Last edited Sunday October 29, 2017
Off-Grid by 2020
Work in progress:
Wouldn't it be great to just be able to collect all the energy you need (lighting, HVAC, vehicles, appliances) from your own backyard?
I have set a personal goal to do so and cut ties with the power company all together. To go off-grid by 2020.
I created a spreadsheet to calculate the battery capacity needs and solar array size necessary to take my entire my entire household and electric vehicles totally off the energy grid.
Importing the last 12 months of daily energy usage/production data, I am able to size a stationary battery and solar array to cover all the energy needs over a 12-month period.
While 9 months out of the year this problem is easy and inexpensive to solve, for December through February, the energy shortfall is enormous. This is mainly due to the shorter days during this time of the year.
It would take a ridiculously large 1000 kWh battery and 20kW addition (almost 3x larger than what I have now) of solar panels to cover this shortfall no matter what.
I have pondered this problem for a couple of years and can’t seem to get past it.
What if I just used a backup generator a few times a year and went off-grid the rest of the time? Playing with the variables in my spreadsheet, I arrived at a more cost-effective solution to this problem.
It is plausible for my household to go off grid with a 70-98 kWh battery pack (5-7 power walls worth) and an additional 12 kW of south-facing, ground mounted, December optimized solar panels. Seven power walls (delivering 5 kW each) would also give me an enormous 35 kW of peak power to play with. Even 5 power walls would provide 25 kW. That’s still more than enough.
December Optimized Array
My current solar array is mounted to my home’s roof which is not ideally pointed for optimal energy generation. Part of the array faces south-south-east and the other half faces west-south-west. The entire array is fixed on a 30° slope.
If energy production is not an issue except for 2-3 months out of the year, why not optimize the solar array just for those times of the year.
At my latitude, a December optimized solar array faces due south, (diagonally across my back yard) and is at a 68° slope. Running some trig calculations, I quickly realized that in December, this steep array will perform the same as an array twice the size mounted on my roof would. This means that if I needed an additional 20 kW of solar panels on my roof to cover December’s energy usage, I will only need to install a 12 kW ground mounted one that is optimized for December.
Another benefit of such a steep angle is the snow will quickly fall off of this array. That’s the problem with solar panels in December and January. One large snow storm kills all energy production even when it’s sunny, because the array is still covered with snow.
Still, an additional 12 kW is an enormous array to have mounted in my backyard.
Then, the other day, it hit me. What if I could supplement the solar panels with another energy source during those few times that they are not producing enough?
I don’t really like the idea of a backup generator because I would still be dependent on fossil fuel and they are only like 18% efficient. That would be a waste of fuel and defeat the purpose of going off grid. The energy that it produces would be far dirtier than just staying grid-tied.
What if I could just bring home a bunch of electricity a few times a year?
As an EV driver who closely monitors his energy usage, I have begun to measure distances by the energy it takes to drive some place. For example, I work in Salt Lake, 4-5 kWh away from my home in Kaysville. It takes me 7-8 kWh to drive to WSU in Ogden after work.
I live less than 6 kWh away from the closest Tesla super charger station in Salt Lake. An electric car with a 100 kWh battery could make the drive home, power my house that evening, recharge the stationary battery pack and still get me to work and back the next day.
Running the numbers in my spreadsheet, I would only have to do this about 4 times a year. Twice in December and twice in January. That’s not all that terrible. I would gladly spend 4-5 hours a year charging the car’s battery instead of having to buy and burn propane.
Besides, Tesla gives every owner 400 kWh per year for free at the super charger stations so it wouldn’t cost me a dime for the energy either.
While technically, I would not be totally off-grid for this energy, the other 360 days a year, I would be.
Too Much Energy?
The remaining 9-10 months out of the year, Only about 10-30 kWh of this large stationary battery pack is ever used. More often than not, this battery will be full by 11AM and the energy that the solar panels make all day would otherwise be wasted.
This is what my mentor calls a Higher Quality Problem. When you increase the quality of your life, your problems don’t just disappear. Well some problems do but you will have new problems enter your life, higher quality problems. Like having too much money or having too many sales, or too much business or too many options for a family vacation.
These are higher quality problems. Having too much energy is also a higher quality problem.
The rest of the year, I will just have to get creative as to how I will consume the 14,000 kWh in surplus energy that the solar panels will produce all year.
- Teach a pottery class and run a large electric Kiln.
- Manufacture my own nitrogen fertilizer.
- Condense water from the air and go of the water grid too.
- Split water into hydrogen and oxygen.
- Offer free supercharging at the house.
- Give energy away to the neighbors for free.
- Mine bit-coins.
Actually, running one or two 1200 watt bit coin miners continuously from March through October would solve the energy surplus problem. As icing on the cake, they would also generate revenue as a waste product. That was easy.
Additional passive hot water tank capacity.
Wind turbine? I know you have tried this and it doesn’t work, but try again with a 3-blade turbine and an inverter better matched to run on the voltage produced.