---
title: "Renewable energy and trapping solar energy"
subject: "Building Technology"
chapter: 1
key: "semester_6/building_technology:energy-renewable-solar-066j"
source: https://www.bctengineer.com/q/semester_6/building_technology/energy-renewable-solar-066j
site: BCT Engineering
---

# Renewable energy and trapping solar energy

Building Technology · Chapter 1: Functional Requirements of Buildings

- Asked in: 2066 Jestha (old course), 4+6 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/energy-renewable-solar-066j
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1

## Question

Describe briefly about renewable and non-renewable sources of energy highlighting the world scenario. Explain the different ideas to trap the solar energy in building with the concept of energy efficient design.

## Short answer

Renewable sources (solar, hydro, wind, biomass) are naturally replenished; non-renewable (coal, oil, gas, uranium) are finite. World energy ~80% fossil fuels. Solar trapping in buildings: east-west orientation with south glazing, direct gain with thermal mass, Trombe walls, sunspaces, roof collectors, PV panels, insulation, and overhangs for summer shading.

## Answer

#### Renewable and non-renewable sources
**Renewable energy** comes from sources that are naturally replaced in a short time: solar, hydro, wind, biomass and biogas, geothermal, tidal. **Non-renewable energy** comes from fixed stocks formed over millions of years: coal, oil, natural gas and uranium.

**World scenario:** About 80 % of world energy is still from fossil fuels (oil about 30 %, coal about 27 %, natural gas about 23 %). Renewables, including hydro, supply roughly 15 to 20 % of primary energy and about 30 % of electricity, and are growing fastest in solar PV and wind. Fossil fuels are limited and cause climate change, so countries move to renewables. Nepal gets most of its electricity from hydropower, and most household energy from firewood, with petroleum fully imported.

#### Trapping solar energy in buildings (energy efficient design)
1. **Orientation and layout**: Long axis east-west and living spaces facing south.
2. **Direct gain**: Large south windows; the sun heats floors and walls of high thermal mass (concrete, stone, adobe).
3. **Trombe wall**: Dark masonry wall behind a glass pane with vents; absorbs heat and sends it by convection and radiation.
4. **Sunspace (attached greenhouse)**: Glazed space on the south side which collects heat and shares it with the rooms.
5. **Roof collectors / solar air heaters** and **water heaters** for hot water.
6. **Roof pond or water wall** to store heat.
7. **Photovoltaic panels** for electricity.
8. **Insulation and weather sealing** to keep the gained heat, and overhangs to avoid summer overheating.

```text
 winter sun ->|glass| air gap |dark mass wall| room
                   vents top & bottom: warm air loop
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which is a non-renewable source?
   A. Biomass
   B. Natural gas
   C. Tidal
   D. Geothermal
   Answer: B. Coal, oil, gas and uranium are fixed stocks. (Key point: Renewable vs non-renewable)

2. About what share of world energy is still from fossil fuels?
   A. 20 %
   B. 50 %
   C. 80 %
   D. 95 %
   Answer: C. About 80 % of world energy is fossil. (Key point: World scenario)

3. A Trombe wall is:
   A. A dark masonry wall behind glass with vents which sends heat by convection and radiation
   B. A white reflective wall
   C. A water pond roof
   D. A PV panel
   Answer: A. It absorbs solar heat and releases it to the room. (Key point: Trombe wall)

4. Why are overhangs used in solar design?
   A. To avoid summer overheating
   B. To block winter sun
   C. To reduce daylight
   D. To hold PV panels
   Answer: A. Overhangs shade in summer while letting the low winter sun in. (Key point: Overheating)

## Related in Building Technology

- [Passive solar design and building layout](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apassive-solar-design) — Building Technology, chapter 1
- [Energy conscious design considerations](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aenergy-conscious-design) — Building Technology, chapter 1, asked 2×
- [Active and passive solar control](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aactive-passive-solar) — Building Technology, chapter 1
- [Moisture sources and control in basement](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-sources-basement-control) — Building Technology, chapter 1, asked 2×
- [Sources of moisture and moisture control](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-sources-control-methods) — Building Technology, chapter 1
- [Structural and non-structural cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acracks-structural-nonstructural) — Building Technology, chapter 10, asked 4×

## Related in other subjects

- [World renewable energy scenario](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aworld-renewable-scenario) — Power Plant Design, chapter 1
- [Renewable energy trend in world](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Arenewable-energy-trend-world) — Energy Environment and Society, chapter 2
- [Energy sources and solar power generation](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-solar-power) — Power Plant Design, chapter 1
- [Types of renewable energy sources](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Arenewable-energy-types) — Power System Analysis I, chapter 1