Solar collection includes 4kW of ground mounted panels, optimised for winter sun, at a slope of 45 degrees
Credit: Dr Gordon Weiss, Principal Consultant with Energetics/One Step Off The Grid
Recently on these pages I discussed some of the issues to be considered when contemplating reduced dependence on the grid, or, (a little tongue-in-cheek) going off-grid altogether.
When Dr Gordon Weiss was considering utility connection for his weekender, with grid connection priced around $270,000-$300,000, going off grid became very attractive. “That’s a lot of solar panels & batteries!” As suggested in my previous article, a fossil fueled generator (5 kVa diesel) was required to cope with extended cloudy weather.
http://onestepoffthegrid.com.au/despite-the-tesla-hype-going-off-grid-is-not-that-simple/ / Dr Gordon Weiss Principal Consultant Energetics carbon and energy management large energy users manage carbon emissions energy costs designed built off-grid system home beautiful Blue Mountains techs technology specs specifications his system Tesla PowerWall energy storage low cost batteries advantage householders widespread defection from the electricity grid building a weekender home Megalong Valley Blue Mountains, NSW property sub-divided farmland no grid connection water phone sewerage connection construct modern house utilities supply power occupied local network service provider 2 km HV power line local 25 kVa substation cost of around $300,000 solar panels batteries designing off-grid solar power supply off-grid solar PV supply photovoltaic photo voltaic typical daily electricity consumption typical consumption overnight size of both the solar panels battery capacity peak power demand of the house inverters batteries sufficiently large instantaneous peak demand expected weather patterns cloudiness trade-off between battery size likely use backup generator top up batteries graph average daily solar exposure sunlight sun light insolation Little Hartley closest weather station periods cloud cover reduced the solar exposure several days much lower solar exposure winter compared to summer placing the solar panels horizontal angle to the latitude maximise the power generated over the course of a year system design solar PV system 3kW panels roof slope of 11 degrees 4kW ground mounted panels slope of 45 degrees orientated due north purpose ground mounted panels catch maximum winter sun modelling demand house average demand during the year 15 kWh average Australian house design included extensive LED lighting no air conditioning no electrically powered space heating LEDs additional hours of darkness in winter average power demand time of year 20% greater than the summer demand performance of the system in winter inverters batteries diesel generator other elements our system Kaco Powador grid invertors Selectronic SP PRO inverter-charger 32 kWh battery storage batteries are gel-acid depth of discharge battery service life effective storage capacity 20 kWh extended cloudy days backup 5 kVa diesel generator size solar panel array capacity batteries was determined using HOMER free former US Department of Energy program optimising off-grid systems design likely hourly power demand hourly solar exposure cost system including cost of fuel perform four month period maximum instantaneous power demand 12 kW in-rush current of an electric motor other household appliances electric kettles highlight importance correctly sizing the system undersized system shut-down power demand was too high graph operation of the solar PV system several important features system design batteries fully charged state of charge equals 100% output solar panels constrained just meets the load evening peak partially discharge the batteries overnight load refrigerators aerator waste treatment system morning peak before there is any output from the solar panels significant daytime load solar panels fully recharge batteries mid-afternoon challenge of cloudy days data challenges off-grid when Sun is not shining household load greater overnight batteries just over 40% charged morning load rose system inverter-charger shut down the load protect the batteries diesel generator raise the state of charge batteries external supply graph generator tested test-run generator cloudiness recharge the batteries night time impact of cloudy days occupied unoccupied reduced power demand solar panels fully recharge batteries very cloudy days solar panels some output total generation cloudy days instantaneous outputs recharging sunny days batteries charged cloudy period 2 kW spikes small hot water heater maintain water temperature panels recharge batteries cloudy days more panels installed better the system can deal morning power demand reduces probability generator will be required trade-off size panels storage capacity experience going off-grid conclusions understand daily seasonal power demand properly size the system smaller demand solar array batteries capacity average daily demand house adequate except very cloudy days solar panels run house recharge batteries larger array morning power demand alternative spending $270,000 grid connection watching the system in action comes out on paper go off-grid install as many batteries as they can afford minimise use back-up generator /
