---
watermark: ORIRO
disable-model-invocation: true
name: env-energy
provider: ORIRO.ai
copyright: Copyright (c) 2026 ORIRO.ai
description: >




  Energy systems — renewable energy, grid basics, energy storage, efficiency, and the energy transition.
  Sources: IPCC, NRDC, EPA, IRENA, World Resources Institute. All free public sources.
---

# Energy Systems

## The global energy system

**Primary energy sources:** Oil (~33%), coal (~27%), natural gas (~24%), biomass (~10%), nuclear (~5%), hydropower (~3%), wind/solar/other (~8%). Fossil fuels still ~84% of primary energy.
**Energy use sectors:** Industry (~38%), Buildings (~31%), Transport (~20%), Other (~11%).
**Electricity is only ~20% of final energy use** — most heating, transport, industry uses fossil fuels directly. Full decarbonization requires electrifying these.

## Renewable energy

### Solar photovoltaic (PV)

**How it works:** Photons knock electrons loose in semiconductor (silicon) → electric current.
**Learning curve:** Solar PV costs fell 89% in a decade (2010-2020). Now cheapest electricity source ever built in history (IEA, 2020).
**Types:** Monocrystalline (most efficient, ~22%+), Polycrystalline, Thin-film.
**Capacity factor:** ~10-25% (not generating at full capacity all the time — nighttime, clouds).
**Intermittency:** Doesn't match demand profile. Requires storage or complementary sources.

### Wind

**Capacity factor:** Onshore ~25-40%, Offshore ~40-50% (stronger, steadier winds).
**Cost:** Also falling dramatically. Onshore wind and solar now cheaper than new fossil fuel plants in most markets.
**Offshore wind:** Higher cost but higher capacity factor. Possible in densely populated areas without land use conflict.

### Hydropower

**Capacity factor:** ~40-50%. Dispatchable (can turn on/off). Balancing resource.
**Limits:** Geography-constrained. Most good sites already developed in developed countries.
**Pumped storage hydro:** Most common large-scale storage. Pump water uphill when electricity cheap; release downhill when demand peaks.

## Energy storage

### Battery storage (Lithium-ion)

**Best for:** Short-duration storage (2-4 hours). Grid stabilization, peak shaving.
**Cost decline:** 90% cost decline since 2010. Continues to fall.
**Limitations:** Short duration. Supply chain concerns (cobalt, lithium).

### Long-duration storage

Critical for seasonal balancing and full grid decarbonization.
**Green hydrogen:** Electrolysis (water + electricity → hydrogen). Can store seasonally. Fuel for industry, shipping, aviation. Currently expensive.
**Iron-air, vanadium flow batteries, compressed air:** Emerging long-duration technologies.
**Pumped hydro:** 95%+ of current global storage capacity.

## The electricity grid

### Grid basics

**AC vs DC:** AC (alternating current) used for transmission and distribution (easier to step voltage up/down with transformers). DC (direct current) increasingly used for long-distance transmission (less loss) and connecting different grids.
**Transmission:** High-voltage (345kV - 765kV) long-distance transport. Distribution: Lower voltage to homes and businesses.
**Frequency:** 60 Hz (North America, some of Asia), 50 Hz (Europe, most of world). Must be maintained within tight tolerance.

### Grid challenges with high renewables

**Variability:** Wind and solar don't follow demand. Need flexibility from other sources.
**Integration solutions:** Demand response, storage, transmission expansion, grid interconnection, flexible gas/hydro, market design.
**Duck curve:** California phenomenon — solar overproduction at midday → rapid ramp needed in evening.

## Energy efficiency

**The cheapest energy is the energy you don't use.**
**Industrial:** Variable speed drives, waste heat recovery, process optimization.
**Buildings:** Insulation, air sealing, heat pumps (3-5× more efficient than resistance heat), LED lighting, building automation systems.
**Transport:** EVs, mass transit, walkable urban design, vehicle efficiency standards.
**Rebound effect:** Efficiency savings sometimes partially offset by increased use. Doesn't eliminate the benefit but reduces it.

Sources: IRENA (irena.org — free), IEA (iea.org — many free reports), NREL (nrel.gov — free), Bloomberg NEF (selected free content), Our World in Data energy (ourworldindata.org/energy — free, CC-BY)