STO implementation main problems

As can be seen in the RCCTE FAQs [19], the main questions are of two different types. One type is related with basic questions denoting the lack of knowledge of some stakeholders (“what is a solar thermal collector?”, and so on). Other, are related with requirements which need clarification or have not good criteria.

One example of those that are not good criteria is the rule of 1 m2 of solar thermal collector per conventional occupant, without any reference to the thermal performance of the product.. The problem is that a solar collector with both lower performance and lower cost is enough to satisfy the requirement, but the production cost of the sanitary hot water it is not always lower. The rule was also disturbing the market because the unique imposition of the collector area, was giving advantage to the lower performant and potentially lower cost products.

To overcome this problem, it is presently allowed that a lower value of collector area (in comparison to “1m2 per person” rule) can be accepted if the designer shows that an alternative solution collects yearly an equivalent energy of that of a standard solar thermal collector, which was defined with the following characteristics:

I) optical performance = 69%;

II) thermal losses coefficients a1 = 7.500 W/(m2.K), and a2 = 0.014 W/(m2.K2);

III) incidence angle modifier at 50° = 0.87;

IV) apperture area = 1.0 m2. —

The definition of the previous standard collector also permits to quantify the energy for sanitary purposes captured by solar thermal collectors, that can be substituted in the annual base, by other renewable sources and equipment (PV, wind, geothermal), even for other purposes.

Another example of a requirement which needed clarification is “what is a significant obstruction?”: Quantification of this requirement was agreed recently. First, it must be considered significant obstruction, a permanent obstacle between the solar thermal collector field and the Sun, which originate shadow for both a certain collector area an a certain time, to be evaluate under the following step by step methodology ([19] FAQ M.15):

i) evaluate the solar thermal system contribution for heating of sanitary hot water with SolTerm, using an obstruction with an angle of 20° to the horizon (situation correspondent to that of a total solar exposition in a period between 2 hours after sunrise and 2 hours before sunset), without the introduction of any other obstructions;

ii) maintaining the referred obstruction angle of 20°, add the obstruction to be studied “as significant”, and evaluate the solar thermal system contribution for heating of sanitary hot water with SolTerm;

iii) if the ratio of the two values of the solar thermal system contribution for heating of sanitary hot water obtained with obstruction and without obstruction is less than 0.7, the obstruction is considered “significant”.

Concerning the general problem of the lack of adequate knowledge by the stakeholders, it must be said that the problem is being studied within the framework of an European project [20], where INETI participates. Some points already identified are:

■ Information on Certification schemes (also of Solar Keymark) and on the tests performed and their interpretation among manufacturers and installers of Solar Thermal Collectors and Systems, although the Certification based on European Standards is already implemented and several products are already being certified;

■ Development of good practice manuals, for design and installation of solar thermal systems as well as for maintenance of both medium and large solar thermal installations, is needed;

■ Preparation of updated materials for courses specifically dedicated to i) maintenance of installations, ii) teachers of secondary schools (for children from the ages of 11 to 18), and

iii) consumers, addressing the selection of best solution.

■ Introduction of modifications in the curricula of architecture courses, covering in large scale the general bioclimatic aspects of construction, as well as, specific aspects related to solar thermal performance and its relation to thermal performance of buildings.