Transporting Energy

Whether energy is transported as electricity, heat, or mechanical motion, losses are inevitable. Understanding the mechanisms behind these losses is essential to designing efficient systems and interpreting monitoring data.

In residential solar installations, energy transport mainly concerns electrical cabling, but thermal and mechanical transport also play important roles.

Electrical energy is transported using conductive materials, typically copper or aluminium cables. As current flows through a conductor, part of the energy is dissipated as heat due to electrical resistance.

Ohm’s Law Reminder

Ohm’s law describes the relationship between voltage (U) (some literatures use E for Energy or V for Voltage), current (I), and resistance (R):
We will not use E in our documentation because Energy (E) and Potential Difference (U) are not the same. Voltage is the energy per unit charge. The battery of a car does not store the same energy as the battery of an electric bike, even though they have the same voltage.
This is important to understand, and we will point this out later when we talk about the energy the PV panels produce vs. the power it provides.

• U = R × I
• P = U × I
• Losses: P_loss = R × I²

Because losses increase with the square of the current, transporting the same power at higher voltage and lower current significantly reduces losses.

DC vs AC Transport

• DC transport: Common between PV panels, MPPT controllers, batteries, and inverters.
• AC transport: Used after inversion, compatible with household appliances and the grid.

DC cabling is often shorter and operates at higher currents, while AC cabling benefits from standardised protections and distribution practices. It is often recommended to place the inverters (DC -> AC) as close a possible to the PV panels, to reduce the costs of thicker copper cables.

Choosing the right cable cross-section is critical for safety and efficiency. Undersized cables lead to excessive losses and overheating, while oversized cables increase cost and installation complexity.

Key Parameters

• Current intensity
• Operating voltage
• Cable length
• Permissible voltage drops
• Installation conditions (air, conduit, temperature)

In photovoltaic installations, voltage drop is often limited to a few percent to preserve overall system efficiency.

Thermal energy is transported using fluids (water, glycol, air) or solid materials. Unlike electricity, heat transport depends strongly on insulation quality and temperature differences.

• Hydronic circuits: Pumps circulate heated fluids.
• Air ducts: Used for ventilation and air-based heating.
• Insulation: Critical to limit heat losses over distance and time.

The greater the temperature difference between the transported heat and the environment, the higher the potential losses.

Mechanical energy transport is less common in residential contexts but still exists in some renewable systems, particularly wind energy.

Rotational motion from a wind turbine can be transmitted directly or converted locally into electricity to minimise mechanical losses and complexity.

Transport losses directly affect system performance indicators. Monitoring voltage, current, temperatures, and flow rates allows these losses to be quantified and optimised.

Comparing energy collected at the source with energy delivered to the load or storage reveals inefficiencies that may indicate design or maintenance issues.

After transport, energy must be transformed into a usable or storable form. This includes electrical conversion, battery charging, heat storage, and integration with household systems.

Continue to Transforming & Storing Energy