Options for the Basis of Incentive Payments

The ecoENERGY for Renewable Heat program is exploring options for the basis of incentive payments. The discussion paper prepared by Marbek outlined and assessed five options:

• Status Quo - based on percentage of costs
• Collector area installed - collectors meet minimum energy performance rating (kWh/m²/day)
• Collector area installed - and based on energy performance factor
• Estimated solar energy produced
• Metered solar energy produced

Apart from status quo, the options presented in the discussion paper primarily rely on incentive payments based on the collector area installed in combination with a minimum energy performance rating or energy performance factors, and energy produced from projects (either estimated or metered). Two of the options proposed would require calculation of energy performance for collectors. NRCan has written this paper as a basis for discussion on how energy performance factors for collectors can be determined.

Background for Methodology

The ecoENERGY for Renewable Heat program accepts solar collectors that meet Canadian Standards Association (CSA) standard F378 or equivalent standards. The testing that is conducted on collectors to assess whether they meet the requirements under Canadian or other equivalent standards (such as in the USA and Europe) for safety and durability, also produces collector energy performance equations (efficiency) and incident angle modifier data that can be used to estimate energy output under almost any operating condition.The methodology for estimating the energy ratings of water and air heating solar collectors is described below.

Methodology for Estimating Energy Ratings

Solar collector energy performance is measured and characterized under Canadian, U.S. and European standards in terms of linear and/or second-order equations that relate efficiency (η_collector ) to an operating parameter which divides a temperature difference between the collector and ambient air (T_c-T_a), by the incident solar energy flux (G). An example of a linear version of the equation is shown below:

In the above equation, parameter A represents the optical efficiency, and B represents the heat loss coefficient, which are determined during testing.

A representative measure of energy performance for each collector is determined as follows:

Glazed water heating collectors [flat plate and Evacuated Tube Collectors (ETC)]: The efficiency equation and incident angle modifier values are determined under standard testing for collector. This data is used to calculate the collector output when it is operated through the "standard day", as defined in CSA Standard F379. This approach accounts for differences in collector performance due to solar radiation intensity and incident angle as the sun moves across the sky, by integrating the energy collected over the day. The spreadsheet used to perform these calculations was developed by National Standard Testing Facility (NSTF) personnel for CANSIA's Canadian Directory of Solar Water Heating Products. For glazed water heating collectors (flat plate and ETC), the collector outputs (kWh/m²/day) at 20°C and 50°C temperature differences are averaged to determine an energy rating for each collector¹. The 20°C temperature difference was selected to represent summer operation and the 50°C temperature difference, to represent winter operation.

Unglazed water heating collectors: The efficiency equation and incident angle modifier values are determined under standard testing for each collector. These data are used to calculate the energy rating (kWh/m²/day) when operated through the "standard day", at a 5°C temperature difference, and at wind speed of 2.5 m/s - representing typical summer operation for pool heating.

Glazed air heating collectors: The energy performance ratings for glazed air-heating collectors are calculated using the approach outlined for glazed water heating collectors.

Unglazed air heating collectors: Standard collector efficiency testing to determine the energy rating of unglazed air heating collectors is carried out at 900 W/m², an air flow rate of 4 scfm/ft² and a wind speed of 1.3 m/s. These operating conditions were selected as typical for this technology in the application of preheating ventilation air and were used to develop efficiency rating for each collector.

Performance Factor and Incentive Payment

Within each of the five technology groups (glazed water heating flat plate, glazed water heating ETC, unglazed water heating, glazed air heating and unglazed air heating), the energy rating of each collector is divided by the corresponding highest energy rating of the collector in that technology group, to calculate a "performance factor". The incentive for a collector would be the product of the performance factor of the collector and the incentive rate ($/m²) for that technology group.

For collectors that have been accepted by the ecoENERGY for Renewable Heat program based on the European thermal performance testing, the efficiency equations (which use T_mean-T_ambient) are being adjusted to the North American standard (T_inlet-T_ambient) before the methodology described above is applied.