Thuyết đổi mới liên quan đến quá trình một công nghệ mới thay thế một công nghệ đang chiếm lĩnh thị trường. Những khó khăn gặp phải, các bước trải qua, việc cần làm. Dưới đây trình sơ lược một số thuyết phổ biến. As stated in , the UK needs to carry out considerable innovation in low carbon technologies (LCTS) in terms of electricity, heat and transport in order to reduce CO2 by 60% by about 2050. In considering innovation theories, processes of innovation and macroeconomics policies will be clarified in order to support low carbon innovation and reach set goals of the Energy White Paper. Joseph Schumpeter was the first economist to explain the three stages of innovation process called invention, innovation, and diffusion in the context of technology-push and demand-pull . This theory is known as the linear model of innovation because it considers that innovation is a continuous process through three stages. According to Twiss (1995) cited in , the innovation process follows the S-curve through stages as shown in Figure 5. At first, the innovator tried to adapt invention for change into an innovation, then after a period of upturn in diffusion stage, the new technology went down until reaching saturation levels. Figure 5. Level of innovation adaption (Twiss, 1995) After Soseph Schumpeter, many other economists developed similar models that described innovation as process from research to commercialisation . Therefore, it can be concluded that to increase a new technology output, the invention stage should be pushed by providing more resources for R&D. As a result, science policies and academic studying science and technology were followed this theory for many decades . For example, in Great Britain, the Department of Scientific and Industrial Research funded industrial sectors to form research organisation after World War I. In America, the National Research Council had missions to promote industrial research. The broad conceptual models of technological innovation by Ruttan (2001) cited in presented three broad approaches of technological change, they were induced innovation, evolutionary approaches, and path-dependent models. The induced innovation approaches focus on market drives like demand-pull. The evolutionary approaches build on Schumpeterian understanding and the idea of bounded rationality. The path-dependent models present that development of a new technology affects its rate of uptake such as returns and positive feedback. These approaches take the linear model into account in a wider context and focusing on the roles of actors like importance of feedbacks, and many parts of the system . Furthermore, as shown in Figure 6, the connection between technological and institutional systems is modelled that includes many actors and the way they work in the model. Figure 6. Roles of innovation chain actors In the chain linked model presented by Kline and Rosenberg (1986) cited in , systems feedbacks of actors were simulated in the innovation process. Feedbacks are within a the whole aspects of a new technology life cycle and among individual units (see Figure 7). The innovation chain starts with potential market opportunity, and then a product is developed for that opportunity, then feedbacks of the product start running to improve necessary characteristics of the product. Figure 7. The chain-linked model (Kline and Rosenberg (1986) cited in )