Projects:2021s1-13006 Weather Station Solar Powered Battery System Optimisation
Contents
Introduction
ElectraNet operates a number of weather stations across the state of South Australia, from Leigh Creek to Mount Gambier. These weather stations are solar powered and equipped with batteries, allowing them to operate in remote areas without an external power source. ElectraNet is looking to change the operating capabilities of the DC power system and to better optimise the power system. The operational requirements, sensor power budget and historic weather data will be used to guide the evaluation and design of the 12 V DC power system. This includes assessing the solar panel sizing and performance at different locations in the state, and under different operating conditions. The charger and battery performance will also be considered, with a focus on the impact of temperature on battery capacity over the planned life of the system. The enclosure design is also expected to contribute to the performance of the overall DC power system. The outcomes of the project will include a power budget, the design of the DC power system, and selection of components including the solar panel, charger, battery, and enclosure that meet the requirements of the weather sensor and remote terminal unit. The system lifecycle will also be evaluated, including the operability and maintainability of the system.
Project team
Project students
- Riley Bass
- Matthew Grear
Supervisors
- A/Prof Dr. Nesimi Ertugrul
- Dr. Gabriel Haines (ElectraNet)
Objectives
Develop a full design of a new and optimised PV and battery powered weather station that meets the following requirements:
- The system is DC and completely off grid.
- The battery must remain above 50% state of charge (SOC) for at least 7 days with minimal solar irradiance.
- The battery must last at for least 5 years.
- Preferred one design to fit all weather station locations.
- The ability to accommodate future component upgrades.
Background
Dynamic Line Ratings
A cheap, consistent, and reliable flow of electricity is desired by all customers. It is the Transmission Network Service Providers (TNSP’s) duty is to continually discover, innovate and maintain ways to deliver these outcomes. In South Australia, TNSP ElectraNet have implemented Dynamic Line Ratings (DLR) throughout their Network.
Traditionally, Static Thermal Ratings have been used in transmission lines, to determine the amount of permissible current through the given line. In reality, the permissable amapacity of transmission lines are constantly changing, depending on various factors that the transmission line is subjected to. Dynamic Line Ratings use live weather data to actively alter the ampacity current rating of transmission line [1]. In good cooling conditions (e.g., low ambient temperature) DLR raises limits to allow higher current to pass through the relevant transmission line, and in hot conditions (e.g. high ambient temperature), DLR reduces the the line ampacity to prevent overloading issues. Figure 1 shows how DLR alters the line ampacities based on weather conditions. In comparison to Static Ratings, DLR enables Transmission Networks to optimise grid usage, minimise grid congestion and capitalise on economic opportunities [1]. This is increasingly important, as the proportion of Non-Scheduled Generation (Solar PV and Wind) continues to rise, and more line capacity is needed at times to meet the output of these renewable energy sources.
Stand-Alone Capability
A large majority of ElectraNet weather stations are situated in remote locations, or where the only source of electricity is at unsuiatable levels (e.g. 275kV, 133kV). Therefore, the weather stations must be stand-alone, and generate it's own electricity. For such applications, Solar PV panels are commonly used, as they are reliable, relatively inexpensive, and easy to maintain. Due to these reasons, the project will design a project using Solar PV as its sole electricity provider. Wind energy could be considered for this project; however, it adds unnecessary complexity, and brings a further point of failure to the overall system.
Solar PV panels harvest their energy directly from the Sun every day. Solar Radiation is an infinite energy resource, easy to maintain and install, and relatively cheap, making it ideal for a remote system . A key limitation of Solar, however, is the intermittent nature of the energy source. The sun rises throughout the morning, peaks at approximately midday, and then disappears at night-time. As a result, the daily energy output for a Solar PV panel has the approximate shape of the supply curve below.
Due to the intermittency of solar radiation, Solar PV alone will not be able power the weather station during the night. To provide a constant power, an energy storage device can be used. This will capture excess Solar PV energy throughout the daytime and use this energy at night. Batteries provide an ideal energy storage solution for this application, due to their simplicity and high energy density.
ElectraNet Weather Stations
Creating DLR’s requires the use of Weather Stations, to transmit live data to the TNSP. The stations must be strategically positioned around a transmission network for an accurate DLR determination to be formed. South Australia’s TNSP, ElectraNet, own 93 Weather Stations, around the network due to this. As the ElectraNet network spans over many rural areas, they are required to be stand-alone structures, and provide their own energy needs. Due to this, ElectraNet’s Weather Stations are currently fitted with a Solar PV system to power the necessary devices.
ElectraNet's existing PV System is made up of several components to facilitate the entire process. These are a Solar PV, Lead-Acid Battery, RTU+Modem, Weather Monitor, Irradience Monitor, and Solar Charger. The load components used for this design are shown below. Therefore, the system uses a 20W Solar Panel, and a 26Ah Lead-Acid Battery to power a 133mA load.
| Load Component | Load (mA) - 12V |
|---|---|
| Solar Charger | 8mA |
| RTU+Modem | 105mA |
| Weather Monitor | 15mA |
| Irradience Monitor | 5mA |
| Total Load | 133mA |
ElectraNet Weather Station
"see-saw" pole
Method
Modelling
PV Watts
PVWatts is a software tool designed by the National Renewable Energy Laboratory (NREL), a U.S government-funded agency. Using PVWatts, the modelling can be performed. PVWatts uses advanced irradiance measurement tools from select locations in South Australia, to determine beam irradiance, diffuse irradiance, and therefore compute the Plane-of-Array irradiance(Itr).Utilising wind speed, dry bulb temperature, and POA irradiance, PV Watts calculates Solar Cell temperature, Tcell. The overarching equation used by PVWatts to determine DC output is:
Sizing Analysis
Using PVWatts, many different options for sizing the battery and panel were modelled. The sizing designs that satisfied the requirements were selected from the original options. From there, the 4 most economical combinations for each load were summarised:
