How does solar thermodynamic hot water work, even at night?
Most people assume solar hot water only works when the sun is out. Solar thermodynamic systems are different: they keep heating your water on cloudy days, in the rain and at night. Here's how.
How it works, in four steps
- The panel collects heat. A refrigerant runs through a thin aluminium panel at about −28°C. Because the air around it is almost always warmer, the refrigerant absorbs heat from the air, rain and wind as well as the sun, and turns into a gas.
- A compressor raises the temperature. A small compressor at the cylinder squeezes the gas, which makes it much hotter.
- The heat moves into your water. The hot gas flows through a coil inside the cylinder and passes its heat to the water.
- The cycle repeats. As the gas cools it turns back into a liquid, returns to the panel and starts again.
The system keeps working unless the outside temperature drops below −10°C. See the full explanation on our How it works page.
How it compares
| Standard electric cylinder | Traditional solar (water) panels | Solar thermodynamic | |
|---|---|---|---|
| Works at night and on cloudy days | Yes | Needs backup heating | Yes |
| Electricity for hot water | All of it | Backup heating only | About 0.5 kWh per person per day |
| Panel | None | Heavy, water-filled | 8kg aluminium, no water |
| Risk of freezing or overheating | None | Yes | None |
What you need
- One panel for most homes. A family of four needs a 250L cylinder and one panel. A family of five needs 300L and one panel, and six or more need 300L and two panels.
- Flexible placement. The 2m × 800mm panel weighs just 8kg. It can go on a roof, wall, balcony or the ground, facing anywhere from east to west.
- Safe hot water. Water is heated to 55°C, and an automatic disinfect cycle protects against Legionella, meeting NZ Building Code clause G12.
- A long life. Expected life is at least 25 years, and some systems in Europe are over 35 years old.
Real homes, real results
In 2016, Nelson couple Jenny and Fraser Magee researched the hot water systems available in New Zealand for their new build. They chose a 250L Energie Eco system as the best way to cut their electricity use.
"I got a 1 panel 300L solar thermodynamic hot water cylinder installed. I'm enjoying the cost savings on my electricity bill and happy that it's a sound environmental choice." Diane, Google review
For bigger projects, see how our systems heat Rongotea's community pool and keep Cardrona's wastewater plant running through alpine winters.
Further reading
- Irish Examiner: the technology behind thermodynamic panels, on how the system copes with a wet, overcast climate
Want to know what it could save you? See our worked savings example, browse the Eco and EcoTop systems, watch our videos, or contact us on 03 540 3003 for a free estimate.