Generator vs UPS vs Inverter

Backup power options

Eskom has made no secret of the fact that is struggling to meet the country’s power demands. Over-loading and maintenance requirements have resulted in power failures becoming more frequent and longer lasting. As an electricity user in SA today, you should not be asking yourself if you will experience a power failure but rather how often and for how long.

Previously when purchasing a UPS, clients would look for units that would merely give them enough time to shut down their computers, but as our businesses become more dependent on computers, this approach is no longer viable. Businesses today are more dependent than ever on their IT and find it difficult to operate without this valuable tool. Businesses today need solutions that can keep them running and fully operational without interruption. The real decision now facing consumers is not if they need power backup, but rather how much of their business do they need to keep running, and for how long. As a rule of thumb, in the absence of other requirements, the runtime should be two to four hours. There are four options for backup systems with extended run times:

  • Inverter with large battery pack
  • Generator
  • UPS with extended battery packs
  • UPS and generator combination

Inverter with large battery pack

An inverter is not a UPS. At best, it can be compared to an off-line UPS, provided it has been fitted with an auto-switch that will transfer from mains power to inverter power should there be a failure. In most cases the unit allows mains power to pass straight through and, when the power fails, switches to the inverter. Switching time is anything from 20 milliseconds upwards, but some inverters are actually designed to have a “dead time” in other words there is a complete loss of power to the load before the inverter power is switched on. The battery pack will be sized according to the run time required.

The advantages of this solution are that it is quiet; emits no exhaust fumes; and requires minimal maintenance. Although the batteries need replacing every three to seven years (depending on battery type), which is expensive, however the typical running expense of this solution is usually cost effective.

The disadvantages are that it offers little or no protection against mains fluctuations, spikes, or surges. Moreover, if it is one of the systems that is designed to have a dead time before the inverter starts, computers will shut down and reboot.

Once battery power is exhausted, 8 to 12 hours are needed for recharging, during which time there will be very little backup available until the batteries are fully charged.


A generator creates a 220/230V supply from either a diesel or petrol motor connected to an alternator. The key advantage is that runtime is unlimited. As long as the unit is refuelled, the generator will keep running. However, the user should check the manual, as some generators have a recommended usage period, after which they need to be cooled down before being restarted.

A standalone generator has a number of disadvantages. Between the mains failure and generator start-up is down time. Even if an auto start is used, this down time will be anything from 20 to 60 seconds. If a manual start is used, A further disadvantage is as loads switch on and off, the generator’s output may fluctuate up and down before stabilising. Depending on the generator, the output wave may not be clean. Generators have the additional disadvantage or needing a suitable storage space, depending on size. Noise and generator fumes can be a problem. Generators must be run regularly even when there are no power failures, to make sure they are working. Running costs are relatively high when taking fuel and servicing costs in consideration.

On-Line UPS with extended battery packs

To many this seems to be the ideal solution, combining the best features of an on-line UPS with the backup time of an inverter. The units offer a number of key advantages. It provides full protection against spikes, surges, dips, and power failures and when the power does fail, output from the UPS is constant and uninterrupted and can be designed to give the user anything from 15 minutes to 8 hours. Computers are not switched off unexpectedly. When the power fails, no user intervention is needed, operation is silent, and it emits no fumes. The batteries will probably need quite a bit of space, but the unit can be set up inside.

Like the inverter, the disadvantage is that once the batteries are flat the unit requires 8 to 12 hours to recharge, and the batteries need to be replaced every three to seven years, which can be expensive.

Generator and UPS combination

For areas that suffer from regular prolonged power outages, this is the best solution. The UPS will ensure that there is no break between failure of the mains supply and start-up of the generator. The power to the computers is clean, as the UPS corrects power problems from both the mains supply and from the generator. Run time is indefinite, as the generator can be refuelled.

The disadvantages of this solution are the need for a suitable storage space for the generator; noise; and exhaust fumes. The generator needs to be run regularly to make sure it is working. Running costs are relatively high, considering fuel and servicing.

Comparison Chart

The information for this article was provided by our UPS partner

One Comment on “Generator vs UPS vs Inverter”

  1. Kudos on a comprehensive blog comparing generator, UPS, and inverter options. The pros and cons you’ve outlined for each solution make it easier to understand their distinctions. This well-structured comparison is a fantastic guide for anyone seeking the right backup power system. Great work!

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