September 17, 2021

Why smart charging is cheaper and cleaner at the same time

An often heard criticism is that Battery Electric Vehicles (EVs) are emissions free when they drive, but not when they are being charged. While they are much less polluting over their lifetime, the criticism is technically correct. However, we can do better! We can greatly reduce the emissions from charging, by doing so at the right moment in time and at the same time, saving a lot of money. Here is how achieves such savings.

Understanding CO₂-emissions from our electricity consumption

The conclusions from the independent and well-respected energy research institute, CE Delft are very clear:

  • On average the prices and CO₂ emissions are positively correlated.
  • This correlation is getting stronger over the years.
  • The most important contributing factor for this is the contribution of wind and solar power generation, while coal plants are being phased out.
  • It is desirable and advantageous to use electricity during midday or at night when the CO₂ prices are the lowest, because it increases the utilization of solar and wind generation.

Their simulation applies to the grid in the Netherlands, which obviously is interconnected with other countries. This makes it a really sophisticated model. Figure 1 and 2 below depict the expected relation between prices and CO₂ emissions based on a simulation from CE Delft:

Figure 1: Simulation for year 2020 (source: CE Delft)

Figure 2: Simulation for year 2023 (source: CE Delft)

You can see that, as we get closer to 2023, the correlation between CO₂ emissions and price is only stronger, which means it’s a better predictor for emissions.

To optimize and give feedback on CO₂-emissions (for the Netherlands) we have integrated the model from CE Delft into our optimization algorithm. Our optimization engine also uses predicted future price and emission-intensity that we preduct with a very high accuracy using Machine Learning ("StekkerML" is explained in detail, here). displays its calculated savings as follows:

Figure 3: estimates savings of 5,8 kg of CO₂ and 3,22 euro's

Note: This was from a partial charging session, which is representative: you usually don't run your battery empty. The savings can be much higher if you smart charge an empty battery all the way to 100%.

Why do low electricity prices and emissions go hand in hand?

The emissions you can attribute to charging your EV are determined by the marginal electricity producing unit, which is the most expensive producer that is being paid to produce electricity at that time. The marginal producer can be a coal fired plant or, at night, it can be subsidized wind-energy. This is why prices can go negative, because rational producers will only reduce the power output if they get paid more than the subsidy they would otherwise earn.

All of the electricity production and consumption must match exactly, otherwise the grid becomes unstable and we risk a black-out and extensive damage to equipment. Utilities and energy producers pay penalties if they cause an imbalance and they can earn income if they improve the balance. If there’s a lot of wind or sun, smart charging can improve the balance on the grid as well by preventing peaks and using surplus solar and wind energy. If a coal plant has to increase its output because of the extra load from EVs, this simply means more emissions. Instead of shutting off solar or wind farms because of overproduction (wasting renewable electricity) we use this to charge EV batteries. The fun part is, it doesn't require any effort.

When prices are negative, you can even earn money while sleeping by letting optimize charging.

Why use vehicle batteries instead of stationary storage?

Electric Vehicles have a battery that is much larger than a typical domestic stationary battery (e.g. a PowerWall). Also, if you need an EV for transportation purposes anyway, you also get a large battery on wheels without additional cost. The mining of minerals and production of batteries isn't emissions free either, so this is why it’s a good idea to make dual use of it. By helping to also balance the grid by storing excess renewable energy, it has a net positive contribution. Normally, while an efficient gas car only pollutes less, it still pollutes. Here, the EV actually helps solve a real problem, storing excess renewable energy and stabilizing the grid. It actually accelerates the energy transition!

Does this really revolutionize our electricity grid?

Without a doubt, smart charging will have a major impact on our grid.

The learning curve and scale of production drive down the cost of batteries. As a result, the cost of unsubsidized EVs have fallen enough to achieve parity with combustion engine vehicles in terms of total cost of ownership (TCO) even without the cost savings from smart charging. This will continue until it's also cheaper to buy an EV.

Figure 2: Battery cost declines are expected to continue
Figure 3: Electric Vehicles are going from cost disadvantage to a cost advantage when compared to gas powered vehicles. Source: Auke Hoekstra

Every year it will be increasingly unattractive to buy a gas powered car.

In the Netherlands, we currently have about 8 million vehicles or about 0.5 vehicle per capita. Now that electrification of the fleet is underway, we're talking about many millions of such batteries. With the same fleet size, but electrified, we might reach something on the order of 340 000 000 kWh of storage on the grid. If these vehicles are plugged in (and they are idle 23 of 24 hours a day on average), this would be enough to time-shift all electricity use of our country without relying on any additional batteries or storage technology. With 11 kW of power delivery per vehicle, we would only need about 1.5 million plugged in EVs to supply power during peak times (18,6 GW) to supply all power use in the country with these EVs. With very basic math, we can show the magnitude of the solution of battery electric vehicles: it has a huge, positive impact on how clean the grid can become.

With very basic math, we can show the magnitude of the solution of battery electric vehicles: it has a huge, positive impact on how clean the grid can become.

How smart charging makes an impact

While power from our grid is getting cleaner every year, we can do more. Electricity demand and supply determine the price of electricity. Increasingly, the supply of electricity is from variable sources that we can't determine because they are a consequence of solar and wind being available. This new source increasingly offsets centralized electricity plants that can ramp up and down on their production. Usually, prices are low when there’s a lot of solar power being generated and/or there’s a low demand. Increasingly, wind turbines at sea and some installations that must run anyway, will be enough to supply the demand at night. It’s not economical to buy fossil fuels and pay for emissions rights if prices are low or even negative due to low demand. And during low demand situations, this demand is more and more often already met (mostly) with renewable energy. The marginal costs of renewable energy from wind or solar are zero, which means that if you reduce the output of a wind turbine or solar installation, you will not save any costs (in contrast with fuel based sources).

By planning your session according to expected CO₂ emissions, saves money and emissions. By doing this together, at scale, we decrease the profitability of the centralized fossil-fuel based plants while improving the business case for renewables. We also reduce the need to invest in the grid, e.g. adding more copper in the ground. Because we're using purely software, it's probably the most effective way to increase sustainability and reduce costs for everyone.

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