Doris - A thought experiment in progress (6) - The Mix

Doris is a thought experiment running on a Raspberry Pi and a laptop which is intended to explore sustainable energy, an evolving description and discussion can by found in a previous posts:

• Doris - A thought experiment in progress
• Doris - A thought experiment in progress (2) - Energy Delivery
• Doris - A thought experiment in progress (3) - Storage Sensitivity
• Doris - A thought experiment in progress (4) - You have to do both
• Doris - A thought experiment in progress (5) - Good and Bad Years

It is important to remember that Doris is a computer simulation with some arbitrarily set parameters and rules, it exists only in the imagination and has no physical reality.

Whilst scribbling lines of code, economics have deliberately been pushed into the background, but the loose assumption has been that both solar and wind generating capacity (excluding ancillaries like storage, inverters and bits of wire) each cost £1k/kw and the that the total cost is within sight of £5k and a lot of inconvenient issues have been ignored.   The rules which have been used suggest that a load of 2,500 kw/year can be matched with 2 kw of generating capacity.  The base configuration pretends it has 1 kw of wind and 1 kw of solar.  Changing the mix of wind and solar gives different results.

The objective is to minimize the dependency on conventionally generated sources.  These comments relate to a temperate maritime climate (Koppen: type Cfb), different climates would result in different results.  For example a hot desert (Koppen type: Bwh) would get a better yield from solar due to the relatively minor seasonal variations and the absence of cloud.  Subarctic climates (Koppen type: Dfb)
would get a low yield from solar due to the low sun and short days during winter months, in these places wind might offer a solution.

The graph shows the results of the simulations in which solar accounts for 25%, 50% and 75% of the generating capacity.  The graph shows maximum monthly draw down from conventional sources (which usually in December or January)  The dependency on conventional sources is lowest when the proportion of solar to wind is 25%/75%, this is primarily due to the low yield from solar during the winter.

In these simulations, the load is constant throughout the year, this is not realistic as the load would almost certainly be greater in winter than in summer  Future simulations may introduce seasonal variation in load, this will probably increase the amount of energy drawn from conventional sources with the low solar configuration.

A somewhat different results when the annual utilization of sustainable sources is plotted, in this case the high solar configuration uses approx. 82% of the energy it generates.  This is in part due to the high yield during the summer.  In its current form, the code gives priority to solar sources, but it is not thought that this has a major influence on the outcome (this may be tested in future simulations).