Photovoltaic-thermal (PVT) collectors are commonly designed for use in domestic hot water systems, however it can be interesting to incorporate them into ground source heat pump (GSTIP) systems. Because of the historically narrow use case, many PVT models are created with a collection of assumptions which may not apply to novel collectors designed for use in PVT+GSHP systems. The aims of this study are to review existing PVT collector models for use in TRNSYS, identify any potential error sources, and test for possible improvements. Type 560 is found to be the most promising theoretical model, however two potentially limiting features are identified; the radiation absorption model and the confinement to sheet-and-tube configurations. The absorption is tested using a recreation of Type 560 in Matlab where two alternative models developed specifically for PV modules are compared. The results show a marked increase in power during low angle, low light hours, and a 14.36% increase in electrical energy and a 10.91% for the thermal energy over the course of a day with one of the models. Collector geometry is tested by creating a ID model in EES and comparing it to several geometries in Type 560. A method of packing as many tubes as possible together is shown to give comparable results as the ID model. The results of these simulations will be compared with empirical data from currently ongoing testing.