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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