As renewable energy sources continue to increase globally, they have brought with them a new set of challenges for the energy industry. The most common concern associated with the increase in renewable energy technologies for energy production is intermittent availability. Particularly in relation to weather-dependent renewables, such as solar photovoltaics (PV) and wind turbines.

What is ‘intermittent availability’ and why is it a problem?

Intermittent availability means that electricity produced by renewable energy technologies is subjected to irregular alternations throughout a 24-hour period, week-to-week or even monthly. As expected, solar photovoltaics and wind turbines have favourable conditions in which they will efficiently produce electricity. However, it is often assumed that these technologies will only produce energy when there is a particularly sunny or windy day. This is not entirely true as PV panels will continue to function even in cloudy/rainy conditions, however, efficiency declines significantly, and wind turbines can continue to generate electricity from wind speeds of 5-6 m/s.

So why is this an issue? The intermittent nature of such renewable technologies means that electricity from these sources will not be continuously available. Today, we are used to having our electricity supply on demand and for some, it seems unrealistic to integrate a growing proportion of intermittent energy sources to our future energy system if is compromises reliability of the current system.

How can the intermittent availability of renewables be overcome? 

Large-scale integration of renewable energy into the electricity distribution grid supply creates technical challenges due to their intermittent nature. Therefore, intermittent availability has been at the forefront of renewable energy research for a number of years to try and alleviate the impacts of intermittent production. A general consensus is that an energy system which aims to integrate intermittent renewable energy sources must have a well-established energy storage system to complement it and reduce the impact of intermittent generation, by storing excess energy for use on demand.

Intermixing Solar and Wind Energy

An increasingly popular solution is a simple balancing approach in which the production of intermittent renewables such as wind and solar are monitored and intermixed so as to utilise the available energy from both sources at a given time. The approach allows the maximum possible power to be delivered by combining dominating and non-dominating resources all of the time – and mitigates the intermittency of individual resources.

Battery storage systems

Another approach to addressing the issue with intermittency is battery storage. Batteries have become the most broadly accepted solution to overcome the intermittency challenges associated with renewables. Batteries can help us to make the most of renewable electricity, particularly if this is a residential installation as solar panels typically produce electricity during daylight hours when most occupants would be at work. The electricity generated is therefore unused if the occupants have not installed a battery storage system. A battery storage system allows the generation from the solar panels to be stored for use on demand.

In the case of household solar photovoltaics, the capacity of a typical battery storage system within a home is 16kWh, but this can be increased depending on need. In addition, battery storage within the home will typically decrease household import from the grid leading to a decrease in energy bills. The most popular battery storage technologies are discussed further in another of our blogs: ‘The future of storing excess electricity in Northern Ireland’.

There has been significant research into how the energy system can address the intermittent availability of renewables, and battery storage appears to be the most commonly suggested solution. Regardless, any system put in place to help alleviate some of these challenges must ensure a secure and reliable supply of electricity to all.