A PPA (Power Purchase Agreement) is a contractual agreement between two parties, where one party (usually a producer of renewable energy such as solar or wind) agrees to generate energy and sell it to the other party (usually a company or sometimes an energy supplier) for a specified period and at a predetermined price. PPAs are often used to provide financial stability to renewable energy projects because they provide long-term revenue security. 

However, in light of flexibility markets, the attractiveness of PPAs may be different. Flexibility markets are markets where energy supply and demand are matched in real-time. These markets can, for example, consist of energy network balancing, demand response services, or trading in energy storage capacity.

The lower attractiveness of PPAs in the context of flexibility markets may be due to various factors:

1. Fixed Prices and Quantities: PPAs often set fixed prices and quantities of energy. This can be limiting in a flexible market where prices and demand fluctuate and opportunities can arise from responding to real-time changes.
2. Less Flexibility: In a dynamic and rapidly changing energy market, the long-term and fixed nature of a PPA can limit the flexibility needed to take full advantage of the opportunities that the flexibility market offers.
3. Risk and Uncertainty: Flexible markets often involve higher risks and uncertainties due to the nature of fluctuating supply and demand. PPAs offer stability, which is attractive in more traditional energy markets, but may be less relevant in a market where flexibility and adaptability are more important.
4. Technological Advances: With rapid advances in energy storage technologies and smart grid solutions, new and more flexible models may emerge that are better suited to flexibility markets than traditional PPAs.

That said, the situation may vary depending on the specific market conditions, regulations and the nature of the PPA. In some cases, PPAs can still be valuable in flexibility markets, especially if they build in some degree of flexibility or as part of a broader energy portfolio