# Energy in buildings: Engineering methods

Six everyday machines that run a modern home

Source page: https://www.materialinsights.org/energy/e_buildings/methods/

What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.

Six everyday technologies cover most building energy use outside space heating and air conditioning.

#### Comparison

| Method | Efficiency | Scale | Economics | Limitations | Reliability |
|---|---|---|---|---|---|
| **Gas and induction cooking**^[1](https://www.energystar.gov/about/2021_residential_induction_cooking_tops) | Gas about 32%, resistance 75-80%, induction about 85% | 1-3 kW per burner or zone | Induction hobs cost more and need compatible pans; running cost depends on tariffs | Induction needs a ferromagnetic pan and a strong enough wiring circuit; gas releases combustion products indoors | Gas burners are simple; induction electronics can fail from heat or power surges |
| **Solar water heater and electric geyser**^[2](https://eerem.delhi.gov.in/faqs/345) | Geyser element turns almost all electricity into heat, but the tank loses heat while standing | Solar systems from 50 litres per day (evacuated tube) or 100 litres per day (flat plate) | Solar Rs 18,000-25,000 per 100 litres per day; geysers cheaper to buy, dearer to run | Solar needs about 4 m2 of sunny roof and backup in cloudy weather; hard water scales collectors | Solar heaters last 15-20 years with a 5-year warranty |
| **Fans and pumps**^[3](https://energetica-india.net/news/eesl-unveils-5-star-rated-ceiling-fans-with-bldc-technology-in-india)^[10](https://www.iea-4e.org/emsa/publications/policy-brief-electric-motor-systems-why-are-they-important/) | BLDC ceiling fan 28-32 W against 70-75 W | Tens of watts (fans) to a few kW (building pumps); motor systems use 53% of world electricity | BLDC fans cost more but save about 40 W each while running | Electronics are sensitive to voltage spikes | Induction-motor fans run for decades; BLDC controller boards are the weak point |
| **Rooftop solar and inverters**^[4](https://www.pmindia.gov.in/en/news_updates/cabinet-approves-pm-surya-ghar-muft-bijli-yojana/)^[5](https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/Photovoltaics-Report.pdf) | Modules 22.7% average; performance ratio about 80% | 1-10 kW for homes | About Rs 50,000 per kW benchmark in India before subsidy (calculated); 900-1,500 EUR/kWp in Germany | Output only in daylight; needs shade-free roof | Modules last 25 years or more; inverters usually need replacing once in that time |
| **Home inverter and UPS**^[7](https://kunwersachdev.com/bee-make-inverter-efficiency-standards-mandatory/) | Battery 70-85% round trip; conventional inverters waste 12-20% at part load; best designs about 90% | Typically 0.5-2 kVA with 100-200 Ah lead-acid batteries | Cheap backup, but losses continue every day even when there is no outage | Heavy lead-acid batteries need topping up and replacement every few years | Simple and widely serviced |
| **Phones and laptops**^[8](https://legislation.gov.uk/eur/2019/1782/annex/II?view=plain) | EU minimum about 85% for a 20 W charger, 88% above 49 W (calculated) | 5-100 W | Running cost is tiny; energy cost lies mainly in manufacturing the device | Batteries lose capacity with heat and full charge cycles | Batteries typically limit device life |

The largest savings come where an old technology wastes most of its input: gas cooking (about 32%), induction-motor fans (more than double the power of BLDC) and home inverters with lead-acid batteries (roughly a third of the energy lost). Solar water heaters and rooftop panels change the fuel rather than the efficiency, replacing bought energy with free sunlight, so their economics depend on upfront cost and subsidies. Chargers are already efficient and matter more in aggregate than per device.

#### How each method works
**Gas and induction cooking**

A gas hob burns fuel under the pan. An induction hob uses a coil fed with high-frequency current to induce heating currents in a magnetic pan.
**Solar water heater and electric geyser**

A flat-plate or evacuated-tube collector heats water that rises by natural circulation into an insulated tank. A geyser heats water in a tank with a resistance element controlled by a thermostat.
**Fans and pumps**

An electric motor turns blades or an impeller. BLDC motors use magnets and electronic control, and variable speed lets the motor slow down when less flow is needed.
**Rooftop solar and inverters**

Silicon modules turn sunlight into DC electricity; a string inverter or microinverter converts it to grid-synchronised AC and tracks the best operating point.
**Home inverter and UPS**

When the grid is on, a charger keeps a battery full; during a power cut an inverter converts battery DC to 230 V AC for lights, fans and routers.
**Phones and laptops**

A switch-mode charger rectifies mains, chops it at high frequency through a small transformer and regulates the low-voltage DC; a charging chip in the device fills a lithium-ion battery.

#### Sources

1. [2021 ENERGY STAR Emerging Technology Award: Residential Induction Cooking Tops](https://www.energystar.gov/about/2021_residential_induction_cooking_tops) US EPA ENERGY STAR, 2021
2. [FAQ: Solar water heating systems](https://eerem.delhi.gov.in/faqs/345) Energy Efficiency and Renewable Energy Management Centre, Government of NCT of Delhi, 2024
3. [EESL unveils 5 star rated ceiling fans with BLDC technology in India](https://energetica-india.net/news/eesl-unveils-5-star-rated-ceiling-fans-with-bldc-technology-in-india) Energetica India, 2022
4. [Cabinet approves PM-Surya Ghar: Muft Bijli Yojana](https://www.pmindia.gov.in/en/news_updates/cabinet-approves-pm-surya-ghar-muft-bijli-yojana/) Prime Minister's Office, Government of India, 2024
5. [Photovoltaics Report (updated 14 July 2026)](https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/Photovoltaics-Report.pdf) Fraunhofer Institute for Solar Energy Systems ISE, 2026
6. [An open letter: BEE, make inverter efficiency standards mandatory (Kunwer Sachdev, founder of Su-Kam; advocacy, not independent data)](https://kunwersachdev.com/bee-make-inverter-efficiency-standards-mandatory/) kunwersachdev.com (personal blog), 2026
7. [Commission Regulation (EU) 2019/1782, Annex II: Ecodesign requirements for external power supplies](https://legislation.gov.uk/eur/2019/1782/annex/II?view=plain) legislation.gov.uk (retained EU law text), 2019
8. [Policy brief: Electric motor systems, why are they important?](https://www.iea-4e.org/emsa/publications/policy-brief-electric-motor-systems-why-are-they-important/) IEA 4E Electric Motor Systems Annex (EMSA), 2025

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_buildings/index.md)
- [Overview](https://www.materialinsights.org/energy/e_buildings/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_buildings/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_buildings/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_buildings/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_buildings/economics/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_buildings/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_buildings/links/index.md)