Solar hot water cylinders are a popular choice for New Zealand homeowners wanting to reduce energy costs. However, the right option depends on your existing setup, roof space, and which type of solar system you are connecting to.
This post covers the main solar system types, what makes a cylinder solar-ready, and what your plumber needs to assess.
What Are the Two Types of Solar Hot Water System?
Two distinct approaches use solar energy to heat water in a New Zealand home, and they work differently.
Solar thermal systems use roof-mounted collectors to capture heat directly from the sun and transfer it to water stored in a cylinder. These systems suit homes where water heating is the primary goal and can supply a large share of a household’s annual hot water needs.
Solar PV systems generate electricity from sunlight, which then powers an electric hot water cylinder or heat pump water heater. This approach suits homes installing solar panels for broader household use, not just water heating.
Both options can work well, but each requires a different cylinder configuration and plumbing setup.
What Makes Solar Hot Water Cylinders Different?
Not every cylinder suits solar integration. Solar hot water cylinders are specifically designed for solar systems and include features a standard cylinder does not carry.
MBIE building guidance recommends a larger cylinder capacity for solar thermal systems than for a single-source gas or electric setup. This allows the system to store heat effectively during periods of strong solar gain. A 300L cylinder is common for solar thermal installations.
The position of the backup heating element also matters. MBIE guidance notes the element should sit in the middle of the cylinder rather than at the bottom. This avoids displacing solar-heated water at the top of the tank with unnecessary element heating.
Some cylinders include a coil heat exchanger inside the tank, which suits closed loop solar thermal systems. Others connect to an open loop system where water circulates directly through the collectors.
What Does a Solar Hot Water Cylinder Installation Involve?
A licensed plumber must carry out all solar cylinder installation work under the NZ Building Code. Before recommending a system, your plumber will assess the following.
Existing cylinder compatibility
Check whether the existing cylinder suits solar connection. Some can be adapted, while others need replacing with a solar-ready model.
Pressure relief valves
NZ Building Code requirements call for over-temperature pressure relief valves on all solar water heating systems. If the current system lacks one, installation forms part of the upgrade.
Pipe runs and cylinder location
Pipe run length between collectors and the cylinder affects efficiency. Your plumber will assess the layout and advise on the best cylinder location.
Backup heating
A backup heating element is essential for low-solar periods. Your plumber will configure the system to maximise solar use while maintaining a reliable hot water supply.
Solar hot water cylinders offer a sound long-term investment for many New Zealand homes. The right system depends on your roof orientation, household demand, and whether you are connecting to a thermal or PV setup.
Your local GoFox plumber can assess your existing system, recommend the right solar hot water cylinder, and ensure the installation meets NZ Building Code requirements. Visit our hot water cylinders service page to find out what we cover.
For a full overview of our plumbing services, visit our plumbing services page. You can also follow us on Facebook and LinkedIn for practical home advice and updates from GoFox teams across New Zealand.
Frequently Asked Questions
Can I connect my hot water cylinder to solar power?
Yes. There are two main options: solar thermal systems that heat water directly using roof-mounted collectors, and solar PV systems that generate electricity to power an electric cylinder or heat pump. The right choice depends on your existing setup and household needs.
Do I need a special cylinder for solar hot water?
For solar thermal systems, yes. Solar hot water cylinders are designed with features such as a mid-tank backup element and, in some cases, an internal coil heat exchanger. A standard cylinder may not suit direct solar connection without modification.
What size cylinder do I need for solar hot water?
MBIE guidance recommends a larger capacity for solar thermal systems than for standard electric or gas setups. A 300L cylinder is common, as it stores more heat during periods of good solar gain.
Is a backup heating element required?
Yes. Solar gain varies with weather and seasons, so a backup element is essential to maintain a reliable hot water supply during low-solar periods.
Can GoFox help with solar hot water cylinder installation?
Yes. Your local GoFox plumber can assess your existing system, recommend the right cylinder, and carry out the installation to NZ Building Code requirements.
