Short-Term Weather Forecasts Save Additional Diesel Power in PV-Diesel Hybrid Systems

Reuniwatt’s Sky InSight™ located on a client’s installation

Factories located far away from utility grids depend on electricity supplied by diesel generators. For financial reasons, operators often rely on what is referred to as hybrid supply, i.e., a combination of a diesel system and PV system. The core element of the PV-diesel hybrid solution is the SMA Fuel Save Controller. It regulates the electricity supply to ensure that priority is given to cost-effective solar energy.

Weather forecasts play an important role in this equation because if the sun is not shining, a diesel generator must immediately be used to back up the energy supply. With Reuniwatt’s new Sky InSight™ weather camera, forecasting the future short-term cloud coverage, and the SMA Fuel Save Controller, the share of electricity produced from solar energy in hybrid systems can be increased.

Any abrupt reduction in PV generation due to clouds can jeopardize the electricity supply. To prevent shutdown, PV hybrid systems always include a diesel generator running alongside as a backup to immediately step in. This generator must match the size of the largest possible load and must run at a minimum load of 30 percent to ensure it is not subject to increased wear. The electricity produced by the generator is always part of the electricity supply, although the reserve power would be necessary only if weather gets worse. In response, free solar energy would then have to be reduced.

Distinctly lower minimum load for the generator

Thanks to the new Sky InSight™ cloud camera, such precise cloud forecasts are now possible that a large generator, and the electricity it is able to produce, are no longer necessary. Typically used generators can be replaced by generators that produce much less power. If the SMA Fuel Save Controller receives the information that clouds are heading its way, there is still enough time to power up a larger generator with the base load of a smaller one. This compensates for the lack of solar energy. The amount of solar power out of the overall amount of electricity produced thus increases and diesel needs together with CO­₂ emissions decrease. This means that the lower the required base load of the system, the higher the additional amount of solar energy is provided when the Sky InSight™ weather camera is used. See examples below.

Using Sky InSight™, the fraction of PV power used in a hybrid system rises significantly.

Advantages of Short-Term Forecasting

• It enables to avoid underproduction: when all diesel generators are turned off and a passing cloud might compromise the plant’s solar generation, this solution anticipates the turning on of the appropriate number of gensets on time.
• It helps reduce overproduction: after long periods of cloud cover, when all generators are on to maintain enough energy production, it forecasts clear sky passages which mean some of the gensets can eventually be switched off.
• It permits to limit rapid genset switching, which can have a serious impact on the generators’ maintenance costs: when quick turns in weather are taking place (short periods of clear sky followed by quick cloud cover events), it is more cost-effective to keep the gensets running rather than swiftly turning them off and on again.

How Sky InSight™ and the Fuel Save Controller Pilot PV-Diesel-Hybrid projects

Reuniwatt has installed Sky InSight™ cameras across the world: Asia Pacific, Indian Ocean, Caribbean, Africa, Europe.

SMA and French solar forecasting expert Reuniwatt have been working for the past weeks on validating the compatibility of their respective solutions, particularly for the management of off-grid PV-diesel hybrid systems. Sky InSight™ communicates with the Fuel Save Controller by sending it signals which are interpreted according to the current situation: when clouds are forecasted in the coming minutes, the Fuel Save Controller automatically switches the diesel generators on. On the contrary, if a clear sky is predicted, the generators are turned off.

All about Sky InSight™

Sky InSight™ is particularly innovative because it uses an infrared camera, which enables to gather additional and more precise information about clouds compared to visible waveband cameras. Indeed, a thermal infrared imager has the advantage of detecting light transmission through clouds rather than relying solely on reflected and scattered sunlight in the case of a visible waveband observation system. Benefits of using a thermal camera are particularly obvious when you look in the direction of the sun. As shown in the figure below, the pixels of visible cameras tend to be light-saturated which leads to a lack of any relevant information regarding the presence of clouds in the sun’s region. On the other hand, Sky InSight™ shows a very limited saturated region. This is crucial to improve minute-ahead forecasts as irradiance drops from passing clouds over this region can be anticipated more precisely.

Getting rid of sun glares thanks to Sky InSight™

Reuniwatt specialises in forecasting solar irradiance and power production for the coming minutes, hours and days. For very short-term forecasting, Reuniwatt has developed a patented ground sky imager which enables forecasts up to thirty minutes in advance, with a 30-second granularity.

Learn more at www.reuniwatt.com