| Sizing a Generator
Home/Battery System
Sizing your generator is elementary math. Power is measured in watts. A
light bulb, for instance, may require 40 watts of power, a blender 300.
To size your generator, total the wattage requirements
for all appliances you plan to run at the same time. We recommend that you add at least
25% to perceived requirements to allow room for growth.
Appliance wattage is usually listed on the manufacturer's label. If only
amperage is listed, the formula to determine watts is as follows: amps x volts = watts. Most generator
manufacturers measure generator size in continuous watts (or the number of watts the generator will
deliver continuously). Continuous watts should not be confused with surge watts. Surge is the highest
output (in watts) that the generator will "surge" to
briefly startup. TVs,
stereos, and drills have a surge rating 1 1/2 to 2 times their continuous ratings. Power-hungry loads
with large motors such as compressors, water pumps, refrigerators and air conditioners, may surge at
startup 3 to 4 times their listed continuous rating.
Print this work sheet out and use it to determine the generator
/inverter/ battery power
package that fits your individual needs.
| EXAMPLE |
| Step 1: Below is all you need for this.
To determine how much battery storage you'll need for an
inverter system, complete stops 2 through 4. Determine your daily energy budget. (Hours of use times watts equals daily
watt hours used.) |
| AC Appliance |
Hours of Daily
Usage X |
Appliance Watts
= |
Daily Watt
Hours Used |
| Microwave |
.5 |
600 |
300 |
| Lights (x4) |
6 |
40 |
240 |
| Hair Dryer |
75 |
750 |
563 |
| Television |
4 |
100 |
400 |
| Washing Machine |
1 |
375 |
375 |
| Add lines 1-5 |
Total Watts:
1,865 |
Total
Daily Watt Hours Used
1,878 |
| Step
2: Multiply total daily watt hours used by number of
anticipated days of autonomy (days between charging, usually between 1 to 5) to determine your
Rough Battery Estimate. |
x 1 to 5
Rough Battery Estimate
5,634 |
| Step 3: Multiply Rough Battery Estimates x 2 to determine safe battery size in
watt hours. (This allows for 50% maximum battery discharge in normal operation and an additional
50% in emergency situations.) |
x 2
Safe Battery Size in Watt Hrs.
11,268 |
| Step 4: Convert safe battery size to amp hours. The formula is: Safe Battery size
in watt hours ÷ DC system voltage (i.e. 12, 24, or 48, volts DC - Safe Battery Size in amp
hours.) Here 24 Volts. |
Safe
Battery Size in Amp Hrs.
470 |
| To properly
determine generator size, add together the appliances,
including battery charging, that must/will run at the same time, from
column 3 (Appliance Watts, listed above) and add 25% then round up to the next generator wattage
size.) |
Properly
Sized Generator Wattage
2,500 |
| Step 1: Determine your daily energy budget. (Hours of use times watts equals daily
watt hours used.) |
| AC Appliance |
Hours of Daily
Usage X |
Appliance Watts
= |
Daily Watt
Hours Used |
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Add lines 1-5 |
Add lines 1-5 |
Total Daily
Watt Hours Used
______ |
| Step
2: Multiply total daily watt hours used by number of
anticipated days of autonomy (days between charging, usually between 1 to 5) to determine your
Rough Battery Estimate. |
x 1 to 5
Rough Battery Estimate
_______ |
| Step 3: Multiply Rough Battery Estimates x 2 to determine safe battery size in
watt hours. (This allows for 50% maximum battery discharge in normal operation and an additional
50% in emergency situations.) |
x 2
Safe Battery Size in Watt Hrs.
_______ |
| Step 4: Convert safe battery size to amp hours. The formula is: Safe Battery size
in watt hours ÷ DC system voltage (i.e. 12, 24, or 48, volts DC - Safe Battery Size in amp
hours.) |
Safe Battery
Size in Amp Hrs.
_______ |
| To properly
determine generator size, add together the appliances that must/will run at the same time, from
column 3 (Appliance Watts, listed above) and add 25% then round up to the next generator wattage
size.) |
Properly
Sized Generator Wattage
_______ |
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