If you’re trying to incorporate more solar technology into your life and a solar power system is beyond your budget, you may want to consider investing in a solar hot water heater.
After all, heating water is the second largest energy consumer in American households.
A solar hot water heater can help reduce your water heating bills by 50-80% (source), and can usually be integrated into your existing conventional hot water system.
The pros and cons of solar hot water
The pros and cons of solar hot water heaters are no different than any other solar technology.
- takes advantage of a clean renewable resource
- reduces carbon emissions and lessens dependency on fossil fuels
- saves money over the long term
- smaller initial investment than solar energy system, but still eligible for tax incentives and rebates
- minimal costs once the system is installed
- particularly useful in areas that are not plugged into conventional utility grids
- initial costs can be high, despite government incentives to help offset this investment
- require some form of back-up for when there isn’t sufficient quality light
- some may consider the infrastructure associated with solar systems to be unsightly
- only makes an impact on a portion of your energy bill
Components of solar hot water heaters
There are essentially five components to solar water heaters. I’ll do my best to explain each component and give a summary of the most common types along with their pros and cons.
1. Collectors – this is where the solar energy is collected and heat is transferred to fluid-filled pipes.
- Flat plate design: The most common type of collector is a flat plate design. Inside a glass-covered box, there are two horizontal pipes at the top and bottom, called the headers. Running between the headers are vertical pipes called risers. Cold fluid enters the bottom header and as the sun’s rays heat it up, the fluid expands and naturally moves up the risers. The hot fluid exits the collector out the top header. The advantage to flat plate design collectors is that they are very durable. The glass used to cover the collectors can withstand hail and other environmental bombardments. However, the disadvantage is that there is passive heat loss into the environment.
- Evacuated tube collectors: This is the other common type of collector. Essentially, pipes are surrounded by a vacuum created between two concentric tubes. Heat doesn’t transfer across the vacuum, which eliminates the biggest problem with the flat plate design. However, the vacuum may only have a life of 5-15 years and they are more susceptible to breakage due to hail etc.
2. Circulation system – the next component of the solar hot water system is called the circulation system. This is the fluid that runs between the collectors and the storage tank.
- Direct or open-loop system: This style circulates the potable water itself through the circulation system. In other words, you are circulating the water you will be using between the collectors and the storage tank. Though these are cheaper systems, there are no mechanisms for preventing overheating or freezing of the system. In cold climates, the collector pipes have to be drained and the solar system can’t be used during freezing temperatures. As well, if you have hard water, scale can accumulate in the collectors.
- Indirect or closed-loop system: Instead of circulating the potable water, a heat transfer fluid (usually propylene glycol) is used. Heat is transferred from the heat transfer fluid to the potable water using a heat exchanger. This system is more expensive, but it means that antifreeze can be added to the propylene glycol, enabling the system to be operated in cold temperatures.
3. Storage tank– the storage tank is where the hot water is stored just as in a conventional system. It is highly insulated to reduce heat loss and if there is a heat exchanger, it is incorporated into this tank.
This may be the only storage tank for the whole house, or it may be in addition to an existing conventional tank that it feeds into as seen in the system demonstrated in this video.
The other option for the storage tank is where to mount it.
- Passive system: If the storage tank is mounted horizontally on the roof, above the solar collectors, no pump is required to fill the tank as the hot water naturally rises. These types of systems are very economical and extremely low maintenance, however, with the tank on the roof, overheating and freezing can be a concern.
- Active or pump-circulated system: This style enables the tank to be placed below the collectors as a pump is used to actively circulate the water or heat transfer liquid. These systems are more expensive, but allow more freedom with design in where the tank is placed. Also, with the tank inside or at least off the roof, there is less chance of overheating or freezing.
4. Back-up heating system – if you want consistent hot water, you will need a back-up heating system. A solar hot water system that is in addition to a conventional system will reduce the amount of energy required to heat the water in your storage tank. However, if the temperature drops in the tank and there is insufficient solar energy to heat it, the electricity (or gas) will kick in to heat up the water.
5. Control panel – The system needs to have a control mechanism. The objective of this mechanism is to maximize the heat gained from the solar collectors. The control panel has a sensor that measures the difference in temperature between the fluid leaving the collector and the water in the storage tank. When the temperature of the water in the tank is about 8-10 degrees less than the fluid leaving the collector, the control planel switches the pump on to drive colder water from the tank up into the collectors. When this temperature difference drops to within 3-5 degrees, the pump is switched off.
A global perspective on solar hot water heaters
Other countries have adopted solar hot water heaters with enthusiasm. Israel was the first counwhy the installation of solar water heating systems when they passed a law in 1980. Spain was the second country to follow suit, but not until 2006. In 2007, China was the global leader in new solar hot water installations. In less developed countries, simple passive, direct-loop solar water heaters have improved quality of life substantially, enabling households to have easily accessible hot water at no cost.
Solar water heaters are not as popular in the US compared with countries like Spain, Israel and China. However, a solar hot water heater has incredible efficiency for a relatively small investment (as little as $1,500), which makes them one of the most accessible alternative energy options for your household.