The Energy Matrix
A Science Ebook e-zine
Winter 200
8 Edition  
List of all editions

Solar to Home 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



Many Homes are already wired for a future portable Solar Collector. (2-24-08)

The panel at the right is used to interface a generator to a home electrical  system. The purpose of this article is to point out that future solar systems really don't require custom design, permits, or special meters for selling power back to utility. A portable modular system that has been inspected at the factory can simply be plugged into the switch box.  The switch box requires a permit and inspection as does any electrical home installation.  This article analyses the cost of a portable or modular solar systems for homes that have  already got legally installed and inspected switch boxes for portable generators.

Continue reading center column!


Natural Gas could be price competitive with coal.

Per DOE/EIA in fiscal year 2007 utilities coal cost was $1.80 per MMBtu and Natural Gas cost $7.50. per Million.

Natural Gas is ideal for cogeneration purposes.  Gas turbines convert about 33% of the million Btu's $7.50 worth of gas to electricity. About 10% (100,000 Btu) regrettably goes out the chimney. The remaining 57% of the energy can be used for hot water and heating at the building cogeneration site.  Thus, 90% of the million Btu's from natural gas is captured as either electricity or heat.  Coal is still a little cheaper than gas, but the coal has to be fluidized before it can be used in blast furnace.  Two thirds of coals energy is frequently dumped into a river from turbine condensers causing thermal river pollution.   


Feb.1 2008

Today, I took an Poll that asked how people felt about Exxon's record profits.  The results at the time that I took poll were: 

Good for them  11%

It bothers me 86%

Don't Care 3%

The results surprised me, because it was the people and their representatives, not Exxon or the Auto makers who created the perfect storm for the petroleum industry.
Continue reading center column!



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
















Many Homes are already wired for a future portable Solar Collector. (Continued)

The box at right cost about $280.00 including the power cord shown in lower picture. Installation of box including cutting into wall took a licensed electrician about four hours.  Cost of installation including permit and county inspection was less than $500.00.  The box is intended to connect a generator to a circuit breaker panel. When a switch is in GEN position the outlets associated with one of the breakers is isolated from the utility power and is connected to the generator.  Ten circuits can be switched to a generator when there is a power outage. Usually ten circuits are plenty for the short period of a power outage.  Refrigerators, furnaces, sump pumps, and wells are some of the critical ones.  Then you can select the remainder based on convenience. 240VAC for stoves and clothes dryers require ganging of 2 breakers.  We just cook in the microwave during blackouts.




You can actually power some of your home outlets from the generator (GEN) while selecting the utility power (Line) for others. The generator provides a split phase 120/240 VAC service to the switch box. The connector at bottom of box is rated at 300 VAC. 

System Economics

Though it is possible to provide your home power from the portable gasoline generator and the utility at the same time, it would not be economical to do so.  I found that using a inexpensive generator (less than $1000) consumes about a gallon of gasoline per hour with only moderate loading, and will use more than a half gallon an hour with minimal load.  Thus, the box is not used except to provide emergency service.  

However, if I could buy a portable 1000 watt solar generator at the hardware store.  than  I could use the switch box to connect the portable unit to a matching load such as a TV or an air conditioner.  A solar array of about a 100 square foot would be required to produce 1000 watts.  The purpose of this article is point out the low cost of such a modular system, when compared to many of the standard subsidized systems in use today.  The portable system would provide free green energy.  Naturally, the system would require a battery to store energy for periods that the sun is blocked by clouds.  The battery acts as an integrator of the varying solar input.  

The advantage of a modular factory built system would be that there is no permit or installation cost involved.  The system could be tested and inspected in the factory.  Just like the generator was built and inspected in the factory.  All you would have to do is place the solar system in the sun near the house. Than run a factory built cable from the solar collector to the switch box.  For homes with metal roofs a factory tested modular system could be used that has solar panels that simply stick on roof.  See " Smooth Roof Installation" in References below.


System Cost Saving Features:

1. This system does not sell power to or interface with utility.  The circuits using green power are isolated (or islanded) from utility by the switch box. 

2. The battery set could provide some emergency power to home.

3. No Installation of portable or modular solar system would be required.

4. No Installation Inspection would be required.  ( Applicable laws would have to be modified to include solar system as a substitute for electric generator already in code.)



Energy Savings of System:

1. Fifteen Gallons of Gas per power outage.
Assumes that you had your  batteries fully charged up when the power went out and estimates that you could operate furnace for one day and have convenience of electricity for one day.  Convenience means when you click a light switch on, then a light comes on.   You must switch light off when you don't need it, if you want batteries to last a whole day. If you want to live like there was no outage, 15 to 20 of Gallons gasoline will be required. The bottom line is the battery pack will give you less than 50 Amp hours (AH) at 120V AC. Some power will be lost as heat in inverter.


2. Ten Gallons of Gas per cloudy day after first day of an extended blackout.
Assumes that generator runs for six hours providing electricity to house and recharging of batteries.  Liberal use of electricity is permissible when generator is running. Conservation of batteries most be practiced when generator is off. The batteries do not store as much energy as even a gallon of gasoline, but the batteries/inverter can supply loads as large as 3 kilo-watts for short periods, and as low a few watts or less for long periods. Thus, if the microwave, refrigerator, furnace fans and sump pump turned on at the same time you would not exceed maximum load. Yet you could listen to a .5 amp stereo while lighting the house with candles, if you wished.  Thus, you can conserve energy during a blackout and still have the convenience of the bathroom light going on when you flick the switch.  Inexpensive generators will consume 5 gallons of gasoline in five to seven hours even with minimal load.  A cheap  inverter can cost as little as $250.  An inverter that produces a true sine wave output would cost about $500.00, and it would be safer for operation of electronic equipment. Synchronous inverters used to sell power back to utilities cost over $2000.


3. Ten kWhr per sunny day.  


Total System Cost Savings

Estimate: Three Blackouts for a total of 10 days per year and two hundred non-blackout sunny days per year.

1. Fifteen Gallons of Gas per power outage = 45 Gallons/Yr (  At $4.00 a gallon)= 45 X $4.00 = $180 per year savings.

2. Ten Gallons of Gas saving per extended day of outage (At $4.00 a gallon) = 7 X 10 X $4.00 = $280 per year savings.

3.  Two Hundred Sunny Days at ten kWhr per day.
2000 kWhr at 10 cents per kWhr =  $200 per year savings.

Annual Energy Savings Value = $660.00 a year.



Estimated System Cost.

1. 100 square foot Solar Collector:                             $2500.00

2. 10 ea 50-AH Lead Acid Deep Cycle Batteries.     $1000.00

3. Inverter,                                                                         $500.00 
Synchronous Inverters required for selling power to Utilities cost over $2000.00

4. Frame or Cart                                                            $500.00

Total:                                                                              $4500.00 


4500/660 = 6.82 years to pay for itself.  Batteries may last this long.

Continued use of system will require replacement of batteries every six years at cost of about $1000.

Annualized Cost of Batteries =   $166.00
Annual Cost Savings
(From Above) =  $660.00                             


Conclusion: System would be highly cost effective in less than 7 years.  It would be better for the government to provide a tax incentive for the proposed system, and give it to the millions of people who have a legal generator interfaces,  than it is to give subsidies in the tens of thousands of dollars to the few people who wish to turn there houses and outbuilding into solar farms, and then force the utilities to buy back the power at retail or even at a premium price.





Smoot Roof Installation 


Manual Load Shedding:
The system requires a meter that would indicate status of batteries. The user would have to check status  at least once or twice a day.  When battery charge decreased to below 50% load on solar should be shed, at least one switch should be switched from GEN to LINE.  If battery charge were to fall to 20% all switches should be set to line.  Inverters will automatically shut off, if DC voltage input sinks below a certain level.  You would definitely want your refrigerator or freezer on grid power before solar/battery power was lost.  Daily balancing of load and Solar Power might be okay for the solar enthusiast on a budget, but future home systems would want to have automatic load shedding.  The reason that I selected a Manual Switching Box is that I own one. Thus, I was familiar with its operation, and it provided me with a convenient model for my pictures.  In addition to these add on switch panels there are lots Circuit Breaker Panel that include a generator interface in suburban housing.  However, it is obvious that automatically shedding load from solar source to utility source would be far more practical. 

Automatic Load Switching

Automatic load switching simply requires that switches in switchbox be replaced with relays and simple controller be added to control relays.  A single large 24 volt battery might be all that is required to stabilize system during day time operation.  System would simply switch to Line/Utility power at night. However, more batteries would be required for solar service to be extended into night. 

Editorial Opinion: 

Home solar systems that on sunny days produce less electricity than can be consumed or stored by a home in a day make more economic sense than home systems that that sell AC excess power back to the power companies.  The high cost of synchronous inverters, reversible power meters, and automatic isolation systems (called islanding capability) required in event of grid problems is not justified for the small amount of power produced by home solar installations.  

I still believe that electricity produced by distributed solar installations should be collected as DC and converted to AC by the utilities.  Like transformers, AC to DC inverters should be owned by the utility companies.  

Bill of


Read About Distributed Generation  of Electricity








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