on this page (table of contents)
problem: the wind does not always blow and the sun sets
There are times throughout the day that solar and wind plants do not generate any power.
Notably, energy demand typically peaks in the early mornings (8am) and evenings (6-7pm) well outside the peak generating time (noon) for solar power.
in short:
- During peak mid-day solar power generation, the power from other sources must be reduced to balance supply and demand
- Adjustments in output from conventional plants may not always be able to match the variability of solar and wind power generation, resulting in excess energy and waste
- It is estimated that the overall penetration of solar power is capped at 30% and costs start to rise after 20% penetration
- California generates 14%-19% of its power from solar and is approaching these levels
Challenges can be addressed through several means:
- demand response
- Demand response allows electricity consumers to shift power demand to times of high supply
- improved power transmission
- The transmission of power over long distances can help transmit power from distant renewable energy sites and smooth fluctuations in intermittent power generation
In essence: Both techniques are part of the solution, but efficient storage of renewable energy is essential to fully utilizing intermittent renewable energy sources
- energy storage
- Several storage techniques exist, including Pumped-Storage Hydroelectricity (PSH), batteries, and Hydrogen Energy Storage (HES)
- HES converts electricity from renewable sources into hydrogen through electrolysis and stores it for use in fuel cells
- PSH and batteries have high efficiency but may not be suitable for large grids due to land restrictions (PSH) or cost (batteries)
- HES is scalable, allows for long-term storage, and is portable, but other costs have limited its adoption
energy storage process using renewable energy
Why does hydrogen energy cost so much?
- The costs of hydrogen energy storage are due to its low efficiency and the capital costs of power conversion systems
- The efficiency of hydrogen energy storage is estimated to be 35% for round-trip AC to AC and is unlikely to exceed 50%, compared to 70-80% for other systems