The Homestead Generator
Rich “Raspy” Shawver
From time to time the questions come up about the selection of a homestead generator. Should it be gasoline, diesel or what about a multi-fueled option? How much capacity do I need? What Bells and whistles should be added? What about the noise?
Power generators are designed to produce 60 cycle AC. To accomplish this they normally run at 3600 RPM, 1800 RPM or 900 RPM. Obviously the slower the system operates the less stress it is subjected to. Therefore the longer it will be expected to last.
For the prime mover of the system comes in 2 flavors. The standard gasoline and the diesel engines. Multi-fuel systems are modifications of either of these 2 basic engines. Both work on similar principals. Fuel is sprayed into a cylinder with air. The fuel air mixture is then compressed. This mixture is the ignited to produce the power. The difference comes in how ignition is accomplished. The gas engine uses an electrically fired spark plug. The diesel engine, while initially uses a glow plug to get things started, relies upon compression to fire.
In this respect the gasoline engine has the advantage. Aside from running on gasoline they can be modified to run on LP, Propane and Natural Gas commercial fuels. They can also function on homemade fuels of Alcohol, Wood Gas and Methane. The problem with multi-fuel operations is that to operate of different fuels requires major changes for each fuel. To make the engine operate on several fuels in consecutive operations requires compromises. These compromises make the engine less efficient regardless of the fuel used. Additionally the modification piles extra complexity onto the system.
The diesel engine runs on commercial diesel. And function on homemade fuels of almost any vegetable oil with little or no modification. Yes, that means if you run out of fuel in a diesel powered vehicle you can walk into a grocery store, buy a couple of gallons of expensive cooking oil, pour it in the tank re-fire and drive away. The major problem with these fuels is they are temperature sensitive. The colder it get the thicker the fuel becomes. Often below freezing it becomes to thick to flow. This requires either a system to keep the fuel warm in cold weather. Or to store the fuel where it is not subjected to lowered temperatures.
One area where the 2 types diverge is in reliability and longevity. The most common gas powered generators are the small [5000 watt range] portable generators. While nicely portable they are only designed for intermittent use. They operate at 3600 RPM too fast, too annoyingly loud and way too short-lived. Even the larger models still tend to be of the higher RPM variety. Most diesel generators are designed to operate at 1800 RPM and a few can be found tat run at 900 RPM. Diesels have better torque [power at slow speed] characteristics at lower RPMs than gas engines. Consider engine life in vehicles. Typically gas engines last an average of about 100,000 miles. Sure there are those that last to over 200,000 but have needed major overhauls to reach that. Conversely diesels need little more than minor maintenance at 100,000 and usually last much, much longer. Ask any long haul trucker how many 100,000’s trucks average. Diesels not having the need of an ignition [sparking system] have fewer parts to go wrong.
First conclusion is that diesel driven generators are a more viable option for a long term homestead power system.
Sizing the system
To do this you really need to determine 3 separate figures.
1) Minimum needs
2) Average needs
3) Peak or Maximum needs.
Adding up the power requirements of the equipment in each category does this. Generators are rated in watts or rather 1000 of watts or Kilowatts. To find these values you need to read the appliance’s nameplate. Some list the amount in watts, which makes it easy. Others list the amount in Amps. To convert Amps to watts you multiply amps times the voltage to get watts. Most common electrical equipment runs on 120 volts although some use 240 volts. Example: 5 amps at 120 volts equal 600 watts.
Minimum need items are things like refrigeration, heating or cooling, ventilation and communications. This amount can be reduced from the combined amount by running this equipment sequentially. Average is self-explanatory. Peak is the largest single load or combination of loads that can be expected to be run at any one time. Although you might want to add a fudge factor to be safe. It is better to have a little extra than not enough.
For efficient operation a generator should be loaded between 70 to 90 percent. Less the system is not as stable or being used effectively. The upper 10 % are to allow for the surge when a load is started. Also generators last longer and run better if used for a period of time rather than in a series of short runs. The most wear and tear is during the start up.
The generator is selected to meet the desired usage. Usually minimum for emergency conditions or the average requirements of the homestead. This can sometimes be accomplished better by having 2 generators. Either one to meet minimum to average usage needs or combined to full fill any greater demands for longer-term use. Additionally each can be used as a backup to the other during maintenance or repair. Also as a source of spare parts if both are the same.
What bells and whistles are available?
Auto-start. This automatically starts the generator upon a power failure.
Transfer switch. This is a switch that shifts from commercial power lines to the generator and back. This is a safety feature to keep the generator from feeding the commercial grid. This feedback could cause an injury or worse to linemen repairing the cause of the initial failure. These come in manual or automatic. The automatic type switch the power after the generator comes up to speed.
Remote start. This is a nice feature for periodic running and testing or in place of an auto-start or in the case auto-start fails. It saves a trip to where the generator is located.
Remote monitoring stations. Several stations can be set up for convenience of knowing the status of the generator. These gauges would entail information such as if it were running, speed, various critical temperatures, oil pressure and even fuel tank level. These stations can even be fitted with alarms if parameters get out of operational ranges.
Paralleling meter. When more than one generator is used at the same time to supply the same distribution system this is mandatory equipment. In AC electricity the voltage rises to a peak positive voltage and dips to an equal negative voltage in a series of smooth curves. [Alternating current] When hooking 2 or more generators together the switch has to be closed as close to possible when these rising and fallings match. The purposes of the meter is to measure the difference between the 2 machines it shows when they are in sync and when the switch can be closed safely.
Battery bank. To greatly improve the systems efficiency a battery bank is a welcome addition. When the generator is running at lower than capacity it can be used to charge the bank. Which in turn can supply power when the generator is not on line. It can also store energy from alternate sources such as wind, water or solar systems. The battery can also have remote monitoring and controls incorporated with the generator stations. Depending on how it is wired the bank can operate at almost any desired DC voltage. The output of the battery bank can be dealt in 3 different ways.
The first method is straight DC. This requires a separate DC wiring system. A DC system works especially well for lighting. Many DC appliances can be acquired at recreational vehicle centers. Here is an interesting product. It is a variable output LED lighting Module.
http://www.techass.com/el/versalux/ulm/ulm.php?techass=3fe0092186fa2f45faefa96b753e0bbeThe second method is to use one large or a combination of several smaller inverters. Inverters are electronic modules that convert DC into AC.
The final option is the ultimate inverter. This is a motor generator setup. A DC motor drives a small AC generator. The advantage these have over the electronic inverters is longevity. These will last an extremely long time because of their simplicity. One interesting feature of this kind of set up is that it can operate in both directions. If the control circuits are adjusted the AC generator will act as a motor and a DC motor act as a DC generator. This can then be used to charge the batteries from the main generators.
Noise abatement and a few other issues.
If you run a generator in the basement or an attached garage it would not be long until it would drive you crazy. Not to say announcing its presents to the world for miles around. What is required is a separate power house. This structure does not have to be close to a dwelling but it need not be far away either. The trick is to insulate it to contain the noise. The easiest way to this is to think of a root cellar like structure with a well-insulated door. Being situated below ground it uses the earth as a sonic as well as a temperature insulator. Since this also moderates temperature fuels such as diesel are not as effected if stored there. Also the negative effect of cold on the batteries will be minimized. If heating is required it will be minimal in nature.
Final Recommendations. The best engine I would suggest is a diesel. From what I previously stated you might think I would say 2 generators. Actually I would want 3. 2 mid sized units to supply the main power. Each capable of supplying the average power needs. Each as a backup for the other or combined to meet higher levels of need. The third would be a small portable gas generator. This is to take a power source to remote locations. A battery bank to increase efficiency. A separate DC grid and a motor generator setup to supply AC from the battery and to charge the battery.
