Background

ecoENERGY for Renewable Heat program officials presented a descriptive methodology for calculating collector performance factors at the stakeholder consultation sessions organized by Marbek consultants on "Basis of Payment and Level of Incentives for the ecoENERGY for Renewable Heat progam". Marbek in its final report to NRCan included stakeholder views on the methodology for calculation of collector performance factor. This document provides a response to the stakeholder views. The methodology to be applied under the Program can be found in the Methodology Report.

Response to specific stakeholder views expressed at the consultation sessions

Stakeholder views¹: Stakeholders are concerned that the calculation be based on sound data and allow a fair comparison between technologies. In particular, the data used must originate from testing under standard conditions by an approved facility. At the same time, some stakeholders are concerned that current lab testing is not always reflective of true performance.

Program Response: ecoENERGY for Renewable Heat Program accepts solar collectors that meet Canadian Standards Association (CSA) Standard F378 or equivalent (such as EN 12975 and ISO 9806 in Europe and SRCC OG-100 in the United States). Standard test conditions and methods are used to test and assess whether the collectors meet the requirements of the CSA or equivalent standards. The National Solar Test Facility (NSTF) in Ontario tests the collectors to CSA standards. The data from the standardized tests at conditions specified by the standards, at approved facilities such as the NSTF, define collector energy performance equations (efficiency) and incident angle modifiers that are used to estimate energy performance of collectors.

Some stakeholders expressed concerns that lab testing is not always reflective of actual performance. At the consultation sessions stakeholder discussions recognized that the actual performance of the collectors is dependent upon conditions at which the system is operated and also how the system is designed. The science behind using standardized tests to characterize the efficiency of solar thermal collectors is accepted by solar thermal energy experts worldwide. The proposed methodology is based upon collector energy performance data collected under standardized test conditions thus allowing comparison of the performance of collectors under similar conditions.

Stakeholder views: Stakeholders questioned the use of European data to calculate the performance factor. Some felt that the adjustment being proposed by NRCan might not be sufficient to take into account differences in measurement.

Program Response: European efficiency test data are reported in the form of linear and/or quadratic curves and are expressed in terms of aperture area and average fluid temperature across the collector for liquid collectors (outlet temperature for air collectors).

A NSTF-CanSIA spreadsheet² is used to calculate energy output from a collector and requires input data from collector tests to be expressed in terms of gross area and inlet thermal fluid temperature. This spreadsheet calculates energy output from a collector when operated through the "standard day" (as defined in CSA Standard F379) with a standard collector flow rate of 0.02 kg/s/m² of collector gross area (as defined in CSA Standard F378). It is therefore necessary to convert efficiency curves expressed in the European format to the NSTF-CanSIA spreadsheet format.

To obtain the necessary inputs conversion is performed in two steps. First, if a linear curve fit of test data is available in the European test report submitted to NRCan, this is used directly. If not, a linear curve fit of European test data is obtained using the Microsoft Excel function "LINEST". Second, textbook³ conversion equations are applied to obtain the parameters for linear efficiency equations expressed in terms of inlet temperature. European test data used to perform this conversion include: gross and aperture collector area, collector loop flow rate, and the coefficients of the efficiency curve: test value of the solar irradiance, the density and heat capacity of the test fluid (usually water) at an average temperature of 32°C. Measured incidence angle modifiers are used directly and values for missing angles are obtained by simple interpolation.

The ecoENERGY for Renewable Heat program is of the opinion that this conversion process sufficiently accounts for the differences in the measurements and also accurately represents performance from European tests.

Stakeholder views: Stakeholders are concerned that flat plate and evacuated tube collector (ETC) technologies be treated fairly. If they are to use the same incentive rate, it will need to take into account the different performance levels calculated using absorber area versus gross area.

Program Response: The stakeholders discussed the differences in flat plate and ETC technologies. The energy performance characteristics of ETC and flat plate technologies are dependent upon the operating temperature differential (i.e. difference between water temperature in the collector and ambient air temperature) for a given solar radiation. To recognize technology differences and treat these technologies based upon operating temperature differential of hot water projects supported in past, the program redesign has decided to place these two glazed hot water technologies into two separate groups: one group for flat plate and a second group for ETC. This approach allows for the collectors to be compared in their respective groups. The same incentive rate will be used for flat plate and ETC collectors and incentive calculations are to be based upon gross area of collectors.

Stakeholder views: Stakeholders are concerned that normalizing to the current best performing technology will lock-in a standard that will eventually become outdated. It was suggested that a more neutral scale be developed (e.g. based on best possible theoretical performance).

Program Response: The program encourages solar thermal technology providers to bring to marketplace higher performance solar collectors and does not intend to lock-in the current best performing collector as a standard. Therefore, when a new collector with a higher energy rating than current best performing collector is introduced in the Canadian market place, this new collector will receive a normalized rating that will be higher than the current best performing collector. For example, a new collector with a 20 percent higher energy rating than the current best performing collector will receive a normalized rating of 1.20. When an existing collector is modified to improve its energy rating, its normalized performance factor will be adjusted to reflect the improvement in the collector's energy ratings. Using this approach encourages technology providers to innovate and introduce higher performing collectors in the marketplace.

Stakeholder views: Stakeholders expressed the view that the base level incentive (translated from current cost-based approach) should be based on the average performance of technologies. Thus, technologies with better performance would receive a higher incentive and those with lesser performance would receive a lower incentive.

Program Response: New collectors are added to the list of program accepted collectors on an on-going basis. Thus average value of performance factors in a given technology category would frequently change, therefore changing the incentive amount of collectors. This change in incentive amounts adds uncertainty for the technology suppliers in their marketing and sales cycle. Also frequent changes in the average performance factors for collectors would create an administrative challenge for the program.

Stakeholder views: Many stakeholders indicated a desire to review the proposed performance factors before they are finalized.

Program Response: At the stakeholder consultations the NRCan officials presented a descriptive methodology to stakeholders. The methodology was broadly supported. The performance factors are calculated using this methodology and are based upon the data generated during testing collectors to standards. The results of the performance calculations will be provided in advance of their required use on September 1, 2008.