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Sweet Answer from Solar Mango: (updated Jul 2015)

This is an important question that is being asked by many industrial and commercial units in countries such as India that use significant amounts of diesel as a backup power generation fuel. And with the significant escalations in the cost of diesel in the past few years (even after the current drop in crude prices, diesel prices have not gone down much in countries such as India), these segments are keenly considering the use of solar to reduce their diesel consumption.

The following are the brief inferences from Solar Mango, based on the significant extent of research our team has undertaken for reduction of diesel through the use of solar power:

1. Even if you have a large rooftop area, the size of your solar power plant needs to be designed in such a way it is larger than the diesel generator capacity. In fact, in most cases, it is recommended that the solar power plant capacity is only about 30-40% of the capacity of the diesel generator.

2. Diesel gensets need to run at a minimum of around 50% of their capacity, else their efficiency drops significantly. At very low load factors. they could end up consuming significant amounts of diesel to generate 1 kWh. But there will be times, when both solar and diesel genset are operating, when the solar panels generate most of the load required by the user. If left unchecked, the diesel genset could work at very low load factors during these periods and could end up consuming significant amounts of diesel. As a result, during such times, it is important to limit the amount of solar power supplied. Solar power plants hence need to designed such that the diesel gensets do not end up running at very low capacities. A thumb-rule used by some solution providers is to ensure that the solar power capacity is a maximum of 50% of the total load for the end user.

3. During times when the load from the user is low and solar power generation is high, there is a possibility of the excess electricity from solar entering the diesel genset, which could cause severe harm to the equipment.

For all the above reasons, the size of the solar panels should be carefully designed when they co-exist with diesel gensets.

Takeaways?

• Solar Mango’s studies show that users should expect only about 20-25% of diesel reduction owing to the use of rooftop solar power.
• Companies with larger workloads and larger use of diesel genset during daylight hours can see more significant savings than companies for whom workloads and diesel genset use are higher during evening or night times.

Related Articles

• Can rooftop solar PV replace diesel entirely?
• Is rooftop solar power cheaper than diesel/grid power?
• Diesel reduction using solar – what is the reality?

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