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Battery backup vs standby generators: Keep your power on during the next outage

We review the pros and cons of every type of backup power system to help you find the right solution for your home and office needs. TL;DR version: The best system depends on where you live and what you can afford.

There is much to consider when choosing which kind of backup power you need during a power outage or when you use off-grid backup power. To determine if a backup power generator system, uninterruptible power supply, or a battery is right for your home, you need to know the pros and cons of emergency generators or home battery backup systems for your home or office to maintain power supply until utility power is restored.

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You'll also need to consider whether you want to buy a gas generator, diesel generator, air or liquid-cooled, fixed standby generator, or a portable generator. Do you want a seamless switch to emergency battery power, fed by solar, or will a portable air-cooled generator fulfill all of your needs?

Comparing the differences between a generator and a battery backup for your home power supply can be less of an onerous task if you have first carried out a detailed energy audit so that you know how much power you will need during a power failure.

How much power does your home need?

To work out how powerful your battery backup system, standby power system, or home backup generator needs to be, carry out an energy audit by calculating how much power your appliances use. Once you have the details from your energy audit, you can decide to choose which system will be best for your home or office and whether you prefer a battery backup system or a generator.

Performing an energy audit

For my energy audit, I used a spreadsheet to calculate the power requirements in my home and office to determine how large my backup system needs to be. In this example, I have taken an average wattage for a standard type of appliance, and have used 110v to calculate power requirements that might be needed in the US. To calculate amps I divided the watts for the appliance by the voltage required in the US (110v). Then I estimated how many hours per day that the appliance might be in use. The final column indicates the total amp-hours (Ah) for each appliance. You can get a professional energy audit to assess your home's energy usage

My home-grown table looks like this:

Appliance

Volts

Watts

Amps W/V

Daily use (hours)

Total amp-hours

TV

110

38

0.345455

8

2.763636364

Fridge

110

725

6.590909091

18

118.6363636

Vacuum

110

335

3.045454545

1

3.045454545

Laptop

110

70

0.636363636

6

3.818181818

Desktop PC

110

150

1.363636364

10

13.63636364

Broadband router

110

10

0.090909091

24

2.181818182

PC Display screen

110

30

0.272727273

10

2.727272727

Microwave

110

1300

11.81818182

0.5

5.909090909

Coffee machine

110

1000

9.090909091

1

9.090909091

Cooker

110

3000

27.27272727

2

54.54545455

Radio

110

5

0.045454545

5

0.227272727

Sump pump

110

1200

10.90909091

2

21.81818182

Hairdryer

110

1500

13.63636364

0.5

6.818181818

CPAP machine

110

90

0.818181818

10

8.181818182

3 x spotlights

110

120

1.090909091

6

6.545454545

Air Conditioning

110

2400

21.81818182

12

261.8181818

12 x lights

110

160

1.454545455

10

14.54545455

Total

12,133

536.3090909

To get the best efficiency for my battery backup system I want to make sure that the backup battery is large enough to cope with at least twice the total amp hours required in my calculations. So, in this scenario, with under 550Ah, and 12,133W required, I would buy a system of at the very least 12kW capacity. This method of calculating might not be the perfect way to calculate all of your energy requirements, and you might have a completely different way of working out your power requirements, but it helped me with the specifications for my own battery system.

If you want to run only the fridge and the coffee machine from the list above, then the battery will last far longer than if you need to run all of the appliances in the list.

How do battery backup systems work?

Backup storage batteries (either lead-acid or Lithium-Iron Phosphate) are charged during the day either by using solar power or by electricity, which is added to the battery backup system when grid electricity is cheap. If the home battery system is charged by solar panels, then the batteries should be large enough to store all of the battery backup power output (wattage) produced. If you have a 300W solar panel and you live in a sunny area, getting over six hours of sunlight per day, then your 300W solar panel would produce 1800Wh per day, which could be stored in your backup battery system. Obviously, more solar panels mean potentially more Watt-hours produced for your backup battery. You also need to consider buying an inverter to convert the DC power to AC.

Of course, not everything is 100% efficient. You also need to take into account losses from converting DC to AC power, efficiency losses as energy moves from the battery to the inverter and on to the appliance. This needs to be taken into account too when determining your power requirements.

Key differences between battery backup systems and generators

If you choose to have a generator instead of a battery backup system, there are standby generators, air-cooled generators, and liquid-cooled generators, with a range of fuel options. Each has its own benefits and disadvantages that should be taken into account before you decide which system is right for you. There are pros and cons for each type of generator or battery system. Check whether in your state you need a permit for your generator, remembering that your local regulatory body might have other options that apply.

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Standby generators pros and cons

Standby generators can be connected to the electrical system in your home or office. They are usually liquid cooled and fuelled by either diesel, liquid propane, vapor propane, or natural gas. They are fitted with either an MTS (Manual Transfer Switch) or an ATS (Automatic Transfer Switch). When the power fails, the ATS generator will automatically start and keep the power running -- like a UPS system works to keep the power supplied to your servers. The MTS can be switched on manually to switch the power to your premises. For standby generators choose either propane or natural gas as a fuel for your generator. Both have good reliability for starting the generator and, when a large tank is also supplied, will keep running for an extended period of time.

Pros

  • Quickly switches from the grid to the generator
  • Keeps the power on to important appliances such as freezers, water pumps, and servers
  • Standby generator fuel will last for several days of use before requiring replenishment
  • Transfer switches disconnect you from the utility grid when the power fails to protect from power spikes when the power is reconnected. Surge protection is also recommended
  • Will wait until the power supply is stable before reconnecting you to the grid

Cons

  • Standby generators are more expensive to buy than portable air compressors and take a significant amount of time to install. You need to carefully plan your installation to get the best scenario for your home or business
  • The generators are permanently installed in place so are difficult to move if you change premises
  • Standby generators are often noisy and must be installed outside
  • You will need adequate supplies of fuel such as propane for continuous generator use
  • You might need a permit for a standby generator. In the US you will definitely need a permit for both generators and batteries, but check your country-specific regulations.
  • Maintenance costs are higher and the generator will need to be serviced after 100-200 hours of continuous use, and oil changed after 25 hours

Air-cooled portable generators pros and cons

Air-cooled generators are designed to provide temporary electrical power and use the circulation of air to reduce the temperature when the generator is running. A fan blows air across the generator to prevent overheating. Air-cooled generators can be fuelled by diesel, or propane, although some are fuelled by gasoline. They are typically used when power requirements are less than 20kW as they are not as effective when power requirements are greater than this. Make certain that you comply with the grounding requirements for portable generators to avoid potential shocks and electrocution.

Pros

  • Readily available in stores
  • More cost-effective
  • More durable and powerful than air-cooled generators
  • Low fuel consumption, efficient and portable
  • No risk of frost cracks
  • Simple design makes air-cooled generators easier to maintain than liquid-cooled generators
  • Natural Gas fuelled generators are clean burning and quieter than diesel generators

Cons

  • Needs to be installed outdoors and will need to be protected from the weather
  • Needs to be switched off after a few hours to allow the engine to cool down. Some models can run continuosly and some have automatic shut down safety features.
  • Diesel generators produce a significant amount of smoke and are very noisy
  • Natural gas generators need special installation to connect to propane or LPG tanks
  • Diesel generators can be difficult to start in cold weather
  • Generators require regular maintenance
  • Can overheat if used for a long time

Liquid-cooled generators pros and cons

Liquid-cooled generators use liquid or water coolant to cool the generator instead of air. Similar to a car engine, liquid-cooled generators use radiators and water pumps to cool the liquid and recirculate the cooler fluids to the hotter parts of the engine. They are typically used when power requirements range from 20kW to 60kW.

Liquid-cooled generators can run using a variety of fuels. gasoline, diesel, biodiesel, propane, or natural gas. Gasoline has its drawbacks as it forms deposits in the tanks and has poisonous gases. It also is very flammable and does not always burn clean. Diesel is also considered to be a dirty fuel with particulate emissions and exhaust gases. Diesel engines are also difficult to start at low temperatures. Propane and natural gas are better choices for your generator as they are clean burning and great when starting in cold environments. However, you do need to have a propane tank or a connection to the natural gas line.

Pros

  • Can be operated for extended periods of time
  • Better cooling than air-cooled generators
  • Last longer than air-cooled generators
  • Quieter in operation compared to air-cooled generators
  • Can be enclosed to reduce noise output
  • More powerful, robust, and long-lasting compared to air-cooled generators

Cons

  • Liquid-cooled generators are more expensive to build and install
  • More complex in design and require specialized parts
  • Liquid-cooled systems require more frequent maintenance than air-cooled systems

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Battery backup system pros and cons

There are several types of batteries you can use for your battery backup system. The cheapest, and most familiar to drivers are lead-acid batteries, typically found in cars and trucks, which recharge about 500 times, depending on temperature conditions, and frequency of use before replacement. Lithium-ion batteries tend to be smaller batteries and currently power almost all mobile devices. Larger Lithium-ion batteries, which use Lithium-Iron Phosphate as the cathode in the battery, and graphite as the anode can be scaled up for use in your home and can be recharged and discharged about 2,000 times.

Pros

  • Lithium-Iron Phosphate batteries are more environmentally friendly than lead-acid batteries
  • Lithium-Iron Phosphate batteries have a longer lifespan (up to 10 years) compared to lead-acid batteries (one to three years)
  • Battery systems require no regular maintenance and are quiet in use
  • Lead-acid batteries are readily available almost anywhere
  • Will store excess solar during the day for use after sunset
  • Noise levels very low
  • Immediate activation if power is lost
  • Little maintenance required, perhaps once per year - especially if Lead Acid batteries are used

Cons

  • Lithium-Iron Phosphate batteries are three to ten times more expensive than lead-acid batteries
  • Batteries are more expensive to install compared to some generators
  • Complex configuration with solar pv cells
  • Smaller load capacity for the cost
  • Any one of a set of lead-acid batteries can be a significant point of failure
  • Not recommended for heating or cooling loads, or larger loads are required
  • Will need to be replaced several times compared to solar panels

Which backup system is best for keeping the power on at home and in the office?

There are many factors when considering which emergency power system will work for your home. The costs of each backup power system vary considerably, as do the extra costs involved in planning and installation of many of the systems. The life of the home battery backup or solar battery system also needs to be taken into account as well as maintenance schedules for the backup generator.

Which system is best for your specific scenario?

You need to decide whether to buy a generator or a battery system, then drill down into which generator or battery system to use. Your decision should depend in part on where you live.

If you live in an area with long cold winters bear in mind that battery systems do not perform well in very cold weather. Cold can reduce the ability of a lead-acid battery to transfer full power to where it is needed, and it can lose up to 50% of its power. Lithium-Iron Phosphate battery electrolytes can freeze at temperatures of -40 degrees C and should be charged when the temperature is above 32 degrees F. Lithium-Iron Phosphate batteries are your best choice in cold weather (above - 20 degrees C), but will still suffer up to a 10% loss of capacity. Consider a standby generator that is liquid-cooled and has a propane tank.

If you live in an urban area, noise is a huge factor in your choice. Air-cooled generators are significantly noisier in operation than liquid-cooled generators and might upset the neighbors. Lithium-Iron Phosphate battery systems also have low levels of noise when in use. Consider a battery system with solar PV if you get enough sunshine.

If you live in an area when power outages happen frequently and the power stays off for an extended period of time, then a liquid-cooled generator that is fueled by either liquid propane or natural gas is your best option. Gas-fueled generators burn cleaner and tank leaks are rare. Avoid vapor propane if you live in a cold area. The surrounding air must be warm enough for vaporization to happen, and getting the correct amount of gas to the generator might be an issue. Lithium-Iron Phosphate battery systems, if of an adequate capacity, are also an option. Consider a standby generator that is liquid-cooled and has a (preferably liquid-cooled) propane tank.

If you live in the Pacific time zone, then avoid natural gas for your generator due to the possibility of earthquakes. Consider a battery system with solar pv if you get enough sunshine.

How quickly do you want power after an outage? Can you manage with a generator that needs to be hauled out of storage, filled with fuel, and hooked up, or would you prefer to have a standby generator, permanently installed that has an automatic transfer switch to keep the power running with minimal interruption? Do you need an inverter generator, or will DC power be sufficient to power your mobile devices and other battery-powered items? How much maintenance will your home generator need? Which fuel source do you prefer for your emergency generator, do you want an automatic transfer switch? If you need immediate power consider a liquid-cooled standby generator, fueled by liquid propane with automatic transfer switch.

How much power do you need? If you only need a few hours of power for a few appliances, then a portable air-cooled generator that runs on diesel or propane gas is your best option.

How much budget do you have? If cost is an issue, then a portable air-cooled generator that runs on diesel or propane gas is your best option. Standby generators are more expensive, have installation costs, and need regular maintenance by specialist technicians. Battery systems must be planned and installed by specialist firms.

Proper planning now will make sure you have the right system that fits your needs perfectly and will cope with potential power outages.