In praise of the Sun

The sun gives us light and energy. There would be no life on the earth if the Sun did not rise, day after day, without a single day’s rest. People of many civilizations have worshiped the Sun as God since times immemorial. But during the tropical summer, it emerges with brutal fierceness and saps life. Productivity drops to an abysmal low, and those who can afford it, escape to the mountains for a bit of cool air. A hundred odd years ago, air-conditioners were invented, and the rich acquired a new device to save themselves from the fury of ‘surya devata’. In due course, the price of air conditioners dropped and even the middle class could afford to buy them. The flip side of this phenomenon was that we did not have the electric power needed to run these cooling devices. Power cuts, scheduled and unscheduled, ensued. People felt ‘powerless’ and invented nasty swear words to express their anguish. The gap between  supply and demand began to widen and, soon, this became a political issue.

A solution to the problem has now emerged on the horizon. The light radiated by Sun can be converted into electricity, and the system is so simple that you can install it on your own rooftop. I have done it and the details of my system are given below. It is popularly referred to as a ‘Photo Voltaic system’  

Functioning of a PV system

A solar PV power plant converts sunlight into electricity. It does so without any moving parts (unless it has a tracking system) and without generating either noise or pollution. A solar PV system can be installed at any un-shaded location such as on rooftops of buildings, car parking sheds, empty land, or even on top of canals and roads. A typical rooftop solar PV system for a household is between 1-10kW. A solar PV system consists of the following key components.

1. Solar PV array (group of modules)

2. Solar inverter

3. Battery

4. Interconnecting devices (junction box, cables, distribution box)

Some pictures of the PV system installed in our house are given below:

 

This is a 2 Kwp system. There are eight modules, and the men who installed it are seen. They are, Rajiv Sharma and Angrez Singh. They run a firm called Vision Solar.

 

 

This is the rear side of one module. You see wires emanating from a junction box. The dc voltage from the modules is wired up in a series-parallel system and fed to the ‘inverter’

 

This is the power control unit. In this the dc output of the panels is converted into ac, and its frequency and phase are synchronized with the main line for feeding into the grid.

 

The output of the power controller is fed to the meter, which is tested, calibrated and sealed by the electricity board. This is an intelligent meter which gives all the necessary information. The electricity department pays us on the basis of these readings.

 

Some fundamental principles

The PV array consists of solar modules interconnected with each other. The modules convert the energy from sunlight, are held on structures made of galvanized iron, mild steel or aluminum and are inclined at a horizontal tilt, facing either south or east-west. The modules are designed to generate power at either 12 or 24 volt. Inverter models can differ in their input voltage requirements in the range of 12 to 1,000 volt. A junction box connects the modules in series or parallel to achieve the optimum voltage required by the inverter.

Solar modules produce direct current (DC). Almost all electrical appliances in India, however, require alternating current (AC) to operate. The function of converting DC to AC is carried out by the inverter. In the case of a battery backup system, the inverter is also connected to the batteries and is responsible for managing the charging and discharging of the batteries.

The output point of the inverter is connected to the distribution box, which consists of a meter, fuse, a miniature circuit breaker (MCB), and load connections. Cables connect the solar modules, junction boxes, inverters and distribution boxes.

The capacity of the solar PV system depends on the amount of electricity (kWh) required per day by a consumer and the shadow and obstruction free space available on the rooftop. For example, a 2 kWp load operating for 10 hours requires a PV system of 5 kWp. Further, 1 kWp of solar PV requires 10 sq. meters of shadow free area. Therefore, a 5 kWp system would require 50 sq. m. In addition, if the consumption occurs during non-sunshine hours (6:00 pm to 6:00 am) or in case the consumption is not uniformly sufficient throughout the day, batteries to store energy must be added.

Another factor, which affects the system design, is the timing of electricity consumption. For example, residential consumers in Chandigarh have a peak demand during the morning (6:00 am – 10:00 am) and evening (6:00 pm – 10:00 pm). These are not peak sunshine hours (10:00 am – 4:00 pm). Residential demand tends to be lower during the day as household members become engaged in daily activities, mostly outside the house (e.g. adults going to work and children going to school). Thus, the peak power production of a PV system does not match the peak demand of residential consumers. For industrial and commercial consumers, on the other hand, solar generation coincides more closely with peak demand as most of these sites operate through the day.

Solar PV systems could be sized to not exceed the load demand during the day. If they are larger, and solar power is being generated that exceeds consumption at that point in time, wastage can be avoided by storing the excess power. Alternatively, excess power could be injected into the grid. In this case, metering would be required to measure energy transactions between the PV system and the grid. 

Rooftop solar PV with storage

Storage in solar PV systems is required to provide stable backup power when the solar energy is not available (at night) or not adequate to meet the entire load demand. Solar energy is an intermittent source of power. The power generation can vary with a change in sunshine due to, for example, a sudden cloud cover. Batteries can be used to store solar power to safeguard against a short-term fall in solar power generation. Intermittency can also be avoided by connecting the solar PV system to the grid. In this case the grid provides the extra energy at times of inadequate sunshine.

Another application of storage is to protect against grid outages. During an outage it is possible that solar generation is inadequate to meet the load demand (e.g. if it occurs outside sunshine hours). In such a case, the stored energy can be utilized to provide a stable output of power. If the grid condition is good and power outages are rare, batteries would probably be avoided as they add about 25 %  to the system cost. Batteries also need to be replaced every three to five years. Since we do not experience long power cuts in Chandigarh, batteries need not be an essential part of the PV system

Rooftop solar PV with net metering

There are two common ways in which owners of kW-scale rooftop solar PV plants can be compensated for feeding electricity into the grid: FiTs and net metering. For FiTs, solar power generated and fed into the grid is measured through a separate meter and then given a price (the FiT) through which the owner is compensated for the electricity generated. The advantage is, that the price for solar power and the amount of solar power generated can be determined independently. This method is useful where either the cost of solar power far exceeds the cost of grid power and/or where the generation of solar power far exceeds the on-site consumption needs. A risk is the potential for fraud through channeling non-solar power through the solar meter and thus inflating the amount of power for which the – usually high – solar FiT is paid. A household-level FiT is offered in, for example, Germany.

Under net metering, on the other hand, conventional electricity and solar electricity are traded at the same tariff. The billing in this case is based on the net energy imported (energy consumed minus energy generated and fed into the grid). In case more energy is generated than consumed, the utility can adjust the excess in a future billing period (this would be akin to “banking” the power), rather than giving a monetary compensation, as in the case of FiTs. However, over the long term, the amount of solar power that can be generated and monetized through net metering will be limited by the amount of power consumed, where, at most, the consumer can feed as much power back into the grid as he draws from the grid so that the electricity bill is “zero”. Net metering is popular in, for example, the USA and Japan

The Central Electricity Agency (CEA) has initiated steps to set standards and guidelines for the integration of solar PV systems into the grid. A report on grid connectivity of solar PV is under formulation at the CEA. A draft is to be shared with the public for comments by end-June. The CEA’s move is based on its acknowledgement that decentralized solar PV can play a key role in bridging the country’s energy deficit and is set to take off now. During our interactions with senior officials at the CEA, we were told that “solar PV is the future for this country, and we have to make sure that there are standards and guidelines in place to support its integration with the grid”. Various metering arrangements covering grid interaction of a PV system with battery, without battery, with different load battery back-ups, with different load DG back-ups, and with DG and battery back-up combinations, have been laid down in the draft report.

 

The economics of Rooftop Solar Systems

The conversion efficiency of solar panels has been improving during the last ten years, and the prices are gradually diminishing. In my case I had to erect a steel structure to obtain sunshine all through the day. This added to the cost, a bit. In normal circumstances, a system should cost Rs one lac per Kwp capacity. Larger systems are cheaper because the power controller price drops. It is my estimate that a 5 Kwp system can be erected at a cost of under Rs 4 lakhs. The quantum of power generated varies with the seasons. During  winter the days are short and the sun is at a low angle. Consequently, the power generated in a day may be less than one-third of the yield during the summer. On a day when the sky is overcast, the power generated may drop to as little as 15% of the capacity. A study done on the seasonal variation carried out by the Australians is given below.

 

Please remember that in Australia, Jun-July is winter. Notice the seasonal pattern of solar power. Consequently, the capacity is based on the annual yield of a system.

Estimate of power expected and ROI

As per the current estimate, a 1 Kwp system can produce 1300 to 1750 Kwh of energy during the year. Thus I can expect to sell about 3,200 units of power out of my 2 Kwp system. The current rate is Rs 8.40 per unit for those who have not sought subsidy from the government. Thus, on my investment of about Rs 2.15 lakhs I can hope for a return of over Rs 26,000 per year. There being no other cost, the ROI works out to more than 12%. This is much better than the yield on a fixed deposit in banks.

Routine Maintenance

There being no moving parts and no deterioration with time, operation of the solar system entails no running expenses. Just about the only thing which you need to do is to clean the panels whenever dust forms on them or raindrops settle on their surface. For that, we have erected a ladder and steps to access the panels. The pictures below show the architecture.

 

 

The ladder on the right is for climbing and then by walking on steps, the modules can be cleaned periodically

 

This is a picture of our house which shows the rooftop solar system in perspective. It is obvious that my little house can easily  host a 10 Kwp system

 

Our system was ‘commissioned’ on 18 Jan 2016. The sky was overcast, and so during the first five days, we got very little power. But after clouds left, we started getting 5 to 6 units of power. The reading you see in this picture shows 214 units.

 

The future of solar power in India

From whatever I have observed and read, India is at the ‘take off’ stage in the field of solar power. If the current events are any indication, solar panels are likely to become as common as mobile phones. An incidental advantage of installing a rooftop system is that it cools the house, since the solar panels absorb heat.

Given below is a table that shows the growth of electricity generation in India, as envisaged by our government.

 Note that solar power is expected to grow from 18 to 20,000 MW by 2022. This is a massive growth, by any standard!

The Timeline

I started this project on 11 Sep 2015, and estimated that I would be able to commission the system by 15 Oct 2015, since I had gone into considerable detail. In actual fact, it took three months longer. The electricity board created some hassles while clearing the design and they took unduly long in certifying the meter. I really do not blame them because they were new to the game themselves. My contractor claimed to have installed several systems, but they were in a different configuration (where the power is used to charge the user’s own inverter) and therefore the government grid did not come in. So all in all, we were all breaking new ground. However, by the time I finished, it became clear to us that for small rooftop solar systems, government approval of the design of the structure is not necessary. As a result of the noise we made, orders have been issued that rooftop solar systems up to 5 Kwp do not need government sanction. In my view, we will proceed much faster if all controls are removed. In the NDA, we were taught that, ‘The best government is the one that governs the least’

Tailpiece

Solar power systems are coming. No one, not even our infamous bureaucracy, can stop them. The need of the hour is that many of us should install them and talk about our experiences. These systems will succeed the most in cases where the system can operate on DC. And if it can be used at the very time it is generated, the cost gets slashed. I am told  that a student of IIT Bombay has designed a bicycle where the traction of the pedals is assisted by a solar module. In all probability, he is using a dc motor, which draws power the moment it is generated. So he neither needs a battery nor an inverter. And, of course, he needs no sanction from the government!

A picture of the lad riding his bike is given below.

 

 

With a little more sophistication, this concept can be used for short distance commuting. There can be no better solution to pollution.

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A Communication from Joseph Thomas

Jo Thomas is away to North Carolina, USA, visiting his children. Notwithstanding the distance, he has been monitoring this piece on a real time basis. He has sent the following message, and I have all the reason to believe that he must be right.

 Ref the graphic on growth of electricity generation in India.  This is an old graphic from UPA govt times.  In 2014 the govt revised the solar power target to 1,00,000 MW (100GW) plus 60 GW for wind.  J Thomas