RENEWABLE HYBRID ENERGY SYSTEM
India has added 65-70GW of wind and solar capacity so far, with wind
and solar contributing 9.5% of generated energy in May 2019. If the government
target of 175GW is achieved by 2022, this share could exceed 15-16%.
Renewable energy
has three inherent challenges.
- First, it relies on intermittent sources, producing energy only when the sun is shining or wind is blowing.
- Second, its output is constrained to specific hours of the day.
- Third, its use leads to lower utilization of transmission lines.
This can create issues in matching peak power demand with
renewable output (e.g. in evening hours when solar energy is not available),
and raise costs of transmission. Experience in countries which have achieved
renewable energy penetration of over 15% indicates that some flexible energy
resources which can rapidly ramp up or down are needed. These could include hydro or gas-based power, or energy storage
solutions.
RENEWABLE HYBRID
ENERGY SYSTEM
Renewable hybrids can
be one solution to the above issues. Simply put, a hybrid system can
combine wind, solar with an additional resource of generation or storage.
- In India, we observe that solar output is maximum between 11am and 3pm, while wind output is highest in late evening and early morning. Peak demand for power is reached in the evening hours of 6-9pm, which cannot be catered to by either wind or solar.
- If we can store some energy during excess renewable generation hours and release it into the grid during peak demand hours, the combined “hybrid" system can produce 24x7 clean energy in response to varying levels of demand through the day.
- The storage can take many forms, such as batteries, pumped hydro or mechanical storage through flywheels.
- The intermittency of wind and solar could also be balanced by adding a fast ramping source of power; for example, an open cycle gas turbine. The overall output of the hybrid system can thus be matched against a required load on an hourly basis. In this way, it can provide both baseload and flexible power.
Hybrid systems are expected to become increasingly cost
competitive, driven by reducing costs of battery storage and solar energy. An optimal combination of solar, wind and
storage can deliver stable round-the-clock power.
If the above improvements are factored in, wind-solar storage hybrid systems could
generate round-the-clock power with cost as well as reliability levels
comparable to existing coal-fired power plants in the next 4-5 years. For
example, a hybrid system which is required to deliver a flat load of 250MW
could be designed by combining solar, wind and battery storage, at a levelized
cost of energy at 3-4/kWh by 2025. This is, of course,
dependent on the specific location and some seasonal variations.
India’s ministry of new and renewable energy released a solar-wind hybrid policy in 2018.
This provides a framework to promote grid-connected hybrid energy through
set-ups that would use land and transmission infrastructure optimally and also
manage the variability of renewable resources to some extent.
India is not the only country planning hybrid projects;
50-plus hybrid projects of MW-scale have already been announced or are under
construction globally, with Australia and US being the leaders. For larger
capacities or longer duration balancing, pumped hydro is a viable storage
solution, but is restricted by the lack of suitable physical locations.
If the economics of hybrid systems do approach the above
levels, our analysis indicates that they can potentially be competitive with
30-40% of existing coal-fired stations in India. They can therefore become a
viable solution to meeting future baseload power requirements, all at zero
carbon emissions and future cost-inflation proof.
