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OFF-GRID
SOLAR POWER
FOR AMATEUR RADIO
PRACTICAL LESSONS LEARNED IN 25 YEARS
OF
FRUSTRATION
Bill Crowell, N4HPG
ABOUT ME
First licensed in 1982
Amateur Extra 1984
Electronics Technician & Designer
Involved in Solar since 1993
Software and Systems Developer (my day job)
Solar energy supplies my entire station except for the linear amplifier.
[email protected]
DISCLAIMER
I am NOT a licensed Professional Engineer in the State of Texas
pursuant to Chapter 1001 of the Texas Occupation Code.
DISCLAIMER
This presentation features images of TEST apparatus for
experimentation. The TEST apparatus may or may not
have all required safety measures as required by local
codes.
YOU are responsible for your own system safety and
code compliance.
WHAT ARE YOUR GOALS FOR SOLAR?
• What equipment is going to be powered by the system?
• Under what conditions?
• Normal, daily life
• Emergencies
• The End Of The World As We Know It
• You want to help save the planet from global catastrophe
caused by anthropogenic “climate change”
• You want to save money on your electricity bill
• You want to virtue-signal your moral superiority to others
• It just simply looks cool!
ECONOMICS
If your goal is to save money, you have the wrong goal.
• Up-front cost of equipment
• Up-front cost of permitting and inspections
• Ongoing maintenance
• Uncertain regulatory future
• Magic, disappearing incentives
• Traditional power is much, much cheaper
With a 25-year payback, are you really going to stay at the
same house?
MY GOALS FOR SOLAR
• An ongoing experiment for learning
• Global Thermonuclear War
• Charging batteries for flashlights and other devices
• Powering essential devices – water pump
• Emergency power for ARES operations
• Running my radio station separate from mains without a
generator
• Operating low-voltage lights and other DC appliances
DEFINITIONS
OFF-Grid
Not connected to the mains electrical grid in any
way whatsoever.
ON-Grid / Grid-Tied Connected in any way to the mains electrical grid.
Hybrid
Tied to the grid, but capable of operating during a
mains power failure.
PRACTICAL AND LEGAL IMPLICATIONS
• Zoning
• Your local regulators will impose limits on your projects
• Permitting, inspections and licenses
• HOA Restrictions
• Grid-Tied systems are subject to strict regulations to
protect the safety of utility workers
• Anti-Islanding
A SYSTEMS APPROACH
The proper way to think about a solar-energy project is as a
system and not simply a set of components.
Our radios and other equipment operate within the
framework of 2 major systems:
• Our home station with mains power, 13.8v PSU
• Our mobile station with a nominal system voltage of
13.8v.
• Handheld radios with internal batteries
THE STANDARD GRAPHIC
OHM’S LAW ALWAYS APPLIES!
Anyone attempting to break Ohm’s law will have their radio
license revoked and will be removed from the premises.
DEFINITIONS
Load Volts
The design voltage of the powered system
Load Amps
The required current of the powered system
Charge Volts
Voltage necessary to charge the battery
Charge Amps
Current supplied to the battery
Solar Volts
Design voltage of the PV array in full sunlight
Solar Amps
Current supplied by the PV array in full sunlight
WHAT DO WE WISH TO POWER WITH THE
SYSTEM?
This is a fundamental question that is often not discussed
adequately.
We need to have clear objectives in mind when considering
a project.
The devices that we wish to power contribute to the Power
Budget – the total amount of energy available in the system.
CREATING A POWER BUDGET
MAKING EVERY COLUMB COUNT
• Running radios – standby and transmit
• Running inverters for 120v devices
• Recharging other batteries
• Standby losses
• Cloudy days
• Higher-than expected utilization
After we know the power budget, we can select the system
design voltage.
SOLAR SYSTEM DESIGN VOLTAGE
The system design voltage dictates the operating conditions
of the entire system and the selection of components.
For our purposes, the design voltages are :
• 12 volts
• 24 volts
• 48 volts
The choice of voltage will greatly influence the usability of
the system because of impedances.
SOURCE IMPEDANCE
THE KILLER OF MANY A FIELD DAY
Source Impedance is the action against the flow of energy in a
system at the point of generation.
Batteries have source impedances that may be significant and
limit the amount of current supplied at a given voltage.
Batteries are NOT capacitors. They may not give the amount of
instantaneous current to maintain the voltage during surging of
the load .
When you see the radio’s display go nuts during transmit, you are
seeing a lot of source impedance.
OVERCOMING RESISTANCE
We have 2 options to move more energy:
1. We can use thicker wire
2. We can raise the system voltage
Doubling the voltage reduces the
resistance losses by 4 times!
It also means we can go longer distances with thinner
wires.
VOLTAGE CHOICES
MAXIMIZING YOUR POTENTIAL
• 12 Volts
• Nominal voltage of automotive batteries
• Seems to be an obvious choice for direct connections
• Difficult to move any distance
• 48 Volts
• Much lower losses
• Inverters are much more efficient
• Telco equipment is POSITIVE ground!
• 24 Volts
• Standard for aviation and large vehicles
• A very good compromise
12 VOLTS IS FUTILE!
Our mobile and mobile-capable radios are designed to work
on 13.8v.
They are NOT designed to operate on 12v. If you don’t
believe me, check the specifications table.
12 volts is the nominal voltage of a common, lead-acid
storage battery.
13.8v-14.2v is supplied by the vehicle electrical system to
charge the starting battery.
Anyone who has tried to use a 12v battery with a radio for
more than 1 hour during an emergency knows exactly what
I mean.
MAJOR COMPONENTS OF AN OFF-GRID
SOLAR SYSTEM
• Battery Bank
• Photovoltaic Panels a/k/a Solar Panels
• Battery charge controller
• Converters/Inverters
• Interconnecting cables, fusing and protection
• Monitoring devices
BATTERY BANK – TYPES OF BATTERIES
Chemistry
Reference Price
Benefits
Nickle-Iron
$5,820
Indestructible!
LiFEPO4
$2,100
Stable, light-weight, energy dense
Deep-Cycle
$600
Cheaper!
24V MARINE BATTERIES
IN THE GARAGE!
AN ALTERNATE CHARGING SOURCE
It is important to have an alternate charging source – this is
especially true for emergencies.
Leverage your investment in your battery bank to maximize
the effectiveness of your generator! Use the generator at
full power to charge the batteries, then shut it down.
This is hybrid approach saves a ton of fuel!
PHOTOVOLTAIC PANELS
DIODES HIDDEN IN PLAIN SIGHT
PV Cells are:
• PN Junctions a/k/a diodes
• Subject to reverse-current flow and heating
• Electron “pumps” when exposed to photons
PV Cells are NOT BATTERIES. (Repeat 3 times)
PV Cells are subject to electron drift.
MY PANELS
EXPERIMENTAL WITH HOME-RUN WIRING
SERIES OR PARALLEL
Parallel connection of a few panels is indicated where:
The panels are physically close to loads
The wiring is heavy enough to reduce losses
Use of a cheap PWM controller is used
Series connection is indicated where:
Panels are some distance from controller
A MPPT intelligent controller is used
A combination of Series & Parallel may be appropriate.
It is much easier to move power by raising the voltage and lowering the
current.
TAP POINTS FOR TESTING
OUT OF THE REACH OF CHILDREN!
VISUALIZATION OF ELECTRON FLOW
PV CELLS ARE CURRENT DEVICES
This simple fact cannot be overstated. Because they care
current devices, all electrons must flow thorough them or
around them.
PV cells respond to reverse currents just like any other
diode – they heat up and can fail or even catch fire
(reportedly).
Standard practice is to install Schottky bypass diodes to
protect the panel itself.
SOLAR SHADING
1 CELL CAN STOP EVERYTHING!
PV PANELS MUST BE PROTECTED
BYPASS DIODES SHUNT CURRENT AROUND SHADED CELLS
TYPICAL SCHOTTKY BYPASS DIODES
INSPECT YOUR PANELS!
I have received new panels where bypass diodes were
omitted.
I have received new panels where there were more bypass
diodes than are needed – wasted energy and more heating
in the panel because of 2 diode-drops. Only 1 diode is
needed per string of cells in a given panel.
SCHOTTKY DIODES
Power Schottky diodes are:
•
Standard equipment
•
Not very efficient
•
Dissipate (waste) a lot of energy as heat
Texas Instruments Built a better mousetrap
SM74611 ACTIVE BYPASS
• Created by TI to solve the heating problem
• Active Device with power MOSFET
UNOBTAINABLE JUNCTION BOX
I CANNOT LOCATE THESE ANYWHERE IN THE US!
I MADE MY OWN PCBS
BY THE DAWN’S EARLY LIGHT
LOTS OF VOLTS, BUT NO AMPS
HUNDREDS OF TRIPS TO THE TERMINAL STRIP TO MAKE CHANGES
It is imperative to have instrumentation to verify the voltage
and the current supplied by your panels to the charge
controller.
Charge controllers rarely show Solar Amps leaving you to
wonder why your system is performing poorly.
Adding an ammeter and voltmeter to the solar feed before
the controller is a necessity.
CHARGE CONTROLLERS
• Pulse-Width Modulated (PWM)
•
•
•
•
For small systems
Panel voltage is close to system battery voltage
Wiring is relatively short
Cheaper
• Maximum Power Point Tracking (MPPT)
•
•
•
•
•
Enables series wiring of panels – HVDC (150v typ.)
DC-DC Buck/Boost converter
Gathers more energy than PWM
Microprocessor controlled
More expensive, but worth it
MPPT
MPPT – IN PRACTICAL TERMS
Maximum Power Point Tracking simply means that the
charge controller will pull as much power out of the panels
as possible and shove it into the batteries.
This means that there is a DC-DC buck/boost converter and
logic that samples the energy capability several times a
minute.
MPPT Controllers give you the greatest flexibility in panel
configurations.
MY SYSTEM DESIGN - MPPT
• Series-connected panels placed opportunistically
• 150VDC open-circuit design voltage
• 75’ of wire from panels to controller
• 24VDC battery and low-voltage distribution system
• Astron 24-14V converters at the radio table and in the
network room
• 6x 100Ah marine batteries in the garage
• 2x 100Ah gel-cell batteries in the shack
MY SOLAR BOARD (LATEST REVISION)
ASTRON N2412-24
THE DEVICE THAT CHANGED MY LIFE!
ASTRON N2412-XX DC-DC CONVERTER
• Originally designed for large vehicles and aircraft
• Active-Clamp, Forward DC-DC converter
• Provides rock solid 14v at the point of use!
• Ham Radio desk
• Network closet
• Enables 24v distribution voltage
• 14v with input from 18-36v!
• Readily available on Amazon, eBay, etc.
• NON-isolated – 14v negative is also 24v negative
UPSTAIRS EQUIPMENT
ROCK SOLID 14 VOLTS !
MY RADIOS ARE ALWAYS HAPPY!
HOW MUCH POWER CAN WE GET?
WHEN CAN WE GET IT?
MEASURING
SADLY, LIMITED TO 100V
A REALITY CHECK
GETTING THE MOST POWER WITH ACTIVE
BYPASSING
Shaded panels degrade the entire system. Experience
shows that dropping shaded panels out of the circuit greatly
improves system performance.
Not ready for the Hamfest:
• Panel-mounted active-bypass device
• Raspberry-Pi based intelligent controller with relays
These projects are being developed in collaboration with
Prof. Hill (Art of Electronics) at Harvard.
NOISE!
I have not noticed any RFI/EMI from my system.
Panel-mounted electronics are known to be very noisy:
Panel-mounted inverters (per QST)
Panel-mounted MPPT controllers
QUESTIONS?
Notes are on my blog:
N4HPG.WORDPRESS.COM