Doris - Simulation, storage and sustainability (4) - You have to do both

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 current version of Doris is the third attempt to explore a sustainable energy system.  The first took place in 2007/8 which became known as the Solar Bucket.  This was simply a 4 watt solar panel connected to a small lead acid battery, during the day the panel charged the battery which was then used to support some form of load overnight, the most useful being an LED light.  The Solar Bucket worked OK during summer and less well during winter.  One of the lessons of this exercise was the effect of clouds on solar devices.  The second attempt was in 2013 which used the output of an imaginary wind farm to charge a bank of Ni-MH cells, if the make believe wind farm did not produced enough electricity, it kept itself alive using an old mobile phone charger.  This version ran erratically during the winter of 2013 and again in the spring of 2014.  The behavior of this system can be summarized as alternating between a few days on wind power and a few days hanging on the phone charger.

I took away two lessons from this experience, first that messing with hardware is a fun, but a slow way to explore a concept and a software emulation would be more efficient (and cheaper).  Secondly, for the location where I live which has a temperate maritime climate (Koppen type Cfb), a system which attempted to minimize dependency on conventional sources would probably need to utilize both wind and solar sources.

The graphs below show the result of three runs of Doris using historic data for 2011 using the base configuration with 10 kwh of storage and an annual load of 2,500 kwh.  In the first, the system has access to both wind and solar sources.  In its current form, Doris gives priority to solar energy, so the combined graph is biased towards solar and a different set of rules would give a different outcome, but it gives an indication of the direction of travel.

In this configuration, the peak demand for conventionally generated electricity is approximately 30% which can take place more or less anytime except summer.  When access is restricted to wind energy alone, the peak demand for conventional energy rises to 55% in summer with significant amounts being needed throughout the year.

In the solar only configuration, the dependency on conventional sources rises to 90% in winter, but less than 10% in summer.

As with all simulations, the output reflect decisions about the inputs.  for example, different results could be obtained by increasing the access to solar energy.  This would provide a surplus for export during the summer months with less dependency on conventional sources in winter.  The base configuration for Doris is loosely based on a 1 kw solar array (four 250 watt panels) and 1 kw of wind generating capacity.  The location of the wind capacity is assumed to be at a prime location.

History: originally posted on 19-Aug-2015 and revised 24-Nov-2015.

Images: blog_116