The Energy Matrix
A Science Ebook e-zine
Summer 2007 Edition  
List of all editions

DC to Utility Interface

The energy matrix examines the full spectrum of future energy sources and associated problems.  It is meant to be a thought provoking publication for students who will be our future technocrats, engineers, and physicists.  We will include concepts such as solar, DG, CHP and concepts that are not practical today such as ice engines.  Send Comments to




Micro Power Distributed Generation 
The Synchronous Inverter Problem 

As solar electric panels gets cheaper, the question "What to do with the DC power they generate and what do when the sun don't shine, becomes an important question. The most economical solution is to simply sell solar power to the electric company during the day and buy it back at night. To do this a synchronous inverter costing $2000.00 plus is required to convert the DC power to 60 hertz synchronized and phase locked to the utility grid power.  

The editorial below and the GIF animations to right suggests that a DC grid (separate wire) should be added to utility power poles to collect power from all solar and other micro power producers and sent back to a very large inverter owned by the power company.  This could eliminate hundreds of micro power inverters and replace them with one large utility inverter or a motor generator if the utility prefers. The article below is intended for physics, technical, and engineering students (grade 11 - 14) 

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Micro Power Generation
Simple  DC to Utility Interface

This article and animation (center column investigates the feasibility of a separate DC grid for delivering electricity from home or farm micro power systems to the local electric utility. The resistors in simulation represent line resistance (.2 to 1.2 ohms). Line resistance was assigned during simulation setup but values are not shown.  The Wind, Solar, and Cogeneration or Mini Hydroelectric power inputs to the grid are constant current generators. The Hexagon with the arrow indicating current direction is a CAD software symbol for a current generator. 

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Corn Solar Collectors
Follow Up Article

In our last issue Corn Solar Collectors article, I included some rough calculations showing that silicon solar collector farms collect far more solar energy. Reference A compares switchgrass cellulose based ethanol production to solar panels.     

Reference A

Note: All arguments with respect to ethanol versus solar cell technology imply the future existence of electric cars and a power grid for electric cars.  For example electricity for cars should be made available at all US Freeway rest stops.


Japanese CHP for Home

Japan has over 15,000 Combined Heat and Power (CHP) units installed in Japan as of 2006. The Honda Micro-CHP system combines a 95% efficient natural gas furnace or boiler  with the 85% efficient Honda natural gas engine/generator module.  The generator module has a 1 kwHr output.

Reference B


Index for all Editions


Combined Heat & Power (CHP) 

DC Power Grid

District Cooling

Ethanol Viability

Hybrid Cars

Ice made with Coal

Ice Energy Density versus Battery

Heat Storage


Nuclear Energy

Solar Heat Storage in CO2

Solar Heat Storage in Water

Storing Carbon Dioxide

Stoves - Corn Burning

Stoves - Wood Pellet Burning

Stoves - Coal Burning

Tar Sand Oil


Yucca Mountain

Substituting Coal for Diesel

Compact Fluorescent Lights








Simple  DC to Utility Interface
Micro Power


Before I go into the details of the simulation, I will explain why it could of advantage to micro power producers.  To sell solar or other power to the utility you must convert it to precise and synchronized 60 Hz power using an Inverter Unit that typically costs $2000 plus.  In the system I envision, the Micro-power producer could output a low voltage such 24 volts and connect to the power grid using fat (low gage) wire.  The high current wire would connect to a DC to DC converter on the pole.  It would use simple switching power supply  technology  to step the  DC low voltage up DC high (HVDC).  The  DC to DC converter is not shown in the animation.  Each Micro Power subsystem is simply represented as a constant current source feeding a HVDC line. 

The Utility Power Storage ( left side of animation ) hexagon is a constant voltage source representing an 8.0 kV battery.  A bank of 667 twelve volt batteries in series would give us 8004 volts.  The DC to AC inverter is represented as the resistor " DC Inverter Load = XX".  The wattmeter " Power to Grid Inverter." indicates the power supplied to the inverter.  An inverter or motor generator can convert  about 90% of  DC input power to three phase AC which is put on the AC power grid.  This animation is only designed to illustrate the stability that an DC grid has.  Therefore, the DC grid could not only input green energy to Americas power grid, but could  could also help stabilize it with battery power of over 100 Amperes at 8000 volts for a couple of minutes. 

This animation shows the response of the DC grid to a change in load.  At start of animation, current is being delivered to Utility Power Storage.  This indicated by the -14.52 ammeter indication.  The negative sign indicates that power is being delivered to the battery.  As the load increase less current is available for charging battery.  Then the battery is forced to supply current to the Inverter load.  At end of animation the battery is supplying 38. amperes at 8000 volts DC  to the DC to AC inverter. Or is outputting  633 kWh of Power to Grid Inverter.  Note that at end of animation load has increased  from 300 ohms to 100 ohms.



Reference 1     Reference 2     Reference 3     Reference     Reference 5     Reference 6     Reference 7      Reference 8     Reference 9       

Ref 10  Distributed Utility Integration Test

Ref 11 Consortium for Electric Reliability Technology Solutions (CERT.)

R12 Japanese CHP for Home













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