Vacuum Tubes -vs- Flatplate Solar Panels

Both systems have their fans. There are pros and cons for both systems;

A flatplate collector consists of a large metal plate with water tubes running through it, placed inside a box with glass on top of the plate and insulation underneath it. Sunlight passes through the glass, heating the water inside the tubes, and this water is plumbed back to a coil in your hot water cylinder.

There are various types of vacuum tube, but ours is effectively a thermos flask made up of two layers of glass with a vacuum between the layers. Because there are so few air molecules in the vacuum, there is virtually no heat loss between the two glass layers, so it is far better insulated than a flatplate, which loses heat through the glazing. Heat is transferred to the cylinder via a heat pipe. Read more here..

Performance

The important point to know here is that both flat plate and vacuum tube systems systems can be designed to produce the same amount of energy regardless of efficiency. It is the surface area of the solar panel array which determines the amount of energy produced. A vacuum tube system taking up 3m2 on your roof may look more efficient on paper but will not be able to produce more energy than 4m2 of good quality flat plate panel – always check the energy yield of the system not the efficiency of the panel.

Summer v Winter yield

One of the the main differences between flat plate panels and vacuum tube panels is when the energy is delivered. On a hot sunny summers day, flatplates will out-perform vacuum tubes of the same total area. However, it could be argued that on hot sunny days, either sytem will provide plenty of hot water. On cloudy cold, windy days, a vacuum flask will outperform a flatplate like for like. Thus vacuum flasks can be useful if you want to extend the effective season over which the panel operates. e.g. A vacuum tube system will give you more heat in the late Autumn and Winter than a similarly sized flat plate solar panel system. But remember the size of the solar array determines the amount of energy produced so a bigger flat plate array can produce more solar energy than a small vacuum tube array in Winter as well.

Aesthetics

It’s obviouly subjective but from years of selling panels our opinion is that flat plate solar panels are generally considered to be the better looking option and can even be integrated into a roof in quite a neat and attractive way. Vacuum tube solar panels are often considered to be the less attractive option but beauty is in the eye of the beholder..

Ease of Installation

Flatplates that are integrated into the roof like a velux window are the most difficult to install into an existing house but on a new house this is a relatively simple operation because they can be installed as the roof is being slated or tiled. Vacuum tubes and on roof flat plate panels are always fitted on top of slates or tiles, so are easier to retrofit.

Vacuum tube panels are usually the easiest option to fit on a roof due to the modular aspect of the panel meaing it can be lifted on to the roof in stages. Flatplates are usually a lot heavier to lift into place, and this can be a hazardous operation for DIY enthusiasts. Again on a new house, especially in a housing development, lifting gear will normally be available and this should be used. NEVER install a flatplate by lifting it up two ladders as is common practice

Durability and cost of replacement

Flatplates are usually made with toughened glass and our panels have a reasonable life expectancy of 35 years.

Vacuum tube panels will operate for 15 – 20 years on average. Vacuum flasks are made of lighter glass and are quite tough having being tested to withstand hail storms etc.. but they will break if hit hard enough. In the event of this happening, the panel will continue to function on its other tubes, and it is a relatively simple operation to replace the broken flask. Cost should be considered here as well with replacement ecologics flasks costing between €6 and €10 each. However to replace single walled vacuum tubes favoured by other companies can cost over €100 per tube.

Cost

Vacuum flasks used to be a lot more expensive. Often, Chinese made panels were re-badged and sold at inflated prices (virtually all flask systems are manufactured in China..). However, prices of flask systems have come down dramatically and both systems are about the same price generally.