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As HAM operators living under the
motto of "When All Else Fails!", backup power is an
essential element in emergency preparedness.
Backup power comes in several forms: battery,
portable generators, solar panels, water driven
generators, etc. We will
begin with portable generators and add more
information as time goes on so check back
occasionally. To get right into the meat of
the subject, the weak link in power generation is
availability of fuel. Fuel, then, is the main
issue as determining generator size is a simple
exercise in ohms law.
The most common situations are
going to be tornado, hurricane, ice storm,
earthquakes. Worst case scenarios for each:
Tornado - total devastation
but limited in area
Hurricane - damage very severe
and very widespread
Ice Storm - damage confined
mostly to utilities, very wide spread
Earthquake - damage severe
very widespread
The differences in these
disaster types imply different lengths of time until
supplies arrive, utilities are restored, and the
types of fuel that would be available. First
lets look at cost.
To determine the most cost
effective fuel, compare the energy and cost per unit of fuel
:
Fuel costs/energy
comparison:
|
Fuel Type |
Shelf Life |
Energy in BTUs/unit |
*Cost/Unit |
Cost/hr/100,000
BTU |
|
Gasoline |
short |
125,000 / gal |
1.83 |
1.46 |
|
Diesel |
longer |
139,000 / gal |
2.52 |
1.81 |
|
Natural Gas |
no storage |
102,000 / ccf |
2.10 |
2.05 |
|
Propane |
indefinitely |
92,000 / gal |
2.42 |
2.63 |
*As of 2/12/09
It requires 2 horsepower to
produce 1000 watts of energy per hour
Under load, each horsepower consumes 10,000 BTU per
hour
BTU consumption chart
based on generator/engine size and load
|
Generator Wattage |
Engine Horsepower |
Full Load |
75% Load |
50% Load |
|
1850 |
3.5 |
35,000 |
26,250 |
17,500 |
|
4000 |
8 |
80,000 |
60,000 |
40,000 |
|
5000 |
10 |
100,000 |
75,000 |
50,000 |
|
7500 |
15.5 |
155,000 |
116,250 |
77,500 |
|
8000 |
16 |
160,000 |
120,000 |
80,000 |
|
10,000 |
20 |
200,000 |
150,000 |
100,000 |
|
12,000 |
24 |
240,000 |
180,000 |
120,000 |
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Of course, fuel cost is not
the main factor if you can't find it.
For relatively short lived
disasters like a tornado, fuel availability will be
scarce in a small area but available away from the
directly affected area. There may be a small
amount of hoarding initially but a large amount of
fuel will not be required as driving to the next
town will be sufficient to re-fuel. Emergency lighting
and communications equipment along with power for
food storage in the directly affected area.
Gasoline or diesel would be a good choice.
Natural gas supply likely to be uninterrupted.
An ice storm can be a long
lasting event with utilities not being restored to
some locations for periods measured in weeks.
Power for heat and communications is the main issue
as an ice storm will not happen in warm weather!
Gas heat still requires electricity for the fans but
the power requirement is low. Gasoline to
refuel the generator could be very scarce for three
or four days until gas stations get commercial power
back or get generators for themselves. Cold
weather causes gasoline to turn to varnish.
Hurricanes cover such a large
area and damage can be very severe. Natural
gas supply is likely to be uninterrupted.
Gasoline will be very scarce for an extended period
even if the station has a generator as bulk delivery
to stations could be difficult. As supply starts to
appear, demand will be high.
The big cahuna of disasters in
our area is the New Madrid of course. All fuel
supply types will be interrupted and will be
interrupted for an extended period of time.
Stored fuel will be the only option. It is
imperative to keep stored fuel quality high enough
to be dependable. The best choice for stored
fuel is propane. Running a generator on
propane is not without it's own problems.
Because propane has to convert from liquid to gas
and the process is dependant on pressure and
temperature, there are issues with being able to use
the full amount of propane in the storage container
and keeping the generator supplied with a sufficient
amount of fuel to run. As propane is
consumed the container cools. If the propane
is consumed too quickly in relationship to the
container size, it can freeze, reducing the pressure
to the point that it will not be able to supply
enough vapor to run the generator. Container
size is important, especially in winter. It
would be nice if the New Madrid would wait till fair
weather. See the table below to see how
temperature affects BTU output:
|
Vaporization Rates
of Cylinders
Output in BTU's per hour -
Vertical Cylinder 25% full - Minimum
Cylinder Pressure 10 PSI
Cylinder Size
|
Outside Temperature |
20 |
30 |
40 |
100 |
200 |
420 |
|
+60F |
24,000 |
32,000 |
40,100 |
79,700 |
125,900 |
185,500 |
|
+50F |
21,200 |
28,300 |
35,500 |
70,600 |
111,500 |
164,300 |
|
+40F |
18,450 |
24,700 |
31,000 |
61,500 |
97,200 |
143,100 |
|
+30F |
15,700 |
21,000 |
26,400 |
52,400 |
82,800 |
122,000 |
|
+20F |
13,000 |
17,300 |
21,800 |
43,300 |
68,400 |
100,700 |
|
+10F |
10,250 |
13,700 |
17,200 |
34,200 |
54,000 |
79,500 |
|
0 |
7,500 |
10,000 |
12,600 |
25,000 |
39,500 |
58,300 |
|
-10F |
4,780 |
6,400 |
8,000 |
16,000 |
25,300 |
37,100 |
|
-20F |
2,050 |
2,700 |
3,400 |
6,800 |
10,700 |
15,900 |
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To run a 5kw generator at full
bore in 20 degree temperature, a 420 pound tank is
the minimum size tank to supply the needed 100,000
BTU! Conservation would be good.
To be prepared to operate
"when all else fails", you must have reliable fuel
to run a generator. If gasoline is the only
fuel your generator will run on, you may not be able
to operate "when all else fails". For about
$300 you can convert most any generator to a
tri-fuel generator that will truly be able to work
"when all else fails"!
Most of the figures on this
page comes from
http://www.propane-generators.com.
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