Now that our power station has been commissioned, is actually powering stuff, and because it’s been an evolutionary thing over many months, I’ve decided to chronicle how our rather unique stand alone power system is built in one post, for the benefit of all mankind…. as it were!
The solar power is generated by eight 260W monocrystaline photovoltaic panels, for a total of 2080 Watts. They are mounted on a custom made steel frame, installed by the first wwoofer I had working for me here… They are connected in two strings of four with each string producing 1000W at 150V DC maximum. The two pairs of wires are fed underground and through the container’s floor in that orange conduit, to the DC circuit box where two 20 Amp circuit breakers protect the system against short circuits or serious malfunctions. Each circuit breaker is dipole, and simultaneously breaks both the positive and negative circuits.
From this box, the solar power is fed to the MidNite Classic Maximum Power Point Tracker. This magic black box manipulates the incoming electricity so that it is fed into the batteries at the optimum voltage/amperage combination needed to maximise the amount of energy fed into the batteries to keep them charged. I had never used one of these before, but they are well worth the $900 , because it does all sorts of other tricks, like boost charging, battery equalising, floating, and even monitors the amount of energy fed into the batteries, logging all that information where it can be accessed later…… If I decide to later add a wind turbine, I will get a second one to control its output.
The power going into the batteries (and out of them for powering things with the inverter) go through a fuse box with two 160A slow burn fuses. Batteries are capable of producing spectacular amounts of current (think big sparks and fire!) and in the unlikely event of something seriously bad happening to the batteries, these fuses will burn and save the rest of the system. The fuse box is also designed such that it can be used to disconnect the batteries from everything else in an emergency, or for maintenance. There’s one fuse for the positive cable, and one for the negative……
Once charged, the energy contained within the batteries can be extracted back out (through the aforementioned fusebox) by the Victron inverter, which converts the 48V (nominal) DC from the batteries into 230V AC for powering all the things we take for granted in houses, like lights, fridges, TVs and washing machines etc……
This inverter has now had its settings altered to operate at between 64V and 37.5V. It’s because Victrons can be reprogrammed to do this that I opted for this technology, as the Nickel Iron batteries are able to work safely at an even greater voltage range. The blue digital voltmeter is something I added to the inverter to get an instant readout of the battery bank’s voltage.
Just as there is a series of safety devices on the DC side of the system, the AC sector is also wired up to protect the wiring and the people using the electricity! You will also notice the green/yellow striped earth wires to/from the MidNite Classic and the inverter, all connected to the earth in the AC switchboard, all grounded to the container itself.
Before going into the AC circuit box, I wired in an old energy meter I have had for years to monitor how much energy we will be consuming in the house (as well as outside to pump water for the gardens etc…). I used to use it for doing energy audits, and they sure don’t make them like this anymore…!
The 230V output is split into three, with another dipole circuit breaker (one for the active and one for the neutral) taking power to where the house will be built, currently permanently switched off. Another 10A circuit breaker takes current to a power point inside the container for running the freezer and charging cordless tool batteries (so far), while a 15A breaker takes power to an external 15A all weather power point outside the container where I currently plug the new pump in (more about this in a later post).
The two power points are protected with safety switches which are now built into the circuit breakers. It’s amazing how fast technology changes/improves these days….
The battery bank consists of forty 1.2V Nickel Iron cells (to make the nominal 48V). You can read about why I selected this battery chemistry here……
The container is earthed with a copper stake, and everything involved in this system is also earthed through the steel container, one advantage of having a steel building! The safety switches test just fine, the whole system is very safe. To vent the potentially explosive hydrogen gas that bubbles from the batteries, two whirlybird extractors were put into the container’s roof, and six vents at floor level on the western end of the container were also added. It’s where the wind usually comes from, and it will no doubt assist in keeping everything cool, even in summer….
I’m really stoked at how well it’s all working. Even on really rainy days, the solar array was able to feed 4.7kWh of energy into the battery bank, and even on the very worst day when the sky was inky black and it just poured all day long, 1.7kWh was absorbed by the batteries, almost enough to power our old house for a whole day…. The design electricity consumption for the new house is 2kWh/day, though at this stage it’s still unknown how much energy I will need to pump water for the market garden.
I’m finding adjusting to the NiFe batteries a little tricky. Unlike conventional Lead Acid batteries, these prefer to be worked hard. I’m told by people who run them that the harder you cycle them, the more capacity they build up, and the longer they last between electrolyte replacement. Because I’m (so far) only pulling 0.9kWh/day out of them with the freezer, the batteries haven’t been worked enough. So I recently turned the solar power completely off for eight or nine days, just to ‘flatten’ them. They were fully charged again within two days…. Nickel Iron batteries, unlike the other technologies sold everywhere, can be ‘flattened’ as often as you like….. you just need to always make sure there’s enough left to start the freezer again, or else lose the contents!
Now the container sports a 1000 litre IBC for gravity fed water storage….. but you’ll have to wait for the next installment.