Use of solar energy to heat domestic hot water and radiant floors is soaring along with the cost of fossil fuels. New, more efficient heating technology, i.e. evacuated tube absorbers, makes solar even more desirable. Below is a description of the most commonly used methods of heating water with solar energy and the advantages and disadvantages of each.
Most people are somewhat familiar with the standard flat plate type solar collector. This collector is basically a highly insulated box containing a grid of copper pipes bonded to a flat black copper absorber plate. Special glass enhances solar absorption.
Evacuated tube collectors use multiple vacuum filled glass tubes, each with a tiny amount of antifreeze hermetically sealed within a small central copper pipe. When heated by the sun, this antifreeze converts to steam, rises to the top of the tube, transfers its heat to a collector header, then condenses back into liquid and repeats the process.
Because heat doesn't easily transfer through a vacuum, 92% of the thermal energy hitting the absorber plate stays within the evacuated tube and passes to the collector header. This is a huge advantage because a standard flat plate collector radiates much of its accumulated heat to the surrounding atmosphere like any other hot object.
The evacuated tubes are also completely modular. Although rarely necessary, one or more tubes can be removed and replaced without affecting the other tubes in the array. There is no actual liquid transferred from the evacuated tube to the collector header...just heat. Evacuated tubes also start absorbing heat earlier in the day than flat plates due to their convex design and the tiny amount of antifreeze within the tube is freeze protected down to -50 degrees below zero.
Source: Radiant floor company
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