Micro generation (G98) is a simple connection procedure for fully type tested installations under 16A per phase 

Under G98 you are allowed to have a maximum total installed generation capacity of 16A (3.68Kw)per phase, at any one single premises. G98 permits the installation to be carried out so long as the inverters are listed and approved on the ENA type test register, see link ENA , however the DNO must be notified within 28 days of commissioning the system. see link G98 Notification

If your total combined grid connected capacity is over 3.68kW on a single phase, you must apply under G99 see link: Fast track (G99)