Solar Power: Where can we go from here?

(The article is Part 2 of an earlier write-up, which appeared last week)

This article attempts to show how the general electricity consumer can, with a Grid Tied Solar system generate electricity in any amount (5 Kw, 30 Kw, 100 Kw etc. or more) depending on the design and the investments. The systems are such that the power generated may be used up all by the consumer/house or, if there is an excess capacity, may feed the mains/grid power. The amount of energy (unit in kwhr) given to the power supply lines is metered and the consumer is paid for it.

Thus every consumer can become a potential point of power generation, supplying power to the grid, increasing the percentage of solar power in the total power generation.

Stand Alone Systems
There are two basically two types of solar PV systems: stand-alone and grid-connected. Stand-alone systems work with batteries. The solar energy is stored in the battery and used to feed building loads after conversion from DC to AC power with a stand-alone inverter.

The battery systems are perhaps more suited to remote areas where there is no grid power. The disadvantage of these systems is that, the batteries may require constant attention and replacement every 2-3 years. Battery systems in general ,unless essential is not the preferred system.

How does the Grid Tie System Work
A PV (photo voltaic) solar panel as mentioned in the part 1 of this article produces a DC. This voltage produced is fed into an inverter, in this instance is a Grid Tie inverter, which is slightly different from the inverter we mentioned earlier. The inverter produces a AC voltage which is similar to the mains voltage. Similar in frequency 50 Hz, similar in voltage about 220 V and similar in wave shape, which is a sine wave or a modified sine wave. More expensive ones produce pure sine wave which have some distinct advantages.

Grid-tie solar PV systems feed solar energy directly into the building loads. Surplus energy, if any, is fed i.e. directed to the mains power supply grid. If the home requirement is more than what the PV system can produce, it will also draw power from the mains. However the important point to consider is, Grid Tie systems only work in places where there is reliable power supply, the system gets disconnected if there is power failure.

Selling the Power, Net Metering
Why feed to the mains? When more power is generated by the solar system then is consumed in the premises, the excess may be fed to the grid through the meter to sell the electricity to the power company, such systems are known as net metering, the power company pays for the power that was supplied to them. The customer's grid tie inverter automatically takes power from the mains when not enough power is produced by the system.
If a customer consumes 600 Kwhr (unit) in one month and his solar system has given to the power company say 400 kwhr, the customer will in effect, be charged for 200 kwhr, thus reducing his bill by a sizeable amount. The existing meter in that case has to be replaced by a bidirectional meter (for the net metering).

When you are connected to the grid/mains, your meter runs backward whenever you are producing a surplus of energy and feeding it to the mains. This is net metering, which is summing the KWh you are taking from the mains and subtracting the Kwh you are giving back to the grid.

Feed-in-tariff/Gross metering
In gross metering, entire energy generated by the solar PV system is fed back directly into the utility grid. In this case, the owner gets incentives based on feed-in tariffs proportional to the energy fed back to the grid. This will be very attractive for commercial firms who pay a much higher rate per unit. They may put up a dedicated Solar System for the express purpose of feeding to the Power Company. The income obtained will to some extent pay for the power bill of the company, depending of the power generated by the Solar System.

Some Technicalities
Grid tie inverters have the in-built safety, whereby it disconnects from the grid if the power goes down for maintenance purpose or a technical failure, this ensures that the power line does not remain live because of the feed from your inverter and that the workers may safely work on the line.

In normal operation the AC produced by the inverter is synchronised and paralleled with the mains voltage in order to transfer power. Only when the output parameters (voltage, frequency and wave shape/wave form) match can the inverter output be synchronised with the mains power. There is a window or range within which these values can vary, if any one of them go beyond specified limits say 55 Hz instead of 50 Hz, the inverter will cut out i.e. disconnect from the mains; this is an inbuilt safety feature of the inverter. The inverter must also must produce a voltage slightly higher than the grid itself for the energy to flow outward to the grid.

Some more detailed Technicalities
It may be difficult to understand the effect of several generating sources at the tail end of the grid and particularly so if the overhead cabling does not have the requisite capacity to handle the load, one of the calculations the power operators do is to estimate the power handling capacity of the lines in question. The executive agency has to oversee such scenarios before giving permission for connections. There has to be an upper limit as to how much power can be paralleled i.e. injected into the grid. The lower limit takes into account the expediency and economics. There is no point in making the minimum as 5 Kw, we should be expecting many small individual consumers even a spill over capacity from the solar pump systems discussed separately in part 1 of this article or even as a spill over from a system designed to decrease the power bill say of a commercial firm.

It can be investment with a reasonable return as a power Producer:
The package of incentives should be such so to lure people as an investor, the consumer may decide to have a exclusive and dedicated system with the sole purpose of selling power to the grid. In which case, the model becomes an investment proposal in lieu of the other investment opportunities that exist.

Alternatively the Grid Tie system power generated, can be a net metering arrangement, whereby power generated may be transferred to the grid power whenever possible, consequently the electricity bill will be reduced by the amount transferred to the grid.

Some Advantages of Grid Tie system
1. No requirement of additional land
2. Electricity generation at load centre with savings in Transmission
3. Improvement of tail end grid voltages
4. Local employment generation

Putting in, unwittingly, dis-incentives
As is very often the case over zealous policy makers and executing agency will put in conditions which will kill the effort before it has taken off. The policy makers must view it as an investment on the part of the public expecting a return much better than the prevailing bank rates. It should appeal to them as an alternative investment. In fact the incentives should be all en-compassing. Favourable power buy back rate, tax incentives for the imported goods and hopefully one stop application and approval service.

A few points may be noted from the Indian experience. In some of the Indian states, very high accuracy meters were specified. Though this may make sense for a system producing 30 Kw or more, for a domestic or a 2 Kw system such a meter (for net metering) may run into 15-20 % of the total cost, and is likely to act as a deterrent. We also notice that the various Indian states do not have any unified regulations. Some are too rigid on one or more of the requirements, as a result the effort did not have the expected result or enthusiasm among the public.

It is on to the government and relevant authorities to tap into the possibility with virtual nil or nominal investment on the part of the government. What has to be done is to put in place incentives, and take policy decisions in the lines mentioned as follows:

a. Really attractive power rates i.e buyback rates for selling to the grid
b. Low import duty to make the investment feasible
c. Policies, guidelines and procedures at the executive level

d. The projects of capacity upto 1 KWp to 500 Kwp to be permitted on the rooftop
with an indicative space requirement figure of 10.8 sq feet per kwp
e. Training at the executive level and other levels will be required to make a smooth transition.

Who may put up Grid Tie Systems
• The Government may promote solar rooftop systems on public buildings.
• Commercial buildings may put up roof top installations, commercial rates are generally higher, the saving therefore is therefore substantial. Commercial and industrial establishments may work on gross and or net meter basis. Commercial firms will in general have sufficient funds to put up a sizable system to decrease their own power bill.
• At an individual level, if you have a rooftop space the system will greatly reduce your electricity bills, and net metering is the solution, whereby monthly bills will be reduced.
• The grid Tie system may also become a part of Apartment Block Pumping system, where besides lessening the bills for common service, it may generate some earning as well.
• A group of individuals to make an investment and expecting a reasonable return by selling the generated power to the power company grid, in gross metering arrangement or it can be even a lease model.
• Private or Govt or joint Solar Parks.

Some comments
Solar energy has its peculiarities. It is free when it is available, and that only by day with an average peak sun hour of 4+ hours in our latitude and obstructed by cloudy days and shade and so on. Many critic will argue with the extraction percentage, which is the difference between the installed capacity and output. The main argument for all criticism is that solar is not cheap and it is a part of energy mix we may have, to attain any degree of energy security. It may perhaps open our way of thinking if we list a few rooftop system owners in India.

Punjab Engineering college, Chandigarh 1 Mw, IIT Madras 300 Kw, Manipal University Jaipur 404 Kw, private hospital Delhi 500 Kw and many in private commercial buildings. India has reached a grid tied solar capacity of 4102 Mw.

Summing Up
Any electricity user domestic or commercial can become a source of power for the Power Supply authority by using Grid Tie PV (photo voltaic) systems. Such a system feeds directly into the mains power line/grid. If the user generates excess power, i.e. in excess over his requirements he basically directs that excess to the mains through a system known as net metering.

If the power generation is less than the required power in the premises, the solar system/inverter gives all the power within its rated capacity and the excess is taken from the grid. This also implies that no power is sent to the grid under such circumstances, however the monthly will be much reduced; by the same amount generated by the solar system.

Dedicated system only for selling to the power company is referred to as Gross metering. Grid Tie inverters can only work where there is reliable grid power.

It was shown that the whole concept can only work after a policy decision and after suitable steps are taken by relevant authorities. The package must be made attractive as regards the rate at which the power may be sold and other incentives so that it may be received as a form of investment with a reasonable return and a reasonable payback period. It will require top level involvement and monitoring.

In the final note, the success or failure of this effort will depend entirely on how attractively the package is presented. In this instance we must understand that the people are helping the government to help themselves.