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A Small Solar Power System for Radio Operations

Putting together a small solar power system to power your transceiver is quite simple with modern components, and it is affordable with most budgets. This article provides some general background and guidance on building a simple solar power system, and these concepts can be applied to construct systems across a range of power capacities.

Components: A solar power system typically consists of three main components that can be purchased separately or in packages. Individually purchased components can be mixed and matched to construct systems of different powering capability. As illustrated in Figure 1, the three main components are:

Solar power system showing three parts
Figure 1: A simple solar power system for a transceiver is comprised of a photovoltaic panel, a charge controller, and a storage cell.

  1. Photovoltaic panels (solar panels) - These are arrays of individual solar cells that convert sunlight into electrical power. Typically, numerous individual 0.5-volt cells are connected in series to raise the panel output voltage to a higher value, and multiple sets of series cells are connected in parallel to provide increased current. The power of a panel, in units of watts, is determined by the product of voltage x current. Commercially available panels can produce 100 watts or more in bright sunlit conditions. Combinations of panels can produce much more power.

  2. Charge controller - A charge controller receives the output of the photovoltaic panel(s) and conditions it for the purpose of safely charging a battery that will store the energy produced by the panels. A solar charge controller keeps the battery from overcharging, avoiding damage. It also blocks current from flowing in reverse, from the battery to the panels. The charge controller varies the voltage and current required by the battery chemistry type as the battery charge begins to approach its maximum.

    1. PWM Charge Controller - An older type of charge controller is the pulse width modulation charge controller. It gradually reduces the current to the battery during charging by reducing the duration of pulses of applied voltage. PWM controllers are less efficient than the newer MPPT controllers because they operate at a constant voltage. Excess voltage produced by the panels cannot be converted into increased current for charging and is wasted.

    2. MPPT Charge Controller - A maximum power point tracking charge controller is more efficient than the PWM type of controller because it does convert excess panel voltage into charging current. The MPPT controller allows the panel to produce power at its maximum power point of current and voltage, converting this power into a safe and optimized charging profile for the battery chemistry type. MPPT controllers are generally more expensive than PWM controllers, but they provide reduced charging times.

  3. Battery - Often one or more deep cycle cells, the battery or battery bank stores the energy produced by the panel. The most common battery chemistries used today are lithium-ion (or the very similar lithium iron phosphate) and lead-acid. Each chemistry type has unique charging profile requirements, and the charge controller should be set to match the battery chemistry. A wide range of battery capacities are available, expressed in amp-hours, and higher capacity cells will be more expensive than lower capacity cells.

Cables & Connectors: Most solar panels will use photovoltaic (PV) cables with MC4 connectors. The MC4 means "multi-contact, 4 mm diameter." The MC4 comes in male-female pairs, and they have a locking clip to prevent accidental disconnection. They are sealed, weather proof connectors that provide excellent conductivity and represent an industry standard promoting interoperability among separately purchased components.

MC4 connector
Figure 2: The MC4 connector is typically used with PV cables. (Image courtesy

Most photovoltaic panels will provide short leads of PV cable with MC4 connectors from the back of the panel. Longer PV cables are connected to the short leads with the MC4, leading to the charge controller. Typically, a charge controller will have input ports requiring pigtail termination of the PV cables rather than an affixed MC4 connector.

Heavy gauge wire is used from the output of the charge controller to the battery terminals. Heavy ring connectors crimped or soldered to the heavy gauge wire are convenient for many battery terminal connections. For most small solar power systems, 12 AWG or 10 AWG insulated wire is recommended for the controller-to-battery connections. A good safety practice is to install an in-line fuse in the positive connection rated for the maximum output current of the charge controller.

Connection of the transceiver to the battery should use transceiver manufacturer-recommended wire gauge, or the manufacturer-provided power cable. Ring clamps may also be convenient for this battery connection, and including in-line fuses near the battery in both positive and negative connections is a good safety precaution. Since you may want to easily disconnect your transceiver from the battery, the use of quick disconnects such as Anderson Powerpole® connectors is recommended for the battery leads.

Example System: Figure 3 shows an example of a small solar power system used by the author to power a portable 100-watt transceiver along with various camping equipment such as LED area lighting, a small refrigerator, and a device recharging station. The system is comprised of two 100-watt photovoltaic panels connected in parallel using two PV Y-cables and feeding an MPPT controller mounted in the top of a dual-storage cell holding box. The controller is connected to two lithium-ion deep cycle storage cells housed in the box and connected in parallel to provide 85 amp-hours capacity and 13.8 volts output. A Powerpole® connector distribution bus is connected across the two storage cells, with various fuse ratings among the eight available outputs. A separate (green wire) battery recharging connection is seen extending to the left of the battery box for an alternative AC recharging connection.

Small solar system with two 100-watt panels.
Figure 3: A small solar power system including two 100-watt panels, an MPPT controller, 85 amp-hour storage cells, and a Powerpole power distribution bus.

Figure 4 shows the back of the solar panels. The panels are hinged together and close in a clamshell approach that stores the PV cables and aluminum props used to stand the panels at desired angles to the sun. The PV Y-cables are visible that connect the two 100-watt panels in parallel and join to the two PV cables that lead to the battery (red & black).

Back of solar panels.
Figure 4: The back side of the hinged solar panels showing PV Y-cables and storage of aluminum props.

This example system provides continuous power for the camping needs and 100-watt radio operations when at least modest sunlight is available to recharge the storage cells. In bright sunlight, recharging the storage cells from 50% capacity to 100% capacity is accomplished in about 7 hours (~42 amp-hours). Daily recharging of 10% (8.5 amp-hours) or less of the storage capacity is usually accomplished in under 2 hours, even with irregular sunlight.

Recently, the two rigid 100-watt photovoltaic panels were replaced with an integrated set of folding panels weighing 18 pounds and rated at 200 watts. These make transportation and storage of the solar system much easier and efficient.

The products used in the rigid panel example are:

  • Renogy 100 watt, 12 volt, monocrystalline PV panels (2)

  • Renogy RoVER 30 amp MPPT charge controller (1)

  • Renogy PV extension cables, 20' (+/- pair)

  • BougeRV solar connector Y branch parallel adapter cables (2)

  • Renogy 30 amp ANL fuse and fuse holder (1)

  • Ionic 50 ah lithium ion deep cycle storage cell (1)

  • Ionic 35 ah lithium ion deep cycle storage cell (1)

  • Chunzehui F-1005 9-port 40A connector power splitter distributor (1)

  • Anderson Powerpole® connectors (various)

  • 10 AWG and 12 AWG insulated wire (various)

Be sure to do your homework before purchasing components to ensure compatibility and desired feature sets, as well as the desired power capacities. But a DIY solar power system can be constructed easily from the components highlighted in this article that provides excellent long-term power for your portable station.



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