PHEV powertrain: An accidental climate solution?

A PHEV (plug-in hybrid electric vehicle) powertrain incorporates a gasoline or diesel engine, generator, battery, motor(s), and charging port. Just add a DC/AC inverter and it is a mobile power plant. The charging port can be used to accept renewable energy or grid input and it becomes a wonderful backbone for a mostly renewable energy microgrid. The motors are not needed to build the microgrid.

PHEV has always been like this all these years since the Prius dating back over 20 years ago. What makes it different that today it can be a climate solution? And as a fossil fueled generator, what makes it different from a diesel genset that has been playing a marginal role as backup generator in past few decades?

Numbers matter! The engine in a PHEV powertrain and the associated generator stands out in a number of metrics. The integrated battery at about 1/5 the price of just a few years ago materially changes the economics. Intense competition in the automobile market and the need to survive between an ICE (internal combustion engine) vehicle or BEV (battery electric vehicle) dictate that the PHEV needs to pack both the engine-generator and the battery-motor in about the same space of its rivals, and the efficiency of the engine-generator-battery-motor powertrain needs to match that of a direct ICE powered car to make it an attractive alternative to consider. Also, new car models must meet very tight particulate and greenhouse gas emissions standards. Let's review some numbers.

Efficiency: The heat efficiency of the engine in an PHEV is already 40% or better as of 2022 for the major brands, potentially reaching 45% near term and 50% long term. This is better than most diesel gensets (generator sets) and coal fired power plants, as well as beating prevailing gas peaker plants that are less efficient than full-feature combined cycle power plants. What's more, it is dispatchable power that delivers peak efficiency nearly 100% of the time.

Emissions: With mandatory compliance to Euro 6 or China 6 emission standards, the engines in PHEVs are likely to be cleaner than most power plants and gensets. Based on 200Wh/km power consumption for light electric vehicles, we can translate the emission limits of Euro 6 or China 6 to be about 5g/kWh of CO, 0.8g/kWh of HC+NOx, and 0.03g/kWh of PM. These figures are probably better than all but the newest large coal or gas power plants, which means they can probably replace existing gensets and small power plants with much improved emissions reduction. At these levels, they likely emit less greenhouse gas than household gas stoves and produce less particulate matters than tyre and brake wear.

Noise: It is hard to find noise level of the engine from whole-car specifications. Indirectly, if they are used in cars without complaints, we can safely assume that noise is so low as to be unnoticeable.

Size: At typical power around 100kW, the PHEV powertrains are surprisingly compact, thanks to competition pressure and the need to be carried around on wheels. Compared with a conventional genset, the engine in a PHEV can be designed to run at high speed instead of the typical 1500/1800rpm that direct AC output generators operate at. This gives them a few times better power density than gensets of previous generation that don't have access to low-cost battery storage. So instead of 1,000kg for a genset, a 100kW PHEV engine running at 4,000-8,000rpm with integrated generator and battery may be just 200-400kg.

Cost: A 100kW engine paired with a generator and a small 30kWh battery plus electronics is likely around US$10,000-15,000 given that some PHEV models are less than US$30,000. This gives capacity cost as low as $100/kW! It makes the firming cost of intermittent renewables a non-issue. At 40-45% heat efficiency, after provision for generator and charge-discharge loss, we can expect about 3-3.5kWh electricity per litre of gasoline/diesel. A 300L tank can provide 1 MWh at a cost of US$300 (US$0.3/kWh) based on gasoline price of US$1/litre or about US$4/gallon. Not cheap, but is acceptable, and very justifiable in many situations. What more to expect if for US$300 we are assured several days of energy access in freezing winter when other options fail or become too expensive.

Potential applications

So, what can a low-cost, 40-45% efficiency,100kW power generator small enough to put on a pallet or trailer do for us? At the community level, it can replace baseload power plants without the penalty of unavoidable operation during times when electricity price is low or negative; it can work just like a peaker plant although many units are needed to give similar power; it can be used to firm up renewable energy sources that makes their intermittency a non-issue; it can be deployed almost anywhere for emergency relief or temporary work. And it achieves these at fairly low cost.

There is a pledge of providing universal energy access for all by 2024, and this target seems not so remote if we use the PHEV powertrain strategically. There is also a clean-cooking initiative targeting the 3 billion people who are still using biomass stoves for cooking resulting in millions of pre-mature deaths and sicknesses each year. Each system of 100kW can now provide about 50 families of 3 to 6 people each with enough electricity to support an induction stove of about 2kW and other useful electrical appliances.

When this system is incorporated into a renewable energy microgrid, there is no longer the issue of intermittency. People can add renewable sources as they see fit to reach optimal utilization. So instead of arguing about the intermittency issue, we can start working on what to do with this reliability supporting, fuel-based generator. For example, in tropical and sub-tropical areas, a 100kW system can be matched with a 200kW or even bigger solar farm and encourage people, by way of different day- and night-time tariff, to make their meals early so that most cooking energy is supplied by solar power and fuel power is used to serve less energy hogging needs at night such as lighting and computer use for studying. Then a single system can support energy access for several hundred people. If the LCOE (levelised cost of energy) for the solar system is US$0.05/kWh and only 20% of electricity need be provided by the PHEV engine and we take LCOE with the fossil fueled PHEV engine at US$0.3/kWh, then the average cost is US$0.1/kWh. Much more acceptable than using just fossil fueled power generation. The configuration can be further improved with addition of wind power, which is somewhat complementary to solar and provides appreciable electricity at night and in winter. That will further drive down proportion of fossil fueled power.

The renewable+PHEpowertrain solution is a game changer to build microgrids at minimal capital expenditure, thereby enabling support to remote and sparsely spaced locations without the delay and high cost of grid expansion. It gets around bottlenecks in grid development, copper supply, and construction works. Utilities can now make use of this new possibility to profitably honour their mandate to support even remote customers.

Scalability

Okay, this solution is very cost-effective. But how scalable is it? Well, it is already at scale. While the number of PHEVs shipped in 2022 was only about 2 million and maybe reach 3 million in 2023, the potential is the ICE production capacity, which is 80 million a year. In terms of resource needs, each million units at 30kWh is 30GWh. At the current battery production capacity of over 1,000GWh and increasing, a few million units can be comfortably supported by existing battery supplies. Stationery battery do not have strict power density requirements, so we can choose from a wider range of options including LFP (lithium iron phosphate) and sodium-ion battery having less issues with materials supply. If the deployment scale is 10 million units of 100kW engine system a year, it is already a 1,000GW power generation capacity addition a year, it is more than twice the renewable energy capacity addition in 2022. The existing generation capacity in the hands of people with the over 3 million PHEV they have bought is already 300GW and over 500GWh integrated battery storage! So, it is not even a question of whether the required scale is possible, but rather how to make this power generation capacity serve those who already own the PHEVs but have not provided the key to access it for their electricity needs.

Feasibility

From system cost and project planning level, the PHEV powertrain greatly reduces the need for infrastructure investment in transmission network and fuel transportation. It will need the existing refueling infrastructure, however. That can cut deployment time from years of waiting to just weeks or days and turn an otherwise overbudget/overtime megaproject into thousands of simple mini projects. We can fit 300kW worth of solar panels and the PHEV powertrain including 100kWh of battery or more into a single 40ft container and provide firmed renewable electricity to support a farm, a factory, or a village as long as you can deliver a container there. Cost wise, a 200kW solar system may cost $300,000 at $1.5/W whereas a PHEV powertrain with 100kW engine and 100kWh battery may be around $20,000, which is but a single digit percentage of total project cost. As an enabling technology, it sets the stage for Tera-Watt level renewable energy deployment at scale of 100kW to 300kW per system. At 2022 solar panel production level of about 350GW and 25% historical CAGR (compound average growth rate per year), the solar PV industry need to worry more about production ramp up than overcapacity in the next few years.

How to proceed?

This sounds too good to be true. Now we are talking about something much cheaper than existing solutions and with better performance figures. Normally, when something is too good to be true, it is not true. But what if it is the case that in the course of competing to make the best new energy vehicle, we have accidentally perfected the PHEV powertrain to the point that it becomes far better than existing power generation alternatives?

It is common that people winning the lottery lose all their money, and they never win another lottery to support their increased spending habit. Given all the performance and cost advantages, it doesn't mean this breakthrough in the PHEV powertrain will naturally lead to a fast decarbonisation of our energy system. This can be the perfect case that Jevons Paradox applies, meaning that improved efficiency encourages more widespread use and hence increased total fuel consumption. A few million units will consume more than a million barrels of oil a day while the annual 1,000GW solar and 300GW wind are not there yet, or may never happen.

Another pitfall is hurrying to launch immature and non-adaptable systems that will go to junk yards, like the millions of shared bikes by money flooded startups that were scrapped. Energy system optimisation is non-trivial and poor algorithm will lead to curtailment of renewables and overuse of the engine, which can get unnoticed when the overall cost is low. It is much harder to enforce good practices for millions of users than enforcement for a small number of large energy providers. Poorly designed first attempts of closed systems will almost certainly make sub-optimal systems. We need provisions for performance to be improved as we gain knowledge for better optimisation of the system.

The ideal case is like the Apple II computer with well documented expansion capabilities to start a new era of user empowerment that liberates the imagination and talents of smart users, third party developers and service providers to grow the industry. The ease of configuring a system should be as simple as plugging in a USB device that automatically negotiates the best match with the host port, giving all products extended life, and may even give rise to new applications for old devices. The component parts can be made to public-domain, standards-based interconnections and protocols for easy reuse and repurposing. The 18650 battery form factor is an example of a de-facto standard, though it is probably far from optimal now. To maximize the virtues of this accidental possibility calls for early communication among industry practitioners to quickly define standards and hopefully this does not lead to cases of market manipulation probes or legal challenges.

Now let's return to this possibility of using the PHEV powertrain and to achieve energy autonomy, avoiding the potential pitfalls while realizing its enormous prospect to enable our rapid decarbonisation. It should be easy to quickly assemble a system with a simple robust first optimisation designed to absorb as much renewable energy as possible, and field test it to get real life performance and cost data. This will be our base case as a public domain reference design, and we can move on to make improved systems that have already incorporated features to avoid obvious pitfalls and a guaranteed minimum performance. That would be interesting!

That's not the end

What if we finally make the PHEV powertrain a climate solution that enables us to provide energy security to many and achieve a rapid decarbonisation of our energy system? Maybe even make up for lost time to make limiting global warming within 1.5C possible?

That would be great! But there's still challenges ahead. The loss of biodiversity, pollution of our environment, some climate tipping points already set in motion, and the collapsing ocean ecosystem are still haunting us. Hopefully we need not exhaust our resources and attention just for decarbonising our energy system. Then with the experience gained from this success and the resources left, we would have more chance to avoid the 6th mass extinction.

And still we have not tackled the root cause of our self-destruction tendency, one of it being consumerism and obsession for excesses. We are often retreating to our primal instinct of accumulating materials as a source of security and haven't advanced too much along building resilience through the cooperation and synergies in communities.

Human civilisation has gone a long way with countless magnificent achievements, we also have problems that can lead to our demise and collapse, creating collateral damages of a possible mass extinction. We are on a trajectory of over 2C warming above pre-industrial levels with dire consequences. Now it seems an accidental climate solution is upon us. We must not miss this opportunity to escape the upcoming mass extinction. But even so, it is a long road ahead for us to build up sufficient resilience to return us to safety. But at least, there is reason to be hopeful. We must make it work so that we can face our children and say that we have passed to them a planet that is better than what we inherited.

Conclusion

The PHEV powertrain based on a low-emission, high efficiency fuel consuming engine and compact generator with integrated battery storage and charging input can be a backbone for a microgrid that can take up intermittent renewable energy and deliver firmed power at low capital expenditure. It can support us to deploy renewable sources at Tera-Watt level annually for an accelerated energy transition and provide energy security affordably. The performance and prices are so good that it can lead to even more emissions by enabling much more demand. Hopefully, industry standards and good practices can be set before large scale rollout to avoid the pitfalls and deliver the benefits.

Is the PHEV powertrain an accidental climate solution? I don't know. But being aware of the potential pitfalls, we can go ahead with cautious optimism and increase our odds of success.

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What do you think? Are there any overlooked weaknesses that make the whole idea impossible? Is it possible but some crucial aspects are missing here? I would like to learn from you and hope that somehow, we can work out our climate solutions.