Wednesday February 18, 2015: Updated January 31, 2016
How to go Totally Off Grid using only PV solar panels
Many people make the claim that they are living off-grid. While that could be true for all their electrical needs, they still might depend heavily on gasoline/diesel for their vehicles and propane or wood for heating their homes, (you could argue that wood is a sustainable fuel if you had your own forest and lived out in the middle of nowhere, but it is not an option in populated areas that already have increasingly poor air quality).
Others may truly live off grid but by so doing have to give up on all modern comforts and necessities in the process.
Hypothetically, what would it take to live totally off of the energy grid, without giving up all the amenities? With no other energy dependence other than what freely shines down upon us from the sun each day?
What would it take to power my energy efficient home and vehicles completely from solar power and off grid, 12 months out of the year, indefinitely?
While it is relatively easy (through increased efficiency measures and grid-tied solar panels), to make a home net-zero, going totally off grid, all year long, (especially in regions with cold winters) is much more difficult.
A vision for my home, (sometime in the future) is a very comfortable and energy independent one; That when off-grid, will run on solar panels in the day time and off of a battery bank at night. That battery bank will consist of a modest sized stationary battery, 11-24 kWh in size, (Tesla residential power walls?) and a couple of electric vehicles, (with batteries of 24-85 kWh each) that can power the house when they are parked inside the garage.
Using all-electric appliances, a ground loop heat pump and driving only electric cars, solar panels can quite easily power all my family’s energy needs with all the comforts of any other American home. This is all due in part to using the grid as energy storage when the sun isn’t shining and when the shorter days in winter time prevent sufficient energy collection.
In December-February, the sun is not up long enough, (at our latitude) to shine sufficient energy down to supply the required energy demand. Needing extra energy for winter time heat makes these winter months even more energy demanding than summer months. This is tricky because the energy demand is higher but the available energy from the sun on a short, winter day is lower.
Why not just add more solar panels?
While a 11.4 kW solar array is sufficient to power my entire home and vehicles while grid-tied, because of differences in available solar energy throughout the year, taking my home off-grid would also require a battery at least 2000 kWh in size in order to make it through the dark winter months. To put that into perspective, that's like 20 of the Tesla utility grade power walls worth of storage.
Another option would be going with a brute-force, design for winter illumination method. For my home and vehicles, that would be an enormous 25 kW PV array. That wouldn't even come close to fitting on the house roof.
In a worst case scenario, there might come several days in a row where it's very snowy and cloudy outside where we also need to drive drive a few hundred extra miles during those worst case scenario days. A modest sized battery bank would not be able to store it all. The energy would all be depleted in only a few days, and even faster if you were driving around in those EVs.
While winter time with its short days, snow storms, and heavy cloud cover would be a famine of energy collection, during the rest of the year, the solar panels would make too much extra energy such that ~20,000 kWh of energy (more than our house and cars consume all year) would be thrown away because there would not be sufficient battery capacity to store it all.
Added 1/31/2016: Hypothetical Surplus Energy Uses:
Hypothetically, what if I did install a massive off-grid 25kW solar array? And what if I could find practical application for all the surplus energy during those times of overabundance and schedule its use with energy consuming activities that need to be done anyway?
Here are a few ideas for using all that extra energy:
- Make your own water -- Use excess PV energy to pull humidity out of the air and condense your own, endless supply of water. I don't have a water well on my property so why not go off-grid on water use too and make my own water? I should note that during the summer time, all air conditioners do this already, (1-20 gallons a day depending on indoor humidity), only the water is a waste product and is just discarded.
- Manufacture your own Ammonium Nitrate fertilizer -- And in small enough quantities so that you don't get put on the FAA's no-fly list. Just make enough so that you use it on the garden as you make it. Manufacturing fertilizer using renewable energy requires electricity, water and nitrogen from the air. You split water into hydrogen and oxygen. Then using high pressures, temperatures and a catalyst, you can make ammonium nitrate.
- Grow cold weather crops inside during hot summer months -- Using grow lights you can grow almost anything indoors.
- Make pottery and fire them in your own electric kiln.
- Make/store Hydrogen -- Energy Storage to be run through a fuel cell later in the year.
- Make your own superconductors -- Really? Yes! You can make your own superconductors. I have never tried this before but apparently with just 3 ingredients, a computer controlled kiln and a constant supply of pure oxygen you can roll your own. Oh and since you are already splitting water for hydrogen using electrolysis, you can collect and use the oxygen too.
- Use a freeze dryer -- Kitchen grade freeze dryers are currently all the rage for preppers. However they are expensive and use tons of energy, like 1500 watts continuously for days at a time. Perfect for when you have an overabundance of energy.
- Make hydrocarbon fuel -- Fuel molecules are just long chains of carbon and hydrogen, aka carbohydrates that have fossilized and are later refined. Well if you have an abundance of electrical energy, why not just take CO2 from the air, hydrogen from water that you have split and make your own liquid fuel? This fuel would be carbon neutral since when it is burnt, it is simply returning the CO2 back to the air. I don't know what you would use it for since EVs don't need gasoline. ;)
- Share it -- If you have exhausted all options for using energy for your own useful purposes, you can always share it with the neighbors or even sign up for Plug-Share and help some random EV driver passing through who needs a charge.
- Waste it -- This is the dumbest suggestion of all but I guess if you absolutely have no good use for excess energy and nobody else wants it either, you could dump the extra into a large resistive load, turning it into heat.
As an alternative to an overkill sized solar array, hydrogen storage is a plausible solution but it would require a 13,300 gallon tank filled with hydrogen at 300 psi in order to store 2000 kWh worth of energy. Plus, the process required to produce hydrogen (from splitting water), storing it and converting it back into electricity is far from efficient. You would need about 5000 kWh in electricity energy to produce and store sufficient hydrogen to later run it back through a PEM fuel cell to generate 2000 kWh worth of electrical energy.
While some may call this “stupidly inefficient”, (much like using hydrogen to power cars), if you already have an over-abundance of free renewable energy and a lack of long-term energy storage, it may be a necessary compromise and reasonable solution.
Hydrogen in this application is not the energy source but rather the energy storage mechanism. Unlike chemical batteries, hydrogen itself can be stored indefinitely without wearing out.
While a 13,000 gallon tank is out of the question for my home and neighborhood, a 1000 gallon one isn’t that un-reasonable. At 300 psi, that tank could store about 150 kWh worth of energy in hydrogen. That size of battery bank would not get the house and cars through an entire winter but could certainly last us through several cold, cloudy, non-solar collecting days.
Supplement with wind:
Wind power is a great solution to areas that receive a lot of wind. In fact, if you live in a really windy area, don’t even bother with solar panels at all. A small, inexpensive wind turbine blowing 24-7 will generate all the energy you need. Unfortunately I don’t live in a windy area and the wind we do receive is sporadic at best.
Sorry the audio is so poor in this video. Click on CC for captions.
Plus the HOA is vehemently opposed to me putting wind turbines on the house roof. Believe me, I tried. So for me, wind energy is out.
Further energy efficiency improvements:
My house was not designed for efficiency. I did what I could to make it energy sipping, without anyone knowing any different. But if a house can be designed from the ground up for energy efficiency, then energy demand would be much lower.
Perhaps there are more hidden improvements yet to be discovered?
Use less energy:
We Americans waste energy like crazy. If we can just design our cities to be more efficient? Lay them out so people can walk more and drive less. Driving less and driving more energy efficient vehicles could save a lot of energy.
Fussion in the home? Matter/Anti-matter? Probably not in my lifetime. I'll stick with the proven, super affordable PV solar.
Update May 29, 3015:
I finally got around to wiring up the dedicated off-grid circuit on the new SunnyBoy 5000TL inverter. Now, in an an emergency when the grid goes down we can still have up to 1500 watts of daytime backup power without batteries.
Check it out
Pretty neat feature eh? At least this will allow basic daytime electric needs until such time that I add some actual batteries.