Residential uses of thermal solar panels

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Solar Panels Types and their Residential Uses

When choosing the solar panels type for your home, take into account….

- the types of thermal panels: 1) Solar unglazed panels, 2) Solar flat-glazed panels and 3) Solar evacuated tubes panels (and eventually in some very special cases concentrating panels…)

- the uses intended for the residential solar panels: 1) swimming pools heating 2) solar water heating (including their uses in radiators, radiant floor or in other heating system) 3) solar space heating and 4) solar air conditioning

- the price of the different types of panels

- the temperatures demanded by the applications and the temperatures offered by the different type of panels

- the climate issue

We develop these topics below.

Best solar panel: the price issue

It doesn’t exist a best type of solar panel. The best depends much on climate and on the type of the intended residential solar applications, and is also closely related with the price issue.

As we pass from 1) unglazed solar panels to 2) glazed solar panels and on to 3) evacuated tubes panels the prices increase. We can use evacuated tube solar panels in swimming pools heating, but it would be too expensive. Evacuated tubes panels are more efficient (30% or so) than unglazed panels but these last collectors are much cheaper (1/5 – 1/10 of the cost of evacuated panels), and with some extra unglazed surface we can reach the same effectiveness of evacuated tub panels.

Similarly, we can also use evacuated tube panels in domestic water heating, but in most cases the difference of efficiency doesn’t justify the difference of price. Flat-glazed panels usually present a better relation efficiency/price in spite of recent developments in evacuated tube panels technology and correlated increases of competitiveness.

Best solar panel: the temperature demanded by the application

Different residential applications demand different temperatures from the solar panels, which explain that each type of panel dominates a particular range of applications:

- unglazed pool collectors dominate in low temperature applications (0-25 °F/0-14ºC above ambient temperatures),
- flat plates panels dominate in the mid-range temperature applications (25-125 °F /14- 50ºC above ambient temperatures)
- evacuated tubes panels dominate at upper temperatures (125+ °F / 50+ ºC above ambient temperatures).

The reason of these needs is rather obvious: whereas panels on most pools operate within 10-20 °F above ambient temperatures, residential solar panels for water heating, for instance, operate in a wide range of temperatures above ambient in close connection with season, climate and the particular applications. That’s why in the first case unglazed solar panels are perfectly suitable, but not in the last case, where it is needed a flat glazed solar panel or even an evacuated tube panel…

Climate Impact on Solar Panels Performance

Climate – expressed by solar irradiance, that is, the amount of sunshine received on the collector – is an important factor for determining the most suitable solar panel.

The basic rule is: the lower the amount of sun, the greater the advantage of flat-glazed over flat-unglazed and of evacuated tube over flat-glazed and unglazed panels.

In climates with many sunny days, glazed flat panels may outperform evacuated tubes in many residential applications. They are cheaper and in average and they have a better relation performance/price.

In other words: while some applications in cold climates demand evacuated tube panels (capable of generate higher temperatures), these same application in mild and hot climates may only demand flat-glazed panels or even unglazed panels.

Anyway the results vary according with the particularities of local climates (namely with the number of cold and cloudy days) and in the future with the variations on the prices of the solar panels. Evacuated tube panels are becoming cheaper, and begin to gain some of the segments of the market previously occupied by the flat-plate panels.

Summary on the residential uses of the different types of thermal solar panels

Since choice depends greatly on 1) prices, 2) temperatures and the 3) climate and uses intended for the solar panels, it is possible to draw some rough conclusions about the most suitable solar panels for the several solar applications:

Solar Unglazed panels

They are used in swimming pools and simple house space heating (solar air heater panels with no heat storage, designed just to heat a room or a small part of the house). Unglazed panels are used in solar applications demanding low temperatures. They have a wider range of particular applications in sunny climates, where they can substitute more expensive panels.

Image credit: EERE

Solar Air-Flat glazed panels

They are mainly used in solar space heating, and may be tied to forced air systems. They have some advantages over solar liquid-flat panels (they produce heat earlier and later in the day than liquid systems, they do not freeze and the consequences of eventual leaks are minimal) but they are also less efficient than liquid collectors, and aren’t as flexible in their applications.

Solar Liquid-flat glazed panels

These panels can be used in solar domestic water heating systems and for central heating (integrated in systems involving forced air systems, radiators or radiant heating). They are a flexible, tested and competitive option.

Evacuated tube panels

They share most of the applications of flat glazed panels, mainly the more demanding applications (those that demand higher temperatures); they are the most powerful solution for more demanding applications: solar cooling, demanding radiant heating systems. They aren’t as common as solar flat glazed panels, but their presence are increasing in cold and cloudy climates, due to their higher average performance. A possible scenario is an increasing use of evacuated tube panels technology in cold and cloudy climates, while flat panels technology will maintain or even increase its importance in sunnier climates.

Solar Electric panels

The production of solar electricity demand a special type of collectors: the PV solar panels. See Solar Electricity: Photovoltaic PV Systems