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Hydropower has reigned as one of the most established forms of renewable energy for decades. Hydropower facilities are now making large investments in their plants in order to meet a growing mandate to enhance their effectiveness in innovative ways.

The industry is now asking: How can hydropower work with other forms of renewable energy to overcome the shortcomings faced by a single source of energy? One answer involves a cutting-edge approach that combines the increasingly attractive economics of solar power with the reliability and storage capability of hydropower.

Each industry has a weakness

On its own, any form of energy will have its limitations. Hydropower depends ultimately on rainfall, which is problematic given that many areas of the world are experiencing prolonged periods of change in rainfall levels¡ªsometimes resulting in drought. When rainfall decreases, we see lowered reservoir levels and reduced power generation. This means during a drought, there is excess hydropower capacity because there isn¡¯t enough water to run the plant at full speed. In extreme cases, a reservoir may even dry up, resulting in no power production and depriving a community of an important water-storage asset.?

Solar energy also has its challenges, including intermittent availability. Solar is dependent on the sun shining, meaning no power at night or reduced power during a cloudy day. Also because of lack of current energy-storage options, excess solar energy can not be stored in many locations.?

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Partnering to ensure consistent power

This is when a hybrid approach becomes an ideal option. Floating solar panels at existing hydropower facilities can provide the reliability needed by solar while reducing evaporation at hydropower facilities. With this approach, hydropower units operate at minimum or reduced output when the solar output is high. That means the hydropower units are mainly used to regulate power frequency. When the sun goes down or solar output is reduced by clouds, the hydropower units are ramped up (subject to the available water supply). In this way, each form of energy compensates for the other¡¯s limitations, and the combined system can more closely match energy demand.?

We¡¯ve completed a?pilot project¡ªwith more coming in the near future¡ªthat adds 40-kilowatt floating photovoltaic panels to a hydro-plant basin in Italy. The approach enables even modestly sized hydropower reservoirs to act as cost-effective energy-storage facilities, all without reliance on batteries.

And it¡¯s great for the grid: Pairing hydropower and solar is remarkably effective in that it allows us to keep a constant energy supply to the grid while not overtaxing it.

Conserving water and mitigating drought

There are parts of the world¡ªlike California¡ªcurrently suffering from major changes in rainfall. Water storage is an ongoing issue for these communities. Existing hydropower facilities are not only used as power sources but essential water storage and recreational facilities for the community. The use of floating solar panels can reduce evaporation of the reservoir while enhancing output from the panels due to the temperature-moderating effect of the water.

Creating a combined hydro and solar facility may seem like a considerable investment. However, during drought, an existing hydropower facility has excess generating capacity, and this may be enough to support the addition of a substantial photovoltaic power station or solar park. Having both hydro and solar capabilities together in one power system can keep output at a high level while conserving water in the reservoir. The principal also applies when there is no water shortage, assuming the hydropower units are not 100% utilized 24/7.

We call this concept ¡°time-shifted energy storage.¡± Time-shifted storage is the ability for a hydropower plant operator to decide when and how much water to run through the hydropower facility. By running less water while the sun is shining, they can ensure the community is getting the needed power through solar and the reservoir can refill.

This approach can reduce water consumption, increase the penetration of solar power in the energy picture, and enhance frequency regulation in power generation systems. Ultimately, the cost can be very attractive, particularly for existing hydro systems. Two is truly better than one with these renewable energy sources.