
more computationally efficient models, most of the machine learning work still focuses on the
opposite: building larger models with more parameters to tackle more complex tasks [8]. Recent
work poses the question of how much is the performance gain worth [8], specially in these applications
where deployment of a simple technology could already have a big impact. The move towards less
computationally intensive models has already happened once in weather forecasting, as deep learning,
despite its competitiveness, has often lower computational requirements than numerical weather
prediction based on differential equations [12, 13].
Through our work, we study low-resource and shallower predictive models and try to estimate the
benefit that they could bring if they were deployed large-scale for solar nowcasting
2
. The models,
which are build on one Tesla T4 GPU available through Google Colab, could be deployed large-scale
around the world independently of hardware limitations. The reason we are interested in researching
this low-resource setting, by studying smaller models, is because those are the models that could
be deployed to support the grid in emerging economies, which are where the real need is for clean
energy solutions, i.e. where the energy demand is rapidly growing.
2 An empirical comparison of PV yield nowcasting: Experimental results
For the task at hand, we study convolutional neural networks (CNNs), Long Short-Term Memory
networks (LSTMs) and their intersection [13] (ConvLSTMs). In theory, this comparison may seem
futile as LSTMs and ConvLSTMs should outperform CNNs, because of their use of state information.
However, Bai et al [1] argue that simpler CNNs can often outperform LSTMs. Moreover, ConvLSTMs
require a large amount of memory simultaneously available in order to process and update the state
information used in its predictions, which means they often take longer to train, leading to more
energy usage and hence higher emissions.
Dataset
Solar generation data refers to the yield from specific solar panels. The dataset
3
is
composed of satellite imaging and PV readings. The satellite images are provided by EUMETSAT,
covering the northern third of the Meteosat disc every five minutes. Open Climate Fix developed the
eumetsat_uk_hrv
dataset [6] which takes the ‘high resolution visible’ (HRV) channel for a reduced
time period and geospatial extent. The dataset was reduced in this paper to meet computing resources
available. A 64 x 64 crop was randomly chosen to focus on Devon, selecting images taken between
05:00 and 20:00 as there is minimal PV output outside of this window for most of the year. However,
this still left many readings in winter when the sun was below the horizon, and the PV yield was
zero, so readings when the solar altitude was below 10 degrees were also dropped. Open Climate Fix
provided a dataset of 1311 energy yield readings from PV systems in 5 minute increments for most
of 2018-2021, originally provided by a PV operator. The size of the dataset varied slightly based on
the prediction window. For the shortest window, there were 2018 observations of (12, 64, 64) and
(12, 1) to predict a series of 12 readings. For the longest prediction window, there were 659 blocks of
the same sizes described earlier to predict a series of 48 readings.
Learning task
We formulate our learning task as predicting a sequence of values representing
the future PV yield. All models take as input 12 sets of 5 min data, i.e., 1 hour of data as input,
and predict forward between 1 and 4 hours. We also consider two learning scenarios: i) learning
exclusively from past PV data only, and ii) learning from both past PV and satellite data as inputs.
Models compared
For each learning scenario (with and without satellite imaging), we test both
CNNs and LSTMs, our objective being comparing their prediction efficiency and carbon footprint at
the task at hand. Additionally, LSTMs encode time relationships explicitly, and we are interested
in evaluating if this additional complexity increases the prediction performance of our models to a
significant extent (and at what potential carbon cost). For the PV only models (CNN and LSTM),
which are the simplest models we test, we take in past PV through multiple layers of CNNs, followed
by a fully connected layer. The other PV only model has a similar structure but uses LSTMs in place
of CNNs. The second group of models take both satellite images and past PV yield as input. The
Conv3D is a CNN which uses multiple levels to try to learn abstract features. After each convolutional
2
Our low-resource settings are not simulated, this project has been done as part of a MSc thesis dissertation,
with no other computational resources.
3Thanks to Open Climate Fix for providing the datasets.
2