Doris – A thought experiment in progress (2) – Energy Delivery

Doris is a computer simulation designed to explore the use of sustainable energy by a typical household.

The post which describes the background to the project, also contains links to related posts.

The core functionality of Doris is the facility to make estimates of the output of wind and solar generators using aviation weather reports (Metars).  The version running on the Raspberry Pi runs the base configuration and uses a live feed from NOAA, but the same code can be fed with historic data which makes it possible to explore a range of configurations and scenarios.

Wind and solar sources are weather dependent energy sources subject to seasonal variation, this distinguishes them from fossil/nuclear plant whose output is controllable.  Storage and diversity helps to match supply and demand.

The first graph shows the estimated breakdown of energy sources for a configuration with approximately one day’s storage.  There are several things happening in this graph, the first is the seasonality of wind and solar sources.  Solar works well during the summer months, but makes little contribution during the winter.  Another issue is the constraints on the amount of energy that the system can import, these have been set at low levels and may restrict the amount of energy that can be stored.  During the winter months, the system falls back on to the grid more than is desirable. This is partly due to the differences in the pattern of delivery from wind and solar sources.

Wind energy comes in pulses at intervals ranging from a couple of days to a fortnight.  In winter during the calm periods, Doris maintains it’s imaginary load from the grid.

In contrast the delivery of solar energy is regular, within a given month the greatest variation comes from variations in the nature of the cloud cover.

A relatively small amount of storage will provide a reasonable match between supply of solar energy during the summer and the load it is maintaining.  It is probable that a much larger storage capacity is needed to meet a constant load from wind sources.

The next step is to run a sensitivity analysis on the amount of energy taken from the grid and the storage capacity of the system.


About SolarBucket

I trained as a mechanical engineer in the 1970's and then spent most of the following 25 years doing sums and software for Oil and Gas Exploration. Current interests are the study of wind and solar resources.
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