Inverters

An inverter system runs a floor, a shop or a house through an outage for hours rather than minutes. It is the alternative to a generator for loads that can be carried on batteries - lights, fans, computers, routers, tills - and it is silent, needs no fuel and starts instantly.

The inverter rating is not what decides how long the power lasts. Battery capacity does. A 5 kVA inverter with two batteries carries a heavier load than a 3 kVA unit but not for longer, and the enquiry that asks only for a kVA figure is asking the wrong half of the question. Tell us the load and the hours and we will specify both halves.

What the system cannot carry matters as much as what it can. Air conditioners, water heaters, pressing irons and anything with a compressor draw far more than their steady-state figure at the moment they start, and putting them on an inverter designed for lighting and computers is how a new system is written off in its first week.

Battery type is the other decision. Tubular lead-acid costs less to buy and needs watering and ventilation; lithium costs more, lasts several times longer and needs neither. Over a five-year horizon lithium is usually the cheaper of the two, and we will show the arithmetic rather than assert it.