Abstract:
Methods and apparatus are provided for using a renewable source of energy such as solar, wind, or geothermal energy. In some embodiments, the method may include generating electric energy from a renewable form of energy at a plurality of locations at which reside an electric power line associated with an electric power grid. The electric energy generated at each location may be transferred to the electric power line to thereby supply electric energy to the electric power grid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 13/351,075, filed Jan. 16, 2012, which is a continuation of U.S. patent application Ser. No. 11,860,450, filed Sep. 24, 2007, now U.S. Pat. No. 8,097,980, issued Jan. 17, 2012. The aforementioned related patent applications are herein incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    The present invention relates to an electric power producing plant that is distributed along the path of existing power lines, and which is connected to the electric grid at multiple locations along the power lines. 
       BACKGROUND 
       [0003]    Renewable energy with low carbon dioxide profile is becoming increasingly important, as the world works to reduce the carbon dioxide emission and preserve the Earth. In many cases smaller renewable energy plants, like solar photovoltaic farms, wind turbines farms, solar thermal plants, etc. are selling their excess energy into the existing external electric power grids. The current mode of operation consists of concentrating the power sources from the entire farm and combining their outputs into one, which is then connected to the grid. There are obvious advantages in this approach main of which is the ease of maintenance. Nevertheless, there are a number of disadvantages, which this invention is addressing. 
         [0004]    One of major requirements for an energy plant is the availability of a sufficiently large parcel of land to locate the plant. In busy and densely populated areas this requirement can be a big obstacle, since the land can be very expensive or unavailable. 
       SUMMARY 
       [0005]    A new method of supplying energy from power generators to an energy grid is provided. In accordance with the present invention, the electric power generators are distributed along the grid and each individual energy generator is directly connected to the grid at these locations. Such an arrangement can be referred to as a distributed energy plant. One of the advantages of a distributed plant is that it can be located in areas were a traditional plant could not otherwise be located. 
         [0006]    In contrast to the present invention, when an energy farm is positioned outside the area of use, the transmission losses can be quite significant. Moreover, the energy farm is usually connected to the energy grid at a single connection point. Thus, the entire supply of energy is only as robust as this connection point. The present invention reduces the risk of complete failure by providing multiple points of connection to the energy grid. This arrangement also advantageously reduces transmission losses, since the energy generators are in close proximity to the electric power lines in the energy grid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows one example of a distributed energy plant constructed in accordance with the present invention. 
           [0008]      FIGS. 2   a  and  2   b  show specific examples of an energy generator that includes a solar photovoltaic cell with and without a concentrator, respectively. 
           [0009]      FIG. 3  shows an example in which the energy generator is a wind turbine. 
           [0010]      FIG. 4  shows one arrangement for connecting the energy generators to an existing AC grid utilizing low pass and high pass filters. 
           [0011]      FIG. 5  shows an example in which a variety of different energy sources are employed. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The proposed scheme is illustrated in  FIG. 1 . Here individual energy generators  103  are mounted on utility poles  101 , and connected to the grid  102  at connection points  104 . It is assumed that at each point  104  a DC-AC or a DC-DC converter is facilitating the energy transfer between the energy generator and the grid. An energy generator is typically a photovoltaic solar cell or a wind turbine. Since the utility company usually has the rights to use the land where the grid is located, or owns it outright, no extra land is required to build such an energy plant. Multiple connections inherent in the scheme ensure that the alternative energy supply will not be interrupted, if some of the connections fail. 
         [0013]    While this approach could potentially require a larger initial investment to implement, as compared to a traditional localized energy farm and therefore may not look attractive, the main contributors to the initial cost would be the voltage converters. However, future developments in solar cells and other power generators should lead to integrated converters of much lower cost, removing this potential limitation. 
         [0014]    Furthermore, inverters and other electrical components that may be needed may be located in other more readily accessible parts of the overall electrical grid, which would dramatically reduce both the installation and maintenance costs of a distributed power plant. For example, a large number of solar panels each positioned on a different electrical pole could be electrically connected to a single inverter. The electrical connection could be provided by either dedicated electrical lines or existing electrical lines. In the former case, a large number of solar cells are first connected to a small or medium size DC electrical grid, which directs solar-derived electricity into a large AC electrical grid through a connection point containing a single inverter. In the latter case shown in  FIG. 4 , the same solar cells  402  could be electrically connected directly to the existing AC power lines  401 , thus overlaying a DC-based grid on the existing AC-based grid. The cross-connection(s) between the two grids could occur in a few selected locations via a combination of low pass-filters  403 , high pass filters  405  and an inverter  404 . Thus an entire distributed solar power plant with a multitude of solar panels could be subdivided into a much smaller number of sections or islands requiring electrical services such as DC-to-AC conversion and others. The latter approach is particularly attractive since it dramatically cuts both the installation and maintenance costs. 
         [0015]    This concept of multiplexing different types of electrical energies into the same electrical power line could be used along with other AC-based renewable energy sources as long as the characteristic frequency of such electrical generators is different from that of the main power line frequency. In this case, electrical bandpass filters could be used to isolate different energy sources from each other and allow electrical connection to the same power line. Thus, a power line  501  with a multitude of different energy sources can be envisioned as shown in  FIG. 5 , in which various types of electrical energy  502  are provided and multiplexed via bandpass filters  503  at different characteristic frequencies □ 1  through □ N , where N is the number of different types of energy sources. A number of electrical energy converters  504  could be connected to the same power line, which would convert different current frequencies to a common line frequency □ Line  and thus making it usable for customers elsewhere on the grid. In order to limit electrical current propagation through the grid at non-standard frequencies (different from a common line frequency), electrical buffers or narrow line bandpass filters could be positioned at a few key points along the power grid. Some appropriate insertion points for such buffers include converter connection points, edges of the power grid, and edges of the renewable power sub-grids. 
         [0016]    A number of potential implementation of the above idea can be envisioned. The energy generator can be a solar cell, a wind turbine, a solar thermoelectric mini-turbine, etc. An example of an implementation with a solar cell and wind turbine are given below. Most attractive implementations of a distributed power plant are those involving maintenance free components such as solar cell panels or modules. 
       Example 1 
     Solar Cell 
       [0017]    An individual energy generator of small enough size, such as a solar cell, can be positioned directly on the utility pole and connected to the grid.  FIG. 2   a  illustrates such an arrangement for a solar cell with a concentrator. Concentrator  202  is mounted on the pole  206 , and concentrates the rays  205  on a solar cell  201 , which is connected to the grid at the point  204  through DC-AC converter. Holder  203  supports the concentrator. One example of such cell is T1000, manufactured by Emcore. It achieves 37% conversion efficiency under proper concentrator illumination.  FIG. 2   b  illustrates an arrangement for a standard solar cell without a concentrator. Here solar cell  201  is mounted on a pole  206  and connected to the grid via connection in point  204  through a DC-AC converter. An example of such cell can be a polycrystalline silicon photovoltaic cell KC50T manufactured by Kyocera. With 16% conversion efficiency and 25 years power output warranty it is a representative example of the current technology that may be employed. 
       Example 
     Wind Turbine 
       [0018]    In this example a wind turbine is positioned on the utility pole and connected to the grid.  FIG. 3  illustrates such an arrangement. A wind turbine  301  is mounted on a pole  303  and connected to the grid at point  302  through an appropriate converter, supplying energy directly into the grid. One example of such turbine is the Inclin 600 manufactured by Bornay. 
         [0019]    Although various embodiments and examples are specifically illustrated and described herein, it will be appreciated that modifications and variations are covered by the above teachings.