# Hydro module The hydro module mainly governs reservoirs, hydro power plants and the connections between them. The very basics is the unit of a reservoir and a connected hydro power plant with water paths leading to the sea. ## Basic reservoir and hydro power plant unit The most basic unit of hydro power production is a three part unit: The reservoir, a discharge water way and a hydro power plant connected to the discharge path. Start by setting up the reservoir itself. Please refer to [reservoir documentation](lmreservoir) for specifics on fields and propertys. With a logical model created [reservoir documentation](lmlogicalmodel), first set up a price area. Waterways sets up how the stored water flows to and from the reservoirs. There's a few types of [waterways](lmwaterway). For basic use cases discharge, bypass and spillage are needed. Discharge is a waterway with an associated power production, this is the waterway that runs through a power plant. Bypass bypasses the power station, but is transported through the waterway system. Spillage is the pathway the water takes should the volume exceed the physical limit of the reservoir. If this pathway spills into the surrounding area without running down to another reservoir, set the waterway to drain into the sea. ## Reservoir minimum and maximum limits A reservoir with a volume limitation requirement is set up with two stages. The reservoir needs certain properties set in the logical model and a corresponding time series with the limit itself must be supplied to the data set. Refer to the [reservoir documentation](lmreservoir) and the [module documentation](modulehydrobasic) for information on which properties to set. Maximum requirements have two types; soft and hard. ### Minimum volume Minimum volume requirements attempt to keep the volume of the reservoir at above a certain minimum. The limit incurs a cost directly when the reservoir dips below the limit. This cost is user configurable. ### Maximum volume This limit can be set as a "tactical" max below the physical limit of the reservoir. Both soft and hard limits introduce an extra variable and cost of going above the limit, although the cost for the hard version is higher than the soft version. These two penalties are user configurable. ## Target reservoirs Target reservoirs are reservoirs with a specific target volume that the model will try to follow as close as possible. Moving away from this target incurs a user configurable penalty. To set up a target reservoir the reservoir needs to have the target type property value set to a value that is not NONE, [reservoir documentation](lmreservoir) as well as having a supplied input time series denoting the target. Please not that certain other features may be disabled should the target type be set. For example, minimum and maximum limits does not make sense for a target reservoir. These reservoirs do not get an end valuation due to the control of the volume being external. ## Waterways and hydraulic nodes The flow of water through the reservoirs all the way down to the sea is modeled by adding [waterways](lmwaterway) and hydraulic nodes. Waterways representing pathways with different behaviours and hydraulic nodes being connection points for the pathways. In order to set up a waterway, the hydraulic nodes that the waterway connects between should be created first. Hydraulic nodes include reservoirs, junctions and the sea. Reservoirs are explained further up. Hydraulic junctions can be considered reservoirs with no volume, requirements or limits, just a junction point with inflow and outflow. The sea is a special node, an all-purpose drain for water that exits the system. ### Discharge waterway The discharge waterway is the pathway for power production using the water from a reservoir. The discharge path can have requirements such as minimum and maximum flow through the path. See [module documentation](modulehydrobasic) for more information. ### Bypass waterway Bypass models directing the water through the station without producing power. The bypass also has minimum and maximum requirements. See [module documentation](modulehydrobasic) for more information. Usage of the bypass waterway incurs a small cost to prioritize not using this pathway. This penalty is user configurable. Certain situations might force the bounds of the bypass variables to a large value to ensure model feasability. ### Spillage waterway The spillage waterway models water spilling over the reservoir limits. This water might run down to another reservoir, or be lost to the environment. The spillage path does not need limits set through input data, as this variable is free. Usage of the spillage waterway incurs a small cost to prioritize not using this pathway. This penalty is user configurable. Default sets the penalty larger than that of the bypass pathway to properly prioritize using bypass if possible. ### Tunnels Reservoirs can have tunnels between them. These tunnels have little more features than flow limits. Combining tunnels and hydraulic junctions can model hydro power plants having more than one reservoir connected to it, either by direct connection between reservoirs or more than one reservoirs flowing to a junction which flows through a power station. Note that these tunnel are modelled as totally controllable and may flow against pressure. ### Pump tunnels Speciality waterway for use with pumps. While there's no limits that must be configured through input data, the special feature of this waterway is that it flows from downstream to upstream reservoir. ## Pumping Pumps can be set up by adding a pump and pump tunnel to the logical model. First, start by creating a pump tunnel between two reservoirs. This type of waterway is special due to having upward flow, i.e. from downstream to upstream. Next, create a pump that is associated with the pump tunnel. See [pump documentation](lmpump) for the propertys that need to be filled in. Additionally, limits for when to stop pumping needs to be supplied. See [module documentation](modulehydrobasic) Note that during validation, these values will be checked against the efficiency of the power plant should the pump and the plant be connected to the same up- and downstream reservoirs. This check can result in a warning or blocking error depending on the run configuration.