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| watt-hour per kilogram | |
|---|---|
| Unit system | Unit accepted for use with SI |
| Unit of | Specific energy |
| Symbol | W⋅h/kg |
| Conversions | |
| 1 W⋅h/kg in ... | ... is equal to ... |
| SI units | 3600 J/kg |
The watt-hour per kilogram (unit symbols: W⋅h/kg) is a unit of specific energy commonly used to measure the density of energy in batteries and capacitors.
Conversion to SI units
The watt, kilogram, joule, and the second are part of the International System of Units (SI). The hour is not, though it is accepted for use with the SI. Since a watt equals one joule per second and because one hour equals 3600 seconds, one watt-hour per kilogram can be expressed in SI units as 3600 joules per kilogram.
Typical values
The batteries that Tesla uses in their electric cars deliver about 254 W⋅h/kg, compared to supercapacitors that are typically rated between 3 and 10 W⋅h/kg, with the best commercially available supercapacitors as high as 47 W⋅h/kg.
Nuclear batteries based on betavoltaics can reach up to 3300 W⋅h/kg, although over much longer time periods.
References
- "Tesla’s batteries have reached their limit – here’s how they could go further", theconversation.com, 2017-11-16
- Hao Y, Santhakumar K (2013). "Achieving Both High Power and Energy Density in Electrochemical Supercapacitors with Nanoporous Graphene Materials". p. 3. arXiv:1311.1413.
- Ronald Brakels, "Arvio Supercapacitor Energy Storage — Powerful Enough To Beat Batteries At Their Own Game?", Solarquotes.com, May 15, 2018. Retrieved 14 Oct. 2021
- Prototype Nuclear Battery, phys.org, June 6 2018
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