As installers of both generators and solar/battery systems, we’re often asked about the pros and cons of each. Here are the answers to some common questions.

PROS AND CONS:

Generators: Generators have several obvious advantages over solar/battery.

 

PROS

– They can reliably provide enough electricity for your entire home under almost all circumstances.

– Installation costs are much lower than those for solar/photovoltaic systems. The development of economy air-cooled generators has brought the cost of a typical installation by a licensed electrician down to a range between $7K and $11K, including a warranty.

 

CONS 

– Generators require annual or biannual inspection and maintenance, including an oil change and a battery check.  The cost can be anywhere from $99 to $250 per year, not including repairs.

– Generators are dependent on your supply of fuel. Natural gas delivery can be interrupted, and liquid propane is a finite resource. During Hurricane Florence, my parents ran out of gas after four days and spent the next eight days without power, leaving them no better off than those who didn’t own a generator at all.

 

SOLAR/BATTERY:

 

PROS

– These are self-regulating and require essentially no maintenance. If the batteries reach a certain level, the system shuts itself down until sunlight or the grid can recharge them.

– You’ll see a lower electric bill. The system will continue to collect energy to power your home even when the batteries are full. And if it generates more power than you need, in most cases the utility will buy the excess from you.

 

CONS 

– Compared to generators, they’re expensive. The price range for a solar/battery combination begins at $15K and goes up from there.

– The amount of energy that batteries can store is finite. You’ll need to learn how much energy your house requires at various times to ensure a steady supply. The up side is, as you get more familiar with your energy usage, you’ll see opportunities to cut back and save even more money.

 

How much power do you need?

Energy consumption is measured in kilowatts (kW) and kilowatt hours (kWh). A kilowatt (1,000 watts) is the amount of energy needed to perform a specific task at a specific point in time. A kilowatt hour is the number of kilowatts needed to perform that task for an hour.  Generator capacity is measured in kilowatts, the amount of power that generator can supply at any given point in time. A battery’s power is expressed in kilowatt hours, the amount of energy that it can store.

For example, a refrigerator might use roughly 800W or 0.8kW per hour. However, refrigerators do not operate continuously. Instead, they run intermittently as the doors are opened and closed and the temperature inside changes.

 

800W – The instant load that your electrical system must carry

800W x 1 hour = 800 watt hours or 0.8kWh

 

Assuming the refrigerator actually runs for 10 minutes (1/6 or 0.16% of every hour):

 

800W x 0.16 = 128W

128W x 24 hours = 3.072 watt hours or roughly 3kWh

 

So, to run this refrigerator for a day, a generator would need a capacity of at least 800W and a battery would need to store at least 3kWh to manage the load.

We’ve found that a 20kW generator or a 10kWh storage device will meet the basic needs of the average home (including refrigerator, freezer, TV, lights, well pump, and receptacles).

 

How to decide?

The choice between a generator and a solar/battery backup can be a tough call. For many people, the deciding factor is their budget.

 

10-Year Cost Analysis:

Generator:

Purchase price   $10,000

10 years annual maintenance $2,500 (assuming $250 per year)

10 years fuel consumptions  $11,500  (assuming 10 mins per weak for general exercise and up to 6 full days of outage per year.)

Tax incentives     $0

10-year total cost $24,000

 

Solar Installation + Battery:

Purchase price $35,000 (assuming 10kWh battery plus 5kW solar)

Annual maintenance $0

Tax incentive -$10,500 (30% federal tax credit)

Annual energy production -$9,581 (5kW solar @ $0.14 over 10 years)

 10-year total cost $14,919

  

Conclusion:

While there are important differences between solar/battery systems and generators, in our experience the decision comes down to the individual’s needs and cash on hand. We believe that, if you can afford the up-front costs, solar/battery is the better choice in the long run.