar panels) is what powers a solar generator. Having ample solar PV input allows for continuous solar generator usage during the day and low recharging times after night usage.

Solar panels are rated by their watt-generation capabilities. For example, a 140 watt PV panel generates 140 watts of inbound power in full sun. Full sun lasts about 6 hours during the day, generally from 10am to 4pm. At other times of the day, PV input still comes in, but can be less than rated.

However, having a solar generator that is portable or with separate PV panels will allow for solar tracking. Solar tracking is the ability to move your panels with the sun’s arc to continually capture the best solar input.

PV input is directly related to storage capacity in a solar generator because of the need to store energy for use at a later time. Based on this, a good measuring stick for a solar generator is its recharging time after depletion of its allocated usable watt-hours.

Six hours or less of recharging time for systems that have under 2500 usable watt-hours is appropriate. Anything over this time begins to affect usability.

It is important to note that using the solar generator while it is recharging will increase the time to full capacity.

Furthermore, letting batteries sit without a full charge or not fully charging the batteries before night usage cuts their lifespan short. This further cements the need for solid PV input to have available day usage whilst recharging and fully recharged batteries at night.

Utilizing our above examples, having a solar generator with one 100 amp/hr battery and one 140 watt PV panel would yield a 5.7 hour recharging time after using its allocated storage capacity (800/140).

What to Watch Out For
  • Solar generators that don’t actually come with solar panels (panels not included)

    A “solar generator” without solar panels is absurd. It is probably best not to buy from companies that would engage in shady marketing techniques like this, as the question of what else aren’t they telling you comes to mind.

  • Solar generators with lengthy recharging times

    With less sun in winter and on cloudy days, and none during night, having manageable recharging times supports reliable usage.

Inverter Rating

Inverters convert low volt DC to standard 120 volt AC power. This allows you to easily use the power that comes in from PV panels (in DC form) for a variety of power applications.

Inverter chargers (an upgraded type of inverter) also grant the ability to externally charge your battery bank by plugging it into the grid or gas generator and routing the incoming AC power to the batteries in DC form.

Ultimately, inverters rate the maximum watts you can pull at any one time from a solar generator. For example, a 1500 watt inverter lets you pull up to that wattage in AC power.

However, it should be noted that pulling the maximum watts from an inverter depletes lead-acid batteries at a faster rate (lithium batteries protect against this effect).

Most solar generators use the inverter rating as the overall generator rating, which is understandable based on the need to know what you can pull from a unit.

Unfortunately, inverter size alone does not correlate with solar generator capabilities. For example, using our above specs, we see that having a 1500 watt inverter with one 100 amp/hr battery renders the system a bit useless. Pulling 1500 watts continuously would deplete the 100 amp/hr battery in around a half an hour (800/1500).

The best, most usable, and most reliable solar generators have at least a 1.5:1 usable watt-hours-to-inverter-rating ratio (i.e., 1500 watt/hrs to 1000 watt inverter).

What to Watch Out For
  • Solar generators with big inverters and little to no battery storage

    Rating a solar generator by its inverter is all well and fine, but if the generator does not have much battery storage, it’s dubious at best.

  • Solar generators without inverter external charging capabilities

    Having the ability to plug a solar generator into the grid or a gas generator for quick charging purposes vastly increases its reliability. Inverter chargers make this an easy process.

Component Quality

Beyond the component ratings, quality is a huge factor that can affect the usability and durability of solar generators.

Owning a solar generator for any application brings about a need for reliability. Specifically, having a solar generator as the sole power source for off-grid living or in an emergency backup situation means that it has to work when needed.

In this respect, it is imperative to have component warranties and capable life spans. American made inverters and solar controllers have been proven in rigorous conditions and tend to have 2-5 year warranties, ensuring long-term usability. Unfortunately, the same cannot be said for some of the cheaper imported components that many solar generators utilize.

Durability is also a key issue for solar generators that is negatively affected by component quality.

Explicitly, solar generator casing that is plastic breaks down over time with natural wear and tear, as well as heavy sun exposure, let alone if it is being used in rugged conditions like off-grid living, emergency response, or construction sites. Metal casing confirms that solar generators can stand up to exacting use and continue to protect their valuable components over time.

It is important to note, with respect to solar PV panels, that China (the dominant player in PV manufacturing) produces quality that matches world standards. However, most of the developed world (U.S. and Europe) is in a struggle with China over its unfair (and illegal) dumping of solar panels at below-market prices. Buying panels at these prices, while not proven to adversely affect solar generator quality, does not support a sustainable solar industry or competitive domestic economy.

What to Watch Out For
  • Solar generators with un-named components

    Having unknown components limits quality checks (i.e., online comparisons), cuts out warranty availability and brings into question overall solar generator (and company) reliability.

  • Solar generators with plastic casing

    Plastic casing, especially the standard box used for most solar generators, is cheap and of low quality. If you live in the suburbs and keep your solar generator in the garage, except for when you buy it and throw it away, it probably doesn’t matter. If you actually plan on using it, look for a solar generator with durable casing.

Portability

Most solar generator applications (off-grid, emergency backup, events, construction, etc.) require a degree of portability. If the system itself can be moved, this allows for solar tracking, point of use power, and on-demand usage.

Batteries increase weight significantly, so having solid storage capacity naturally makes for a heavy system and reduces mobility.

Most solar generators skirt this issue by not having much storage capacity. However, even one-battery systems can weigh quite a bit (100+ lbs), limiting their basic movement.

To ease this problem, most companies came up with the ingenious idea of mounting these heavy systems (in plastic casing) on small, cheap plastic wheels. The result is “portable” solar generators that look like they would have a hard time being pushed on flat pavement by a body builder.

Bicycle wheels and proper weight distribution secure the ability for portable solar generators to be used off-grid (dirt trails, steep hills, potholes, etc.), pushed easily on location, or wheeled via ramps into a truck or van.

What to Watch Out For
  • Solar generators with weak, cheap, or no wheels

    “Portable” solar generators should be moveable, not just when you first purchase them or in the best conditions, but in real environments

  • Solar generators that are insanely heavy without proper design

    Any substantial battery capacity will make a solar generator very heavy. If the unit’s design does not account for this fact, “portable” may be a bit of a stretch.

Balanced System Design

Bringing all the key factors for solar generator usability together gives a clear picture of the overall need for balanced system design. Solar generators that really work when needed have quality components that fit well with each other and have ratings that support end-usability.

The key combination of factors for a balanced system design is the pairing of usable storage capacity, solid PV input, and appropriate inverter rating. As stated, this means having at least a 1.5:1 usable watt-hours-to-inverter-rating ratio and 6 hours or less of recharging time from recommended depletion.

In actual terms, 1500 usable watt-hours is a baseline for storage capacity that can handle most solar generator applications. To balance the system out, 250 watts PV input and a 1000 watt inverter would be ideal.

Adding high quality components and balancing the system design to boost portability will assure that a solar generator can work in a variety of environments, applications, and needs.

What to Watch Out For
  • Solar generators lacking any of the key components

    Solar generators are systems in which components complement each other. Companies selling solar generators without key components are doing the customer a disservice.

  • Solar generators with disproportionate ratings

    Balancing the system out is not just a recommendation, it is necessary if you want a solar generator that lasts and works when needed.

~ Chaz Peling


SolSolutions designs and manufactures portable solar generating equipment. The SolMan line of portable solar generators and light towers is available for purchase or rental, with applications for off grid power, emergency backup power, temporary needs, events and construction sites.

SolSolutions also incorporates the key elements of solar generators into its designs to ensure durability, sustainability and usability. In this respect, SolSolutions is a proven provider of high-quality equipment that really works when needed.

www.sol-solutions.com - 800-828-2965

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2 Comments

GregGGH's picture
GregGGH
Status: Member (Offline)
Joined: Mar 13 2011
Posts: 10
battery drain

I am far from the expert ..but I have always been lead to beieve that you should NOT drain the lead style battery beyond 50% ...but artilce says 66% ...make a difference on capacity of system for sure ...

http://www.scribd.com/doc/110610451/MARINE-and-RV-Battery-Lead-Acid-Batt...

see figure 3 on page 4 of this article .. 

Greg

ps- I think this is a great batterty help guide ...when I saw it ...and posted it to scribd a while back

Arthur Robey's picture
Arthur Robey
Status: Diamond Member (Offline)
Joined: Feb 4 2010
Posts: 3936
The Life of a NIFE.

Please consider NIFE (Nickel Iron) batteries. They are bullet proof. The downside is that they are only 50% efficient. Some of them made by Edison are still working.

Mobile applications need to take into consideration that they yield 100W per kilogram.

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