Hi Al,
OK in a nut shell
The system has to be registered with OFGEM at the renewables site.
https://www.renewablesandchp.ofgem.gov.uk/ - it is down, overnight, at the moment for maintenance
A real person ultimately checks it and will contact you to ask questions. I had a very helpful woman who was able to answer questions and make things clear. (she also spotted that a friend who applied at the same time had very similar answers to the questions as we did it together - I felt like we had copied homework!)
You fill in a series of questions, probably about 50.
You have to have an aproved total generation meter, the serial number has to be registered with OFGEM. Not a problem as they are available from Navitron for about £20 I think.
You have to run on liquid bio mass and convince them that is is not contaminated by an non organic material.
The double ROCs are dependant on the system size.
The amount received is about 9p per unit, as stated by Justme, and you get nothing for the heat, but if you are doing it anyway it is money for nothing. I get about 2kW electric and 4 kW heat for each L of oil. As I am 'on grid' each unit also saves me 10p in electric not bought. This time of year I only run for a few hours a day to cover main load consumption as I have no use for the heat.
I would imagine that SVO would not be a problem other than cost and the moral concern of using a food product for energy.
The advantage of a stationary engine is that it can run on very poor oil, if it is hot enough, so there is more scope for getting it than 'good oil' for use it in a vehicle. Chip lard is fine, I have just modded the Lister fuel system to run on oil that is solid at 30 degrees C and is no good for bio diesel so is readily available.
You will only get ROCs for the veg oil generated electric not for the PV.
It took some months for it to come through for me but the payment is backdated to the time you register.
You have to send the meter reading in once a year.
I have not had a visit so how they know you are not giving a false reading I have no idea.
If you want a chat I will send you a phone number.
Hope this helps
Dick