Sun & Wind Energy 1/201548

Solar thermal ecoDeSign

An energylabel for solar collectors?As of 2015 the heating sector will flood the market

with efficiency labels for energy-related products

(ErP). Solar collectors are not going to be labelled –

or are they? This is a guest article by Stefan

Abrecht.

Modern heating technology with boilers and heat pumps already achieve at least a class A product label for room heating. The dele-

gated regulations (EU) No. 811/2013 and No. 812/2013 do not explicitly plan in efficiency classes for solar collectors; they are merely considered in so-called packages. Anyone asking the large heating manu facturers about solar thermal for a single- family house is going to be disappointed. This is because although you can already get an A+ package label rating for 2 to 4 m² of collector area in combination with a condensing boiler for room heating, more than this is hardly on offer. Even worse is the fact, that accord ing to the updated guidelines of the EU the label step A+ could be reached with a boiler in pack-age combination with a smart control only. This is thus preventing the use of larger solar systems which could be used for partial solar heating. It cannot be excluded that a further market decline will result from this.

ErP – renewables sidelined?

In explanation it is said that the energy label was only intended for units using primary energy sources. It is thanks to the solar associations that solar thermal is included at all in the directive. But there will soon also be a label for biomass boilers. It would then make sense to look at the amount of primary energy which is required in relationship to the useable energy delivered and not the other way round, as has been the case so far with the energy classes. Solar collectors can show here that they have very low running costs compared to other heat generators.

The situation in the sector

For room heating, solar heating available only in a mini-package and under the direction of conventional heat generators can merely make a small contribution to improve a label from A to A+, for example. Suppliers

Fig. 1: Primary energy con­sumption against useful energy Source: Solar-Experience GmbH

Photo: Solarbayer

Solar Edition 49

without a boiler in their portfolio do not have a system label and generally have to classify a solar storage in category C if it has a volume under 500 l, which can-not be explained to a customer. The large manufactur-ers will be most likely to benefit from this as they can supply everything from one source. But even the full-range manufacturers with their diverse product port-folios will have problems with price- conscious, quality-conscious and high-end customers if the col-lector types for the relevant fields and brands are not distinguished from one another even in the system labelling. A demarcation through a dedicated collec-tor energy output label can help matters here. Additional difficulties arise for boiler manufacturers through the competition with heat pumps, which can achieve an A+ rating for room heating with its product label only and without any solar system at all.

True solar specialists, for whom the collector is the main heat generator with over 50 % of coverage, are completely out of the race. Although new solar homes with large collector areas and a very large storage are becoming more popular, and even build-ings renovated energetically can achieve over half of their demands from solar, there are no official guide-lines on how a “solar collector” should be classified as a heat generator. Retrofitting a solar system with-out exchanging the boiler can also not be labelled. A voluntary marking of solar collectors can help here.

Collector efficiency methodology

Regulation 811/2013 describes in detail the directions for assessing heat pumps ( = heating unit category without low-temperature [LT]-HP) and LT-HPs. Each type has its own classification. For heating units with-out a low-temperature heat pump (normal heat pump) the A+++ rating already begins at 150 % (see table, yellow field), for a low-temperature heat pump it does not begin until 175 % (see table, blue field).

The different grading can be explained by the higher energy provision of the normal heat pump, which also achieves higher temperatures. Based on this, two different scales are to be used for solar col-lectors depending on whether higher (75 °C) or medium (50 °C) temperatures are being looked at. To keep the classification simple an annual efficiency ƞa is being introduced. It is calculated from the annual yield of a solar collector module for a specified tem-perature (75 or 50 °C), based on the solar collector gross area and the specific sum of irradiation. Using a dataset which describes solar efficiency, taken from a test according to the current collector norm DIN EN ISO 9806 (or even older tests according to no-longer valid norm EN 12975-2), the annual yield of solar col-lectors for constant working temperatures (medium solar collector temperatures) is determined from a calculation process recognised around the world, which was developed during the course of the European research project QAiST (Quality Assurance in Solar Thermal Heating and Cooling Technology). The calculation is carried out using an Excel

programme (ScenoCalc v4.06), which is freely avail-able. Two worksheets from this are used for the Solar Keymark certification.

The Solar Keymark certification determines the solar collector yield for four sites in Europe and lists these on page 2 of the worksheet. The relevant annual efficiency for average climate conditions is deter-mined for Würzburg, Germany, as Würzburg is the location most similar to Strasbourg from regulation 811/2013. The annual efficiency is denoted as ƞa (xy °C) and calculated according to the following formula:

Classification

First we look at solar collectors for medium tempera-tures (50 °C). The benchmark for an energy efficiency rating of A+++ has been set at a solar collector efficiency of 52 % (see tab. 1, green field). By compar-ing this value with a low-temperature heat pump, we get a conversion factor for the other classes. The adjustment can be recognised as such because the respective characteristic curves of the low- temperature heat pump and the solar collectors meet at 50 °C. The efficiency classes for higher temperatures (75 °C) orientate themselves on the classification for heating units without a low-temperature heat pump.

A possible look for the pro­posed solar collector label for 50 °C Graphic: Solar-Experience GmbH

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Here too, the annual efficiencies are adjusted in such a way that the respective characteristic curves correspond to the relevant heating units.

Label proposal

In principle a so called “output class” may be de-termined for a solar collector for both higher and medium temperatures according to its annual effi-ciency. The manufacturer decides whether the collector is only suitable for medium or also for higher temperatures (district and process heating) and chooses the relevant label. In addition to the output classes, the marks will explicitly state in kilowatt hours per year (kWh/a) the yields of the collector module for colder (Stockholm), medium (Würzburg) and warmer ( Athens) locations. They can be directly calculated and taken from the out-put sheet used for the Solar Keymark datasheet 2. For this reason a reference to the version used (for

example ScenoCalc v4.06) should also appear on the label. A small market overview of representa-tive collectors shows that the collector industry does not have to hide itself away.

Collectors with an identity

With its own label, each collector will receive the at-tention and importance it deserves in the future as a heat generator. It shows output classes of solar heat with green bars of different length only as eve-ry solar thermal collector is more environmental friendly than any other conventional heat genera-tor. Furthermore, output bars are leading the way in the new direction of renewables by reducing prima-ry energy and CO2 emissions. As ErP-labelling is re-stricted to primary energy using conventional heat generators its bars may only lead into the other di-rection of more primary energy consumption, more or less efficient shown by colours green to red. The really green and good ErP classes can only be reached by renewables, first of all by solar thermal. The new collector label visualises this fact which is quite hidden in the package label.Fair competition between conventional and renew able energies will advance the aims of the regulation. The proposed output label would be a first step towards closing gaps in the regulation and creating a basis for fu-ture revisions. All solar collector manufacturers are upon to look into this seriously and to get classifi-cation for their product for medium temperatures (50 °C) and additionally for higher temperatures (75 °C) if applicable. The collector label is a tool to further explain the potential of called solar thermal in combination with the ErP label and in stand-alone solar thermal application as well. www.antifrogen.com

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Table: Derivation of the energy efficiency classes for solar collectors Source: Solar-Experience GmbH

Solar Edition 51

Perspective for thermosiphonic systems

The method shown is actually only applicable for solar collectors. But typical solar DHW systems of southern Europe, so called thermosiphonic systems (collector + storage), face the same problem. As solar- only application they cannot be labelled as well, in combination with an electrical immersion heater the label results for a solar water heater will be rather poor. Moreover, the top class is restricted to an A. But there is a good chance that Solar Keymark output data sheets provide results which can be used to establish a similar method creating output classes.

Stefan Abrecht

The idea and the mathematical methodology for the collector label presented here come from the author Stefan Abrecht of Solar-¬Experience GmbH. As the creator, he grants all those interes-ted the free use of the method to determine the output class as long as the source is stated. The draft design of the collector labels shown, is under investigation not to breach EU rights. Actually the use can explicitly not be authorised yet. Liability in any shape or form is excluded. Detailed guidelines on how such a label may be created can be requested for free at: s.abrecht@solar-experience.de

Further information:Worksheets used for Solar Keymark certification:www.sp.se/en/index/services/solar/ScenoCalc/Sidor/default.aspx

Fig. 2: Frequency of the efficency classes Source: Solar-Experience GmbH

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