Energy in buildings: Engineering methods

Six everyday machines that run a modern home

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 cooking¹	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 geyser²	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 pumps³¹⁰	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 inverters⁴⁵	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 UPS⁷	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 laptops⁸	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

2021 ENERGY STAR Emerging Technology Award: Residential Induction Cooking Tops US EPA ENERGY STAR, 2021
FAQ: Solar water heating systems Energy Efficiency and Renewable Energy Management Centre, Government of NCT of Delhi, 2024
EESL unveils 5 star rated ceiling fans with BLDC technology in India Energetica India, 2022
Cabinet approves PM-Surya Ghar: Muft Bijli Yojana Prime Minister's Office, Government of India, 2024
Photovoltaics Report (updated 14 July 2026) Fraunhofer Institute for Solar Energy Systems ISE, 2026
An open letter: BEE, make inverter efficiency standards mandatory (Kunwer Sachdev, founder of Su-Kam; advocacy, not independent data) kunwersachdev.com (personal blog), 2026
Commission Regulation (EU) 2019/1782, Annex II: Ecodesign requirements for external power supplies legislation.gov.uk (retained EU law text), 2019
Policy brief: Electric motor systems, why are they important? IEA 4E Electric Motor Systems Annex (EMSA), 2025