Pourquoi les collecteurs solaires à tubes sous vide sont-ils parmi les plus efficaces dans les climats nordiques ?

Introduction

Le chauffage des locaux et de l'eau chaude sanitaire représente entre 66 et 75 % de la facture d'électricité d'une maison canadienne typique. À l'exception de la région de Vancouver, la plupart des maisons et des entreprises canadiennes ne sont pas habitables sans un système de chauffage adéquat. Trouver un système de chauffage fiable et efficace (pourquoi pas gratuit) et abordable pour le chauffage des bâtiments devient une nécessité avec le changement climatique, l'augmentation des prix de l'énergie conventionnelle et des codes de construction plus exigeants.

La pandémie de Covid-19 a mis en évidence les risques liés à la mondialisation et à la connectivité mondiale. La vitesse à laquelle le virus s'est propagé au Canada et aux États-Unis a perturbé la circulation des biens et des services entre les pays. Cette perturbation de la chaîne d'approvisionnement mondiale a eu un impact sur la vie de chaque personne en Amérique du Nord et a créé un mouvement d'autodurabilité et d'indépendance par rapport à toute perturbation future de la chaîne d'approvisionnement mondiale. Le code de la construction canadien exigera qu'après 2025, toutes les nouvelles maisons au Canada soient prêtes pour le Net Zero. D'ici 2030, toutes les nouvelles maisons au Canada devront être nettes zéro.

Cela signifie que, dans un avenir proche, chaque ménage devra être prêt à produire (en partie ou en totalité) sa propre énergie (solaire, éolienne, géothermique, etc.) et de l'alimentation (légumes, fruits, etc.) localement afin de survivre à l'ère pré-Covidus-19.

Pourquoi le solaire thermique et non le solaire photovoltaïque ? Pourquoi un chauffage solaire de l'eau et non un chauffage solaire de l'air ?

La technologie des panneaux solaires photovoltaïques (PV) est idéale pour fournir de l'électricité gratuite pour les prises de courant, l'éclairage ainsi que l'électricité pour les réfrigérateurs et autres appareils. Cependant, l'efficacité énergétique annuelle des panneaux photovoltaïques au Canada est inférieure à celle des autres technologies solaires (such as Capteurs solaires à tubes sous vide). Dans la plupart des installations canadiennes, les panneaux photovoltaïques sont installés à un angle d'inclinaison de 30 degrés par rapport à l'horizontale. Ils sont donc recouverts de neige presque 4 mois par an, ce qui limite leur efficacité énergétique annuelle à environ 15-17%.

Compared to PV Panels, Tubes à vide Capteurs solaires have 2 to 3 times the annual efficiency of PV panels, requiring 2 to 3 times less roof space. Also Vacuum Tube Collectors have empty space between tubes and are installed at a steeper tilt angle (45 to 70 degree). This makes snow less likely to accumulate on them, which increases their heat output in winter (When Heat is needed the most).

Solar Air Heating is also a promising Technology. In Residential and Light Commercial Applications where space heating is forced air, Hot Air is only required in winter, which leaves the solar air heating panels useless in summer time. Compared to Solar Hydronic Heating, Hot water demand is 12 month a year and 24 hours a day. In winter, Hot Water is required for Domestic Hot Water Heating and/or Space Heating and in summer for Pool/SPA Heating as well as Domestic Hot Water Heating (there are other advantages of using hydronic heating versus forced air heating, This Blog details them all)

En excluant la chaleur inutilisée générée par les panneaux solaires de chauffage de l'air, les capteurs solaires à tubes sous vide deviennent le moyen le plus prometteur de produire de la chaleur hydronique pour notre climat canadien.

Kit collecteur solaire à tubes sous vide, certifié SRCC, SÉRIE VT58 - Complet avec collecteur, cadre, tubes et kit de cadre 45⁰.

$ 1,132.57 CAD

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Kit collecteur solaire à tubes sous vide, certifié SRCC, SÉRIE VT58 - Complet avec collecteur, cadre, tubes et kit de cadre 30⁰.

$ 1,132.57 CAD

Ajouter au panier

Chauffage solaire de l'eau Capteurs solaires

Measuring Solar Collector's thermal efficiency is a complicated and expensive task. This why the Solar Rating and Certification Corporation (SRCC) and the Canadian Standard Association (CSA-F378) have accredited various labs in the US and Canada to provide more accurate, consistent and standardized efficiency values.

What defines collector's thermal efficiency and thermal energy outputs are the following factors:

Ti : Collector's entering fluid temperature in ⁰F or ⁰C.
Ta : Ambient Dry Bulb temperature in ⁰F or ⁰C.
I or G: Insolation Rate expressed in Watts/m² or Btu/hr.ft².
Type of Collector: Flat Plate (Glazed and unglazed), Evacuated Tubes, etc...
Collectors' thermal efficiency (Which is no more than the ratio of thermal energy output divided by solar insolation) is then drawn as function of (Ti - Ta)/I (or G) 

Comme le montre le graphique ci-dessus :

Solar Collector's thermal performance decreases when Ti (entering fluid temperature) is higher and/or Ta (ambient temperature) is lower.
Solar Collector's thermal performance increases when Ti (entering fluid temperature) is lower and/or Ta (ambient temperature) is higher.
Ainsi, dans les climats plus chauds, où (Ti-Ta) est faible, les collecteurs les plus performants sont ceux dont la courbe de performance est plus inclinée et dans les climats plus froids (comme au Canada et au nord des États-Unis), les collecteurs les plus performants sont ceux dont la courbe de performance est plus plate.

HOW DO VARIOUS HYDRONIC SOLAR COLLECTORS PERFORM? 

La ligne bleue reflects unglazed solar panel performance. They offer the steepest (Highest Y intercept value) curve, meaning they perform very well the entering fluid temperature is low and ambient air temperature is high (warm air). The steep slope shows that decreasing air temperature (or increasing entering fluid temperature) take a big toll on performance. This type of solar collector is great for heating pools in the summer because pool temperatures are usually fairly close to daytime air temperatures in the summer when pool use occurs (Ti-Ta is at its minimum, and efficiency is at its max).

La ligne rouge reflects glazed flat plate solar panel performance. They offer slightly lower Y intercept values because the glass coating reflects some light, but the efficiency slope is flatter than unglazed panels because the glazed panels have insulation inside and trap the absorber's heat inside the collector's box. as a result the panel looses less heat when outdoor air is cooler.

Les lignes vertes represent evacuated tube performance. These collectors offer lower Y intercept values and their slope is even flatter that glazed panels. On sunny hot days, they don't perform as well as flat plates, but the excellent vacuum insulation makes them more efficient that flat plates when it's very cold outside or sun is weak (low insolation values). This flatter slope also means that evacuated tubes are more appropriate for projects requiring high fluid temperatures in colder climates such as space and process water heating.

Lectures complémentaires :

• How do Vacuum Tubes Solar Collectors Work?
• Comment fonctionne le chauffage solaire thermique hydronique ?
• Decarbonization by Producing Medium Temperature Hot Water with Vacuum Tube Solar Collectors
• How to install a Solar Panel on an inclined roof?
• How to lengthen the lifespan of Vertical Geothermal Well with Evacuated Tube Solar Collectors in Nordic Climates?

WHAT IS THE USEFUL COLLECTOR'S THERMAL EFFICIENCY? 

Having free hot water from your solar panels is fun but to payback your investment (the cost of panels, storage tank, piping, control, etc...) you need to make use of the generated heat. Living in Canada or the Northerm part of the US and having a lot of hot water in July and August in excess of your domestic hot water demand is simply a waste.A solar generated unused heat, is a wasted heat that don't count in your installation annual efficiency and savings, because that wasted heat do not offset any KWh from your utility bill.

L'intersection entre les lignes de performance verte et rouge de la figure 2 se situe à (Ti-Ta)/G=0,4. En supposant que nous nous trouvions à Montréal (Québec) où :

Température extérieure is at -30⁰ C and our Solar Panels are used for space heating where the heating loop is heated from 104 ⁰F (Ti=104 ⁰F=40⁰C) to 120 ⁰F. In half sunny half cloudy day with G=500 W/m². = 158 Btu/hr.ft² (Ti-Ta)/G= (104+20)/158=0.78 way on the right of the intersection point. This gives us a thermal efficiency of 0.35 or 35% for vacuum tube collectors versus a 0.1 or 10% efficiency for glazed flat plate collector.

Température extérieure is at 0⁰C and our Solar Panels are used for space heating where the heating loop is heated from 104 ⁰F (Ti=104 ⁰F=40⁰C) to 120 ⁰F. In half sunny half cloudy day with G=500 W/m². = 158 Btu/hr.ft² (Ti-Ta)/G= (104-32)/158=0.45 way on the right of the intersection point. This gives us a thermal efficiency of 0.4 or 40% for both types of collectors.

For températures extérieures above 0⁰ C, Flat Plate solar collectors are more efficient but heating demand is much lower than in extreme winter conditions. Higher Thermal efficiency at mid-winter season generate more energy than needed, thus increasing the volume of wasted energy.
In the city of Montreal we have 121 110 Heating Hours for outdoor temperatures below 0⁰ C (where heating demand is high to medium) and 54 385 Heating Hours for outdoor temperatures above 0⁰ C (where heating demand is moderate to low).

Running Polysun Solar simulation and comparing our Capteurs solaires à tubes sous vide HydroSol VT58 (2 x 30 Tubes Collectors) to a Glazed Flat Plate solar collectors (having a Y intercept of 0.792, slope of -7.517 W/m².⁰C and same Gross Area) and after putting the monthly Generated KWh and the Building Monthly Heating Demand into a graph, we get the following result:

As we can see in the above graph:

• Between the months of May and September, Glazed Flat Plate Collectors generate much more energy than Vacuum tubes Collectors, exceeding Building Hot Water demand. Generated Hot Water in Excess of demand is not counted toward annual Collectors' thermal efficiency.  
• Between the months of October and end of April, Glazed Flat Plate Collectors generate much less energy than Vacuum tubes Collectors in a scale far below Building Hot Water demand.  

Because Vacuum Tube Solar Collectors energy production is more aligned with demand presence, they do cover a larger % of montly and annual heating demand. This means that in this case Vacuum Tubes Solar Collectors are (91.3 - 66.8)=24.5% more efficient than Glazed Flat Plate.