Solar Farm - Minimum Land Area
An interesting question, to me and possibly others considering a solar farm is, what is the smallest area possible that can support a family (in this case a family of 4 people).
Solar cells:
Theoretically, with photovoltaic cells now able to operate at a (claimed) 18% efficiency maybe 1,200 square feet of solar cells could provide enough electricity for home and electric car and a small surplus to sell to the utility if efficient appliances are installed in the home. (1,200 sq. ft. of solar cells at 18% efficiency produce about 29,000 Kilowatt hours or Kwh of electricity per year - 24 Kwh per square foot per year assuming 460,000 Btus of energy fall on a square foot area per year (southern Michigan climate and one Kwh equals 3413 Btu).
Solar greenhouse:
In addition to solar cells; a thousand square feet of solar hydroponic greenhouse could provide enough food to eat and sell and a surplus for extra income. For example such a greenhouse might grow 10 pounds of tomatoes or lettuce per square foot per year, saleable at $1 or more per pound. So 1,000 square feet may yield you $10,000 per year - a decent income if you are practicing the other techniques of extreme frugality.
So a 2200 square foot lot (with your house under the photovoltaic cells and your hydroponic solar greenhouse attached to the south side) could be large enough to live on in comfort. Zoning may have building setbacks of 10 feet on the sides and back and 40 feet in front - but still a lot of 60 x 100 feet or 6,000 square feet would accommodate these requirements. And, if setbacks are less - 5 feet in some locations (and even 0 in some places) you could live on a very small parcel of land. (And thus, your property taxes could be kept low).
Solar cells:
Theoretically, with photovoltaic cells now able to operate at a (claimed) 18% efficiency maybe 1,200 square feet of solar cells could provide enough electricity for home and electric car and a small surplus to sell to the utility if efficient appliances are installed in the home. (1,200 sq. ft. of solar cells at 18% efficiency produce about 29,000 Kilowatt hours or Kwh of electricity per year - 24 Kwh per square foot per year assuming 460,000 Btus of energy fall on a square foot area per year (southern Michigan climate and one Kwh equals 3413 Btu).
Solar greenhouse:
In addition to solar cells; a thousand square feet of solar hydroponic greenhouse could provide enough food to eat and sell and a surplus for extra income. For example such a greenhouse might grow 10 pounds of tomatoes or lettuce per square foot per year, saleable at $1 or more per pound. So 1,000 square feet may yield you $10,000 per year - a decent income if you are practicing the other techniques of extreme frugality.
So a 2200 square foot lot (with your house under the photovoltaic cells and your hydroponic solar greenhouse attached to the south side) could be large enough to live on in comfort. Zoning may have building setbacks of 10 feet on the sides and back and 40 feet in front - but still a lot of 60 x 100 feet or 6,000 square feet would accommodate these requirements. And, if setbacks are less - 5 feet in some locations (and even 0 in some places) you could live on a very small parcel of land. (And thus, your property taxes could be kept low).
If you have a bike and no car then virtually no parking space is needed. But, possibly a car could be parked under the house using a 10 x 20 or 200 square foot space so no space need be lost to parking. So 2,200 square feet is the minimum, right?
Discussion:
A solar greenhouse, using hydroponic growing methods, could produce 5 times the produce of a garden, or maybe 10 pounds of food per square foot over a year. So 1,100 pounds of food per person per year times 4 people would require, for 4,400 pounds of food, only 440 square feet of growing area. Add some area for produce to sell to pay property taxes and other expenses - maybe another 560 square feet (or 1,000 square feet total) growing 5,600 pounds of produce worth $1 per pound (for beans or more for other crops - much more for some crops) so $5,600 would be earned by this method. Enough for most other living costs in a 'Zero Cost Living' lifestyle including seed, fertilizer, electricity (unless you have photovoltaic panels).
A solar greenhouse, using hydroponic growing methods, could produce 5 times the produce of a garden, or maybe 10 pounds of food per square foot over a year. So 1,100 pounds of food per person per year times 4 people would require, for 4,400 pounds of food, only 440 square feet of growing area. Add some area for produce to sell to pay property taxes and other expenses - maybe another 560 square feet (or 1,000 square feet total) growing 5,600 pounds of produce worth $1 per pound (for beans or more for other crops - much more for some crops) so $5,600 would be earned by this method. Enough for most other living costs in a 'Zero Cost Living' lifestyle including seed, fertilizer, electricity (unless you have photovoltaic panels).
A small simple basic car, easy to repair, getting high miles-per-gallon might almost be affordable with this 560 square foot area of greenhouse producing a surplus to sell. At a minimum such a car would require $1,500 per year for insurance, repair, legal fees, and conventional fuel (if you didn't drive too much).
However, the car could be fueled by electricity from the 1,200 square feet of rooftop photovoltaic panels and (if a hybrid vehicle) fuel from biomass (bio fuel) perhaps methanol produced from plant wastes.
You may want to get your plant wastes off site, saving your on site wastes as mulch and compost (if you use some organic farming methods).
It would still be much simpler to live where you can get everywhere on a bike, avoiding the costs, complexities and headaches of a car. The $1,500 (minimum) you need for the car could be used for vacations or saved for emergencies or anything you could think of.
In conclusion (for now), excluding area for photovoltaic panels: if the house was entirely beneath a greenhouse - a greenhouse that covered the entire roof area; and bikes were used (and practical in a compact efficient city), possibly under 1000 square feet of area could be sufficient to support a family of 4 living with extreme thrift. Many apartments are no larger. (But of course are stacked up on top of one another - and only the south facing apartments would get sunlight for growing or solar cell electricity. Also, apartment residents are burdened with rent, $12,000 or more a year, a crushing burden for anyone attempting to life with extreme frugality).
Minimum area needed to grow food: (This discussion affects the one just presented suggesting the possibility that a very small space indeed, efficiently used could support an efficient lifestyle).How much space is needed to provide one person with food for one year? The short answer to this question is surprising.
In a solar greenhouse: 110 square feet.
How did I come up with this area?
From my book, a person needs about 3 pounds of food per day and about 1100 pounds per year. In a garden growing 2 pound per square foot, 550 square feet of area is needed to feed one person for one year.
But wait. A hydroponic solar heated green house could produce 5 times as much food per square foot or about 10 pounds per square foot per year. Therefore, 1100 pounds of produce could be grown in an area of 110 square feet or 11 x 10 feet.
This is a theoretical estimate. Actual production will depend on the design, efficiency, operation, management etc. of a solar greenhouse.
Update: After further consideration I realized this is wrong. The weight of food eaten is not the key factor. The ENERGY CONTENT of the food you eat determines the food needed per year.
110 square feet would work if you grew and sold most of your 1100 pounds of food at $1 or $2 per pound - perhaps growing lettuce and then using that money to buy food with a higher energy content. If you earned $1100 or more that could be sufficient to buy all of your food for a year: using the $1100 to buy grain or beans or rice or other high energy (but low cost per pound) content food.
To actually provide all of your own food yourself , growing beans I estimate you would need 670 square feet of greenhouse space - based on the energy content of beans and the solar energy conversion efficiency of beans to edible food.
How did I come up with this number?
I will convert calories to BTU or British Thermal Units because it is easier for me to use this unit of energy for all calculations. One food calorie is actually 1000 ordinary calories or one kilo-calorie (the dirty secret of the food industry).
One BTU equals about 250 ordinary calories. One person requires about 3000 food calories per day if eating for health and moderately active. 3000 food calories equals 3,000,000 energy calories per day divided by 250 equals about 12,000 BTU per day.
12,000 BTU x 365 equals about 4.4 million BTU per year.
Field grown beans convert solar energy to food at an efficiency of 0.33% or 1/3 of 1 %. In a hydroponic solar greenhouse assume 5 times field grown efficiency or 1.67%
Solar energy gain in the Midwest averages about 450,000 BTU per square foot per year so a 1000 square foot greenhouse realizes 450 million BTU of solar energy. One percent of this amount is 4.5 million BTU. 1.67% equals 7.51 million BTU.
But you only need 4.4 million BTU per year so the greenhouse can be smaller than 1000 square feet - about 1/3 less or about 670 square feet. Therefore a hydroponic greenhouse of 670 square feet growing beans might provide sufficient food for one person for one year.
Doing these calculations for corn, which is only 0.25% efficient or one fourth of one percent you come up with about 880 square feet.
Doing these calculations for wheat which is only about 0.1% efficient or one tenth of 1 percent you come up with about 2,200 square feet.
For spirulina algae at 25% efficiency in converting solar energy to food only 88 square feet of solar greenhouse would be needed.
But consider, as described at the start of this discussion a greenhouse of only 110 square feet, producing 1,100 pounds of food or 10 pounds per square foot per year - produce that could be sold for $1 per pound could yield $1,100 - enough to buy low cost high energy foods for one person for one year: 25 pound sacks of grain at 50 cents a pound for example, or dry beans for $1 per pound.
110 square feet, the size of an average bedroom. Not much space really.
Below is a very tentative discussion still under consideration:
Growing under lights: Of course, as a further step, it is possible to use artificial light to grow food. What is the economics of that? How does it fit the minimum area estimates given above? The cost of electricity or solar cells to produce electricity on site must be considered. Would it pay to use electricity to power lights to grow food even if bought from the power company?
Assume 13 cents per Kwh. To light 100 square feet of growing space through half a year lights will require x Kwh of electricity costing The 100 square feet will grow 1,000 pound of produce valued at $1,000. The space must be heated but assume it is well insulated and the lights alone heat it enough. Therefore, only 100 square feet of space is needed and the other 900 square feet of the roof of a 1,000 square foot house could be used for electricity production.
Below is a very tentative discussion still under consideration:
Growing under lights: Of course, as a further step, it is possible to use artificial light to grow food. What is the economics of that? How does it fit the minimum area estimates given above? The cost of electricity or solar cells to produce electricity on site must be considered. Would it pay to use electricity to power lights to grow food even if bought from the power company?
Assume 13 cents per Kwh. To light 100 square feet of growing space through half a year lights will require x Kwh of electricity costing The 100 square feet will grow 1,000 pound of produce valued at $1,000. The space must be heated but assume it is well insulated and the lights alone heat it enough. Therefore, only 100 square feet of space is needed and the other 900 square feet of the roof of a 1,000 square foot house could be used for electricity production.
