EB: How important is solar power for a developing country like India?
There are indeed several reasons. Primarily, we have a severe power shortage and blackout in most parts of rural India that accounts for two-third of our country. This primary input of societal development can’t wait for the grid to reach those unfortunate people in the hinterlands.
Equally, the lack of power leads to poor productivity of rural artisan and farmers. They lose five hours each day when they can create wealth productively, purely because of lack of power after sunset.
Solar power is everywhere; I call it the ‘solar grid.’ It is nature’s bounty and available to every rural farmer and artisan. Fossil fuel based power generation also emits more CO2 per watt delivered today.
EB: Is India well equipped to reap full benefit of solar power?
Luckily, harnessing power from solar heat and light energy is a proven and very simple technology. Solar heaters produced in millions would be very useful in harnessing solar heat for water and liquid heating. This alone will save us millions of kilowatt hours of electrical power.
The same is true about photovoltaic (PV) solar panels. The demand is huge and businesses are ready to provide these products. With competition and volume, prices will drop further. Even at current prices, PV solar power costs almost two-third of the cost of power from diesel gensets. Replacing them with solar power will lead to a sharp drop in carbon emission and noise.
EB: What are the technologies in use for PV cells?
Currently, a PV cell is the least expensive way to harvest solar electric power. It works at 16-17.5 per cent efficiency and a 161cm2 PV cell delivers 3-4W power at about 0.5V.
Monocrystalline and polycrystalline are the two types of cells currently used. Several of these cells are connected in series and sandwiched under specially toughened glass to produce PV solar panels.
EB: Which of the two is more efficient and more economical?
Monocrystalline offers higher efficiency but since the input energy is free, the cost per watt of peak power determines the choice.
The main problem till now was loss of power harnessed in the process of connecting the cells in series to obtain a usable voltage level. Unless these cells are matched, each cell in a series string delivers energy as little as the least efficient amongst them. This happens in factories making PV panels from PV cells as well as when PV panels are connected in series, as is always done in PV solar arrays currently deployed.
The loss of power could be as high as 12 per cent unless unit cells and panels are carefully matched when these are connected in series. That’s why our technique to process solar energy with an embedded controller inside a PV panel is important for the country.
EB: What is the role of a solar charge controller?
Depending on the strength of solar radiation during a day, a 12V PV panel outputs voltage that varies from about 7V (poor light) to 20-21V under open circuit with bright light. The panel gives its highest power at a voltage, Vp, that varies between, say, 13.5-18V depending on the cell efficiency. Most of the loads, however, need constant voltage.
A PV panel is basically a current source and the current level depends on the intensity of the incident sunlight. That’s why for harvesting maximum energy from a PV panel, it is essential to use a current controller to ensure that the panel delivers its peak potential energy under all light conditions.
In case one is using a solar panel to charge a battery, the use of a current controller is a must. Without it, the user will damage the connected battery. The most widely used current controller uses a microcomputer that tracks peak energy delivery point of the panel or an array all the time and ensures that the associated DC-DC converter delivers maximum peak power (MPPT).
EB: How does it help to improve the solar power output?
As described above, MPPT type controller is a must for any serious application of solar power above, say, 50Wp. The controller cost makes it unadvisable to use it below that power. For lower power panels, a simple switch type controller is used. It ensures that the connected battery or the other load does not get damaged.
EB: What’s an embedded solar panel?
In an embedded solar panel (ESP), under a process that is awaiting the grant of a patent, the solar energy generated by a solar panel of any type is processed such that it is harvested to its full potential under any solar condition. This energy processor delivers the energy over a range of high voltage up to 300V so that all panels have identical performance.
EB: In what way does it improve the efficiency and lower the cost?
There are several ways in which ESPs improve the power plant’s efficiency. At the panel level, the embedded circuit of an ESP ensures harvesting of peak power from the host panel using a unique MPPT algorithm and delivers it any voltage that the load requires. The best advantage of ESPs is that they allow an array designer to use ‘all parallel’ architecture because of its capacity to connect hundreds of panels in parallel, each panel delivering its peak power into a bus bar. Since each panel delivers power at high voltage, the array designer can avoid completely the series strings and expensive work to select and match panels. Such a parallel array of ESPs helps to harvest 10-12 per cent more energy than the conventional configuration currently used. Ten per cent more of free energy will change the ROI of every solar plant in the world.
EB: What all are the ideal applications for it?
Any power plant from a 200Wp to a several megawatt capacity can use ESPs cost effectively.
EB: Which segments are picking up and why?
Till the subsidies, as in the western countries, are put in place, small applications that provide backup power during blackout, terrace mountable systems for urban use and telecom applications for field equipment powering will not grow as rapidly as these should.
The absence of government subsidy for solar plants below a megawatt doesn’t make sense. As of today, government policy is to buy solar power from bulk producers having megawatt size installation. The government plans to pay these large investors Rs 18 per unit. In comparison, a 10kW rooftop power plant by a housing society or a group of rural homes will get nothing for the units of power it would generate. This makes no sense.
In Germany and most other countries, even a small producer of solar power can feed it into the grid. A bidirectional metering keeps account of what is fed back into the grid, and for what is fed the power plant owner gets higher price per unit (Rs 18 in India).
Further, even in case of large plants, it is not just the question of current government buying the grid power at Rs 18 per unit but also a guarantee from the government that this rate will be valid for the entire 20 year life of the plant as the ROI will entirely depend on the government subsidy being available throughout the plant life.
EB: What can we expect in solar power technology in the near future?
There is little chance to find an alternative to PV solar panels for a direct conversion of light into electrical power. Over the next five to seven years, PV solar will prevail. Current power conversion efficiency of 17 per cent will go up to about 24 per cent with process innovation. Solar thermal power plants look like a good supplement to PV solar.