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Electricity β€” Fundamentals & Photovoltaic Systems

Last reviewed: 2026-09-17

Purpose: Reference for electricity fundamentals, DC/AC theory, battery chemistries, and photovoltaic system basics.

Electricity is the set of physical phenomena associated with the presence and motion of electric charge. Understanding electricity fundamentals is the prerequisite for electronics, embedded systems, and power engineering.

Overview

This article covers the core principles of electricity: voltage, current, resistance, power, AC/DC theory, photovoltaic systems, and basic electrical safety β€” aimed at embedded systems work that needs a solid theoretical foundation.

Core Concepts

Fundamental Quantities

Quantity Symbol Unit Description
Voltage V Volt (V) Electrical potential difference
Current I Ampere (A) Flow of electric charge
Resistance R Ohm (Ξ©) Opposition to current flow
Power P Watt (W) Rate of energy transfer
Energy E Joule (J) / kWh Work done over time

Ohm's Law

The fundamental relationship in DC circuits:

V = I Γ— R
I = V / R
R = V / I

Power

P = V Γ— I
P = IΒ² Γ— R
P = VΒ² / R

Series vs Parallel

Series Parallel
Current Same through all Divides across branches
Voltage Divides across components Same across all branches
Resistance R_total = R₁ + Rβ‚‚ + ... 1/R_total = 1/R₁ + 1/Rβ‚‚ + ...

AC vs DC

Direct Current (DC) Alternating Current (AC)
Direction Constant one direction Reverses periodically
Source Batteries, solar panels, PSUs Grid, generators, transformers
Application Electronics, EVs Household, industrial power distribution
Frequency 0 Hz 50/60 Hz (grid), variable (audio/RF)

Battery Chemistries

Chemistry Voltage (nominal) Energy Density Cycle Life Safety
Li-ion 3.7V High 300–500 Moderate
LiFePOβ‚„ 3.2V Medium 2000+ High
Lead-Acid 2.1V per cell Low 200–300 Moderate
NiMH 1.2V Medium 500–1000 High

Safety

  • Current kills, voltage doesn't β€” 50 mA across the heart can be fatal
  • Always disconnect power before modifying circuits
  • Use fuses or breakers to limit fault current
  • Capacitors can hold lethal charges after power-off
  • Working with mains AC requires proper training and equipment

Practical Notes

  • A Virtual Power Plant (VPP) aggregates rooftop solar, home batteries, and EV chargers into a grid-balancing resource managed by a cloud platform β€” a key concept for renewable energy integration.

Photovoltaic Basics

PV systems follow the same series/parallel rules as any DC circuit:

Element Behaviour Practical notes
Panel DC source, ~0.5–0.6 V per cell 60/72-cell modules β‰ˆ 30–40 V open-circuit
Series string Voltages add, current unchanged Higher voltage means lower IΒ²R cable loss and fits MPPT input windows
Parallel strings Currents add, voltage unchanged Strings must match in voltage; protect with fuses / blocking diodes
MPPT charge controller Tracks the maximum power point Sits between array and battery; typically 95–98% efficient
Inverter DC β†’ AC conversion Grid-tie, off-grid, or hybrid with battery
Battery bank Stores energy (see chemistries above) LiFePOβ‚„ is the usual choice for solar cycling