How should I set value of site id attribute?

Value of attribute id is only for informative purposes (doesn't affect results of WS API calls) and is mostly used for API usage monitoring reports etc. 
Therefore as such it's entirely up to you what value you will choose for attribute id, however we recommend that you try to follow these best practices:

Other than: value of site id must follow common practice for variable names in programming languages:

Can I set minutes precision of timezone i.e. "UTC+07:30"  (instead of only whole hours precision)?

Unfortunately this is not possible, WS API currently supports only timezones that are integer multiples of hourse, i.e.: "UTC+07:00" or "UTC+08:00" and timezones like "UTC+07:30" are not supported.

Why 1 day of data in MIN_15 summarization doesn't sum up to 1 day of data in HOURLY or DAILY summarization (for GHI, DNI, GTI, PVOUT...)?

This is because MIN_15, HOURLY and DAILY all use different units on the output, furthermore irradiation data also uses different units on the output than PVOUT.
You can always check the units used for each output column in the metadata section:

For irradiation variables (GHI, DNI, GTI, DIF...) we have:

MIN_*W/m2 (Power / m2)
HOURLYWh/m2 (Energy / m2)
DAILYkWh/m2 (Energy / m2)

For PVOUT variable we have:


Therefore when summing up values in one day and comparing against different summarizations we need to make sure that they are all in matching units.
For example conversion of GHI MIN_15 to GHI HOURLY should be like this:


(Here dividing by 4.0 is consequence of converting average power over four 15 minute intervals into how much energy that power will generate over duration of one hour)

Unable to get WS API working

Quick checklist (things you can quickly try first)

Request still not working / no idea what's wrong

First we need to establish that that you are able to call the request with demo key, in order to do so please follow these steps: