For a vast majority of commercial, industrial, health care and educational facilities, a significant portion – and oftentimes the largest portion – of their energy consumption is utilized for generating heat or hot water. Heat accounts for over half (51%) of global energy demand and is still generated primarily through the burning of fossil fuels. In pursuit of reaching net-zero carbon emissions for these facilities, the common default solution is to deploy photovoltaic (PV) solar panels to generate electricity. While this solution can be quite effective for a portion of the energy usage, when it comes to heating and hot water generation, renewable CHP is proving to be a more effective and efficient solution.
Solar thermal systems and PV systems used to heat water for domestic or industrial purposes have different efficiencies and operating principles. Here's a comparison of the two approaches:
Solar thermal efficiency for hot water: Solar thermal systems are designed specifically for capturing and utilizing solar energy to directly heat water. They typically consist of solar collectors (such as flat-plate collectors or evacuated tube collectors) and a system to transfer the captured heat to water. The efficiency of solar thermal systems can vary depending on several factors, including design, location and weather conditions. Here are some key points:
- Efficiency range: Solar thermal systems can achieve high thermal efficiency, often in the range of 50% to 70% or even higher. This means that they can convert a significant portion of the solar energy they capture into usable heat.
- Direct heat conversion: Solar thermal systems capture solar energy and convert it directly into heat energy, which is then used to heat water. This direct conversion process can be highly efficient because there are fewer energy conversion steps compared to PV systems.
- Thermal storage: Solar thermal systems can incorporate thermal storage tanks, allowing excess heat to be stored for later use, which can improve overall system efficiency.
PVs used to heat water through electricity: In this approach, PV panels are used to generate electricity, and that electricity is then used to heat water through resistive heating elements or heat pumps. Here are some key considerations:
- Efficiency losses: PV panels have an efficiency rate for converting sunlight into electricity that typically ranges from 15% to 20% for standard silicon-based panels. This means that not all the incoming solar energy is converted into electricity.
- Electricity-to-heat conversion: When using electricity to heat water, there are additional energy losses because of the conversion of electrical energy into heat. This process is not as efficient as direct solar thermal heating.
- Complexity: The use of electricity to heat water adds complexity to the system because it involves two energy conversion steps (solar to electricity and electricity to heat).
As with any energy solution, real-world applications are rarely one size fits all. A recent example of this is a system that ELM Solar deployed at Creighton University’s newest student housing facility, Graves Hall. The university had a plan to deploy traditional PV on the roof of the facility to help reduce its carbon footprint. Working with the university and its facility planners, ELM designed a system that replaced half of the PV with solar thermal collectors (VirtuHot from Naked Energy) paired with a solar thermal storage system that more than doubled the amount of renewable energy that was going to be produced from the PV alone – in the same footprint.
There is still a significant amount of PV solar panels installed at the site, but the energy produced from those panels is being used solely for electrical demands instead of to generate hot water.
As we continue our march toward net-zero emissions and zero-carbon footprints, it will take a broad arsenal of solutions to meet our growing energy demands. Renewable CHP systems can be a powerful weapon in this battle and their high efficiency, compact footprint and ability to integrate seamlessly with other existing energy solutions are proving they are up for the fight.