I have a self built system, 3kW peak, batteries, inverter, 240AC changeover switch.
aims:
to replace some power usage each day.
The amount of power available on any day is indeterminable and also could vary from 1 kWhr to 20kWhr
depending on season and weather.
IF insufficient power available from solar, use street power for balance required.
facts here in Melbourne:
$0.31/kWhr for electricity from any supplier.
approx 4.5 hours sunlight per day average over a year.
facts world-wide in modern Western economy households:
short high peak electricity loads on top of a steady, low power base load.
My house has a base load of 600-800W which is present 24 hours a day.
This means 0.6 x 24 = 14.4kWhr base load plus short period peak power values.
My daily average energy usage is 17-20kWhr/day over entire year.
This 600W can easily be supplied from a well sized, efficient and decent inverter.
So I can save 3/4 of my energy usage by simply providing this 600W for 24 hours a day.
So, I chose a 3kW peak solar panel array, to feed a 15kWhr battery bank via a 60 Amp peak
charge controller (Tristar 60Ampr MPPT)
Inverter is Victron 3000 W peak, 2,500W continuous inverter. Max efficiency is at about 1/3 peak power,
this allows some headroom for growth.
system is based on 48V DC nominal battery.
Now, typically I obtain about 10 kWhr from the solar array, and this gets put into the battery with about
95% (NO! more like 80% edited 12:14pm) efficiency. Then during the day and following evening, I pull this power out of the battery via the inverter
to power SOME but NOT ALL of the house power. I might use 9kWhr of inverter power, which I do NOT have to buy from power company.
I have run separate general power outlets into most rooms that are all connected to the single 240VAC output
of the inverter, via other equipment.
I have all TV, DVD, computers, 4 fridges (don't ask, 4 fridges..that's insane)
kitchen toaster, kettle and pool pump etc all connected to the one 20A trunk line, supplied
via an 16A RCD contact breaker which is then connected to a change-over relay then the inverter.
The change over relay is the key to the entire system.
This can sense when one input stops and change over to the secondary input, and connect this
to the output. This allows me to provide 240VAC power for any period of time from the inverter and when not available, the relay will change over to use the street power as a substitute until the inverter powers up again.
All transparent and no need for human intervention.
Cost to me so far:
$3,600 solar panels
$2,300 Victron Multiplus inverter 48V/3000W
$700 Tristar 60A MPPT charge controller
$xxx contact breakers, big-ass high rupture current DC fuses, wiring, etc
$400 Latronics change-over relay ACTS40
300Ahr 48V battery bank came free of cost. (ex Telstra mobile phone tower batteries destined for recycling)
I have data to show I am averaging about 8kWhr self supplied energy per day.
This is 8 x $0.31 = $2.48 per day saving of electricity. Does not sound much.
365 x $2.48 = $905 /year.
break even on investment approx 7 years
And we get to tell the foreign investors of our privatised power companies
to stick their product up their fucking arses. (value of this = $priceless)
Note well:
Electricity costs will increase in the future in large increments because they can.
After the faux privatisation of state electricity here in AUS, the Elec suppliers can name their own prices now
All in the name of "Free enterprise/competition/captured markets/corruption/what-have-you"
So my system will get better as the price of elec. rises as it must.
I chose a nominal 100V DC solar array, coming into the charge controller to charge a 48V nominal battery bank.
This optimises the I2R (resistance) losses in the cable from panels to the charge controller (15 meters x 2)
and it then permits the highest efficiency inverter, being 48V DC.
Your installation may require different design factors for optimum performance.
go for it if you have the $$$. No need for a complete stand alone off grid system.
You can make 3/4 of total savings possible at 1/4 the cost.
A full on off-grid system needs 5X the batteries, 4x solar panels, 2X inverter and changes to house lifestyle.
All for the final 1/4 savings. Not worth it unless you must go off-grid.