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With this system installed by Greenwood Solutions at picturesque Trentham, we're talking about three separate forms of energy:
- Talking about the grid which hopefully is always there but in this case it's not so as there's a lot of blackouts and brownouts
- We're talking about the solar component
- We're talking about the batteries
Also talking about the fact that the customer has access to an off-peak tariff, in other words, there's a time of the day between 10 pm and 7 am where she pays less for her electricity.
We have used that to our advantage because the brains of the system, the inverted charger can ‘see’ if there's not enough solar gain during say the winter months, so we can charge the batteries off the grid because of the differential between the peak tariff and the off-peak tariff makes it worthwhile.
In this particular situation we've got nearly 15 kilowatts of solar; 7.2 kilowatts on one inverter and 7.2 kilowatts on another so the exact figure is 14.4 kW of solar
Now in Melbourne we work on one kilowatt installed that will output around 3.5 to 3.6 kWhours a day.
We have a storage component of 28 kW hours total but remember, we don't take all of the storage out. In this case we ‘extract’ from the batteries about 80% and out of that 80% we've allocated a certain percentage to the loads every day and in case the grid fails, as a certain amount is left over to service the loads when the grid fails.
Because we don't know when the grid fails we look at the worst case scenario in regards to the level of battery maintained for backup.
If the grid fails during day time the solar will be there charging the batteries but we always design for worst case scenarios. For example if the grid has failed at night time and the batteries have already been discharged considerably during the day and there's no no solar component . . . . . . .
These systems aren't easy. There's a lot that goes into them. For example one of the stipulations is mechanical protection and that’s why we have installed some bollards.
Mounting the components
The inverter charger then the two fronties are mounted on 17 mmm form ply which we find very structurally sound and then we basically create a subframe behind that attaches to the shed structure.
We have signage on the battery cabinet signage, battery system dc isolator, inverters and we have signage obviously at the main switchboard.
The batteries are Power Plus which are Lithium Iron Phosphate, 4 kWh’s. There are seven cells at 48 volts each and they're all paralleled together. This particular battery chemistry at this point in time is the safest of the lithium solutions.
Each battery has its own DC circuit breaker built in but of course there is a breaker between the battery bank and the inverter, an inverter charger, 7500 watts, the brains of the system.
The switchboard in the shed effectively becomes the main switchboard. So how it works in this situation is that the existing main switchboard is on the house which is approximately 50 - 60 metres away so we had to trench to this shed and then cable from the shed back to the main switchboard.
Source and load
So in this case we have a source and load and the inverter charger is the first port of call after the main 63A breaker in the switchboard and then the source comes into the SP PRO and then comes out.
There are 63A breakers for both the load and the source. In addition there are breakers for the two Fronius and we've got a few other breakers there as well.
In this situation we're using a two-tiered switchboard: AC on the top, DC on the bottom. With this particular install we have tried to hide the cabling as much as possible.
There's no external DC isolators for the solar because the Fronius Primo has one built-in that works in conjunction with the DC isolators on the shed and house roofs. The inverter charger must be isolated from the batteries so we have a 250 amp dc isolator that is housed in an enclosure and a very short run of 70mm2 multi-strand that goes to the DC bus bar in the back of the Power Plus cabinet.
Trentham is a beautiful spot and a lot of people from Melbourne are coming are coming up to these rural areas and what they're finding when they come up to these rural areas in conjunction with beautiful scenery and great atmosphere is the issue of the stability of the grid and that's why and well that's one of the reasons why the customer decided to go the road of a hybrid system in other words solar and battery storage because of this inconsistency of supply out in these rural areas and we're seeing a lot of customers coming to us talking about this.
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