In solar thermal plants, the solar field supplies some or all of the heat needed by the cycle. The field may deliver hot thermal oil, hot water, saturated steam, or superheated steam.
THERMOFLEX has a completely user-defined solar field where the user directly specifies solar field heat input to the working fluid used in the cycle. In this case, no detailed field modeling is done by THERMOFLEX, rather the user’s specified field performance is applied directly. This simple approach makes including manufacturer-specified performance quick and easy.
THERMOFLEX also allows the user to model the solar field’s thermal-hydraulic-optical performance directly, in detail. At design, THERMOFLEX computes number and length of each collector row, the total solar field size, fluid pressure drop, land use requirements and estimated field cost based, on desired field performance. At off-design the solar field model estimates field heating capacity and fluid-side pressure drop for given solar irradiance and field operating conditions.
The THERMOFLEX solar field model is a general line collector model with options to pick specific parabolic trough and linear Fresnel collector configurations, and ability to specify user-defined collector characteristics.
The Main Inputs menu for design calculations is shown here. The Collector Hardware & Characteristics menu is shown at the top of the next page. These two menus allow the user to specify the desired field thermal-hydraulic performance and the physical and optical characteristics of the collector used. Default values are supplied for all inputs, and the user can always adjust the inputs to suit their needs.
At design, THERMOFLEX uses these inputs to compute the field’s thermal-hydraulic performance and estimate the collector size and land requirements.
The solar field consists of a number of flowpaths connecting cold supply header to the hot return header. Each flowpath spans one or more collector rows. Large trough fields typically use two collector rows per flowpath so the hot and cold headers are at the same end of the row banks.
Some linear Fresnel collectors, especially with direct steam generation use one flowpath per collector row so cold fluid enters at one end, and steam exits to a steam drum at the opposite end.
Smaller roof-top heating collectors often have many collector rows per flowpath to accommodate the desired temperature rise in a limited footprint.
The Flow Path Hardware menu (below) is used to specify hydraulic parameters affecting the pressure drop from cold header to hot header. The fittings specified here together with the straight run of receiver tube with its specified roughness are used to compute an equivalent length of straight piping. The pressure drop is computed using that length together with flow conditions and temperature/pressure-dependent fluid properties.