Lighted artwork and costumes can be amazing!  Look at some of the LED based art projects at Burning Man or costumes by Austin Bright Light Design.   Using LEDs and technology to create art is a relatively new genre that is growing fast and has brought delight to millions of people around the world.   This article looks at options to build an inexpensive and long-lasting portable solar generator for off-the-grid powering of your art projects, lighted costumes and more.

Get in the Flow - Current Types

There is tremendous variation in the specific LEDs, controllers and application of the technology used by artist and makers of powered projects.  One constant in lighting design is the need for electricity – specifically direct current (DC).   DC current is necessary because light emitting diodes (LEDS) only work with current flowing in one direction.  For installations in areas with readily available alternating current (AC) electricity from the grid, rectifiers are used to convert alternating current to direct current.   You likely use rectifiers every day from powering your computer to charging your cell phone.   Why?  Because computers, phone and nearly every other electronic device contains diodes (not all diodes are light emitting).  The “brick” attached to your laptop is a rectifier.    (NB: An “inverter” is used to convert DC to AC power.)

Energy Vampires….

Unfortunately, many rectifiers are inefficient with some cheap linear rectifiers delivering an appalling efficiency as low as 20%.   In 2001, President George W. Bush, referring to inefficient rectifiers as “Energy Vampires”, issued an Executive Order to study and take action to reduce the power consumption of these devices, especially in standby mode.  The International Energy Agency estimates that between 1 and 2% of ALL electricity generation worldwide is wasted by rectifiers. Scientists from Lawrence Berkeley National Lab estimated that up to 10% of household electrical energy was wasted through the use of rectifiers in 1999.  

The One Watt Initiative was established through the cooperation of US and multiple countries in 1999.  It seeks to reduce standby power consumption for rectifiers to less than one watt.   As a result of the One Watt Initiative and other efforts, more advanced rectifiers have been coming online.  One estimate puts average rectifier efficiency at 75-80% in new consumer products sold in 2016 - a huge improvement since 2000.  Still, rectifiers are less efficient than generating direct current for electronics.  Using a modern switching rectifier even today can result in a 10 to 15% efficiency loss.   This may not be a big deal when plugging into a wall outlet but could be significant when you are generating the power at a remote location.

So how do you generate DC power for LED installations and charge batteries when there is no readily available power from a grid?  Gas, diesel or propane generators?   They are certainly one solution but generators can be loud, expensive, require constant refueling and must use efficiency-sapping rectifiers to convert AC to DC power.

A relatively simple solution to address the power needs of LED projects and more is to build a portable solar generator.   Solar generators collect energy, store it in batteries and deliver DC current on demand.   A small (<300W) can be constructed for a few hundred dollars and be reused for years.  Below, I will attempt to provide a basic primer on creating your own low cost solar generator to power your lighted projects, cell phones, rechargeable portable batteries, fans or any other low power item. 

Portable Solar Generator

There are four major components to a solar generator – photovoltaic (PV) cells, deep cycle batteries, controller and wiring.  

Solar panels/Photovoltaic Cells (PV)

There are at least 7 types of solar panels (photovoltaic cells) available;  monocrystalline (mono), polycrystalline (poly), amorphous silicon, thin film, concentrated photovoltaic cell, Cadmium Telluride and Biohybrid Solar Cell.   The two most commonly used photovoltaic cells (PV) today are monocrystaline and polycrystalline followed closely behind by amorphous.   It is likely that the solar system set up on you or neighbor’s roof utilizes one of these three types of PVs.   

Recent technology advances have made the cost of manufacturing mono and poly crystalline panels the best choice for a constructing a portable solar generator.  These panels offer the highest efficiency and potential output vs. cost, size and weight.

Figure 1:  100W moncrystaline PV panel with mounted PWM controller charging boat battery

There is a lot of exciting research on PV technology.  In the future, one or more the emerging PV technologies may overtake mono and polycrystalline panels for household use.  For now, I would only consider mono or polycrystalline panels for creating a portable solar generator because they represent the best choice when balancing efficiency, size, cost and portability.   These PVs are also conducive to a “set and forget” set up.

Solar Charge Regulator/Controller

Solar charge controllers (regulators) manage the power output of the PV panels and regulate the distribution of power to and from the deep cycle storage batteries to the electrical load (your LED project).   They are an essential component of any solar power system.

There are two types of solar controllers:  MPPT (Maximum Power Point Tracking) and PWM (Pulse Wave Modulation) controllers.

MPPT (Maximum Power Point Tracking) controllers are up to 25% more efficient than PWM controllers.   The MPPT controller dynamically manages the output of the PV cell, status of storage batteries and current environmental conditions to achieve optimal efficiency.   MPPT controllers are definitely the controller of choice for whole house use or large (>250 watt) portable solar generators.    The downside is that MMPT controllers can be significantly more expensive than PWM controllers with similar capacities.   In some cases, especially smaller systems, it is more cost effective to increase the power capacity of the PV cells (adding another solar panel) rather than purchase an MPPT regulator.

PWM (Pulse Wave Modulation) controllers can be a good choice for portable solar generation systems especially for small systems and in areas with reliable sun.   PWM controllers are less expensive than MPPT controllers and, due to their simpler design, may be less likely to fail after repeatedly setting up, transporting and tearing down.   Above a certain size system however (>300W), the MPPT controller is almost always the best choice.  

Figure 2: 20 Amp PWM controller

There is an excellent Youtube video explaining the difference between MPPT and PWM controllers here.

Regardless of the solar controller you select, it is extremely important to ensure the controller has the capacity you need to support your project.   Controllers are generally measured in current capacity, measured in amperes (amps).   This refers to the amount of current that can be safely drawn from your storage batteries through the controller at one time or delivered from the photo-voltaic cells to your storage battery.  It is a wise practice to use components in your solar generator that exceed the calculated needs of your project by at least 25%.

Example:  A project calls for the use of four, 5 meter long 12V WS2812 LED strips with 30 LEDs per meter.   If we assume each 5 meter 12V strip will draw 33 watts (at maximum brightness), a total of 132 watts (4 x 33w) will be required to fully illuminate the LEDS.   In this example, we will assume the controller uses 12 watts.  So the whole project – not accounting for voltage loss as current is passed through wiring (more on that later) – is 144 watts (132w + 12w=144w).

So how you determine how many amps your solar generator needs to deliver since solar regulators and panels are rated in amps?  To convert watts to amps simply divide the watts by the voltage of your project.   In this case, 144 watts/12 volts = 15 amps.  To learn more about watt/amp conversions, check out this neat little primer on Wikihow.   These calculations are all a product of Ohm’s law.

In this example, I would recommend solar regulator of at least 20 amps at 12 volts or 240W (20amps x 12V = 240W) which is approximately 33% more than the minimum power requirement.

When selecting a solar regulator, it is important to ensure that the controller is optimized to charge the type of storage battery you will be using.  Most controllers have the option to select lead acid, absorbed glass mat (AGM) or gel batteries.   Make sure to set any controller to the charging algorithm designed for the type of deep storage battery you are using.

Solar Generator Batteries – Deep Cycle by Nature….

There are four main types of batteries commonly used in solar generators: flooded lead acid, absorbed glass mat (AGM), gel and lithium ion.   Each battery type has it’s own pros and cons.    For this discussion – creating a low cost solar generator – we’ll look at flooded lead acid batteries and considerations for use of absorbed glass mat (AGM) battery.

What is a deep cycle battery? 

Batteries are not designed to be fully discharged.  Fully discharging a battery – of any type - will permanently damage the battery, reduce charge cycles or worse.  The usable amount of battery capacity is measured by amp hours.  Amp hours refer the number of usable amps a battery can deliver over a set period of time.  Remember, rechargeable batteries are not meant to be fully discharged.  “Depth of discharge” is a percentage that indicates how much of a battery’s capacity has been used.   A simple way to estimate the depth of discharge on a 12V lead acid, AGM or Gel battery is to measure the voltage between the connectors.   The usable voltage range for most lead acid batteries is between 11V – 12.6V.  A battery measuring 11.9V may be 25 – 30% discharged, while a battery measuring < 11V is likely close to fully discharged.

Lead acid batteries commonly come in two types:  “cranking” and “deep cycle”.   A cranking battery is designed to discharge a lot of current (amps) quickly in order to start a vehicle or some other high-energy application.  It is the type of battery used in your car.   While a cranking battery shines in delivering a lot of amps at once, it has a low depth of discharge before damage may occur to the battery.   A cranking battery may only have a depth of discharge limit of 20%  - 30% before reducing battery life.  Due to the low depth of discharge capacity, CRANKING BATTERIES ARE NOT RECOMMENDED FOR SOLAR GENERATORS.  

Deep cycle batteries have a much higher depth of discharge limit vs cranking batteries.   Deep cycle battery can be safely discharged to 50 – 70% of capacity without reducing the expected charge cycles (life expectancy of the battery) or causing damage.  Unlike cranking batteries, deep cycle batteries are designed to deliver lower current slowly.   Perfect for low current applications like powering LED projects or recharging phones and other small batteries.   DEEP CYCLE batteries are an EXCELLENT CHOICE FOR A PORTABLE SOLAR GENERATOR. 

The downside to the use of deep cycle batteries is that they are not designed to deliver a lot of current (amps) at once.   If a lot of current is needed for an application – running a refrigerator or AC system for example – you will need multiple deep cycle batteries and proper wiring to deliver the current to the application.   While high current loads using deep cycle batteries is beyond the scope of this primer, Handy Bob’s blog is an excellent resource to learn more about going off the grid completely.  In his detailed blog posts, you can learn how create a complete off-the-grid system to power an RV, camper or even a whole home.

Applied Gas Mat (AGM) Batteries

AGM batteries are offered as both cranking and deep cycle configurations.  They are often referred to as “sealed lead acid” batteries.  The primary difference between flooded lead acid and AGM batteries is the electrolyte in an AGM battery is absorbed in thin fiberglass mats instead of free flowing as a sulfuric acid solution in a flooded lead acid battery.   AGM batteries require no maintenance, do not emit fumes and can be mounted in any position.  They are extremely durable and unlikely to be damaged during rough handling or in when mounted in places where there could be significant shock (ATV’s, transporting) and much more resistant to cold weather because the electrolyte is not subject to freezing.   The capacity of AGM batteries is usually higher than flooded lead acid batteries based on weight.   AGM batteries are even approved by the FAA for transport on commercial passenger airplanes.   They tend to self-discharge slower than flooded lead acid batteries and can maintain their functionality and more of their capacity in hot or cold temperatures. The downside of AGM batteries is that they can cost up to twice as much a flooded lead acid battery.

Battery Capacity – Amp Hours

Battery capacity is measured in amp hours.    This is an indication of how long a battery can safely deliver current (amps) over a period of time.   It is a measure of usable capacity, not the total capacity of the battery.    

A 12V battery listed as “100 amp/hours x 20 hours” means that the battery is capable of delivering 5amps for 20 hours before falling below usable voltage.  For a 12V battery, the lowest a battery should be discharged is around 10.5 volts.   A battery labeled “80AH@10hours” means the battery can continuously deliver 8 amps for 10 hours.   Most 12V car size batteries are based on a 20 hour rate so many batteries may just list amp hours.   A 100 AH battery can deliver 5 amps for 20 hours.

It is important to note that the relationship between battery capacity and rate of discharge (amps used) is not linear.   In other words, a “100AH@20hour” battery would not be capable of delivering 100 amps for one hour, instead the battery might be able to deliver 100 amps for 30 – 40 minutes.    The reason for this is a law of physics called Peukert’s Law.   

Wiring – Yes, it matters.  A lot.

Wiring is the most overlooked item on solar generators - especially store bought kits like the ones you might find at Harbor Freight.   The reason is that braided copper wiring is expensive and a serious condition called “voltage drop” occurs when using thin wire and/or attempting to deliver DC current over long distances.   While supplied thin wires in a store bought kit might work, efficiency may be reduced dramatically.

A typical solar panel will come with short wiring to go from the panel to the solar controller.  These cables are generally standardized and use an industry standard connection called MC4.  These wires are connected directly to the solar controller.

The next wiring is from the solar controller to the deep cycle storage battery.  This is a critical part of the solar generator and often the weak link in getting the most efficiency from a solar generator.

Wiring of DC systems is a lot like piping used in household plumbing.   A narrower pipe will have less flow of water than a wider pipe.    Over a long distance, the resistance of a narrow pipe or resistance of a narrow wire will reduce the transfer of water or current while decreasing the pressure or voltage.   This leads to a condition called “Voltage drop” that occurs when attempting to conduct DC current over a long distance with narrow wires. 

If voltage drop is severe enough, it will not have enough voltage to charge a battery.    So while it might seem nifty to set up a solar panel “out of the way” on a sunny hill 100 yards away from the deep cycle storage battery - perhaps after finding a great deal on three cheap, 100 ft ,16 gauge extension cords - a 12V solar generator will likely not work due to voltage drop.   Current reaching the battery in such a configuration may only be 9.5 – 10 volts - below the voltage necessary to charge the battery at all.

Solar Generator Wiring Tips

*          Use the shortest wire between the solar controller and battery as possible.

*          Use the thickest (lowest gauge) wire that will fit into your charge controller.

*          If you buy a pre-packaged solar generator, inspect wire thickness and consider replacing if the supplied wire used between the controller and battery is thin.   Thick, stranded copper wire is expensive and dominated by world commodity pricing.  Makers of many pre-packaged solar generators cut costs by using thinner wire.

Pro Tip:  Use (8 gauge or thicker) automobile “jumper cables” as wiring between battery and controller.  The jumper cable alligator clips are convenient for attaching/detaching battery.  Remove the clips from the end to be attached to the controller, shorten cable as much as feasible and insert into the charge controller taking care to ensure polarity is correct (+/+,  -/-).   

Always use the “output” connections on the solar controller to power your projects.  NEVER USE POWER DIRECTLY FROM THE BATTERY.   Solar controllers regulate the both the charging of storage batteries and the output of the solar generator.  A solar generator will shut off power if the battery state of charge is too low.  This feature protects the battery from over-discharging and destroying the battery.

Cost estimate for 100W solar generator, April 2019

 

Renogy Solar 100W mono panel  - $106.00

 

 

AllPowers 30Amp PWM Solar Controller - $28.00

 

 

4 Gauge 20ft Jumper cables  - $23.00

12V 100AH AGM (Sealed) Battery - $168.00

NB:  This is for an AGM deep cycle battery.   Standard (non-AGM) batteries can be found for significantly lower prices.  I prefer sealed AGM batteries because they are safer to transport and less prone to damage from vibration or rough handling and more applicable to portable solar generators.  I have used an 80AH AGM battery with a100W solar panel, 30 amp PWM controller - in near ideal desert conditions - and was able to recharge the battery to full from about 50% depth of discharge daily.

Total cost for 100W solar generator (April, 2019) - $325.00

The only component that should need replacing is the battery after 3 – 5 years.

I hope that this was helpful, and that you have a great time at your next campsite or off-grid excursion with these tips.  Stay lit my friend!   

Until next time!

Cheers,

Gerry Gilligan

Co-Founder

Austin Bright Light Design