Doris - Simulation, storage and sustainability (3) - Storage Sensitivity

Doris is a computer simulation of household energy consumption designed to explore the relationship between storage and the consumption of energy from sustainable sources.  It exists only in the imagination and has no physical reality.  A description can be found here:

• Doris - Simulation, storage and sustainability (1) - Description

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The base configuration for Doris is a household which consumes 2,500 kwh/year.  It is connected to the grid and has access to electricity from conventional, wind and solar sources.  In the base configuration (config 3) there is 10 kwh of storage.  Follow the above link for a more detailed description.  Incorporating storage into the household energy economy makes it possible to get a better match between the availability of electricity from weather dependent sources and the regular pattern of demand which comes from sleeping, work, college and preparing meals.

The proportion of sustainable energy consumed by a household from the grid is roughly 10 - 15% but on any given day this might vary from zero to 20% depending on the season and the prevailing weather. If a household has an element of storage, this might increase to 50 - 70%.  The Doris model assumes that the household has direct access to wind and solar sources, thus the output is not comparable to data from the national grid.

Obviously the the greater the amount of storage the better, but there are also economic constraints and this series of runs was intended to see where the law or diminishing returns set in with the objective of defining the base configuration.  As with any simulation, the output is determined by the assumptions used in the model and as there are many combinations, the graphs below only indicate the direction of travel rather than precise forecasts.

 The rules used by the Python 2.7 code give precedence to solar sources, if no solar generated electricity is available it then checks to see if there is any which has come from a wind farm, if insufficient power is available, the demand is met from storage and when this is exhausted if falls back on conventional sources from the grid.  Any surplus sustainable energy is used to recharge the storage.

The storage capacity affects the consumption of wind and solar sources differently.  The availability of solar sources is based on a 24 hour cycle with significant variations resulting from sun-earth geometry and cloud cover, thus diminishing returns set in with around 5 kwh of storage.  Wind energy tends to come in pulses a few days apart and the consumption of wind generated electricity increases with increasing storage.

The graph below shows that the proportion of energy from conventional sources falling as the storage capacity increaes.

Bases on these runs, the storage capacity for the base configuration was arbitrarily set at 10 kwh.  This is thought be a reasonable balance between cost and performance and there are available products for this capacity.

Note

This is a simulation, not real life.  This post was originally published on 17-Aug-2015 and substantially revised on 23-Nov-2015.