• Highlights
• Overview
• Advantages
• Constraints
• Typical Load
• Our Recommendation
• Cost of a Rooftop Solar Plant
• Prominent Installations

Advantages

• Energy security – Rooftop solar plants can deliver power during load-shedding, ensuring that critical loads are always running
  • Not all solar plant configurations can deliver power during load-shedding. More details here
• Cost-effective – Rooftop solar power has a levelised cost of Rs. 4.5-5/kWh (or less), considerably lower than diesel power cost at Rs. 18/kWh (or more). Additionally, your energy cost is now fixed for the next 25 years, unlike diesel power which keeps increasing
• Reliable – A solar power plant has no moving parts, ensuring reliable power over 25 years
• Minimal maintenance – A solar plant requires very little maintenance from the energy consumer
• Flexible configurations – Solar panels can be installed on different kinds of roofs, including covered parking areas, as long as the structure can bear the weight of the panels. They are also highly scalable, with rooftop plants ranging in capacity from less than 1 kW to more than 1 MW

Constraints

• Rooftop space – The capacity of the solar plant that can be installed in a hotel may be constrained by lack of sufficient shadow-free rooftop space. Roof requirements are discussed in detail here; a rule of thumb is that you will need about 100 SF of shade-free roof area for 1 kW of solar panels. Insufficient roof area will mean that the capacity of the solar plant on your roof may be sufficient to meet only part of your electrical load
  • When estimating the available roof area any alternate uses of the roof, including seasonal usage, should be considered
• Infirm power – Solar power is dependent on the sun shining, and output varies depending on meteorological conditions e.g., passing clouds can temporarily reduce the solar plant’s output. Therefore solar power for critical equipment should be used in conjunction with another source of power
• Daylight power – Solar power is only available when the sun shines. Therefore night time applications will require other sources of power, or power from batteries charged through solar
• Load-shedding timings – If your hotel experiences load shedding primarily at night, solar power may not help in reducing your diesel consumption as it is available only during the day
• Inverter weight – The DC power output from the solar panels needs to be converted to AC via an inverter which can be very heavy: a 100 kW inverter will weigh about 1,000 Kgs but occupy only a few square feet of space. If the construction cannot support this weight the inverter may need to be placed on the ground floor, with appropriate cables chosen to compensate for energy loss

Typical Load

As the rooftop space may not be sufficient to support the entire electrical load of your hotel with solar, it becomes necessary to estimate the different kinds of loads to identify loads that can be/need to be supported by solar.

Electrical loads are estimated by calculating the wattage or amperage of electrical equipment in use (as shown here), which can be further classified as light loads and heavier loads, with solar being used to support the light loads.

Typical electrical loads in a hotel include

• Lighting
• Electronic Entertainment
• Refrigeration units
• Air conditioning
• Elevators and Escalators

Air conditioning is usually the heaviest load, accounting for more than half the energy consumed. Air conditioning is not a critical load in many industries, but for many hotels air conditioning is a critical load in guest areas.

When evaluating the load, hotels will also have to consider if the load is seasonal. If the solar system is sized for peak season, there is the risk of solar power going to waste in the off-season as the solar plant will generate power whenever there is sunlight even if the power is not required – and unlike running a diesel generator, costs are not saved by turning off a solar PV plant as the bulk of the investment is made at the time of installation.

If your hotel is located in a state that allows net metering, your solar plant can still be sized for peak season loads as excess power generated in the off season can be monetised based on the state’s policy.

Our Recommendation

Based on the need for uncompromised guest experience and the variable nature of solar power, Solar Mango recommends

• Net metering – If available for hotels in your state, net metering can ensure that excess solar generation (such as during off season when loads are low) can be monetised
• Multiple power source integration – As the output from a rooftop solar plant varies, it must always work in conjunction with other sources of power, typically utility grid power and diesel power. This is achieved using
• Hybrid inverter – A rooftop solar PV system that utilises a hybrid inverter allows the solar plant to integrate with a diesel generator in addition to the utility grid. Here the rooftop solar plant serves to reduce diesel bills by supporting part of the overall load
  • Integrating a rooftop solar plant with a diesel generator involves several challenges (discussed here) that need to be overcome with careful design and sizing of the rooftop solar plant
• Load sizing – If the hotel has seasonal demand, the solar plant should be sized to avoid wasting solar power generation in the off-season
• Load scheduling – If possible, the hotel can consider shifting part of the load at night (such as baking activities) to daytime to take advantage of solar generation

If your hotel already includes a rooftop solar water heating installation, we do not recommending disturbing this as a solar water heater (which uses solar thermal technology) is more cost-effective than using electricity from rooftop PV to heat water.

Cost of a Rooftop Solar Plant

The cost of a rooftop solar plant is discussed in detail here (including incentives and subsidies) and returns from substituting diesel with solar are discussed here. As a rule of thumb, a 1 kW solar plant that generates 4 kWh of solar power per day (on average) will cost Rs. 1 lakh (without considering subsidies, including installation charges but excluding batteries).

Batteries, if required, can add about 30% or more to the cost of the plant depending on the extent of battery backup required.

Prominent Installations

• India
  • Lakshmi Hotel – Thanjavur (40 kW)
• International
  • Mandalay Bay – Las Vegas, USA (6.2 MW)
  • Grand Palladium Lady Hamilton Hotel – Montego Bay, Jamaica (1.6 MW)