What is Earth's Energy Budget?
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Although the term "energy budget" is widely used, the flow of energy in and out of the Earth is actually measured in units of power (watts), not units of energy (joules). Therefore, "power budget" would be a more accurate term.\n\nWell, ideally, the Earth's Energy Budget should have been at equillibrium; but due to the effect of Greenhouse gases, deforestation, Ozone leakage, etc. the equilibrium has already been disbalanced and the net Earth's energy content is increasing steadily. Added to this grave problem are the Solar Storms, which are increasing in number and intensity; increased amount of meteor shower; increase in the sun's radiation, etc. are calling for the end of life in our Solar system.
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The Sun.\n\nEDIT: Yes, what other people have said about the Earth's tilt and whatnot are true in that they affect the atmosphere, but you asked for the source of energy. That is solely the Sun.
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Any energy liberated by a reaction is indeed heating up the planet.\nHowever, the real problem with global waming is the amplification caused by green house gasses, like methane and CO2, wich traps the heat from the sun.  The sun gives about 1300 watt per square metre, over the surface of the planet this is over 10000 times more energy than all the installed power (the sun energy hitting earth is equivalent to 27 gigawatt per person on the whole planet; no one uses that much power). So, doubling our power production would have a negligible effect on global warming, but adding just a bit of gas that traps the huge amount of power that the sun sends will, however, have a huge impact.
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1.27 X 1022 KG (0.0021 Earths)
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Energy. That is the concern over the greenhouse effect, that energy will be trapped in the atmosphere raising temperatures. The average surface temperature of the earth would be -18 degrees zero without a greenhouse effect and 72 degrees zero without a biosphere which counteracts the Greenhouse effect.
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themal energy is the vibrational energy of the disordered motion of microscopic particles such as molecules and atoms.\nThe sum of all the kinetic energies.\nthere are many forms one is:\nocean thermal energy;\nThe oceans cover a little more than 70 percent of the Earth's surface. This makes them the world's largest solar energy collector and energy storage system. On an average day, 60 million square kilometers (23 million square miles) of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil. If less than one-tenth of one percent of this stored solar energy could be converted into electric power, it would supply more than 20 times the total amount of electricity consumed in the United States on any given day.\nthermal energy is in every matter. it has been proven that everything that is matter is always vibrating.
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Only 70% of the power flux reaches the surface ot the earth.\nThe electric field is defined a Newton per unit charge..\nThe power flux from the sun is really radiation power its Usually measured in Joules per second per meter^2. \nVolt per meter is = to force per unit distance. Its resulting units are kg /sec^2. which is not equal to joules/sec/meter^2.
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Even though I like Oz's answer, it is actually the flow of magma in the Earth's mantle on average about 30 miles below the surface, where molten rock flows from high to low, nearing the earth's outer core where the temprature reaches to near 10000 degrees F.  Another heating element (or actually energy element, that has a side effect of heating) is radioactive decay.  Though most of the Earth's heat energy is released throught the much thinner parts of the crust that makes up the ocean floors.
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The ultimate source of energy in all. living systems is the sun
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The enormous amount of energy continuously emitted by the sun is dispersed into outer space in all directions. Only a small fraction of this energy is intercepted by the earth and other solar planets. \nThe solar energy reaching the periphery of the earth's atmosphere is considered to be constant for all practical purposes, and is known as the solar constant. Because of the difficulty in achieving accurate measurements, the exact value of the solar constant is not known with certainty but is believed to be between 1,353 and 1,395 W/m2 (approximately 1.4 kW/m2, or 2.0 cal/cm2/min). The solar constant value is estimated on the basis of the solar radiation received on a unit area exposed perpendicularly to the rays of the sun at an average distance between the sun and the earth. \n\nIn passing through outer space, which is characterized by vacuum, the different types of solar energy remain intact and are not modified until the radiation reaches the top of the earth's atmosphere. In outer space, therefore, one would expect to encounter the types of radiation listed in Table 1, which are: gamma ray, X-ray, ultraviolet, and infrared radiations.
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No energy is required. Following Newtons first law of motion, a body (such as the Earth) will continue moving until a resultant force causes it to stop. In space there is no atmosphere, so the Earth just keeps flying around.
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Describes the Solar Radiation that falls on an area above the atmosphere at a vertical angle: s = 1.37 kW / m².\n\nIn space, solar radiation is practically constant; on earth it varies with the time of day and year as well as with the latitude and weather. The maximum value on earth is between 0.8 and 1.0 kW / m². In Germany, the average annual amount of insolation varies between 950 and 1100 kWh / m², depending on the region.
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It is mainly from residual heat from when the earth first formed & the breakdown of radioactive elements w/in the earth. Pressure from the overlying material can also create heat.\n\nThe earth is actually cooling but it will take a very long time for it to "completely" cool.
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The Earth is surrounded by atmosphere, which is made up of many greenhouse gases. The Earths temperature\n      depends on the solar constant.\n      The Earths surface absorbs heat from the sun and re-radiates it back out to space with the help of clouds, snow,\n      atmosphere dust and sea surfaces, the rest is absorbed by other gases and aerosols, examples of these is the\n      gases from power stations and volcanoes which can be liquid or dust, some solar radiation does not reach\n      space this remains trapped in the atmosphere by greenhouse gases. \n      The temperature of the Earth has changed and is continuing to do so with the help of human activity in rising \n      Co2 levels, from 1850-1996 Co2 rose from 285 p.p.m to 360 p.p.m a 0.7ºc rise in surface temperature.\n      We know how trees and plants are vital to us as they convert Co2 into oxygen to help us breathe, but industry\n      will continue to cut and burn down forests allowing more Co2 into the air, with this decrease in vegetation this\n      means more Co2 will remain in the atmosphere and with the burning of fossil fuels we are also producing more \n      Co2, causing the Earths temperature to warm up.\n      Clouds also play a role in the surface temperature; they absorb radiation this increasing the amount of infrared\n      radiation that is emitted by the atmosphere depending on their altitude and thickness, a cloud is formed when\n      water vapor condenses.
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The mass of the earth is 5983 Yg (yottagrams), and it gains another 40 Gg (gigagrams) every year from captured meteorites and cosmic dust.\nor\nThe mass of the planet Earth is 5.97 * 1024 kilograms.\n\nMost of the mass of the Earth is in the mantle, most of the rest in the core; the part we inhabit is a tiny fraction of the whole earth
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I am going to take a guess and say the moon.\n\nNo, I am kidding, it's the Sun\n\nSolar energy can be converted in to electricity and heat.
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Space near the earth is actually filled with a gas called the interplanetary medium (see first source). This gas, which is mostly gas coming from the sun, is quite hot, around 100,000 degrees C. But, it's also only 10^-18th the density of sea level air, so it carries very little heat.\n\nAir is relatively thick, so we're used to conduction and convection determining an objects temperature.  There's very little of either in space, so radiation dominates.  The sun's light is about twice as strong in space as it is on earth.  How hot this heats an object depends on the objects shape and color, but it's fair to say that most things will heat up to a few hundred degrees. \n\nBecause there's no air in space, everything looses heat very slowly, like being in a thermos. So, anything that produces heat, like a human body or machinery, will gradually warm up--space suits have built-in coolers to deal with this. \n\nIf you're out of the sunlight and have used up all your internal energy, you eventually cool down to about -25 to +25 C.  Infrared radiation from the earth is what prevents you from getting colder.  If you were also far away from the earth, you'd cool down to something between -240C and -270C.