A solar water heater is a system that collects solar energy from the sun and uses it to heat water to high temperatures for use in homes, industries, hospitals, hotels, swimming pools etc.
The system is composed of various parts:
Hot water cylinder
Control panel (optional in some systems)
Circulation pumps (for some systems)
The difference between flat plate and evacuated tube systems is the solar collector panels on the roof whereby the flat plate system uses a flat plate while the evacuated tube system uses vacuum tubes. Please note we have various types of vacuum tubes but that is for another day.
Let’s get to it.
Which one is the right option for you?
A longstanding argument exists between proponents of these two technologies but we will go straight to the technical comparison and let you have an informed choice:
The main advantage for evacuated tubes is its low heat loss at high temperatures relative to ambient temperature. This is due to the insulation properties of the vacuum between the inner and outer tubes of the collector.
The argument over which type of collector is easier to install is subjective. Both collectors have their advantages and drawbacks in terms of installation. Proponents of evacuated tube argue that because they come unassembled, one person can easily carry the evacuated tube components onto the roof without needing any special equipment. Proponents of flat plate argue that because they are fully assembled, once hoisted onto the roof, no assembly is required thus greatly reducing installation time.
Which type of collector is easier to install is therefore based on the installer’s personal preference. As you think about it, think of situations where you have a flat roof many stories above ground and you want to use a lift or small passages especially in an existing facility to carry the system for installation on the mentioned roof. In general, you can say flat plate collectors take more effort to hoist onto the roof while Vacuum tube collectors take more time to assemble.
Nearly all evacuated tube and flat plate collectors sold carry a 10 year limited warranty and both types
of collectors are designed to last 20 years or more. However, evacuated tubes are more prone to damage especially given that a quality flat plate collector will use thick (usually 4 millimeters), tempered glass which can take quite a beating under harsh weather conditions such as hail storms. Evacuated tubes use thinner glass (usually 1.6 millimeters) which is more susceptible to breaking and needing to be replaced.
The main drawback of flat plate is that if something does break (such as the glass), the installer will usually need to replace the entire collector. Though evacuated tube collectors are more prone to breaking, the tubes can be replaced individually without having to replace the entire collector. The modularity of evacuated tubes can be advantageous in terms of extensibility and maintenance, for example if the vacuum in one tube diminishes.
Flat-plate collectors usually lose more heat to the environment than evacuated tubes, as an increasing function of temperature. They are inappropriate for high temperature applications such as process steam production. Evacuated tube collectors have a lower absorber plate area to gross area ratio (typically 60–80% of gross area) compared to flat plates. Based on absorber plate area, most evacuated tube systems are more efficient per square meter than equivalent flat plate systems. This makes them suitable where roof space is limiting, for example where the number of occupants of a building is higher than the number of square metres of suitable and available roof space.
In general, per installed square metre, evacuated tubes deliver marginally more energy when the ambient temperature is low (e.g. during winter) or when the sky is overcast. When employed in arrays and considered instead on a per square metre basis, the efficient but costly evacuated tube collectors can have a net benefit in winter and summer. They are well-suited to cold ambient temperatures and work well in situations of consistently low sunshine, providing heat more consistently than flat plate collectors per square metre.
There you have it. Make you choice.