DRAFT
What is a solar system?
A solar system is a setup that uses solar panels to capture sunlight and convert it into electricity, either for direct use or storage in batteries. A solar system uses the Photovoltaic (PV) effect to convert sunlight into electricity.
What is the use of a solar system in our context?
A solar system can be used to generate electricity where no (or unstable) utility grid is available (off-grid). The electricity can be used to power computers, printers, modems, light bulbs etc.
What are the basic electrical principles and key terms that I need to know to understand and design solar systems?
To understand and design (off-grid) solar systems, it's essential to know and understand some basic electrical principles and key terms.
Voltage (V)
Voltage is the force that pushes electrical current through a circuit. It’s measured in volts (V). Think of it as the pressure in a water pipe—the higher the pressure, the more force there is to move water (or in this case, electricity).
Example:
In a solar system, your solar panels might produce 12, 24, 48 or more Volt. Higher voltage systems can be more efficient over long distances since they reduce energy loss.
Learn more:
Current (I)
Current is the flow of electrical charge in a circuit, measured in amperes (A). It’s similar to the flow rate of water in a pipe. The more current you have, the more electricity is flowing.
Example:
If you have a solar panel that produces 10A of current at 12V, it means the panel is pushing a certain amount of electricity through the circuit at that voltage.
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Resistance (R)
Resistance is what opposes the flow of current in a circuit, measured in ohms (Ω). It’s like friction in a water pipe that slows down the flow of water.
Ohm's Law:
R = V / I
Where:
- ( R ) is the resistance in ohms (Ω)
- ( V ) is the voltage in volts (V)
- ( I ) is the current in amperes (A)
Example:
Wiring in a solar system must have low resistance to ensure minimal energy loss. For instance, if you have a 12V solar panel and the current flowing through the wire is 2A, the resistance in the circuit would be:
R = 12V/2A = 6Ω
High resistance can lead to heat buildup and reduced efficiency, so selecting the right wiring and components is critical.
Learn more:
- Victron Wiring Unlimited - Theory - Ohm's Law
- Victron Wiring Unlimited - Theory - Conductivity and resistance
- Victron Wiring Unlimited - Theory - Connection resistance
- Victron Wiring Unlimited - Theory - Current, cable resistance and voltage drop
Alternating Current (AC)
Alternating Current (AC) is a type of electrical current where the flow of electrons switches direction periodically. This is the type of electricity commonly used by household appliances like computers and printers.
Example:
A solar system typically generates Direct Current (DC), but most household appliances run on AC. An inverter is used to convert DC from the solar panels or batteries to AC.
Direct Current (DC)
Direct Current (DC) is a type of electrical current where the flow of electrons is in a single direction. This is the type of electricity typically generated by solar panels and stored in batteries.
Example:
Solar panels in an off-grid system produce DC electricity, which is stored in batteries and can be used directly by DC appliances or converted to AC.
Watt (W)
A watt is a unit of power, representing the rate of energy consumption or generation. It is calculated as Voltage (V) multiplied by Current (I):
Power (W) = Voltage (V) x Current (I)
Example:
If your solar panel operates at 12V and 10A, it produces 120W of power. This means it can power a 120W appliance with full sunlight.
Learn more:
- Victron Wiring Unlimited - Theory - Power
- Victron Wiring Unlimited - AC wiring - System current, VA and Watts
- What’s Watt? | GTIS Power and Communications Systems
Volt-Ampere (VA)
Volt-Ampere (VA) is a unit used to measure apparent power in an AC circuit. It’s similar to watts but accounts for both the active and reactive power in the circuit.
Example:
An inverter might be rated at 2000VA. If it's operating at full capacity with a pure resistive load (e.g. light bulb, heater), this would be equivalent to 2000W. However, with other types of loads (e.g. pumps), the actual power in watts could be lower.
Learn more:
Power Factor (PF)
In an AC circuit, the relationship between Watts (W) and Volt-Amperes (VA) is determined by the power factor (PF), which is a measure of how effectively the current is being converted into useful work. The power factor is the ratio of real power to apparent power.
W = VA x Power Factor
If PF = 1 (or 100%): All the power is used effectively, meaning W = VA. This happens in purely resistive loads where there is no reactive power (e.g., heaters or incandescent light bulbs).
If PF < 1: Not all the apparent power is used effectively, so W < VA. This occurs in circuits with inductive or capacitive loads, where some power is wasted in the form of reactive power.
Example:
If an inverter is supplying power to a load that consumes 100W and has a Power Factor of 0.8, the inverter needs to have a capacity of at least 100W / 0.8 PF = 125VA.
Ampere-Hour (Ah)
Ampere-Hour (Ah) is a unit of electric charge that indicates the amount of current a battery can supply over a period of one hour. It is often used to measure the capacity of a battery.
Example:
A 100Ah battery can theoretically supply 1 amp of current for 100 hours, 10 amps for 10 hours, or 100 amps for 1 hour. In an off-grid solar system, knowing the Ah rating of your batteries helps determine how long you can power your devices before needing to recharge.
Learn more:
Watt-Hour (Wh)
A Watt-Hour (Wh) is a unit of energy that measures the amount of electrical energy used or produced over time. It’s calculated by multiplying the power in watts by the time in hours:
Energy (Wh) = Power (W) × Time (h)
Example:
If you have a 120W light bulb and you use it for 5 hours, it will consume:
120W×5h=600Wh
In an off-grid solar system, Watt-Hours are used to determine the total energy consumption of your appliances and the energy storage required in your batteries.
Learn more:
Depth of Discharge (DoD) and State of Charge (SoC)
Depth of Discharge (DoD) refers to the percentage of a battery's capacity that has been used relative to its total capacity. In simpler terms, it measures how much of the battery's energy has been drained. For example, if a battery has a capacity of 100 Ah (ampere-hours) and you use 50 Ah, the Depth of Discharge is 50%. The remaining 50 Ah is the battery's state of charge (SoC), which would be 50% in this case.
Example:
Imagine you have a 200 Ah battery in an off-grid solar system used to power a small office. If you consume 120 Ah of the battery's capacity overnight, your Depth of Discharge is 60% (120 Ah used out of 200 Ah) and your State of Charge (SoC) is 40%.
A common practice is to limit the DoD to a certain level to extend the battery's lifespan. For instance, if the battery's manufacturer recommends a maximum DoD of 50%, you should only use up to 100 Ah before recharging (200Ah battery). Going beyond this recommended DoD can reduce the battery's lifespan by increasing wear and tear on the battery cells. Lead Acid batteries typically have a maximum recommended DoD of 50% and Lithium batteries can easily handle a DoD of 90% or more without doing any damage to the battery.
What are the basic components of an off-grid solar system and how do they operate?
Solar Panels
- Function: Solar panels consist of multiple solar cells that capture sunlight and convert it into electrical energy through the photovoltaic effect.
- Operation: When sunlight hits the solar cells, it excites electrons in the material, generating a flow of electricity.
- Example:
- Learn more:
Solar Charge Controller
- Function: The charge controller regulates the direct current (DC) electrical energy coming from the solar panels so it can be used to charge the batteries.
- Operation: It ensures efficient battery charging and protects the batteries from overvoltage damage.
- Example:
- Learn more:
- Choosing a Charge Controller | GTIS Power and Communications Systems
- Which solar charge controller: PWM or MPPT?
- How does a Victron Energy MPPT Solar Charge Controller work?(includes French subtitles)
Battery Storage
- Function: Batteries store excess electricity generated by the solar panels for later use, particularly when sunlight is not available (e.g. during the night or on cloudy days).
- Operation: The battery system is charged by electricity from the solar panels (through the charge controller) and/or from the utility grid or a generator. Stored energy can be drawn from the batteries when needed. Batteries can be connected in series and/or parallel to create a battery bank. Most common battery bank voltages are 12V / 24V / 48V.
- Example:
- Learn more:
- Choosing Batteries | GTIS Power and Communications Systems
- Sizing and Building a Battery Bank | GTIS Power and Communications Systems
- Choosing a Low Voltage Disconnect | GTIS Power and Communications Systems
- Victron Wiring Unlimited - Battery bank wiring
Inverter
- Function: The inverter converts the energy stored in the batteries into alternating current (AC) electricity, which is the standard form of electricity used by most devices.
- Operation: The inverter ensures that the electricity is efficiently converted from DC to AC.
- Example:
- Learn more:
Battery Charger
- Function: Converts AC electricity into DC electricity to charge the batteries.
- Operation: The battery charger ensures that the batteries receive the correct type of current for efficient charging. This device may be a separate component or integrated into the inverter. Some inverters include an integrated battery charger (inverter/charger).
- Example (battery charger):
- Example (inverter/charger combi):
Mounting System
- Function: The mounting system secures the solar panels in place, either on rooftops, the ground, or other structures and makes sure they are positioned to capture the maximum amount of sunlight for a given geographical location. In the southern hemisphere, panels should face geographical north, while in the northern hemisphere, they should face geographical south. The tilt angle, typically equal to the location's latitude, is important because it allows the panels to be as perpendicular as possible to the sun's rays.
- Operation: It positions the solar panels at the optimal angle and orientation to capture the maximum amount of sunlight.
- Example:
- Learn more:
- Choosing Solar Panels | GTIS Power and Communications Systems (pointing the panels)
Electrical Wiring, Connectors and Fuses
- Function: Wires and connectors link all the components together, allowing the flow of electricity from the solar panels to the batteries (via the charge controller) and from the batteries to the loads (via the inverter). Fuses protect the wiring from overheating.
- Operation: Proper wiring ensures efficient energy transfer and safety throughout the system.
- Example:
- Learn more:
- Victron Wiring Unlimited - DC wiring
- Victron Wiring Unlimited - AC wiring
- Choosing Circuit Breakers and Fuses | GTIS Power and Communications Systems
Surge and Lightning Protection
- Function: Protects the solar system from electrical surges and lightning strikes, which can damage sensitive components and pose safety risks.
- Operation: Surge protectors absorb and redirect excess voltage away from the system, while lightning protection systems, including lightning rods and grounding systems, intercept and safely conduct lightning strikes into the ground.
- Example:
- Learn more:
Generator (Optional)
- Function: Provides an additional source of power to charge the batteries when there is no or insufficient sunlight or as a backup power source in case a solar system component fails.
- Operation: The generator supplies AC power to the battery charging system (either a battery charger or an inverter/charger combination), ensuring continuous power availability even during extended periods of low sunlight.
- Learn more:
Control and Monitoring (Optional)
- Function: Provides real-time data, remote access, and system optimization for the solar system.
- Operation: It manages battery usage, controls loads, and integrates with other solar system components, ensuring efficient energy management and system reliability. Additionally, it offers alerts, historical data analysis, and easy configuration. A current shunt is often used to measure in real-time the energy production and consumption.
- Example (Control Centre):
- Example (Current Shunt):
How are these components interconnected?
Find below 3 schematic examples of how the basic components can be interconnected.
Basic setup:
Basic setup with generator backup:
Basic setup with generator backup and inverter/charger combi:
Victron Energy has a booklet which gives you more details on how different system components can be connected together.
How to design an off-grid solar system?
GTIS has developed a comprehensive guideline on how to design an off-grid solar system. The steps are:
- Calculating Loads | GTIS Power and Communications Systems
- Choosing Solar Panels | GTIS Power and Communications Systems
- Choosing a Charge Controller | GTIS Power and Communications Systems (includes information on choosing PWM / MPPT type of controller)
- Choosing Batteries | GTIS Power and Communications Systems
- Sizing and Building a Battery Bank | GTIS Power and Communications Systems (includes information on choosing system voltage 12/24/48)
- Choosing Circuit Breakers and Fuses | GTIS Power and Communications Systems
- Choosing a Low Voltage Disconnect | GTIS Power and Communications Systems (essential to protect the battery from deep discharge)
- Choosing an Inverter | GTIS Power and Communications Systems
When selecting components for your system, make sure you select quality components from well-known manufacturers like e.g. Victron, Outback, Midnite, Bussmann etc. They are covered with a multi year warranty, are serviceable and have a user community that is available to answer questions. There are cheap components around that are notorious for early failure and even causing hazardous situations (fires).
When selecting batteries, consider Lithium batteries. The upfront investment is higher (compared to AGM/GEL batteries), but they can easily last 10+ years and are less heavy and bulky which makes the logistics easier when they need to be installed in remote locations.
When working with batteries, make sure you understand Depth of Discharge (DoD) and make sure your system has protective measures in place to avoid discharging the batteries beyond the advised DoD to extend their lifetime. Quality inverters and inverter/chargers usually have an option to set the cut-off DoD. Beware of the cheap inverters that cut-off only at a very low voltage. When you supply DC power to DC loads directly from the battery, make sure you have a low voltage disconnect (LVD) device installed.
Make sure your protection measures are in place to avoid as much as possible damage by power surges and lightning. Cabling (outdoor AND indoor) can easily pick-up electrical energy from lightning strikes (near or far) and transport this energy to your valuable equipment. Protective devices make sure this energy is diverted to earth to not cause any harm.
Fuses should be in place to protect your DC and AC wiring from overheating that could potentially cause a fire. Batteries should be protected by a DC fuse installed as close as possible to the battery. Batteries have a very low internal resistance and a short will cause a huge current that can easily cause a fire.
Contact GTIS Power and Communications Systems for expert advice and/or a second opinion when you’re working with a local supplier/installer.
How to maintain a solar system?
Maintaining an off-grid solar system requires regular monitoring and upkeep to ensure optimal performance. Check/do following on a regular basis:
- Routinely clean the solar panels to remove dust, dirt, and debris, as these can significantly reduce energy absorption.
- Inspect the connections, wiring, and mounting structures for any signs of wear or damage, addressing issues promptly to prevent further complications.
- The batteries, a critical component of the system, should be checked for proper charge levels and inspected for corrosion or leaks, ensuring that they are regularly equalized if they are lead-acid types.
- The inverter and charge controller should also be examined to verify they are functioning correctly and efficiently. Tighten screw connections.
- If your system includes a generator as a backup for charging batteries during periods of insufficient sunlight, regular generator maintenance is essential. This includes checking oil levels, replacing oil and air filters, and ensuring the fuel system is clean and free of blockages. Running the generator periodically, even during non-essential times, will help maintain its readiness and extend its lifespan.
Resources: