5 Questions with Richard Perez: The Path to a Clean Energy Future

Even though any renewable electricity we can’t use or store gets curtailed ─ essentially “spilled” and not used ─ building a bit more renewable capacity than we strictly need can actually make the whole system more reliable and cheaper.

Here’s why:

When weather conditions are poor for long stretches ─ dark winter weeks for solar or long wind lulls (sometimes called renewable droughts) ─ an oversized fleet of solar panels and wind turbines still produces more energy than a smaller one would. That extra output during the toughest periods means we don’t need nearly as much expensive energy storage to get through those low‑generation times.

In other words, paying for a little more renewable generation upfront, and accepting that some of it will be curtailed during high‑production moments, often costs less than building huge amounts of storage that would only be used during prolonged renewable energy shortages.

This approach is sometimes called implicit storage, because the overbuilt renewable capacity effectively reduces the amount of physical storage we need.

How does this report fit into the implicit storage strategy?

The idea of implicit storage was originally developed by my son, Marc Perez, in his PhD work and then expanded in several peer‑reviewed publications starting in 2018. His research showed that strategically oversizing renewable generation—so that some energy is occasionally curtailed — can dramatically reduce the amount of physical storage needed to run a reliable, 100% renewable grid.

What this new report adds is scale and international validation. By bringing together experts from multiple countries, the IEA created a common framework to apply the implicit storage approach across many different climates and grid conditions. The results in this report show that the strategy consistently works. Oversizing renewables to smooth out low‑generation periods can make a fully renewable power system both technically feasible and economically competitive in many regions.

In short, the report takes a concept proven in earlier academic work and demonstrates its global relevance. It shows that implicit storage isn’t just a niche idea — it could be a practical pathway to affordable, 100% renewable electricity almost anywhere in the world. 

What else is needed, beyond more solar panels and wind turbines, to ensure renewable energy is reliable?

Several ingredients are needed to turn variable wind and solar into a fully reliable power system, and each plays a different role.

Storage batteries, the “glue” of the system: Batteries help turn the moment-to-moment ups and downs of wind and solar into a steady supply. But by building more renewable capacity than we need at peak times, we can cut battery needs by over 90%.

The right blend of wind and solar: Wind and solar produce power at different times. Combining them in the best proportions for each region reduces gaps in generation and lowers the need for storage or backup.

Flexibility helps match the load to wind and solar output: This comes in two forms, either by adjusting demand (demand side flexibility) or by using dispatchable generation to complement wind and solar (supply-side flexibility).

• Demand-side flexibility: Shifting activities, like EV charging, to times of high renewable output.
• Supply-side flexibility: Using small amounts of fully controllable backup power during multi-day periods of low wind and sun.

The backup power can run on 100% renewable “e‑fuels”, made from renewable electricity and designed to have zero net emissions. Only a tiny fraction of total energy — about 2–4% — needs to come from these turbines, but it ensures the system stays reliable even during rare renewable droughts, while keeping overall costs low. 

Do you believe the United States can realistically reach 100 percent carbon-free electricity in the near future?

Absolutely. The numbers already show that it’s achievable. A fully renewable, around‑the‑clock power system could deliver electricity at roughly 5-7 cents per kilowatt‑hour by 2040 — even without subsidies. That’s on par with today’s wholesale prices, and far more stable over time because wind and solar have zero fuel cost and aren’t exposed to global market volatility.

But while the technology is ready, our regulatory framework is not. The main barriers are market rules designed decades ago for fuel‑based power plants. Those rules don’t recognize or reward the strategies that make a 100% renewable system both reliable and affordable.

For example:

• The implicit storage strategy is currently treated as waste and penalized in markets, even though this approach dramatically reduces storage needs and keeps overall firm power costs down.
• There is no mechanism to coordinate the full suite of renewable resources — wind, solar, batteries, flexible demand, and dispatchable renewable fuels — into a single optimized system designed to deliver firm, 24/7 power.
• Market structures encourage siloed, independent operation of renewables and storage, which indirectly leads to congestion, long interconnection queues, and non-optimal use of renewable assets.

In short, reaching 100% carbon‑free electricity is not a technical challenge. The challenge is updating market rules so they can support the modern strategies that transform variable renewables into a dependable, always‑available power supply.

What lessons can we learn from the communities already transitioning to renewable energy?

Local communities play a crucial role in the energy transition by improving efficiency, reducing consumption, and strengthening resilience. Better buildings, smarter energy use, and community preparedness all ease pressure on the grid and accelerate decarbonization.

But even ambitious local renewable projects operate within today’s grid rules, which weren’t designed for high renewable penetration. A town with widespread rooftop solar — or a household with a large net‑metered system—may look “net-zero” annually, yet still rely on the broader grid as backup. This works when only some follow the model, but if everyone did, the grid could no longer provide the invisible balancing that makes individual net‑zero possible today.

Achieving true 100% renewables requires solutions beyond individual or community-scale deployment. Communities are the trees; the fully renewable, reliable system is the forest. Local efforts strengthen the trees, but without modernized market rules to coordinate generation, storage, and flexibility across the grid, even the most successful local initiatives may fall short system-wide.

In short, local leadership is vital, but it must be paired with market frameworks that align community success with the least-cost, system-wide reliability of renewable energy.