# Energy content of biofuel

The energy content of biofuel is the chemical energy contained in a given biofuel, measured per unit mass of that fuel, as specific energy, or per unit of volume of the fuel, as energy density. A biofuel is a fuel produced from recently living organisms. Biofuels include bioethanol, an alcohol made by fermentation—often used as a gasoline additive, and biodiesel, which is usually used as a diesel additive. Specific energy is energy per unit mass, which is used to describe the chemical energy content of a fuel, expressed in SI units as joule per kilogram (J/kg) or equivalent units. Energy density is the amount of chemical energy per unit volume of the fuel, expressed in SI units as joule per litre (J/L) or equivalent units.

## Energy and CO$_2$ output of common biofuels

The table below includes entries for popular substances already used for their energy, or being discussed for such use.
The second column shows specific energy, the energy content in megajoules per unit of mass in kilograms, useful in understanding the energy that can be extracted from the fuel.
The third column in the table lists energy density, the energy content per liter of volume, which is useful for understanding the space needed for storing the fuel.
The final two columns deal with the carbon footprint of the fuel. The fourth column contains the proportion of CO$_2$ released when the fuel is converted for energy, with respect to its starting mass, and the fifth column lists the energy produced per kilogram of CO$_2$ produced. As a guideline, a higher number in this column is better for the environment. But these numbers do not account for other green house gases released during burning, production, storage, or shipping. For example, methane may have hidden environmental costs that are not reflected in the table.
| Fuel Type | Specific energy (MJ/kg) | Energy Density (MJ/L) | CO$_2$ Gas made from Fuel Used (kg/kg) | Energy per CO$_2$ (MJ/kg) |
| Solid Fuels |||||
| Bagasse (Cane Stalks) | 9.6 | | ~+40%(C$_6$H$_{10}$O$_5$)$_n$+15% (C$_{26}$H$_{42}$O$_{21}$)$_n$+15% (C$_9$H$_{10}$O$_2$)$_n$1.30 | 7.41 |
| Chaff (Seed Casings) | 14.6 | | [Please insert average composition here] | |
| Animal Dung/Manure | 10– 15 | | [Please insert average composition here] | |
| Dried plants (C$_6$H$_{10}$O$_5$)$_n$ | 10–16 | 1.6–16.64 | IF 50%(C$_6$H$_{10}$O$_5$)$_n$+25% (C$_{26}$H$_{42}$O$_{21}$)$_n$+25% (C$_{10}$H$_{12}$O$_3$)$_n$1.84 | 5.44-8.70 |
| Wood fuel (C$_6$H$_{10}$O$_5$)$_n$ | 16–21 | Archived 2007-02-13 at the Wayback Machine 2.56–21.84 | IF 45%(C$_6$H$_{10}$O$_5$)$_n$+25% (C$_{26}$H$_{42}$O$_{21}$)$_n$+30% (C$_{10}$H$_{12}$O$_3$)$_n$1.88 | 8.51–11.17 |
| Charcoal | 30 | 5.4–6.6 | 85–98% Carbon+VOC+Ash 3.63 | 8.27 |
| Liquid Fuels |||||
| Pyrolysis oil | 17.5 | 21.35 | varies | varies |
| Methanol (CH$_3$-OH) | 19.9–22.7 | 15.9 | 1.37 | 14.49–16.53 |
| Ethanol (CH$_3$-CH$_2$-OH) | 23.4–26.8 | 18.4–21.2 | 1.91 | 12.25–14.03 |
| Ecalene | 28.4 | 22.7 | 75%C$_2$H$_6$O+9%C$_3$H$_8$O+7%C$_4$H$_{10}$O+5%C$_5$H$_{12}$O+4%Hx 2.03 | 14.02 |
| Butanol (CH$_3$-(CH$_2$)$_3$-OH) | 36 | 29.2 | 2.37 | 15.16 |
| Fat | 37.656 | 31.68 | C$_{55}$H$_{104}$O$_6$ | |
| Biodiesel | 37.8 | 33.3–35.7 | ~2.85 | ~13.26 |
| Sunflower oil (C$_{18}$H$_{32}$O$_2$) | 39.49 | 33.18 | (12% (C$_{16}$H$_{32}$O$_2$)+16% (C$_{18}$H$_{34}$O$_2$)+71% (LA)+1% (ALA))2.81 | 14.04 |
| Castor oil (C$_{18}$H$_{34}$O$_3$) | 39.5 | 33.21 | (1% PA+1% SA+89.5% ROA+3% OA+4.2% LA+0.3% ALA)2.67 | 14.80 |
| Olive oil (C$_{18}$H$_{34}$O$_2$) | 39.25–39.82 | 33–33.48 | (15% (C$_{16}$H$_{32}$O$_2$)+75% (C$_{18}$H$_{34}$O$_2$)+9% (LA)+1% (ALA))2.80 | 14.03 |
| Gaseous Fuels |||||
| Methane (CH$_4$) | 55–55.7 | (Liquefied) 23.0–23.3 | (Methane leak exerts 23 × greenhouse effect of CO$_2$) 2.74 | 20.05–20.30 |
| Hydrogen (H$_2$) | 120–142 | (Liquefied) 8.5–10.1 | (Hydrogen leak slightly catalyzes ozone depletion) 0.0 | |
| Fossil Fuels (comparison) |||||
| Coal | 29.3–33.5 | 39.85–74.43 | (Not Counting: CO, NO$_x$, Sulfates & Particulates) ~3.59 | ~8.16–9.33 |
| Crude Oil | 41.868 | 28–31.4 | (Not Counting: CO, NO$_x$, Sulfates & Particulates) ~3.4 | ~12.31 |
| Gasoline | 45–48.3 | 32–34.8 | (Not Counting: CO, NO$_x$, Sulfates & Particulates) ~3.30 | ~13.64–14.64 |
| Diesel | 48.1 | 40.3 | (Not Counting: CO, NO$_x$, Sulfates & Particulates) ~3.4 | ~14.15 |
| Natural Gas | 38–50 | (Liquefied) 25.5–28.7 | (Ethane, Propane & Butane Not Counting: CO, NO$_x$ & Sulfates) ~3.00 | ~12.67–16.67 |
| Ethane (CH$_3$-CH$_3$) | 51.9 | (Liquefied) ~24.0 | 2.93 | 17.71 |
| Nuclear fuels (comparison) |||||
| Uranium -235 ($^{235}$U) | 77,000,000 | (Pure)1,470,700,000 | [Greater for lower ore conc.(Mining, Refining, Moving)] 0.0 | ~55 – ~90 |
| Nuclear fusion ($^2$H -$^3$H) | 300,000,000 | (Liquefied)53,414,377.6 | (Sea-Bed Hydrogen-Isotope Mining-Method Dependent) 0.0 | |
| Fuel Cell Energy Storage (comparison) |||||
| Direct Methanol | 4.5466 | Archived 2005-09-11 at the Wayback Machine 3.6 | ~1.37 | ~3.31 |
| Proton-Exchange (R&D) | up to 5.68 | up to 4.5 | (IFF Fuel is recycled) 0.0 | |
| Sodium Hydride (R&D) | up to 11.13 | up to 10.24 | (Bladder for Sodium Oxide Recycling) 0.0 | |
| Battery Energy Storage (comparison) |||||
| Lead–acid battery | 0.108 | ~0.1 | (200–600 Deep-Cycle Tolerance) 0.0 | |
| Nickel–iron battery | 0.0487–0.1127 | 0.0658–0.1772 | (<40y Life)(2k–3k Cycle Tolerance IF no Memory effect) 0.0 | |
| Nickel–cadmium battery | 0.162–0.288 | ~0.24 | (1k–1.5k Cycle Tolerance IF no Memory effect) 0.0 | |
| Nickel–metal hydride | 0.22–0.324 | 0.36 | (300–500 Cycle Tolerance IF no Memory effect) 0.0 | |
| Super-iron battery | 0.33 | (1.5 * NiMH) 0.54 | (~300 Deep-Cycle Tolerance) 0.0 | |
| Zinc–air battery | 0.396–0.72 | 0.5924–0.8442 | (Recyclable by Smelting & Remixing, not Recharging) 0.0 | |
| Lithium-ion battery | 0.54–0.72 | 0.9–1.9 | (3–5 y Life) (500-1k Deep-Cycle Tolerance) 0.0 | |
| Lithium-Ion-Polymer | 0.65–0.87 | (1.2 * Li-Ion)1.08–2.28 | (3–5 y Life) (300–500 Deep-Cycle Tolerance) 0.0 | |
| Lithium iron phosphate battery | | | | |
| DURACELL Zinc–Air | 1.0584–1.5912 | 5.148–6.3216 | (1–3 y Shelf-life) (Recyclable not Rechargeable) 0.0 | |
| Aluminium battery | 1.8–4.788 | 7.56 | (10–30 y Life) (3k+ Deep-Cycle Tolerance) 0.0 | |
| PolyPlusBC Li-Aircell | 3.6–32.4 | 3.6–17.64 | (May be Rechargeable)(Might leak sulfates) 0.0 | |