To check how many solar panels you need to fully provide for your house, the best option is to look at your monthly electric bill. This will show you how much you use each month (in kWh).
If you are planning a new build or don't pay for your own electricity, the average household in the US uses 900 kWh per month.
Free & Easy Energy Calculator Tool
Solar panels have improved dramatically and are continuing to get more efficient and more cost effective. This means you can get significantly more electricity per dollar than you could even 5 years ago.
Solar panels are a great way to invest in a long term energy solution for your home to either supplement or completely replace standard electric providers.
For those of you not interested in the science or math, here's a tool to tell you how many solar panels you need based on the amount of electricity you need (or want)
Math & Science & Shit...
For those of you who want a little more information, I charge 10$ if you'd like to keep reading. You can send it to me via Paypal.
W= watts (amount of energy) ((small))
kW= Kilowatts (amount of energy=1000 watts) ((bigger))
kWh= kilowatt hours (amount of energy consumed in one hour)
So if you want to power a 1000W drill, it is a 1kW drill. It requires 1,000W to make it work. If you want to run this drill for 1 hour, then you will use 1kWh of energy. (1 hour worth of 1000W)
First calculate your monthly energy needs (We'll say 900kWh)
This means I have 900,000 Watts per hour being used. (this is more than the hours in a month because you have your computer, your tv, your microwave and your washing machine running at once. )
Then divide your monthly kWh energy usage by 30 to get daily usage.
900kWh / 30 days = 30kWh per day.
So to replace that 900kWh with solar sources, you need to get enough solar panels to absorb at least 30kWh of sunlight every day.
A rough rule of thumb is:
250W solar panel produces 1kWh per day. (or 10W per sqft of solar panel)
This assumes an average of 4 hours sunlight per day. You may get more or less depending on your location. (Arizona and New Mexico are closer to 7 hours per day. California and Colorado are 5-6. Seattle and Chicago are closer to 3 hours)
So with this formula you would need 30 x 250W solar panels to make 30 kWh per day.
Now we calculate the cost...
Cost for a Solar System
As of January 2018, 25kWh system would cost you about $78,000. ($3.14 per watt)
After some 30% off discount from Federal ITC you're looking at $54,950 (plus more savings if your state has incentives)
You'll need more than just solar panels. (And that's what drives the cost up)
As you can see from the diagram above, the solar panel absorbs the sunlight, then sends it to a controller which then stores it into a battery. The Battery has DC current which has to be switched to AC current in the inverter so that it can be used by your normal household appliances.
I would also recommend extra batteries as they will need to be replaced over time (like a car battery) and its good to have spares in an off-grid situation.
Written by: Page Ollice
Founder of Good Old Fashioned, Page has spent over 7 years researching off grid and sustainable living techniques to design one master project: A self reliant homestead in New Mexico that takes into account shelter, water, fuel, food, waste management, heat/cooling, and electricity. He is putting all his notes online open source for public use so that anyone can follow his plans to building their own autonomous, self-reliant homestead.
About the "Good Old Fashioned" Project
I love systems. Everything in our solar system has a cycle. Trees, Nutrients, Water, Air, Heat, Plate Tectonics, Cells, Food, Carbon, Plants, Rocks, everything.
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