Can plug-in solar power my electric hot water cylinder?

Your hot water cylinder is quietly one of the biggest electricity users in your home. For most Kiwi households, heating water accounts for 30 to 40 percent of the power bill. So it makes sense to ask: could plug-in solar take a bite out of that?

The answer is yes, and hot water is actually one of the best matches for plug-in solar in a NZ home. Here’s why.

Why hot water cylinders and plug-in solar work so well together

Most appliances need power at unpredictable times. Your fridge cycles on and off. Your washing machine runs when you do the laundry. Your lights come on at night.

A hot water cylinder is different. It doesn’t care when it heats the water, as long as the water is hot when you need it. That flexibility is everything when it comes to solar.

Standard electric hot water cylinders in New Zealand heat water using an element, typically 1.8 to 3 kilowatts. They run for a few hours a day to maintain temperature. With a simple timer, you can tell the cylinder to heat water during the middle of the day, exactly when a plug-in solar system is generating at its peak. (Timers can be retro fitted, if yours does not have one)

The cylinder stores that heat. You use the hot water in the evening when you shower. The solar did the work hours earlier.

In effect, your hot water cylinder becomes a thermal battery.

How much electricity does a hot water cylinder actually use?

A standard 180-litre electric cylinder uses roughly 3 to 5 kWh per day, depending on household size, temperature settings, and how much hot water you use. At 39.3 cents per kWh, that works out to around $430 to $720 per year just for hot water.

A two-panel plug-in solar system generates approximately 1,000 kWh per year in Auckland, and up to 1,200 kWh per year in sunnier regions like Nelson. On a good day in summer, an 800-watt system can generate 4 to 5 kWh during the peak sunshine hours of 10am to 3pm.

If your cylinder is timed to heat during those hours, you’re directly offsetting some of the most expensive electricity your home uses. Not all of it, but a meaningful portion.

Setting up your cylinder timer

Most electric hot water cylinders have a timer or can have one added cheaply. The goal is simple: set the heating window to roughly 10am to 3pm.

A few things to check:

Your cylinder may have a boost setting for cloudy days or high-demand periods. Keep that available for when you need it.

If your household uses a lot of hot water in the morning (showers before school or work), you may want to also allow a short heating window in the early morning to top up temperature. The solar window handles the main load through the day.

What about heat pump hot water systems?

Heat pump water heaters are more efficient than resistive cylinders. They use roughly one-third of the electricity for the same amount of hot water. That’s good for your bill overall, but it also means plug-in solar offsets a smaller absolute amount of energy, because there is less energy to offset.

If you have a heat pump water heater, the same timing principle applies. Set it to run during solar generation hours and you still benefit. The numbers are just smaller.

If you’re choosing between upgrading to a heat pump cylinder or adding plug-in solar, they are not mutually exclusive. A heat pump cylinder reduces your hot water energy use. Plug-in solar then offsets part of that reduced use. Both together make a bigger dent in the bill than either alone.

The NZ regulatory situation

Plug-in solar is currently not legal to connect to the grid in New Zealand under a 2012 prohibition notice. The Ministry for Regulation launched a formal review in May 2026 to address this, and that process is ongoing.

We’re actively involved in that review and will update our waitlist as soon as there is news. If you want to be first to know when plug-in solar becomes legal in New Zealand, join the waitlist below.

The bottom line

Hot water is the single best load to pair with plug-in solar in a typical Kiwi home. The cylinder is already there, already using a significant amount of electricity, and can easily be timed to run during solar generation hours. No complicated setup. Just a timer and some sun.

When plug-in solar becomes legal in New Zealand, this will be one of the first things we walk customers through.