OFF GRID POWER COST

On this page I show you three different size installations and their off grid power cost.

1. HOW MUCH POWER DOES THE AVERAGE HOUSEHOLD USE?

One of the hardest tasks is to determine how much power one needs. It depends on your lifestyle, your habits, the equipment you use, are you home all day etc. I can start by giving you an example of the average household.

Mind, there is also a seasonal effect and is your climate coastal or inland. 

  •  The lowest usage is spring, autumn is 6% higher, summer is 10% higher, winter is 35% higher.
  • The average is 14kWh and now the seasons compare spring -11%, autumn -6%, summer -2%, winter +20%. That makes the highest daily usage 15.5kWh
  • Away from the coast this average increases by about 20% to around 17kWh per day on average, but winter is at 20kWh.
  • My usage is only valid for 2023, because there have been many changes in the past. Mind, there have been operation changes, like I did shutdown the Tank farm during rainy weather, I only installed the incinerating toilet 2 months ago. I cannot get a seasonal fluctuation, but I can give long term kWh Aver, max, min per day by function.
    • Average 15kWh, max 20, min 10
    • Home before incinerating toilet                      5.6kWh, max 5.6, min 4.7 and after  8.0kWh (an increase of 2.4kWh)
    • Air con 5kWh, max 13, min 0
    • Hot water 2.5kWh, max 3, min 2.3
    • Tank farm 1.2kWh, max 2.6, min 0.5
    • Pump house 0.3kWh, max 0.4, min 0.25
    • Workshops are insignificant at 0.5kWh with a max of 0.7 kWh.
  • OBSERVATION. I am slightly more frugal than the average consumer, but I still am, and have always been, a big power consumer.
  • NOTES: The hot water also runs a second fridge, and soon I also run a freezer there.
  • The laundry is in container 6 and does not register, yet the washing machine has a 0.04 Amp standby current, (or 9.2Watt) which equals 0.22kWh per day, or 3kWh in the periods of a fortnight between washes. So, I turn the power off after washing and try not to forget.
  • The home runs the toilet, the fridge, the computer (24/7), (but I turn the screen off, when not in use), Foxtel, lights for 16hrs, small device battery charging, cooking, the 4G amplifier (24/7). (The aircon is on its own circuit.) But if it is raining for a few days, and I do not use the air con, then home will run the batteries dry (75% drawdown) in 3.7 days. With average aircon use 8 + 5=13 and the batteries are flat in 2.3 days.

2. WHAT CAN WE DO TO TAKE CONTROL OF OUR CONSUMPTION.

On a sunny day, when the solar panels are charging the batteries fully by lunchtime, I am actually wasting valuable solar energy. But storing this waste is again costly. 15kW of batteries cost $9000. These batteries can fill up in 2-3 hours, so that is only 1 day benefit. If we take this over a year that is $24/day. Which is an extra cost of $1.6 per kWh on top of my average consumption. But the batteries last 10 to 15 years. Let’s say 10 years, that is still about 16 cents/kWh extra.

So, what should we do:

  • Any power used after dark is a burden.
  • We need to use high demand items during the four top sunny hours in the middle of the day. (Like pumping water.) But do not think starting at 4pm is helpful, it needs to be around midday.
  • Perhaps hot meals should be cooked in the middle of the day, and then just re-heated in the evening.
  • As a matter of routine, we should heat our water storage around mid day. Also if we shower, say every second day we need to work out a smart way of heating the water. The day that I am not using water, it still heats water. So, I will experiment by reducing the temperature, and have less heat loss.
  • If it is cloudy during the day we may have to turn some circuits off. (like grey water processing.)
  • If the battery state of charge is low in bad weather, once more we may turn circuits off.
  • When we use air conditioners (and I have 2) we need to do the following:
    • We need to get the inside temperature beyond our desired setpoint, before dark.
    • Be prepared to adjust your clothing to the inside temperature.
    • My aircon’s have a standby current of 0.5 amps each, but at a very low power factor, meaning it is reactive or wasted power. But my batteries still have to deliver the 0.5A x 2 air conditioners = 1A/hr for 24hr = (1A x 24hr x 230V = 5.5 kWh). That means if we have 20kW batteries, we can only draw say 75%. Then this standby draw will drain those batteries in 2.5 days. So when not in use I turn the circuit OFF!
    • The same could apply to other standby devices. Some are very good like Foxtel, but some battery chargers and the washing machine still draw current when not operating. So be careful and check.
    • Cooling the inside during a hot sunny day is easy, but in winter we are usually heating the inside after dark. The best thing is to run them for short periods, twice at night and once when waking up.
    • I sleep under a doona, but on top I have a folded open minus10 degree sleeping bag. I keep comfortable all night, regardless of the temperature. 

3. WHAT IS INCLUDED FOR THE PRICE?

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BATTERIES:

  • The number of batteries in brackets behind batteries. It includes a battery management unit, a 4 battery cabinet + cables for DC and AC and DATA.

SOLAR PANELS:

  • The number of panels is in brackets behind, each panel is 415 kW each at this stage. 

SOLAR FRAME:

  • This is a frame built to carry the number of panels, which lives on a container roof facing the sun at 30 degrees angle. Plus all rails and mounting brackets plus a role of DC cable plus connectors and 4sqmm AC cable.

INVERTERS:

  • A 5kW solar panel inverter that can handle up to 12 panels. Also an 8kW grid creating inverter that can deliver 6000Watt continuous at 26Amps.

GENERATORS:

  • It would be foolish to think you can run off grid without a backup generator. This includes 2, an 8kVA and a small portable backup 2kVA. The 8 kVA is a dedicated off grid unit and it has auto start, but I am not using that. The machine runs on Petrol. There is also some cable to connect to the inverter.

SWITCH BOARD:

  • I have not included any costs for a switchboard. To copy my installation would be an overkill. But I built it to learn, manage and understand the overall installation. Plus I got caught with a battery dilemma created by the supplies. (So I can advise others.) The current one is version 3. The first version cost me about $1500 excluding any labour. The last one was double that and it took me weeks to build. It has some 30 relays and about 300 meter of cable. Actually the switchboard belongs as much with the electrical wiring as the generating part.

4. SOME MORE NOTES ON BATTERIES AND THE OTHER EQUIPMENT.

  1. Please note from a 20kW battery bank you can only count on drawing 15 to 16kW of power per day. That equals my average usage. So if it rains for a day you are destined to the generator for the next day. In reality you depend fully on the batteries from 4pm to 10am, regardless of the sun intensity during the day.
  2. The 20kW system has 2 inverters. One looks after the solar panels, the other creates the grid and looks after the batteries. That will give you a maximum steady supply current of 26 Amp. In my mind that is plenty. But if you need more you need an extra grid inverter at  around $6,000. These inverters are designed and built in Germany by SMA, the most reputable manufacturer. The grid supply inverters can be coupled in an array to each time double the output capacity.
  3. The solar panels frame, in this suggestion, is an easy tilted frame that can handle 10 solar panels per container. My system is mounted on poles. That system is a lot more expensive (probably double) and more involved, particularly installation wise. However for this suggested system to work, the container length has to face North.
  4. In the first column the 10 Solar panels are rated 4150 Watt, but on a sunny day they should easily create 4x 4150= 17kWh. I am aiming to roughly equal the battery capacity. Only 10 panels can fit on one 40ft container. The trade off is spend more on generator fuel in cloudy days against purchasing more batteries and solar panels. If you spend $10,000 extra, that amortizes at $1000 pa. An 8KVA generator uses about 10L petrol per day, which is about $20. You will break even at 50 days/year.
  5. Solar panels are relatively cheap, so you may think well I buy 3 times what I need. But in a rainy day 10, 20, or 30 panels still won’t charge the batteries. On most sunny days my batteries are at 100% by lunchtime.
  6. I started off with 1 x 3kVA portable generator then upgraded to 8kVA. But over the 4 years I pensioned off 5 generators. I finally spend more and bought a dedicated off grid generator and so far no regrets.
  7. Please note I can only supply equipment for off grid installations. The equipment cannot be connected to and work in unison with a public grid.

Click to have a look at my research on wind turbines.

20 kW batteries

Batteries (4)

Solar panels (10)

Solar frame

Inverters (2)

Generators (2)

TOTAL

$11,100

$1,900

$2,800

$7,400

$4,300

$27,400   +GST

$30,140

30 kW batteries

Batteries (6)

Solar panels (14)

Solar frame

Inverters (3)

Generators (2)

TOTAL

$17,000

$2,700

$4,200

$9,200

$4,300

$36,900     +GST

$40,590

40 kW batteries

Batteries (8)

Solar panels (18)

Solar frame

Inverters (4)

Generators (2)

TOTAL

$21,700

$3,500

$4,400

$14,800

$4,300

$47,600    +GST

$52,360

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