There are two main types of Solar Water Heater Panels, the flat plate solar collector and the evacuated tube solar panels, so let’s look at the difference and a few pros and cons for each.

1. Evacuated Tube Solar Panels

Evacuated tube solar panel

This system is powered by a series of glass vacuum tubes that heat a fluid filled copper core. This then heats the water which passes through the top manifold. The heat generated in the copper core is considerable and it is claimed that one of the advantages of this system is that being a round tube it can track the sun. The inside of the vacuum tube is coated with a black layer to assist with solar absorption. The glass is a tough borosilicate glass and will withstand hail, but if one does get broken it is simple and cheap to replace. You only need to replace the broken tubes not the whole lot and there is no need to disconnect water. The system also keeps working well even if a few tubes are broken and your waiting for replacements to arrive.

Evacuated Tube

2. Flat Plate Solar Collector

Flat Plate Solar Collector

These are the large flat solar hot water panels you often see on house roofs, sometimes with a hotwater tank mounted above the panels. These panels are a glass covered box with a series of tubes made into a flat plate inside, through which water or a heat transfer fluid passes. The plate assembly is normally black to absorb more solar radiation. Some brands use a special coating called ‘Tinox’ which is a German developed solar absorption film which increases the solar heat gain. This film also absorbs infrared spectrum heat so works well on cloudy days. Flat plate solar collectors need to be kept clean to work efficiently and if damaged by hail, will either require the glass to be replaced or the whole panel, depending on how severe the damage is.

Flat Plate Solar Panel Tubes

Cold Climates:
Freeze damage used to be a concern when using solar water heating, this is where the water in the panels freezes at night and bursts the tubes in the solar panel, rendering the system useless. All modern systems now employ a heat transfer system for cold climates. This is where a fluid like glycol, that doesn’t freeze, is used to transfer the heat from the solar panel to a heat exchanger in the hot water tank. It is a ‘closed loop’ system so there is no chance of potable water contamination.

Mounting Solar Panels:
Solar panels can be mounted virtually anywhere, on a roof, a wall or on the ground, the only critical consideration is direction; they need to face South and not be shaded by buildings or trees. Your intention is to get as much sun as possible onto the panels for as much of the day as possible. If you are thinking about a combined tank and panel system for the roof, remember, your roof structure will need strengthening to take the weight of the tank which could be 700 lbs or more depending on the size. This will be a major extra cost, I personally prefer split systems with the tank on the ground, easier and cheaper to install and maintain.

Back-up Heating Sources:

Solar Hot Water Heating system with Boiler backup

So you want to use solar water heater panels but get a lot of cloudy days, no problems… all solar hot water systems can have a back-up heating system. These can be gas, propane, electricity or your space heating boiler, the trick is when to turn on the backup system. Probably the best way of describing how this can be done it to describe my own system.

I have a 30 tube evacuated tube solar panel with electric backup, the electricity is on a timer that cuts in around 4pm in the afternoon. The principal is simple, we have showers in the evening so the tank is full of mainly cold water in the morning, it then uses solar heat through the day to heat this water, but if we miss out on sunlight, then the electric heater cuts in when the sun is going down. This way I get the solar heating first and the backup heating is only used to top-up if the water isn’t hot enough. The trick to maximising solar heating is starting the day with a tank full of cold water.

This timing principal can be applied to gas as well, though boiler heating might be a bit trickier to set up, so ask your plumber about how to do it.

System Efficiency:
There are a lot of claims made by sales people about the efficiency of different systems and they can all sound very plausible. Don’t believe a word, there is not a lot to pick between any of the systems, and anyone claiming 90% efficiency is talking BS! A Swiss organisation tested a wide variety of system and found that many performance claims did not hold up and most systems provided similar performance efficiencies.

OK so the chioce is yours, hopefully this has given you a broader background an each of the main systems commonly in use around the world, yes I chose evacuated tube solar water heater panels, but that is not because the other system has problems, they don’t, each has its advantages and dissadvantages, all if installed correctly, work well and save you a heap on energy costs!

Solar Hot Water heating system picture courtesy of : http://www.imaginationsolar.com/