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Photovoltaics or Gas Generators, what is the best backup power?

16 Dec 08 | Solar Electric, Training

Based on my experience during the Northeast Ice Storm of 2008, I thought I would do a comparison of a Photovoltaic system with battery back up vs. gas powered generators.  To be sure, a portable gas powered generator is the fastest least expensive way to get the power back on in an emergency.  They can also be dangerous, as several people have died of Carbon Monoxide poisoning over the last couple of days.

An installed system that automatically restores power can save time and money in the long run.  For that there are two basic options, a gas or diesel powered generator or a PV system with battery backup.

Here is a chart for comparison:

System category Photovoltaic system w/battery backup Portable gasoline generator Installed generator with auto transfer switch
Design Design intensive No Design Design moderate
Installation cost Initial cost high, approximately $20-27K Initial cost low, about $1-2K Initial cost moderate to high, about $10-20K depending on generator type/size
Installation labor Installation intensive No installation Installation intensive
Running cost Negative cost to run Cost to run high Cost to run moderate
Maintenance cost No maintenance High Maintenance High Maintenance
Environmental Non-polluting High polluting Moderate polluting
Fuel Non-fuel dependent Fuel availability dependent Fuel availability dependent
Load size Partial load sizing Partial load sizing Full load sizing
Operation Silent running Loud running Moderate noise running
Hazards Some batteries can produce Hydrogen if improperly charged Carbon monoxide hazard, fueling hazard, fire hazard No carbon monoxide hazard if properly installed
Other In use full time, can be configured to sell power back to grid when batteries are charged, reduces electric bill Standby use only, must be moved into position and use extension cords, does not reduce electric bill Standby use only, does not reduce electric bill

Notes:
1. PV design includes identifying critical electrical loads and doing a load analysis. Also includes local weather considerations, solar resources, sub panels, battery placement, etc.
2. Cost to run includes fuel and maintenance costs. Since PV systems can be configured to sell excess power to the utility grid thus reducing utility bills, it can make money, therefore have a negative cost to run.
3. Maintenance refers to mechanical maintenance, e.g. oil changes, belts hoses, etc. PV systems usually require no maintenance, properly charged batteries require no maintenance and will easily last 10 years if not discharge too deeply.
4. Load sizing refers to the house electrical load.  A PV system will usually be sizing to run critical systems, a generator can run the entire house.  This is a consideration for those that have electric houses (e.g. electric stoves, electric hot water, electric heat, etc)

To that end, I have put together a standard PV with battery backup package that will run most critical household loads during a prolonged power outage.  These include:

  1. Non-electric furnace or boiler and circulator pumps
  2. 1 HP well pump
  3. 1/2 HP sump pump
  4. Standard 20-23 CF refrigerator/freezer
  5. 1200 watt microwave oven (10 minutes per day)
  6. 20 inch TV and DVD player (5 hours per day)
  7. Table top or clock radio
  8. DSL or cable modem and network switch
  9. Battery charger for laptop computer
  10. 5 13 watt CFL lights (6 hours per day)

This system will have 3-4 days autonomy (no sunshine to recharge batteries).  A small wind generator can be added to create a hybrid solar/wind system.  These work well because usually when the sun is not shining, the wind is blowing and vice-versa.

Contact us to learn more about these systems.

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16 Dec 08 | Solar Electric, Training
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Reader's Comments

  1. Photovoltaics or Gas Generators, what is the best backup power … | December 26th, 2008 at 11:26 am

    [...] Photovoltaics or Gas Generators, what is the best backup power …Based on my experience during the Northeast Ice Storm of 2008, I thought I would do a comparison of a Photovoltaic system with battery back up vs. gas powered generators. To be sure, a portable gas powered generator is the fastest least … [...]

  2. Nigel | January 11th, 2009 at 2:12 am

    Great information thanks heaps



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