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Some data from Ireland SEMO (weekday electricity prices) and quarterly prices from the European Commission imply that Irish weekend prices are greater than weekday prices.

The same datasets used showed the correct relationship (weekend prices lower) for France, Denmark, Netherlands, Belgium, and Norway.

  1. Is this actually the case?

  2. If so, why is it the case? Typically wholesale electricity prices are lower during weekends in most countries.

To clarify, I have wholesale hourly prices for weekdays only for Ireland in 2013 and 2014, from the power exchange: http://sem-o.com/marketdata/Pages/default.aspx For intellectual property reasons I cannot upload them, but taking the mean across these weekday-only prices gives quarterly means in 2014 which are lower than that reported by the European Commission Quarterly Report on European Electricity Markets. An example of a quarterly report: https://ec.europa.eu/energy/sites/ener/files/documents/quarterly-electricity_q3_2014_final_0.pdf (page 14, in the little map of Europe with average prices on the map)

Since the mean of weekdays only is below the mean of all days in a given quarter, this implies that the weekends have higher mean prices than the weekdays. This isn't usually the case for most countries, since generally factories and offices use up more energy than people relaxing at home.

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I can imagine that demand is higher on the weekends as people are at home more entertaining themselves with electronics. A higher demand would explain the higher price. – BB King Sep 21 '15 at 19:08
    
To clarify, I have wholesale hourly prices for weekdays only for Ireland in 2013 and 2014, from the power exchange: sem-o.com/marketdata/Pages/default.aspx For intellectual property reasons I cannot upload them, but taking the mean across these weekday-only prices gives quarterly means in 2014 which are lower than that reported by the European Commission Quarterly Report on European Electricity Markets. An example of a quarterly report: ec.europa.eu/energy/sites/ener/files/documents/… – tony Sep 22 '15 at 21:23
    
Since the mean of weekdays only is below the mean of all days in a given quarter, this implies that the weekends have higher mean prices than the weekdays. This isn't usually the case for most countries, since generally factories and offices use up more energy than people relaxing at home. Unless, of course, Irish electricity prices are so high as to discourage all energy-intensive industries from setting up in Ireland. A plausible explanation, one which I will investigate by looking at energy intensity of industry by country. – tony Sep 22 '15 at 21:30
    
99% of the time European countries have lower electricity prices in the weekend than they do in the weekdays. The only time this diverges are on national holidays, christmas and so on. Otherwise prices are higher on weekdays. – Lasse Sep 23 '15 at 12:38
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The fact that it is proprietary does not in any way prevent you from telling us exactly what the name of the data series is, and exactly where it can be found. – EnergyNumbers Sep 24 '15 at 18:00

From looking at the data I have access to, I'd say that things stop early on Friday afternoon in Ireland. So the Friday evening peak is lower than evening peaks on other weekdays: it's the only day of the week where the evening peak is about the same price as the morning peak.

As you haven't provided the metadata of the data you're using, nor links to find that out, I've looked at the SEMO data I know about.

The Single Electricity Market Organisation (SEMO) for Ireland gives prices by trading period (half-hours, starting at midnight), for every day of the year. So I took a 3-month period at random, 1 Feb - 1 May 2015, and looked at the average price for each half-hourly period, for each day of the week. Note that this is a simple arithmetic mean: there's no weighting by volume, no special handling of public holidays, no weather adjustments.

enter image description here

Friday, Saturday, Sunday have heavier lines, because they're the ones I'm emphasising. The four weekdays Monday-Thursday are very similar to each other. Saturday and Sunday each have later and lower morning peaks than Mon-Fri.

But Friday's evening peak is the lowest evening peak of the week. Much lower than any other day. Whereas in-day prices normally peak around 18.00-18.30, due to most industry still being powered, most commerce still being powered, and most homes being active, that's not the case on Friday: peak prices are a lot lower.

Note that there is no single price of any one MWh of electricity. Electricity gets traded many times over, starting maybe a year in advance, a month, a week, a day, an hour in advance, and then within the half-hour trading period itself there will be varying sell and buy prices. So there are huge dangers in trying to draw inferences from two different sets of price data, particularly when you don't have the metatadata that tells you what the data actually represents. The SMP price data I've used here is the System Marginal Price. There's a good description of pricing and scheduling from SEMO here (pdf), including on page 9 the calculation of the SMP.

Electricity prices are complicated. Unit commitment is complicated.

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