I think about this often: without oil, how would I have gained access to these materials and pieces of equipment? How much energy was required to manufacture a product I purchased, and is using it ultimately worthwhile?
How Much Energy Is in This Thing?
While researching the energy required to manufacture everyday products, I found a useful resource: the Circular Ecology Embodied Carbon Database. The database contains information about materials we use every day and estimates their embodied carbon and energy. Some of the materials like aluminum, glass, sand and concrete get overlooked when thinking about our carbon footprint. typically we focus on plastics and transportation but there are more facets to a total carbon footprint, for example mining, refining, manufacturing, storage and finally sales to end user delivery.
So if I can find my materials in the database and their carbon footprint, how does that tie in with oil usage? As an unfortunate truth oil runs our modern world. So many things require oil not only for energy but for material as well, some examples include plastics (oil byproduct), chemicals (urea for gardening is mostly oil byproduct) as well as direct products like gasoline, diesel and lubricants. Oil has an average energy density of 6.12 GJ per barrel. A joule is a measure of energy and a barrel of oil has approximately 6.12 Giga (6.12 billion) joules.
I created a pump and solar-panel setup to water my garden. Looking at the materials, I wanted to know how much embodied energy was required to mine the raw materials, manufacture the products, and deliver them to me, expressed as barrels of oil equivalent. I built the system to move water from my pond to my garden about 250 ft away so I would not have to pay for treated water from my rural water department. Watering a garden during an Oklahoma summer can become expensive, making my goal of growing inexpensive food less practical. Converting the system’s embodied energy into barrels of oil equivalent gives me a clearer idea of the project’s overall energy cost.
The Math…
There is some math to do here but its simple enough napkin calculations will work. First we need to list the materials:
- 12 V well pump
- Group 58 flooded battery (car battery)
- 220 W mono-crystalline solar panel
- Inverter
- 100 ft 16 AWG wire (50 ft extension cord)
- Toggle switch
- 5 A breaker (DC breaker to save the pump from burning up)
- Douglas-fir 2×4, 16 ft
- Treated yellow-pine 4×4, 8 ft
- Miscellaneous screws and hardware
- 300 ft 5/8 in. garden hose
The well pump, inverter and solar panel all purchased from Amazon, mostly for convenience. The car battery I purchased as a backup for my tractor but luckily have not needed it. The wire was an old extension cord I had laying around, same with the toggle switch, breaker, screws and miscellaneous hardware. The wood was leftover from my greenhouse build and the garden hose I purposely bought for this project. Reusing materials and calculating the full embodied energy may be a stretch but I want to know the total oil equivalent—So Im ignoring reuse for the time being. I estimate the total dollar amount of this project at $780.
Once the major components are identified I then have to make some assumptions about the makeup of raw materials. For example the pump is probably made from stainless steel, copper and plastic—there are other materials like magnets and coatings on the motor wires I just cant estimate with any accuracy. From those basic components I need to make an assumption about what percentage of the total mass they make up, in this case 2.8 kg (6.1 Lbs). Stainless is 50%, copper 15% and plastic 35%. I looked for examples for the constituent parts but there inst yet a good resource for determining the total makeup of any object with a high accuracy, so we have to guess if we cant find exactly what we need.
Then I have to find the total energy used to produce that material from the Embodied Carbon Database. For my pump example it was 56.7 MJ/kg for stainless steel, 42 MJ/kg for copper and 80.5 MJ/kg for plastic. Taking the mass of each part of the pump, multiplying it by the energy to produce that material and then adding those together gets 179.5 MJ of energy to produce that pump. Since a barrel of oil has 6.12 GJ of energy I divide my energy used by the barrel and get 0.03 barrels of oil equivalent or about 1.25 gallons.
For simplicity Ive listed the items their mass, energy used and barrel of oil equivalent:
| Component | Total mass (kg) | Embodied energy (MJ) | Barrels of oil equivalent |
|---|---|---|---|
| 12 V well pump | 2.858 | 179.54 | 0.03 |
| Group 58 flooded battery | 14.515 | 450.80 | 0.07 |
| 220 W mono-crystalline solar panel | 12.000 | 5225.00 | 0.85 |
| Inverter | 1.000 | 122.74 | 0.02 |
| 100 ft 16 AWG wire | 0.658 | 38.20 | 0.01 |
| Toggle switch | 0.005 | 0.24 | <0.01 |
| 5 A breaker | 0.005 | 0.27 | <0.01 |
| Douglas-fir 2×4, 16 ft | 8.700 | 64.38 | 0.01 |
| Treated yellow-pine 4×4, 8 ft | 11.400 | 92.69 | 0.02 |
| Miscellaneous screws and hardware | 0.015 | 0.30 | <0.01 |
| 300 ft 5/8 in. garden hose | 21.840 | 1649.79 | 0.27 |
| SYSTEM TOTAL | 72.996 | 7823.95 | 1.28 |
Based on my material estimates, manufacturing the system required approximately 7,824 megajoules of embodied energy. That is equivalent to about 1.28 barrels of crude oil’s energy content, although the actual manufacturing energy likely came from several different sources. Thats quite a bit of oil and I was really surprised to see how much energy/oil was required to make the solar panels and garden hose—both are necessary for this project but I just had no idea how much energy was required.
For a comparison, one barrel of oil (42 gallons) contains between 19-20 gallons of gasoline. My truck gets 22 mpg and therefore I could drive a little over 535 miles with the equivalent oil used above. Im avoiding equating this to dollars because the cost of oil and gasoline fluctuate so much.
Was it worth it?
Now to determine if it was worth all the effort, is it just lower cost to buy water from my rural water department?
A little more math..
My garden is 60 ft x 4 ft with 7 rows, that’s 1,680 square feet. Iowa State University estimates 0.623 gallons of water to supply 1 inch over a square foot. When I water I need approximate 1,046 gallons to get 1 inch of water over the whole garden. Im totally caught off guard by that, I mean that’s a lot of water.. In a typical month my household uses 3,600 gallons, so watering once a week for an exceptionally dry month like July or August will double my water usage.
The pump system can run for about 7 hours on the battery, Im going to assume 6 hours for semi-cloudy days not charging the battery fully. The pump can move 1.25 gallons per minute, in a 6 hour period I can water 450 gallons, I need to do this 2-3 times a week to make the same 1,046 gallon estimate from Iowa State.
According to The National Ground Water Association its costs about 12,420 joules per gallon of water to an urban/public customer, this includes filtration and treatments as well as delivery. My 1,046 gallons per garden water equates to 12.99 MJ or 0.002 Barrels of oil equivalent. The system’s estimated embodied energy equals the energy associated with supplying municipal water for roughly 600 full garden waterings. That does not mean the pond system is environmentally worse overall; its value will depend on its service life. Hopefully my pump system lasts more than 600 waterings. At the cost of the project of $780 I could water the garden just under 30 times at $0.025/gallon, so the value is in dollars saved but not in oil used.
I really enjoyed working all this math out, its basic math after all and it shows how much oil and energy we use for a simple project like this. I probably would have second guessed that my water supply cost so little energy to get fresh water to me. On the contrary it costs so much energy to acquire the pump, hose, battery and solar panel that I need to water the garden for a long time to make up for that. It really shows that there are pros and cons of every decision. Making the right decision seems to be the hardest lesson learned.