A renewable energy source that has been used to heat homes for years throughout Greece’s olive-growing regions comes from the trees themselves. Crude olive cake, the residue left after the olives have been pressed for oil in local mills, is sent to processing plants where it is turned into refined oil and a fibrous residue (known as «exhausted olive cake»), a kilo of which provides 4,000 kilocals of heat, according to Panayiotis Hatzelis, who has a crude olive cake processing plant in Sparta. The same mount of mineral heating fuel will provide 11,000 kilocals (nearly three times as much), he added, but is around five times more expensive. «It is a very economic fuel,» Hatzelis told Kathimerini English Edition. «The starting retail price for a ton of the fuel is 35 euros. A ton of mineral heating fuel can cost up to 600 euros.» Hatzelis said the above retail price applies to those who come to collect the fuel themselves. Packaged quantities of 35-40 kilos per bag are sold for about 10 euros each, less if people bring their own bags to be filled using the plant’s own equipment. Prices vary from region to region, the delivery distance and method, and according to the crop yield for the year. Paraskevas Sotiralis and his wife use the fuel to heat their 140-square-meter home in a Laconia village about two hours from Sparta and are happy with the results. «It is much cheaper than mineral fuel and more environmentally friendly. It costs us about 350-400 euros for the approximately 4 tons we need to heat our home every winter, and we don’t really economize on heating as it gets very cold here,» they said, adding that the only difference in maintaining the furnaces is that the ashes must be removed every day and the vents cleaned every so often. For the past 15 years, the Monastery of the 400 Martyrs, set in the mountains near Sparta, has been using exhausted olive cake to heat the entire monastery as well as to provide hot water. The furnace can be combined with a hot water boiler just like conventional furnaces. «We have it on nearly all the time in the colder weather,» said Father Ephraim. Back to nature According to Myrsini Christou of the Center for Renewable Energy Sources (CRES), all the country’s production of exhausted olive cake is sold – none is wasted. «It is an environmentally friendly, non-toxic fuel, as the carbon dioxide emitted during combustion is the same amount required by the olive trees for photosynthesis. Nitrogen oxide emissions from all biomass fuels are about the same as for conventional fuels, but the particle emissions are very low,» Christou told Kathimerini English Edition. «It burns easily and has all the advantages of a biomass fuel.» Christos Zafiris, who is responsible for CRES’s Biogas Thermatic Unit explained that for every 100 kilos of olive crop, the mills produce 20 liters of olive oil, 40 kilos of crude olive cake, 38 liters of olive mill wastewater and 2 kilos of leaves. The processing plants then take the crude olive cake to be processed into refined oils, which account for just 2 kilos of every 40 kilos of crude olive cake. From the same amount, they manufacture 18 kilos of exhausted olive cake, which they sell as heating fuel to homes and local industries and farms, or keep for their own furnaces. (Another less useful byproduct of the processing plants is the water vapor they emit – about 20 liters in the above-mentioned process.) While the fuel itself is far cheaper, the furnaces are more than double the size and price of those for burning mineral fuels. Panayiotis Michalopoulos of Kalamata, who manufactures furnaces for both mineral fuels and biomass, told Kathimerini English Edition that the starting price for a complete biomass system with a capacity of 35,000 kilocals was around 1,500 euros, compared to 650 euros for a furnace with the corresponding capacity for mineral fuels. Michalopoulos said the comparatively large amount of storage space taken up by exhausted olive cake makes it impractical for apartment buildings, but ideal for homes in the countryside where storing the fuel is less difficult. It seems that the use of this fuel is only limited to the size of the olive crop itself, and any advertisements would only be preaching to the converted. But it is not only farmers, villagers or small provincial industries who benefit. A Spanish electricity conglomerate, Endesa, which supplies 43 percent of the country’s total, is reportedly planning to build two olive-waste-fired power stations to produce 32 megawatts, or enough to supply 100,000 people. www.cres.gr Effluent from local mills a problem Not all waste produced by the olive oil industry is beneficial, unfortunately. According to the TDC-Olive project, an initiative in the European Union’s Sixth Community Support Framework program, for every 1,000 kilograms of olives pressed for their oil, about 350 kg of solid waste (see main article) and 450 liters of wastewater are generated by the traditional process in local mills. (The corresponding figures for the three-phase process used in areas of intensive production are far higher – 500 kg of solids and 1,200 liters of wastewater.) Disposing of the olive mills’ wastewater, a toxic effluent, is a problem, however. In Greece the total annual production of this water from the some 3,500 mills is about 1.5 million tons every year. According to CRES’s Myrsini Christou, new technologies are currently being developed to confront this problem. Since 1980, the area on which olives are grown has more than doubled, providing jobs for 800,000 people in Europe either directly or indirectly. With more than 4 million hectares under cultivation, it is the second-most important agro-food sector in Europe.