PITAGORAS project: opportunities for waste heat and solar thermal energy exploitation

Cities are currently facing major energy and environmental challenges. The development of sustainable solutions for energy supply to cities is an urgent need nowadays. The best use of local renewable sources is key; not only to reduce the carbon footprint of cities and reduce energetic dependence on fossil fuels, but also to mitigate pollution problems and promote a low-carbon based economy, directly affecting the day-to-day living of citizens.

PITAGORAS, a research project co-funded by the European Commission, with a consortium formed by 10 partners from 6 countries, got its start on 2013 and has finished on October 2017. Efficient integration between cities and industries through smart thermal grids has been the main pillar of the project. The urban-industrial symbiosis offers great opportunities that are not fully exploited yet. In this sense, Pitagoras has been focused on developing innovative solutions for the exploitation of two local sources: industrial waste heat and solar thermal energy.

In the city of Brescia (Italy), an innovative pilot plant for waste heat revalorisation has been built in the steel mill of ORI MARTIN. The waste heat recovery system has been installed in the flue gas path of the existing electric arc furnace. Saturated steam is produced which can either be used to power an ORC module for electricity production (summertime) or heat exchangers to provide district heat to the urban district heating (winter period).

The revalorisation of the waste heat which otherwise would be wasted is the main benefit of this project. This means that with this waste heat it is possible to provide heat for about 2000 homes. Additionally, the operation of the ORC reduces the amount of electricity to be purchased from the grid and thus save costs. The installation of a system like this also results in the saving of fossil fuels and thus reducing the CO2 emissions; about 8.000 ton of CO2 can be avoided every year.

The main barrier of this kind of projects is the economic side, due to low energy prices and high equipment costs. A first economic evaluation of the plant showed a payback period in the order of 12 years, which is typically considered as long, especially in an industrial company. Appropriate policies based on sustainability criteria, which might be reality in the future, could help to overcome these barriers. The specific incentive mechanism based on White Certificates that are in force currently in Italy reduce the payback time of the plant to 4-6 years. The PITAGORAS project shows an opportunity for many companies in the field of energy intensive industries (e.g. steel or glass industry) that the utilization of waste heat to provide electricity and district heat is possible, whereas contributing to tackling the energy challenges that cities are currently facing.

Additionally, the project developed a system concept based on industrial integration of solar thermal energy in combination with a seasonal thermal energy storage (STES), including the possibility of solar heat delivery also to the district heating network. The plant is planned for a specific site in the city of Kremsmünster (Austria) and in an industrial area of an oil and gas industry. The system concept is formed by a solar field of 9377 m², with a thermal capacity of approximately 5MW, expected to produce around 4547 MWh of useful solar heat per year, which enables saving up to approx. 1 Mio m3 gas per year. The idea of reconverting an existing oil tank of 60,000 m³ of storage volume (that is no longer been used) into a STES allows to store the surplus solar heat in summer and its use later on in winter months, which significantly increase the solar production capabilities, system performance and energy savings.

The implementation of this plant was one of the objectives of the project; unfortunately, however, it has not been able to be implemented within the PITAGORAS timeframe. Although the technical concept, land use and land lease and an Energy Performance Contract (EPC) were elaborated in detail, have been evaluated positive and economic sound and negotiations with both technical and management boards were already well advanced, the implementation of the demo failed. The reasons for failing were mainly due to the worldwide declining development of the oil and gas prices. The company has been heavily hit by this development and therefore was forced to stop all the new projects and investments, including this solar project.

In fact, this reflects one of the main barriers of large solar thermal plants (e.g. market factors such us low prices on fossil fuels). It should be noted, however, that the price stability of solar energy over the years is indeed one of the main advantages of renewable energy sources. And this cannot be offered by fossil fuels; it is highly likely that the price of fossil fuels will continue to rise. Even solar thermal energy is often still not cost-competitive with fossil fuels at today’s prices, the costs of heat supplied by solar thermal applications can already be lower than alternatives using fossil fuels over the lifetime of the solar thermal system, and this should be the correct economic way to compare heat costs, even not usually done.

Read more about the Pitagoras project in our website!