Low Wind Periods Research Articles

Enhanced energy extraction from wind driven PMSG using digital twin model of battery charging system

The pressing need to meet sustainability and climate objectives has prompted a call for expanding the use of renewable energy sources, improving the intelligence and flexibility of electricity grids, and increasing the adoption of electric vehicles and other electricity-powered products. In light of their numerous benefits, widespread electrification and digital technologies can form the basis of energy and climate policy. This research presents an innovative biased transformer and digital twin battery model to support the wind energy based electric vehicle battery charging system. During periods of low and moderate wind, the biased transformer is utilized to increase the voltage for charging electric vehicles. A digital twin of the battery system creates a window into battery charging and aging levels by evaluating the data gathered based on internal resistance. Furthermore, the State of Charge estimation model and different internal resistance estimation algorithms are also exploited. A novel method for precise State of Charge (SOC) estimation in third-gen battery models is presented, integrating Collaborative Gradient Boosting and Adaptive Extended Kalman Filter (AEKF). This approach, implemented in MATLAB Simulink, combines machine learning and adaptive filtering, enhancing accuracy and adaptability for efficient battery management. The functionalities and resilience of both hardware and software of the proposed system are validated under field operation.

A First Look at Internal Waves in the Great Barrier Reef Lagoon

The Great Barrier Reef lagoon is a large, relatively shallow area of the Australian continental shelf, isolated from the open ocean by a dense matrix of coral reefs. As the lagoon is generally vertically well mixed by strong tidal currents and wind, it is perhaps not surprising there is no mention in the open literature of the occurrence of internal waves there. Nevertheless, high-resolution satellite imagery is shown in this article to reveal the characteristic surface expressions of nonlinear internal waves in the lagoon. The waves are confined to periods of low winds in austral spring and summer, making them a potentially important mechanism for the dispersal of algae and planktonic larvae. The imagery suggests a link between the waves and tidally forced submesoscale jets and vortices, but the actual mechanism generating the internal waves is unclear and requires investigation.

Using power system modelling outputs to identify weather-induced extreme events in highly renewable systems

In highly renewable power systems the increased weather dependence can result in new resilience challenges, such as renewable energy droughts, or a lack of sufficient renewable generation at times of high demand. The weather conditions responsible for these challenges have been well-studied in the literature. However, in reality multi-day resilience challenges are triggered by complex interactions between high demand, low renewable availability, electricity transmission constraints and storage dynamics. We show these challenges cannot be rigorously understood from an exclusively power systems, or meteorological, perspective. We propose a new method that uses electricity shadow prices—obtained by a European power system model based on 40 years of reanalysis data—to identify the most difficult periods driving system investments. Such difficult periods are driven by large-scale weather conditions such as low wind and cold temperature periods of various lengths associated with stationary high pressure over Europe. However, purely meteorological approaches fail to identify which events lead to the largest system stress over the multi-decadal study period due to the influence of subtle transmission bottlenecks and storage issues across multiple regions. These extreme events also do not relate strongly to traditional weather patterns (such as Euro-Atlantic weather regimes or the North Atlantic Oscillation index). We therefore compile a new set of weather patterns to define energy system stress events which include the impacts of electricity storage and large-scale interconnection. Without interdisciplinary studies combining state-of-the-art energy meteorology and modelling, further strive for adequate renewable power systems will be hampered.

AN INVESTIGATION OF THE EFFECTS OF WIND VELOCITY ON THE PERFORMANCE OF TURBINES AND GENERATORS

Variations in wind speed at 4,6 and 8 m altitudes were analyzed using a 24-hour dataset. The greatest recorded wind velocity was 3.3 m/s at a height of 8 meters, and the lowest was around 2.4 m/s at a height of 4 meters. The investigation also identified discrepancies in velocity between the generator and turbine while they were operating with and without a load. The turbine's speed increased when there was no weight present. The peak wind velocity reached 3.9 meters per second, accompanied by a similar variation of 5.4 rotations per minute. The average discrepancy in rotational velocity between the turbine and generator during periods of low wind was 3.74 RPM. This discovery establishes a fundamental basis for comprehending the movement of wind and enabling future in-depth explorations in the field of atmospheric sciences. The generator's performance is assessed by the measurement of current and voltage, which serves to highlight its versatility and effectiveness. The correlation between wind velocity and generator rotational speed is crucial for energy conversion, since the turbine's velocity needs to be adjusted to match the heightened load, affecting the generator's speed.

Power quality enhancement for Thailand's wind farm using 5 MWh Li-ion battery energy storage system

Several studies have stated that an increase in wind power plants and unpredictable wind energy generation face several issues during over-voltage. In this study, an operational 8 MW wind farm in Nakhon Ratchasima province faced severe annual feeder trips 146 times, which is not permissible according to the manufacturers. The feeder trips are mainly attributed to high grid voltage caused by low load demand. This study developed a Battery Energy Storage System (BESS) to minimise feeder trips using DigiSILENT and utilized the higher feeder trip period of September to optimise BESS capacity with a 10 % grid load. Notably, a 5 MWh BESS maintained the grid voltage within an allowable range compared to the 1–4 MWh (increment of 1 MWh) throughout the operational period. Furthermore, a 5 MWh BESS was tested during low and high wind periods to assess the stability of over-voltage management. We found that the 5 MWh BESS controlled over-voltage and prevented feeder trips, resulting in enhanced power generation on selective days with high feeder trips, low wind speed, and high wind speed, generating 28.34 MWh, 0.33 MWh, and 76.67 MWh, respectively, compared to conditions without BESS. Additionally, we recommend that the 5 MWh BESS can enhance wind farm power stability and uphold the manufacturer's warranty.

Wind regime and sand transport in the mid-course of ten tributaries of the Yellow River, Inner Mongolia of China

Better understanding the wind regimes and dune activity criteria are pre-requisites for the successful planning of any sand dune fixation project and hence have a high priority. To fully understand wind energy conditions and the intensity of aeolian activity, we investigated the wind conditions, sand-transporting potential, and sand-transporting capacity of the basins of mid-course ten tributaries of the Yellow River through field observations and indoor analyses. 1) The analysis of wind energy, which is based on sand transport potential, demonstrates that there is substantial spatial variation within the study area. The western part, which is located near the Kubuqi Desert, qualifies as a high wind energy zone. In contrast, the central part belongs to the medium wind energy zone, whereas the eastern part is categorized as a low wind energy zone. Even though there are notable differences in the sand transport potential characteristics across different time scales, the direction of the synthesized sand transport potential tends to be consistent, predominantly leaning towards the southeast. This orientation provides the requisite energy for the sand material to be transported into the river. 2) The prevailing sand-producing wind direction at various timescales in the research area was dominated by westward (W, WNW, NW) and northward (NNW, N) winds, with distinct seasonality. This seasonal variability was especially prominent in spring, which saw the highest frequency of aeolian activity and the largest volume of sand transport. Autumn and winter exhibited similar patterns, and, in the summer, it was the lowest 3) The relationship between sand-transporting potential and sand-transporting capacity, which is a crucial aspect of aeolian geomorphology, could be adequately depicted using a fitting function based on the temporal patterns of wind speed. During periods of high wind, the sand-transporting potential and sand-transporting capacity of the basins of the ten tributaries followed a power function relationship. Conversely, during periods of low wind, they followed an exponential function relationship. These results imply that spring should be deemed as the crucial period for wind-sand prevention and control. Additionally, emphasis should be placed on the western part, which is situated close to the sand source area, as the primary prevention and control zone.

Meteorological conditions during periods of low wind speed and insolation in Germany: The role of weather regimes

AbstractRenewable power generation from wind and solar energy is strongly dependent on the weather. To plan future sustainable energy systems that are robust to weather variability, a better understanding of why and when periods of low wind and solar power output occur is valuable. We call such periods of low wind speed and insolation “Dunkelflauten”, the German word for “dark wind lulls”. In this article, we analyse the meteorological conditions during Dunkelflauten in Germany by applying the concept of weather regimes. Weather regimes are quasi‐stationary, recurrent and persistent large‐scale circulation patterns that explain multi‐day atmospheric variability (5–15 days). We use a regime definition that allows us to distinguish four different types of blocked regimes, characterized by high‐pressure situations in the North Atlantic‐European region. We find that Dunkelflauten in Germany occur mainly in winter when the solar power output is low due to the seasonal cycle of solar irradiance and wind power output drops for several consecutive days. A high‐pressure system over Germany, associated with the European Blocking regime, is responsible for most of the Dunkelflauten. Dunkelflauten during the Greenland Blocking regime are associated with colder temperatures than usual, causing higher electricity demand, and would present a particular challenge as space heating becomes electrified in the future. Furthermore, we show that Dunkelflauten occur predominantly when a weather regime is well established and persists longer than usual. Our study provides novel insight into the occurrence and meteorological characteristics of Dunkelflauten, which is essential for planning resilient energy systems and supporting grid operators to prepare for potential shortages in supply.

Net Zero UK – Generation and Energy Storage Requirements for the UK to Become Carbon Neutral

This paper sets out a quantified scenario for the UK to reach net zero carbon emissions. Wind and solar are the main energy sources and their intermittency is accommodated through hydrogen electrolysis, biogas from anaerobic digesters, and their combination into biomethane. Hydrogen and biomethane stocks are tracked. A daily energy balance model is presented, using the most recent recorded weather data-2017 to 2021. Long periods of low wind in 2021 indicated the necessary energy storage capacities, which were adjusted relative to energy generation capacities so as to achieve an economic minimum cost. The projected levelized cost of electricity is £92/MWh (which is well below the current energy wholesale price of £130) though this does assume greatly improved thermal insulation of most UK buildings. A 10% reduction of this cost is shown to be possible through the application of demand side management (retiming of energy consumption) thus illustrating the value of such flexibility. Carbon capture and storage (CCS) applied to power stations running on the biomethane could provide up to 21 Mt of negative emissions to offset other sectors, imports and even remove some of the excess emissions that have already occurred. The work goes beyond previously published scenarios: energy pricing is calculated, demand response measures have been modelled, and embedded carbon in imported goods is considered. The Python model is available, open-source, for inspection and further development.

Empirical H/V spectral ratios at the InSight landing site and implications for the martian subsurface structure

SUMMARY The horizontal-to-vertical (H/V) spectral ratio inversion is a traditional technique for deriving the local subsurface structure on Earth. We calculated the H/V from the ambient vibrations at different wind levels at the InSight landing site, on Mars, and also computed the H/V from the S-wave coda of the martian seismic events (marsquakes). Different H/V curves were obtained for different wind periods and from the marsquakes. From the ambient vibrations, the recordings during low-wind periods are close to the instrument self-noise level. During high-wind periods, the seismic recordings are highly contaminated by the interaction of the lander with the wind and the martian ground. Therefore, these recordings are less favourable for traditional H/V analysis. Instead, the recordings of the S-wave coda of marsquakes were preferred to derive the characteristic H/V curve of this site between 0.4 and 10 Hz. The final H/V curve presents a characteristic trough at 2.4 Hz and a strong peak at 8 Hz. Using a full diffuse wavefield approach as the forward computation and the Neighbourhood Algorithm as the sampling technique, we invert for the 1-D shear wave velocity structure at the InSight landing site. Based on our inversion results, we propose a strong site effect at the InSight site to be due to the presence of a shallow high-velocity layer (SHVL) over low-velocity units. The SHVL is likely placed below a layer of coarse blocky ejecta and can be associated with Early Amazonian basaltic lava flows. The units below the SHVL have lower velocities, possibly related to a Late Hesperian or Early Amazonian epoch with a different magmatic regime and/or a greater impact rate and more extensive weathering. An extremely weak buried low velocity layer (bLVL) between these lava flows explains the data around the 2.4 Hz trough, whereas a more competent bLVL would not generate this latter feature. These subsurface models are in good agreement with results from hammering experiment and compliance measurements at the InSight landing site. Finally, this site effect is revealed only by seismic events data and explains the larger horizontal than vertical ground motion recorded for certain type of marsquakes.

NEW TYPE OF GLUEING OF REDOX FLOW STACKS

For the energy transition to succeed, the growing amount of solar and wind power need to be stored for night-time or low-wind periods. Redox flow storage offers a good way of balancing out the fluctuations in renewable energies and is considered a promising energy storage system because it is potentially inexpensive and relatively easy to scale. However, the costs are still too high for this technology to be a resounding success. New manufacturing and joining technologies can help here. This will be demonstrated using the central element of the redox flow battery, the stack, as an example. Here, novel bonding ideas will be investigated and explained. The aim was to improve the contact between the gas diffusion fleece on the active side of the bipolar half plates and the current collector on the bipolar edge plates. A media and temperature-resistant adhesive was tested and tried out in different geometries.

Characterisation and mitigation of renewable droughts in the Australian National Electricity Market

In a decarbonising world, the electricity generation mix in Australia’s National Electricity Market (NEM) is likely to be heavily dependent on wind and solar. Designing an electricity system dominated by variable renewable energy generation requires careful examination of periods of low renewable output to ensure storage or other back up generation is sufficient to avoid loss of load. This study uses 15 years of climate and electricity demand data to examine the frequency and nature of the occurrence of low renewable periods. It examines strategies for their mitigation so that unserved energy standards are not breached. We have found that the winter period, May to August, is the time where the NEM is at greatest risk of loss of load. This winter period is when the demand in southern Australian states is higher, solar generation is lower and a series of low wind periods can drain storage. It has been demonstrated that any proposed generation mix reliant on renewable energy generation should be stress tested across a low wind winter, like the complex winter of 2010, not just a single isolated low wind period. Storage was found to be ideal to provide energy for a few hours overnight, but firm dispatchable thermal generation is likely to be a lower cost option than long term storage for extended low wind periods. Diversifying generation with the addition of offshore wind may reduce the need for storage, although the need for floating wind turbines may make this alternative too expensive to add any value in the Australian context.

Whole system value of long-duration electricity storage in systems with high penetration of renewables

Energy storage is a key enabling technology to facilitate an efficient system integration of intermittent renewable generation and support energy system decarbonisation. However, there are still many open questions regarding the design, capacity, and value of long-duration electricity storage (LDES), the synergy or competition with other flexibility technologies such as demand response, short-duration storage, and other forms of energy storage such as hydrogen storage. This paper presents a novel integrated formulation of electricity and hydrogen systems to identify the roles and quantify the value of long-duration energy storage holistically. A spectrum of case studies has been performed using the proposed approach on a future 2050 net-zero emission system back-ground of Great Britain (GB) with a high share of renewable generation and analysed to identify the value drivers, including the impact of prolonged low wind periods during winter, the impact of different designs of LDES, and its competitiveness and synergy with other technologies. The results demonstrate that high storage capacity can affect how the energy system will evolve and help reduce system costs.

Spatial distribution and interannual variability of cyanobacteria blooms on the North-Western shelf of the Black Sea in 1985-2019 from satellite data

Long-term high and medium resolution satellite data are used to study spatial, seasonal and interannual variability of the cyanobacteria blooms (CB) in the North-Western Shelf (NWS) of the Black Sea. High-resolution Landsat data demonstrate that CB were regularly observed in the study area on satellite images in 1985-2020. Comparison of quasi-synchronous Landsat and MODIS images was used to study the characteristic features of CB spectra, which are: a “step” formed by MODIS 3 (469) and 4 (488) channel, probably related to the absorption by photoprotective carotenoids; increased reflectance in near-infrared; maximum at 547-555 nm. On the base of these features, we develop the automated algorithm of CB identification and reconstruct the daily dataset of CB over 2003-2019. The main advantage of the developed algorithm is its ability to filter out non-bloom areas in all seasons and meteorological conditions and during blooms of other algae in the deep part of the sea. Analysis of this dataset, complemented by Landsat data, allows to identify two primary sources of the CB in the NWS: the Dnieper-Bug estuary and the Danube mouth, and study the evolution of CB in these areas in detail. CB can penetrate on more than 150 km from the sources reaching in rare cases the Crimean coast. Such offshore propagation is mainly wind-driven and was often related to the upwelling frontal currents. The climatic seasonal peak of CB near the Danube is observed in May-June following the peak of river discharge in April-May. It precedes the peak of CB near the Dnieper-Bug estuary observed during maximum surface heating in August. At the same time, the case study of bloom evolution in 2009 shows that CB can be observed in these areas several times in a season, triggered mainly by periods of low winds. The strongest bloom of CB in 2003-2019 was observed in 2004-2006 and 2008-2010 following by the sharp decrease after 2011. This decrease is related to the observed reduction of the river discharge and, more important, the rise of the wind intensity in summers of the recent period.

Resource and Load Compatibility Assessment of Wind Energy Offshore of Humboldt County, California

Floating offshore wind is being considered in northern California as indicated by the Bureau of Ocean Energy Management’s issuance of a lease consideration in the Humboldt Call Area. Humboldt County offers access to this enormous resource, but local electric load and transmission are limited. The potential impacts of offshore wind generators at three different scales were studied using a regional grid model of Humboldt County. Offshore wind generation was calculated using modeled wind speed data and 12-MW turbine specifications and integrated with projected load and historical generation. Offshore wind farms deployed in the Humboldt Call Area achieve annual capacity factors between 45% and 54% after losses and maintenance. Power output is variable between and within seasons, with full power output 30% of the time and no output approximately 20% of the time. Electricity from a 48-MW wind farm provides 22% of regional load with limited exports. A 144-MW wind farm serves 38% of local load, exporting 40% of its electricity with the extant 70-MW transmission capacity. A full build-out of 1836 MW would result in 88% curtailment with existing transmission. Across scenarios, offshore wind variability necessitates reliance on existing power plants to meet local demand in periods of low wind.

Potential of Nitrogen/Argon Analysis in Surface Waters in the Examination of Areal Nitrogen Deficits Caused by Nitrogen Fixation.

In marine systems, the loss of nitrogen caused by denitrification in oxygen-deficient zones is balanced by nitrogen fixation mediated by cyanobacteria, which may form extensive blooms in surface waters. In this study, by determining the concentration ratio of nitrogen (N2) and argon (Ar) in air equilibrated with surface water, we were able to detect changes in the N2 concentration attributable to N2 fixation. For this purpose, surface water was pumped continuously into a spray-type equilibrator while the air in the equilibrator's headspace was analyzed by mass spectrometry. After laboratory tests and model analysis to evaluate the sensitivity of our N2/Ar approach, feasibility studies were conducted in the central Baltic Sea in the summer of 2015 during the development of a cyanobacterial bloom. Our results showed that N2 deficits accumulated during periods of low wind and increasing surface water temperatures. A comparison of our results with the N2 deficits calculated from changes in the partial pressure of carbon dioxide in surface water indicated a similar trend. By demonstrating the ability of the N2/Ar approach to resolve N2 deficits in surface water caused by N2 fixation, our study contributes to assessments of the N2 fixation efficiency of cyanobacterial blooms.

Numerical assessment of a deformable trailing-edge flap on aerodynamic load control of a pitching S809 airfoil using OpenFOAM

Due to the unsteady nature of the flow around horizontal-axis wind turbines, the blades are subjected to severe unsteady and fatigue loads. This necessitates an in-depth aerodynamic analysis of flow control techniques to enhance the performance of a wind turbine as well as the lifetime of its components. Using OpenFOAM package in this study, a series of two-dimensional incompressible simulations are performed to present a deeper insight into the aerodynamic characteristics of an oscillating deformable trailing-edge flap, as a promising flow control device, in a sinusoidal pitching motion of an S809 airfoil. Herein, it is of particular interest to investigate the effects of deformable trailing-edge flap size, oscillation frequency, and the phase shift with reference to airfoil motion on lift and drag hysteresis loops. For this purpose, a pure-pitching motion of an S809 airfoil without flap deflection is considered as the benchmark problem in which the airfoil oscillates in the near-stall region at [Formula: see text]. After validation and verification of our simulations through comparison against the corresponding experimental and numerical work, a comprehensive investigation is conducted to study the effects of the aforementioned parameters on the aerodynamic loads. Our results reveal the fact that an out-of-phase deflection of the deformable trailing-edge flap with a frequency equal to the airfoil frequency can significantly mitigate the fatigue load. Under these circumstances, an increase in the deformable trailing-edge flap size can also help the airfoil experience less-severe loads in a cycle of motion. Furthermore, higher values of deformable trailing-edge flap frequency or other values of phase shift except the out-of-phase oscillation cannot alleviate fatigue loads. An airfoil under these conditions can, however, enhance the resultant load required for a blade rotation in the case of low wind periods.

Utility-scale storage providing peak power to displace on-island diesel generation

Peaking power plants are used to provide power during periods that have both high load and limited supply from intermittent renewable energy. Wind power is intermittent and does not always provide electricity during periods of maximum demand. Despite this, it has grown to produce a significant portion of the electricity in some jurisdictions. Electricity systems require firm capacity that operate when called upon. Fossil fuel peaking plants are costly, providing a fraction of the annual energy at a great cost, but ensure system reliability. Utilizing storage systems to provide these services during peak times could allow integration of higher penetrations of renewable energies. Prince Edward Island, Canada has over 40% of its load produced by wind power but requires diesel generators during high load and low wind periods. The diesel generators ensure that the submarine cables are not overloaded and provide on-island power during other curtailments. The 1 MW/2 MWh storage system provided energy and capacity from December 2015 to March 2016 and was paid for these services by their local utility. The payment only covered 9% of the costs due to the high capital cost and short life expectancy of their storage system.

Demand and energy avoidance by a 2 MWh energy storage system in a 10 MW wind farm

Abstract All power generators require power for their auxiliary loads. Unlike conventional generators, intermittent renewable generators such as wind turbines depend on the wind for their fuel. During periods of low wind speeds, they consume power from the public grid to supply their auxiliary load demand. As the wind is intermittent, periods of low wind speed may coincide with periods of peak energy rates on the grid resulting in a significant energy charge. In addition, the peak power demand results in a demand charge. The energy and demand charge represent a net cost to the owner. A battery storage system can be used to minimize the energy drawn from the public grid to supply these loads. The Wind Energy Institute of Canada operated its 1 MW/ 2 MWh storage system, utilizing a wind forecast prediction, to reduce the energy consumption of their 10 MW Wind R&D Park during periods of low wind. The storage system was charged from the Institute’s wind turbines and the energy stored was discharged to the wind park internal network when the wind park power dropped below 0 kW. The discharge rate was determined based on the wind forecast so that the energy would last for as much of the forecasted low wind period as possible. The use of the forecast reduced the number of occurrences of the battery reaching its minimum state of charge, but it was not able to reduce the demand charge. The storage system was able to offset 17.2 MWh, resulting in a cost avoidance of $2804 in the 2 month trial. This financial gain was insufficient to offset the net energy losses in the storage system.

Precipitation instruments at Rothera Station, Antarctic Peninsula: a comparative study

Direct measurement of precipitation in the Antarctic using ground-based instruments is important to validate the results from climate models, reanalyses and satellite observations. Quantifying precipitation in Antarctica faces many unique challenges such as wind and other technical difficulties due to the harsh environment. This study compares a variety of precipitation measurements in Antarctica, including satellite data and reanalysis fields atRothera Station, Antarctica Peninsula. The tipping bucket gauges (TBGs) were less sensitive than laserbased sensors (LBSs). The most sensitive LBS (Visibility and Present Weather Sensor, VPF-730) registered 276 precipitation days, while the most sensitive TBG (Universal Precipitation Gauge, UPG-1000) detected 152 precipitation days. Case studies of the precipitation and seasonal accumulation results show the VPF-730 to be the most reliable precipitation sensor of the evaluated instruments. The precipitation amounts given by the reanalyses were positively correlated with wind speed. The precipitation from the Japanese 55-year Reanalysis was most affected by wind speed. Case studies also show that during low wind periods, precipitation measurements from the instruments were very close to the precipitation measurement given by the Global Precipitation Climatology Project (GPCP) 1-degreedaily (1DD) data. During strong wind events, the GPCP 1DD did not fully capture the effect of wind, accounting for the relatively small precipitation amount. The Laser Precipitation Monitor (LPM) and Campbell Scientific-700 (CS700H) experienced instrumental errors during the study, which caused the precipitation readings to become exceedingly high and low, respectively. Installing multiple LBSs in different locations (in close proximity) can help identify inconsistency in the readings.

Empirical recurrence rates for ground motion signals on planetary surfaces

We determine the recurrence rates of ground motion events as a function of sensed velocity amplitude at several terrestrial locations, and make a first interplanetary comparison with measurements on the Moon, Mars, Venus and Titan. This empirical approach gives an intuitive order-of-magnitude guide to the observed ground motion (including both tectonic and ocean- and atmosphere-forced signals) of these locations as a guide to instrument expectations on future missions, without invoking interior models and specific sources: for example a Venera-14 observation of possible ground motion indicates a microseismic environment mid-way between noisy and quiet terrestrial locations. Quiet terrestrial regions see a peak velocity amplitude in mm/s roughly equal to 0.3*N(-0.7), where N is the number of “events” (half-hour intervals in which a given peak ground motion is exceeded) observed per year. The Apollo data show endogenous seismic signals for a given recurrence rate that are typically about 10,000 times smaller in amplitude than a quiet site on Earth, although local thermally-induced moonquakes are much more common. Viking data masked for low-wind periods appear comparable with a quiet terrestrial site, whereas a Venera observation of microseisms suggests ground motion more similar to a more active terrestrial location. Recurrence rate plots from in-situ measurements provide a context for seismic instrumentation on future planetary missions, e.g. to guide formulation of data compression schemes. While even small geophones can discriminate terrestrial activity rates, observations with guidance accelerometers are typically too insensitive to provide meaningful constraints (i.e. a non-zero number of “events”) on actual ground motion observations unless operated for very long periods.