We all do system engineering to get the number of panels for a certain power. It is also obvious that change from 230 W to 180 W for example is not linear and will involve re-engineering in the inverters, layout and trackers if applicable. Obviously trading equipment goes not by engineering, but by quantities.

Prices in northern Europe are low, but not that low. 2,25 eur per W was in the beginning of last year, when modules were selling at 1 eur per W, inverters at 10 cents per W and so clearly the BOS was within 1,5 with 0,8 for the installation, in the case of the rooftops the installation would get more expensive, since those prices were wholesale and so everything would be slightly more expensive and the small installation cost more. In any case it is a fact that in neighboring Germany average prices per W were 2,6 eur per W in 2009 stated by the German energy agency in Berlin. People think that Fit in Germany are very generous, but they are not. 5% IRR do not mean much, but that is what you get in Germany!

Yes, current PV panels are not that efficient and yes, they do cost a lot. However the energy collected is free...as in free. All this solar/thermal energy bombarding the planet day, day out and we're having debates about rebates, is it worth it, and so on?

I think the whole point of going "green" as they say is to reduce emissions...it's not just about efficiency. Efficiency is important in some aspects but what would people rather have? An "efficient" nuclear plant or a not as efficient solar/wind plant at their doorstep? How clean a technology is doesn't always relate to its efficiency. At least that's my opinion.

At best when an air conditioner first turns on there is a 400%-500% spike in the normal load. There are many gimics that store AC electric power just for the spike during start up. Slow start condensers hurt the electric motors over time. So there is no silver bullet to solve this problem. Now there are other ways to air condition areas we live in. Geo Thermal (very low power consumption less than 40 watts per hour) there is also the solar photovoltaic AC type systems. Here is the problem. Every time you go to run a motor you need a lot of electric power just for the start up of the motors. The solution is to replace all the AC motors with DC motors. Now you don't need to loose electric power because of an inverter. To me this is not the best answer. Second. The spike during start up. In a off grid world you need batteries. Not the expensive deep cell batteries but good reliable batteries. These batteries can handle the spike loads during start up.

Design of Solar Power plant entails considering the following factors:
An estimated total load consumption and load characteristics (DC and Ac load, variable load, alternate supply to grid or standalone).
Sizing of the inverter (this should be 1.6 times the estimated load to allow for future growth)
The PV panel sizes is dependent on the level of insolation level in your region. The PV size should typically be 3 times the estimated load to allow for inefficiencies. However, the use of Solar trackers can actually improve PV panel efficiency.
Then the batteries are sized based on duty cycle and rated ampere hour. (Allow for 1.8 times the actual load to accommodate inefficiencies and future growth).

Recently, First Solar claimed to have broken the $1/watt barrier, saying that they have achieved the lowest manufacturing cost in the industry, $ 0.98/watt. Is there a standard way of calculating this cost across all solar companies or it varies?

To put it politely, accounting voodoo. I'd wager they would count the costs minus whatever rebates that are given for consumers and call that the consumer price. If this is done in Germany, who have the highest level of rebates in the world for solar panels (err, Germany or Japan, I'm not exactly sure) then that number might really be something like $2 a watt or something.

The calibration of solar cell tester and module tester is the one of the important factors. The solar cell calibration from standard lab or certifying agency defines the range (up to +/-0.3%)for the efficiency/power measurement of the calibration solar cell. The mismatch can vary if calibration is done on either side of the range defined or the spectrum of light source used in the testers are different. The spectral response of the calibration solar cell and the calibration module has to be matched to minimize the CTM loss caused by measurement mismatch.

When are speaking about the solar modules that are on the market:
Si-crystalline modules: Higher efficiency than thin-film (average efficiency si-crystalline lies by 15%); but: heavy because of aluminum frame, glass and other material.
Thin-film: Less efficiency than si-crystalline modules (average efficiency lies by 12%); but: light and is at least 20 EUR cent per watt cheaper; flexible so it can be integrated easily in the environment. Copper, cadmium telluride and other semi-conductors.

We are seeing problems here with polarised circuit breakers being wired in reverse polarity that catch fire when turned off under load, Isomax isolating switches that catch fire when operated or have loads in excess of 13 amps and roof top isolator switches that get water ingress and catch fire. Also workmanship issues with the isolator wiring. We have also had inverters failing within 2 years causing fires.

In the last 2 weeks we have had an inverter fire at a residence and a roof top isolator fire on a commercial premise with a 30 kw of solar array. At present the electrical regulatory authorities do not have the ability to respond in a manner to isolate the panels for these types of faults and due to our Solar PV being such a new industry there are limited if any private companies set up in a manner to respond to these types of issues.

What you should be really looking for is a company that can provide complete integrated and optimized solutions rather than individual components that can often work against each other this affecting the overall system efficiency and its life.

However, solar PV market industry that you refer to, in India works a bit different. You will be hard pressed to find companies that manufacture the complete systems in India albeit panel manufacturers are a plenty. Tata and Reliance have washed their hands off manufacturing in the PV industry for now.

Only one system is needed for generation. But because of the different types of loads, office vs. factory, two separate backup systems would be prudent and should be equal or lower in cost over time than a single backup system.

Orientation is simpler to explain so I will start there. I will presume you are looking to install a stationary system (i.e. the solar panels will not move to track the sun). For many sites like yours this is sufficient and is exponentially simpler to design, install and operate. It is what is most commonly seen on the roofs of homes and businesses. There are two orientations to consider. The inclination of the solar panel from the ground plane, and the azimuth of the solar panel (its compass facing from magnetic north).

In my experience, the two primary factors are:
1. How long do you expect / need to have the batteries last
2. What type of load do you expect to handle when on battery

Remember that every element in the system draws some power, including the inverter, and I find it a best practice to base my sizing on peak amp draw rather than average. Yes people can and do suggest smaller backup systems, but when the customer needs them, they must work and be sufficient. So don't be afraid to tell them what they will actually need. They will thank you when it comes into play.

I would suggest you tackle the phase(s) design choice first as they will have dramatic impacts upon the excess/storage/shortage choices. This is where a set of well thought out decision matrix can be of immense help. It will allow you to objective evaluate the choices nest to each other on such things as various costs (set up, operation, termination, etc.), ROI, etc.

Feasibility studies are generally far more complicated than most people wish to admit. What ever assumption you make need to be both carefully documented and researched to confirm validity. Be vary careful when thinking that you can leave out some consideration, generally that is where most people later get stung. The extra time spent up front will quickly pay for itself in a much better fitting design and the ability to make a decision based upon highly improved accuracy of information.