In previous articles (https://edenergy.be/the-myth-of-flexibility-mobility/, https://edenergy.be/the-myth-of-flexibility-dwelling-heating/) we have seen that electrification of 2 major needs (mobility and dwelling heating) can’t be realized solely through flexibility based on demand curtailing, which can only provide a very limited contribution to quench the demand.

Conversely, a redesign of the electric car charging infrastructure – for what concerns mobility – and a focus on thermal insulation and local (dwelling) combined production of heat and power – for what concerns the heating needs – will very efficiently help to reduce dramatically the demand and the related (societal and individual) costs.  These costs reduction is mainly driven by the eviction of grid and production huge capacity investments increase.

In the same time, the realization of these 2 very strategic orientations will leverage the possibilities of flexibility (based on demand curtailing).

It is important to understand that dealing with quenching the energy demand by power production is rather a question of capacity (power, often expressed in kW, MW or GW) than consumption (energy, often expressed in kWh, MWh or GWh). Let’s take an example: assuming your domestic consumption on 1 day is of 12 kWh, with a peak of 5 kW for 30 minutes.  You could say: there are 24 hours in a day, thus with 0,5 kW of power I can produce 12 kWh a day (0,5 × 24 = 12).  But doing so, you will not be able to deliver the 5kW peak.  It is even worst, you would not be able to deliver the necessary power at any moment your demand exceeds 0,5 kW (500 W).  In the practice, nearly never for the large majority of the dwellings !

Conversely, if you have installed a 5 kW production engine, you will always be able to deliver your demand, but your installation will only work at optimal (or design) conditions during 30 minutes by day, and would be quasi unused for several hours.  Your investment would be very high in comparison with its use.

So you need to push down your peaks (flatten your demand) to avoid (very) suboptimal use of your installation and investment.  The same applies for the grid and the production capacities, but at a very much larger scale.

Once both your consumption (energy) and demand (power) are low enough, you can think about short duration (~ 1day) storage capacity and punctual (from time to time along the day) demand curtailing (‘flexibility’ in the following).

In any case, relying on flexibility on long duration (several days till 1 to 2 weeks) to quench the demand will never be possible.  This will be clear after having read the following.

Renewable electricity production is mainly of 3 kinds: sun, wind onshore and wind offshore.  It is important to consider these 2 last separately because their (production) characteristics are not similar.

A look at the Belgium renewable energy production shows us that with and installed capacity of 8,7 GW solar panel, 1,6 GW wind onshore and 2,3 GW wind offshore (the situation by the end of 2023), the lowest ratio production/load in daily averages is of 1,5% and the highest is of 67,9%.  When diving into 15’ values, instead of daily averages, these figures become respectively 0% and 104,3%.

These are the extremes. To get a real good picture we would need to calculate how much electricity storage should be necessary to capture the surpluses and in how far it could counter the scarcities, along the period.

In other words, we have to compare the demand and the production curves along the time, because the peak (or deep) of the one does not necessarily occur on the deep (peak) of the other.

Performing calculation comparing demand and production are typically achieved over long periods (30 years). One could argue that the climate change is now occurring, so that looking to 30 years ago is not so relevant anymore.  That is probably right, but we don’t dispose of reliable forecast for coming years, so we don’t have a better basis.

This forecast should also take into account the electrification of mobility and the electrification of the dwelling heating, or more generally the global electrification of the energy needs.  That is right, but this goes too far for this article and will be addressed in another one soon (I hope).

So, in the following we will focus on the 3 last full years (2021-2023).  So that the conclusions we will draw must be taken with nuances, however we will see that the gap to bridge is so broad that there is no doubt remaining.

Using the sun, wind onshore and wind offshore production and the total Belgium demand over the 3 last years, on 15’ granularity (a bit more than 105.000 records), we can calculate what is the best combination of these 3 production kinds.  Since along the 3 years, the production capacity of each kind has continuously evolved, we will take the load factor (production divided by installed capacity) for each timestamp and production kind.

Doing so, the optimal combination of the production capacity of each kind is the one that minimizes the discrepancies between the resulting realized production and the demand.  To find this minimum, the least square method must be applied.  Freeing you from the underlying math and calculations in, the outcome is:

• Sun: 15,8 GW
• Wind onshore: 11,6 GW
• Wind offshore: 6,0 GW

Surprisingly, at least for me, the wind offshore lays lower than the wind onshore, near its half.  Due to the higher yield (equivalent hours) and stability of the offshore wind I expected it to get a higher optimal level than the offshore one and also of the sun.  But it is not so.  Probably does the wind offshore produce too much in moments where the demand is low, in fact much more (in energy over the period) than the sun does.  However, the wind onshore production produces less electricity over a year (for the same installed power) than the wind offshore, it seems to be more in sync with the demand.  Another point to investigate later.

The question is now whether it is possible to store the surpluses when the production exceeds the demand and restore the stored energy when the demand exceeds the production (scarcities).  Rather, we have to calculate how much storage capacity is necessary to be able to achieve that.

A good indicator for this figure is the standard deviation of the differences between the production and the demand.  This figure is of course depending on the length of the period we want to bridge (how long can last a peak till the storage is filled and how long can last a deep till the storage is empty).  Of course this is just an estimation, a correct calculation needs iterations along the period (the necessary capacity depends indeed on the length and frequency of peak-deep sequences).  That is why the standard deviation is not more than good indicator.

Using a day as period to bridge, the necessary storage capacity is of 85 GWh.  Yes, soooooo much.  Of course, we can think about achieving a part of this bridge by curtailment of the demand (flexibility), but even with so much as 15% of the demand (having daily average of 223 GWh), we can only cover a ¼ of the figure (22 GWh <> 85 GWh), and 15% curtailing over a whole day is enormous.

Even if all the cars in Belgium (6 million) were (full) electric cars, equipped with a standard 40kWh battery (see previous article for the origin of this optimal figure), always plugged in when parked, they could bid a daily storage capacity of around 48 GWh (annual mileage of 15.000 km, thus daily average mileage of 40km, considering a consumption of 20kWh/100km, which is high, thus 8kWh/car on a daily basis).  This could only be achieved if every car parking was equipped with a charging pole (with 3,7 kW of max power: see previous article for the origin of this optimal figure), managed at federal level (with remuneration for the capacity made available).

In the best scenario, there are still 15 GWh missing, in the practice this figure would rapidly reach a 3-fold (ca. 50 GWh missing), and in the short term (till the generalization of electric cars would have been a fact), we can’t hope to get more than 22 GWh available, thus 63 GWh missing.

And 63 GWh on a daily basis means 2,6 GW (2,6 GW × 24 h = 63 GWh) of manageable production assets.  Taking into account the technical unavailabilities (maintenance, but also trips), the necessary installed manageable capacity must at least be of 3,5 GW.

Remember that nuclear power plants are not manageable, so don’t dream and don’t rely on them.  It is rather worst, from 2,9 GW of nuclear power plant there is no optimal combination with renewable possible.

From 2,1 GW of nuclear, you have to stop any increase of the Wind onshore production and limit it to its today already existing installed power, limit the increase of the Sun production to 10% of its today already existing installed power, but increase the Wind offshore to compensate these limits to till around 11 GW.  With 2,9 GW of nuclear, you have to dismantle all the existing Wind onshore production and to stop any increase of the Sun production.

Further, in all the cases, nuclear production does only reduce marginally the necessary storage capacity (from 85 GWh downto 79 GWh).

So, yes, nuclear is a real problem and definitively not a solution.

This all means that a molecule will be the mandatory route.  However this sounds like ‘the fossil fuels strike back’, it is definitely not the case.  Renewable will make the molecules (e.g. via electrolysis followed by synthesis with [captured] CO2) during production surpluses.  And during scarcities, the molecules will be deliver power (e.g. in fuel cells, or burned, with capture of CO2) in easily manageable units, like nano to small CHP’s so that the remaining energy (thermal losses) could be recovered for heating purposes.

With all the elements, in this last and 2 previous of the 3 articles about the ‘myth of flexibility’ (mobility, heating, electricity production) we have demonstrated that:

• the best way to fulfil our mobility needs is to use full electric cars having no more than 40 kWh of battery, install everywhere charging poles of 3,7 kW (and manage them in organized districts), and make the battery pack exchangeable (like you do with the battery in your computer mouse)
• heating needs will become very expensive in grid investment if the heat pump would be generalized, it is much better and cheaper to invest in dwelling insulation and promote hybrid (gas fired) boilers (0,3 – 1 kW electric and 1,5 kW thermal CHP + 5 kW extra boiler) with CO2 capture and injecting back into the grid pipes
• target 0 MW of nuclear power (by the end of the decade) and in the meanwhile limit the nuclear power installed to 2 GW a fast as possible, in parallel stimulate nano to small CHP (roughly from 1kW till 10 MW electric), with CO2 capture and invest in renewable fuel development
• flexibility, although it remains being a part of the solution, is not an option to bridge solely the gaps and shave the peaks (that will last over several days till 2 weeks), it can help but this help is very limited

Any other construction will lead to very important cost increase at societal level, in particular for all residential customers, and establish a permanent climate of anxiety and stress on the grid users (as well households as industrials and commercials).