How hybrid PV technologies can contribute to the decarbonisation of Thailand’s power system Analysis – IEA – IEA

While hybridisation has many advantages, it also adds locational and operational constraints, as well as a loss of visibility to system operators. These disadvantages need to be assessed and weighed against the benefits in order to ensure that the plants construction provides net benefits to the system.

First, in co-located or fully hybridised setups, the developer constructs multiple installations (e.g.solar, wind, battery or hydropower) in the same location. The chosen location, however, may not be ideal for any one of them, which would introduce the need for a compromise when co-optimising the location. This could reduce the potential of individual constituent technologies to provide system services such as non-wire alternatives, or reduce the potential yield.

For example, by installing solar PV and BESS in a hybrid setup, the location decision will be the result of a compromise between the optimum solar resource and the potential of the battery to relieve congestion. It is possible that installing the two resources in different locations could produce more solar PV electricity (due to higher solar irradiation at that location for example), while allowing the battery to serve as a non-wire alternative and thus reduce congestion.

This trade-off is particularly clear when considering hybrid hydropower projects. As the locations suitable for hydropower plants are extremely limited, from the perspective of solar PV siting, the joint locations are often suboptimal.

The decision in favour of hybridisation should therefore be based on verification that the system-level costs of the locational drawbacks are offset by the advantages of the hybridisation. Where in certain cases, the cost-benefit analysis might be positive for the plant operator, it is crucial to check that the setup makes sense from the system-level perspective.

Secondly, hybridisation can also add operational constraints, which result from the shared infrastructure or the operational linkage. In terms of infrastructure, and in the case of a retrofit addition of solar PV to existing plants, a constraint may exist in terms of the capacity of the connection point (described below). Furthermore, in the hybrid PV and BESS setup, sharing an inverter, while bringing some advantages as outlined above, limits the output in times of high generation. In the case of hydropower, the operation range of the plant could limit the full dispatchability of the hybrid system. Hydropower ramping for short-term flexibility, for example, could be constrained by the allowed volumes of water discharge downstream.

Coming back to our modelled example, and looking at the differences between the two additional solar scenarios, one can see that there are slight differences in the way the hydropower generation is adjusting over time. In the co-located scenario, to take into account the shared infrastructure of the hydropower/floating solar plant and the constraint on the PV generation due to the reservoirs location, two additional constraints were introduced into the model. Firstly, the scenario is modelled assuming the use of common transmission and distribution equipment and is therefore limited to the capacity of the existing hydropower plant (5.34 GW) at which they are located. Secondly, there is limited transmission capacity between the hydropower plant that is in the northern region of Thailand and the main load centres located in the centre of the country. These two constraints lead to slight differences between the two additional solar cases. Indeed, the adjustment of the hydropower profile to solar PV availability is stronger in the co-located scenario, as the capacity of the shared infrastructure limits the total output at the site. The fact that the hydropower resource is increasingly used to balance local congestion instead of being controlled at system level reduces the cost-efficiency of the system.

Lastly, in full hybrid or virtual power plant setups, a trade-off is the loss of visibility from the system operators perspective. Indeed, the fact that the hybrid technologies constituents are controlled together renders their individual behaviours invisible to grid operators, who then rely on plant operators to ensure operations are managed in a system-optimum way. Providing incentives and regulations to plant operators to ensure that operations are system-friendly can address this drawback.

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How hybrid PV technologies can contribute to the decarbonisation of Thailand's power system Analysis - IEA - IEA