Ask Pablo: Should I Use a Diesel Generator or Batteries?

A generator placed in front of an RV van.

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Dear Pablo: I work for an international organization for development cooperation. In our projects, we frequently receive requests to provide small generators to be used as back up during power outages, which are quite frequent. The problem is that these small generators are very polluting, very noisy, and provide a low quality electric current. I am thinking of providing deep-cycle batteries and inverters instead. Considering that we can find battery recyclers in these countries, I wonder if the global ecologic balance of this option is better than for fuel generators.

In areas where the electric supply is unreliable, a backup source of power can be very important, especially for the refrigeration of vaccines. Generators, running on costly gasoline or diesel, are expensive to operate and contribute to climate change and air pollution. My intuition tells me that batteries would be the better option, but let's explore both sides.

The Benefits and Drawbacks of Diesel Generators

A yellow diesel generator a wood deck.

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Generators can be a reliable source of power but they consume large quantities of non-renewable fuel and cause even more emissions. Generators do not provide an uninterrupted power supply because they need to be started up first. Finally, the electricity that they generate is prone to power surges and other power quality issues that can damage sensitive equipment such as computers.

Let us assume that you have a 10,000 watt generator. This is enough to run ten hair-dryers or a couple of microwave ovens at the same time. At a 50% load it will use around one gallon per hour. The output is therefor 5 kilowatt-hours (kwh) per gallon. Let's assume that you have 6 hours of power interruptions per day, so you will need six gallons of diesel to generate 30 kWh during this period. The average US household uses 30 kWh each day. At 20 pounds of CO2 per gallon, the six gallons result in 120 pounds of greenhouse gas emissions.

The Benefits and Drawback of Batteries

Portable generator in the snow.

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Batteries do not generate electricity, they merely store it. Therefore the electricity that you get out of them is only as renewable as the source of the electricity that charged them. In many parts of the world this can be from a hydroelectric plant, but it is more likely to be from a coal-fired power plant. Batteries can provide a near-seamless transition when the power goes out, which is why they are used in data centers to bridge the gap before the generators come on line after a power outage. Batteries and inverters need to be sized the meet the demand and can become expensive but this is a one-time capital expense, compared to the continuous demand for fuel with a generator.

Using the same assumptions as above, 30 kWh needed over a 6-hour outage period, we can look at a comparable battery/inverter system. If we assume that the inverter loses 15%, we actually need to store 34.5 kWh. One particular 6 Volt battery can provide 183 Amp-hours, which is roughly equivalent to 1 kWh. This means that we need over 30 batteries. While this may worry the average treehugger, we are not talking about cadmium, lithium, or NiMH batteries, which can have a high environmental burden due to the mining of precious metals. Deep-cycle batteries typically contain lead and sulfuric acid which are contained in a plastic case. While both substances are harmful to humans and the environment, they are recyclable and do not typically spill or otherwise harm the environment when used responsibly.

By my estimates, the battery system would cost up to four times as much as the generator but, when you factor in the cost of fuel, the additional investment has a payback period of about half a year. Of course this is a hypothetical scenario and my result may vary from yours based on the amount of electricity required, the frequency and duration of outages, and the cost of the appropriate equipment.