When I talk about solar power to top management in industrial and commercial enterprises, many of them wish to know whether they can use solar power from their rooftops to completely eliminate the use of grid.

I come across many other companies having a similar need. I hence thought it would be good to have a detailed post of how much grid independence can indeed be achieved using rooftop solar.

Whether an industrial or commercial unit can achieve complete independence from the grid, or what extent of such independence is possible, depends on the following:

• What is your total load consumption?
• What is the rooftop area you have for solar power system?
• What is the pattern of your load consumption?
• What are the end uses for your load consumption?

Total Load Consumption & Rooftop Area Availability

Total load consumption is an obvious parameter that will determine the extent of grid independence you can achieve.

Why is it so?

Let us consider a company with a connected load of 2 MW. Typically, this company will be operating at about 50% load factor for about 10 hours a day, on average. This implies that per day, the total electricity consumed (in kWh), will be 2000*10*0.5 = 10,000 units. (The number of units of electricity consumed equals the Load Capacity * Number of hours * Average Capacity Utilization)

In order to generate 10,000 kWh in sunny regions, you will require about 2 MW of solar power, as 1 MW of solar can generate 4000-5000 units per day, depending on the region.

For a 2 MW of rooftop solar power plant, you will require about 20,000 sqm of shadow free rooftop space. Considering that only about 75% of typical commercial/industrial rooftop spaces will be shadow free, you will need about 27,000 sqm for a 2 MW solar power plant on the rooftop.

This is a large amount of space. EAI has worked with prospects (usually companies in the logistics industry) that have such large warehouse areas, but typically, for most of the rooftop solar companies we have worked with in the manufacturing or commercial sectors, we see that they have less than 30% of the rooftop space required for solar to power all their loads.

As a result, purely from a rooftop area availability constraint, it will be difficult for most commercial/industrial enterprises to achieve full grid independence using solar alone. The exceptions will be warehouses and other similar trading locations that have few heavy loads but large areas of operation.

Pattern of Load Consumption

Even assuming your commercial or industrial enterprise has enough roof area to support all your load requirements from solar, you cannot be certain that solar can give you complete grid independence. And here’s why.

Solar power is “infirm” power; this implies that you cannot be sure that solar power is always available on demand. It is easy to think of examples when solar power cannot help you in your power requirements – rainy days when there is little solar energy the whole day or evenings and night times where there is no sun!

But here too, you cannot directly depend on solar even if the overall math works. Your lights and fans and AC require constant supply of power, and this cannot be done by solar panels alone because the power supplied by them is fluctuating all the time.

Refer to the picture above. While what solar panels can supply over the entire day could be enough to power all your loads (the area under the curve), it might not be able to provide you exactly the amount of electricity you want at all times. During some times, solar panels might be generating more power than you require – at about 1 PM in the graph above. At other times, it could be generating much less than what you require.

One way to stabilize the power from solar is the use of batteries which store the fluctuating power from solar and supply it according to the dynamic load requirements. But batteries are costly and hence can be used only as a backup for max 2-3 hours.

End Uses of Power

The end use of solar power is an important aspect many do not consider while planning for rooftop solar.

At the current stage of evolution of solar PV technologies, solar is an excellent alternative for smaller loads – lighting, fans, desktops/laptops etc. Solar, however, does not do well for heavy loads – especially the HVAC (heating, ventilation, air conditioning) loads. Solar also does not do well when you are running large motors and pumps.

The reason is not hard to seek. Large loads will mean high solar power requirements and as a result large rooftop area requirements; large loads also imply high starting currents in many cases. Where high starting currents are required, direct use of solar power as a pure-play source is very difficult – either the use of batteries, or complementary grid, or diesel power will be required.

EAI worked with a steel mill owner who was having erratic power supply from TANGEDCO (Tamil Nadu power utility). Fortunately, he had significant amounts of rooftop and land area within his factory compound to have enough solar panels to supply most of his loads, including heavy loads he had in his factory. But after a detailed analysis, we came to the conclusion solar PV will be an ineffective source for his machinery power requirements that required constant and reliable power throughout the day. Solar power needed to be complemented in a significant way with grid power for his requirements, but grid power was not available.

Summary

• In summary, for commercial and industrial establishments, don’t expect complete independence from the grid.
• A more feasible scenario is 75-80% independence from the grid for portions of your load – especially your lighting, fans, computer, server and any other light loads.
• Even in this case of a portion of a load, 100% independence might not be possible if your company has significant operations during times when there is no sun
• The use of batteries can to a certain extent increase the independence from grid.

Check out: EAI Consulting for Solar Energy – Solar PV & Solar Thermal