Solar thermodynamic vs traditional solar hot water
Solar hot water has been around in New Zealand for decades. Most people picture rows of tubes or glass panels on the roof, filled with water. Solar thermodynamic systems look similar from the street, but they work in a very different way. Here's how the two compare.
How traditional solar hot water works
Traditional systems use flat-plate panels or evacuated tubes on the roof. Water (or a heat-transfer fluid) flows through them, the sun heats it, and the heat goes to your cylinder. When the sun isn't strong enough, on cloudy days, at night and through much of winter, an electric element or gas booster makes up the difference.
How solar thermodynamic works
A solar thermodynamic panel has no water in it. Instead, a refrigerant flows through the panel at about −28°C. Because the surrounding air is almost always warmer, the refrigerant picks up heat from the air, wind and rain as well as the sun. A small compressor then raises the temperature and transfers the heat into your cylinder. See how it works in more detail.
Side by side
| Traditional solar (flat plate or tubes) | Solar thermodynamic | |
|---|---|---|
| What's in the panel | Water or heat-transfer fluid | Refrigerant |
| Works at night | No | Yes |
| Works on cloudy days | Partly, with a booster | Yes |
| Backup heating needed | Yes, electric element or gas | Not normally needed (optional boost mode) |
| Panel weight | Heavy, especially when full | About 8kg |
| Where the panel can go | Roof, facing north | Roof, wall, balcony or ground, east to west |
| Freezing or overheating | Can be a risk | Not a risk |
| Works down to | Varies | −10°C |
Which is better for New Zealand?
New Zealand gets plenty of sunshine in summer, but winter days are short and often cloudy. That's exactly when you use the most hot water, and when a traditional system leans hardest on its booster. A solar thermodynamic system keeps working through those days, so you get steady savings all year round, not just in summer.
Traditional solar can still make sense in some situations, like a holiday home that's used mainly in summer. For most households, though, the year-round performance of solar thermodynamic gives better value.
Already have traditional solar panels?
If your old system is leaking, losing performance or needs a new cylinder, it may be time to upgrade. Replacing an existing water heater usually doesn't need a building consent. See our building consent guide.
Want to compare for your home? Contact us or call 03 540 3003 for a free estimate. See also our worked savings example and the Eco and EcoTop systems.