10 Years later – My Solar Hot Water Review.
A decade ago, I invested in solar hot water technology, expecting to not only reduce my carbon footprint but also to save on my energy bills. Unfortunately, my experience has been fraught with problems and disappointments, including a hazardous and potentially life-threatening incident that prompted me to write this less-than-savory article.
Solar hot water systems come in various types, both active and passive:
- Active Solar Water Heating Systems: These systems use pumps and controllers to circulate water or heat-transfer fluids within the system. They come in two types:
- Direct circulation systems: Pumps circulate household water through the collectors and into the home. These systems are best in climates where it rarely freezes.
- Indirect circulation systems: Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are most commonly used in climates prone to freezing temperatures.
- Passive Solar Water Heating Systems: These systems do not use pumps or controllers, relying instead on natural convection. They are typically less efficient than active systems but can be more reliable and longer-lasting. They also come in two types:
- Integral collector-storage passive systems: Also known as batch systems, these work best in areas where temperatures rarely fall below freezing. They work well in households with significant daytime and evening hot-water needs.
- Thermosyphon systems: Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design due to the heavy storage tank.
In addition to these, pioneering companies are increasingly using solar hot water systems that use solar photovoltaic (PV) panels to generate electricity, which then heats a traditional electric water tank. Due to falling costs and improving efficiency of solar PV panels, this is where my focus will be for future builds.
In my case, I had two independent Indirect circulation systems, each comprising a hot water cylinder and a dedicated solar hot water panel. This design was aimed at providing redundancy should one system fail and allowed for a shorter distance to each bathroom, reducing heat loss between the panel, the hot water cylinder, and the bathroom faucets.
These systems basically operate by using temperature sensors to activate a pump, circulating the hot glycol and water mix through the solar collector panel and piping to the tank, which then runs through the hot water cylinder via an internal piped coil. The glycol and water mix running through this independent coil essentially acts as a heat exchanger / heating element in the water cylinder/tank.
Our investment in this technology did not deliver the expected return on investment; in fact, it wasn’t even close. Numerous hardware components failed and needed replacement before any significant savings were realised. Even one of the tanks failed within the first two years, necessitating a warranty replacement from the Auckland-based company. My second tank has also just failed necessitating a rethink about which system I use for replacement.
At the time of purchase, I had requested monitoring and data logging for my systems to gauge their efficiency and return on investment. When the systems started to fail, I scrutinised the data. An independent data monitoring company revealed that certain parameters had been coded into the system to make the results appear better than they were, including a set pump flow rate that inflated the efficiency results.
More alarmingly, the internal heating coil that circulates the hot glycol/water mix from the solar panel through the hot water cylinder rusted and leaked glycol into our water supply, tainting the water that came out of our taps and showers. Even in small amounts, glycol is extremely hazardous if consumed and can be lethal. This incident underscored my concern, and I believe there is a critical need for the industry to incorporate additional safety measures for such systems which are still sold today globally.
When I approached the Auckland-based company that supplied the system about these issues they promised to look into this concerning issue but never did.
In summary, my ten-year experience with solar hot water technology has highlighted the significant lack of consumer knowledge and supporting data to justify investment in this technology. The absence of reliable and independent data monitoring leads me to question the cost-effectiveness claims made by the industry. Furthermore, the potential hazards associated with the use of glycol based solar hot water systems are not sufficiently discussed.
The solar hot water industry needs to do more than just market the environmental benefits and potential cost savings of this technology. It must ensure the safety and efficacy of its products, especially for systems that use glycol. We need to make data monitoring the norm, we need more awareness of the efficiency of these systems from independent monitoring institutions, and I cannot take the highly marketed stats from vendors without question.
If you use an Indirect circulation system, then please check your water for any unusual colour changes and smell regularly, especially in systems that are over a few years old.
Being in the building industry for 35+ years now, I’ve heard some shocking stories about unethical companies taking advantage of consumers’ lack of knowledge, and renewable energy certainly hasn’t escaped my attention. However, I hasten to add that renewable energy is something I will continue to invest in, but next time, it will be solar PV coupled with efficient hot water cylinders and rigorous independent data monitoring.