Imagine energy as water, voltage as pressure and current as water flow and you will realize that when you have a water pump at the end of the distribution line, it will supply pressure that is higher than the one in the line. Water will flow from your little pump to your tap, if you open it. If you keep it closed, it will flow to your neighbour or even farther if he is not using it.
Wind turbine is your 6kW max pump, solar system is your 3kW max power pump. The problem is when both pumps do not run (there is no wind and at night no light) – then you need energy from the grid. However, if you can store few units of energy (imagine buffer tank) you can stay independent for some time.
Below example from Gerrard’s setup co.Denegal. 4x160Ah lithium storage and power diverter dumping surplus energy to hot water tank (after the battery is full and export begins). Windspot wind turbine on 6kW SMA inverter and 1.5kW solar system (Fronius inverter).
Energy consumption – last 30 days (note it is higher consumption during higher generation due power being diverted to water via immersion):
Solar energy generation:
Wind energy generation (note scale on Y axe):
Actual exchange with national grid (ESB in this case):
These are 30 days graphs, notice how little power is being imported from grid. Gerard is not a big energy consumer. Here you can explore this system on VRM.
Yesterday James in co.Sligo was switched to hub2 v3 where system stays OFF GRID until the battery level drops to 5% or the load is higher than 5.5kW. Victron Multiplus is connecting to the grid then using his internal contactor. It can support grid as well, but that function is off at the moment, as grid is very weak there and problems are occurring. System goes back OFF GRID whenever battery gets to 30% or load drops below 2kW for 30sec.
From this morning turbine and solar we are generating well, so James started charging his Nissan leaf (3.7kW charger). As you can see below, the consumption of 4kW over 5 hours equals 20kWh, where 10kWh is battery capacity and the rest was supplied directly from wind and solar. At the end of the day wind dropped (also there was no sun), so system switched to grid.
Hourly consumption breakdown:
30kWh is the capacity of Nissan Leaf battery so almost, almost full independent charge which I can remotely observe today. There is wind turbine monitoring from ABB vsn300 card (every 15min data). Here you can explore this system yourself!
The last example is Barry in co.Meath. 9kWp solar system, 2.4kW skystream wind turbine and another 2kW of solar seems plenty but what if your house is power hungry. For example 1.5kW swimming pool pump running every 2h for 1h, not very essential load but consumes a lot over day.
Consumption graph for the last 7 days shows high energy consumption (40kWh per day!) but even this during windy sunny period it is not a problem for this system, as you can see exchange with grid is very minimal. Here is VRM for this system.
Last 7 days system consumption (note usage close to 10kW some days):
Exchange with grid:
All those 3 examples have the same 5kVA Victron Multiplus inverter charger (48V 70A max charge current).