One of the most cost-effective ways of using solar power is to buy or build a solar water heater. How they work is simple: the sun heats solar collectors which then heat your water. Solar hot water systems vary greatly in cost, design, and complexity. The simplest is a batch solar water heater. This type of solar water heater can be a DIY project that is both practical to build and useful once you’ve built it. This is only one of many possible systems, the building of some of which is much more complicated and expensive.
Solar hot water heaters are growing rapidly in popularity in the USA, but also in many other places around the world. The country with the largest number of solar water heaters is China, and the numbers there are rising explosively. Solar hot water is popular in China for a very practical reason – it is much cheaper in many areas than paying for the electric utility to heat the water. Payback time there can be measured in months. Solar hot water is also very popular in Israel.
Solar hot water is not only useful in warm climates. It is also used in places such as Germany and Canada, even in winter. However, in climates like these that have freezing temperatures special systems that use ethylene glycol in the collectors are needed if the system is to be used in the winter.
Solar hot water should be used more widely, and fortunately, that is rapidly becoming the case.
Solar hot water benefits over photovoltaics:
-much cheaper to buy than photovoltaic systems
–payback time is much shorter
-easier to DIY
-most types use only renewable resources
-won’t go out if there is a power outage at the electric utility
Most solar hot water heaters do not use electricity and involve no rare earth metals, although some do use large amounts of copper pipe. This is part of why they are cheaper than many other home-scale renewable energy systems. Because passive solar hot water systems involve no electricity, they are both easier and safer to build yourself than solar photovoltaics. They are also cheaper to buy. This means that the time it will take for you to make your money back is much shorter than with photovoltaic systems.
Downsides of solar hot water systems:
-a rooftop system requires a roof of sufficient strength. Water weighs 1kg/L.
-some systems do not work in freezing weather
-hot water is more available at night than in the morning
-system you build needs to be large enough for your hot water use
-produces hot water only, no electricity
Rooftop strength is important because the collectors contain either water or another liquid, and this is heavy. Most roofs in the USA were not designed with solar hot water systems in mind, and some of them aren’t strong enough. So you should check this out before going ahead and buying or building a solar hot water heater to place on the roof. Fortunately, some systems such as batch heaters can be placed on the ground and work fine, not to mention being easier to install at ground level.
Water freezes, and frozen solar water heaters a) won’t give you any hot water, and b) are in danger of being damaged. The pipes are the most vulnerable part. There are two ways to deal with this if this is an issue in your area a) have a three-season system that you drain in the winter, or b) get a system designed for below-zero temperatures. These systems are usually closed-loop systems using ethylene glycol, which means that the liquid in the collectors doesn’t mix with the water being heated. Ethylene glycol is used because it has a lower freezing point than water.
Solar hot water heaters will still function in the winter provided that they don’t freeze, but won’t give as much heat, especially in cold, cloudy weather. You might want a tankless hot water heater for backup if your winters tend to be cloudy as well as cold.