Mini-grids

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=82 BGCOLOR="#006699" TEXT="#080000"> <div> <FONT SIZE="5" COLOR="#FFFFFF" FACE="Arial" ><B>IEA PVPS Task 11 - PV Hybrids and Mini Grids</B></FONT><B>     |     </B><A HREF="index.htm" TARGET="_top" TITLE="IEA PVPS Task 11 PV Hybrids and Mini Gr"><U><B>Home</B></U></A></div> <div> <A HREF="id32.htm" TARGET="_top" TITLE="PV Hybrid Systems"><U>PV Hybrid Systems</U></A>   |   <B>Mini-grids</B>   |   <A HREF="id35.htm" TARGET="_top" TITLE="Village microgrids"><U>Village microgrids</U></A>   |   <A HREF="id36.htm" TARGET="_top" TITLE="Diesel mini grids"><U>Diesel mini grids</U></A>   |   <A HREF="id37.htm" TARGET="_top" TITLE="Urban minigrids"><U>Urban mini-grids</U></A></div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000"> <div> <A HREF="id18.htm" TARGET="_top" TITLE="Mission"><U>Mission</U></A></div> <div> <A HREF="id27.htm" TARGET="_top" TITLE="Work Plan"><U>Work Plan</U></A></div> <div> <A HREF="id17.htm" TARGET="_top" TITLE="Event Calendar"><U>Event Calendar</U></A></div> <div> <A HREF="id19.htm" TARGET="_top" TITLE="Contact Us"><U>Contact Us</U></A></div> <div> <A HREF="id20.htm" TARGET="_top" TITLE="Participant List"><U>Participant List</U></A></div> <div> <A HREF="id25.htm" TARGET="_top" TITLE="Related Links"><U>Related Links</U></A></div> <div> <A HREF="id26.htm" TARGET="_top" TITLE="Public Downloads"><U>Public Downloads</U></A></div> <div> <A HREF="id31.htm" TARGET="_top" TITLE="Participant Area"><U>Participant Area</U></A></div> </td> <td valign="top" height=398 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>Mini-grids</I></div> <div> A mini-grid can be defined as a set of electricity generators and, possibly, energy storage systems interconnected to a distribution network that supplies the entire electricity demand of a localized group of customers.  This power delivery architecture can be contrasted with single customer systems (e.g. solar home systems) where there is no distribution network interconnecting customers, and with centralized grid systems,where electrical energy is transmitted over large distances from large central generators and local generators are generally not capable of meeting local demand.</div> <bR> <div> A key feature of mini-grids is that they can operate autonomously with no connection to a centralized grid.  However a mini-grid may be designed to interconnect with the central grid and operate under normal conditions as part of the central grid with disconnection occuring only if required to maintain power quality (e.g. if there is a central grid failure).  Alternatively, a mini-grid may be designed to operate autonomously in a remote location with the option to connect to the central grid when grid extension occurs.</div> <bR> <div>  Since mini-grids can operate autonomously, they cannot rely on the central grid to control line voltage and frequency and balance power supply with power consumption.   Instead a mini-grid must manage its own real and reactive power flow and maintain its own control over voltage and frequency.  Although many of the concepts and techniques employed to manage a large central grid are applicable, there are significant differences:</div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Since generators are commonly dispersed around the mini-grid, power flow is more complex than in the conventional centralized grid where power typically flows unidirectionally from large central generators to loads.  </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Mini-grids often contain significant amounts of intermittent generation (e.g. PV or wind) whose power output can't be controlled (dispatched) in the same fashion as conventional generators.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Many mini-grid generators interface to the mini-grid with power electronic inverters whose control characteristics are different from the rotating synchronous machines used in conventional large generators.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">It is usually not economically feasible to install the sophisticated supervisory control systems used in central grids nor to pay for network operators to manage the system on a continuous basis.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">There is often less load diversity in a mini-grid than in the much larger centralized grid, resulting in relatively larger and faster changes in load that must be accomodated by the mini-grid control.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">If the mini-grid is connected to the central grid, it must manage a smooth, transient-free transition between autonomous operation and interconnected operation in parallel with the central grid.  </div> </td> </tr></table></body>