In many countries energy consumers are producing electricity through renewables such as solar generators (PV panels) where surplus power is fed back into the grid. This earns them money from the utility suppliers (Feed-in-Tariffs). The money earned is based on energy produced – and may not necessarily have to be the amount of energy actually put back into the grid. Typically the amount earned per kWh for grid feeding is lower than the cost of energy taken from the grid. So, rather than feed the energy back into the grid for a low value and then buy it back in the evening at a higher value, we have a system that allows you to store the energy on-site which you can use later. You earn money producing the energy, store it on-site and then save money by using this saved energy instead of buying more from the grid.
We can store this energy in different ways, but the most flexible is to simply charge batteries. If the batteries become fully charged preventing us from storing any more, we can divert energy to heat water. To achieve this we have a sophisticated management system which will alter its behaviour according to various pre-set parameters including battery charge status and time of day and also controls external devices with programmable contacts.
Many grid-tied inverters (or AC coupled inverters as they are also known) can have their output controlled via either step change frequency shift or linear frequency shift. This external control is very useful and the frequency shift can be generated by the MFIC in our system.
If grid feeding is not possible or desirable, the system can be set up to operate where the priority is to use energy generated from renewables that is stored locally in the batteries. The system only resorts to taking power from the grid when there is not enough energy from renewables. This way, in an area of high insolation a facility can reduce the cost of energy bills and reliance on the grid. In other areas, the amount of power taken from the grid can be limited – thus allowing small communities to smooth demand and so manage power generation more easily.
In some countries, the rise in popularity of grid feeding has had a knock on effect of causing large differences in demand from power stations feeding the grid through the daily cycle. Operators of power stations would prefer they run at as stable an output as possible. Interestingly enough, one of the key issues surrounding the increase in popularity of micro-generation schemes injecting power to the grid is trying to control the imbalances it can have on the main grid power values (voltage, frequency, etc). The grid was not designed to have any external 'inputs'; it was originally designed to be a source of power - not a destination! Self-consumption by means of storing locally generated energy in batteries on-site, which is then used later on, will not only reduce the demand from the grid but also smooth this demand over the daily cycle. So, the incorporation of self consumption systems will reduce the amount of energy being 'inputted' to the grid and later, say at night time, when more power is needed for cooking and lights, the MFIC units can be set to reduce demand direct from the grid and use, instead, the stored energy.
As the primary tool of any self-consumption system is an MFIC like the Studer Xtender working with a battery bank - a self consumption system is, by default, a grid failure back-up system. So, you could be getting paid for the electricity you generate and store, which helps the grid out by reducing 'input' and then you can relax knowing that if the grid fails, you will still have power - automatically created and delivered to you by the Xtender from your battery bank.