Solar Concrete

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HintLightbulb.png Hint: Lime requires about 1kWhr/kg to produce from rocks.

Working Doc



OSE's interest is local cement production. Currently, the cement industry is highly concentrated, and only 34 of the 50 states have cement production [1]. OSE envisions increasingly localized and ecological production that does not contribute to greenhouse gas emissions. Whereas cement releases large amounts of CO2 into the atmosphere, lime will reabsorb the CO2 created during its manufacture to make it essentially carbon neutral. [2]

Since we are far from mainstream industry taking the lead in solar concrete, OSE intends to lead an industry transformation where abundant solar electric energy is used instead of fossil fuels. With modern technology, it is feasible to distribute cement production.

Use PV to make cement from limestone. PV heats limestone, emits CO2 and produces cement. Cement is used in construction, and it absorbs C02 to make rock-hard structure. Overall process is carbon neutral, and thus solves the issue of vast CO2 emissions from industry standard cement production. OSE calls for distributed production as such, to be deployed in resilient communities worldwide at low cost.

Assumptions and Test Hypothesis

Limestone is hard - anywhere from 2000 - 14000 PSI [3]. When burned, it turns to lime. When water is added, and lime reacts back with carbon dioxide - a rock is formed. It is weaker than the original rock, so a good question is how to make reformulated limestone the same strength as the limestone it came from.

This link [4] shows that 100% lime is only 750 PSI strong. That is still acceptable for a wide range of construction purposes. The disadvantage is a week [5] as opposed to a day curing time for sufficient cure to resist the elements. This means that construction schedules must do concrete work and then possibly wait.

OSE wants to test whether it is feasible to convert limestone into building material - concrete - and whether such concrete is structurally sound and easy to make. How strong is it? What is its practical range of applications? How can we make the quicklime [6] return to as much strength as it turns back into limestone? And, what else can we add to make it stronger or faster to set?

At stake here we have the reinvention of the cement industry - to local production of lime concrete [7] anywhere that limestone can be found.

CSP may be of use too


  1. Hydraulic lime usually gains strength in time greater than the time in which cement concrete gains same value of strength.
  2. Lime cement takes a long time to cure, and while the ancient world had lots of time, today time is money.
  3. Lime cement does not harden in water but stays soft. So there are situations where it cannot be used.

Uses and precautions

  1. Lime concrete is very widely used for foundation bases of load bearing walls, columns, and under layers of floors.
  2. Due to its flexibility it adjusts very well with the underneath base ground and upper construction of cement base.
  3. For better quality of lime concrete it is important to compact & cure concrete properly. Lime causes rashes on human skin so the persons which are dealing lime concrete should be provided with suitable rubber gloves.
  4. Persons should use oil on their skin to avoid rashes and cracking of their skin due to reaction of lime.
  5. To achieve good quality lime concrete, certain admixtures, fibers etc can be used


10kW Array

HintLightbulb.png Hint: Need references for all values. General Outcome is 1 80 lb bag of portland cement per day from a 10kW array. Note energetics are similar to melting steel, pound for pound - around 1 kWhr/kg

  • Embodied energy of portland cement - 5.6 MJ/kg. Note that concrete blocks are about 1.5 MJ/kG
    • But for lime - it is 3.3 MJ/kg. [ref?]
  • 1 MJ = 0.3 kWhr (1 kWhr = 3.6 MJ). 12.5 kHhr electric is the same energy as 1 kg of gas, but the electric energy is much higher quality.
  • Thus, a 10 kW solar panel array, affordable by any University Solar Concrete Project - pr donated for conscience - has 60kW hrs of energy per day
  • Concrete block is only 10-15% cement
  • Check.png1 kWhr gets us .6 kg of cement. This one from China, electric, is up to 2 kg/kWhr, and efficient starting at 70kW. Efficiency of electric may be hire. See Electric Rotary Kiln.
  • Gasoline is 45MJ/kg. 1 kg gasoline gets you about 15 kg of lime cement. Thus, 1 gal of gasoline gets you 35 kg of lime cement (and only 20 kg of portland cement). That is about one gallon of gas per bag of lime cement, and 1/2 a bag of portland cement. Holy cow, there is a lot of gasoline in cement! Take the Construction Trailer which is solar powered.
  • 60 kWhr gets us 36 kg of portland cement or 61 kg of lime cement
  • 8x8x16" cinder blocks [8] are 30 lb or 15 kg
  • Concrete block - [9]
  • 1:3:6 cement for concrete blocks - [10]
  • We can make 36 kg of cement per day with a 10 kW array, or 360 kg of block - or 24 cinder block per day. Or 72 full sized CEB Blocks.
    • Standard concrete blocks are $1.40 each - [11]
    • The value of electricity for 60kWhr is $6. The value of cement is $9 or 50% more. Value of block is $34 or 600% more.
  • The key here is using excess electricity from inexpensive PV, which otherwise may be left unused.
  • Negotiating power sales to the grid can be attractive pending ability to disconnect from grid if company terms are not favorable, so there is a strong case for the negotiating power of small producers. But this depends on the ability of producers to have storage, for night time use, if disconnected from the grid.
  • $25*300= $7500 - a good value per year for an experimental club in school which stockpiles cement or special use block such as pervious pavement blocks.
  • Notes - calculations above are for portland cement, so lime cement should be 30-40% less energy intensive?

50kW Array - Produces 24 CEB Homes per Year Or a Million Dollar Net Revenue Home Building Business

HintLightbulb.png Hint: At the 50kW scale of photovoltaic power, we are able to make one cubic yard of cement per day - enough for one house per 2 weeks

  • For the small/medium microfactory - a load of 50kW for solar cement is reasonable.
  • This gets to industrial productivity on a small scale - which produces 5 bags, 80lb each, of cement per day. That is $50 value on the commodity market, and yields a 400 day ($20k/$50/day) payback time if we were selling concrete.
  • This could be applied to foundation concrete or for cement stabilized compressed earth bricks
  • Value-adding compressed Earth block to that - means we get $400-$800 more for the block at $1-2 ea - making the payback time 50 days if we discount labor.
  • This is only about 400 CEB block - we need more than this. For 5000 block per day - it would take us 12 days to make the cement for the block. This is where a larger array would make sense.
  • This is where production on a windy day using wind power would be effective, in an automated plant.
  • At the 60 acre scale, a commercial quarry can be installed, producing $5M of rock (300,000 tons per year)- 1000 tons per day or 50 trucks worth per day. For a Microquarry, we need only 120 ton*500=60,000 tons per year for 500 homes per year - or about 1/5 an industry standard quarry. Add cement - and we may go to about 1/4 of a standard quarry, or about $1M savings on concrete. Once learned, we add the quarry to the Open Sector for creating worldwide financial independence.

200kW Array

HintLightbulb.png Hint: Mobile CEB production from on-site resources would require carrying on-board hydrogen at a ratio of 1kg hydrogen (5 kWh_e) to 5 kg cement - if using hydrogen electricity. But it's better - we just need heat! This means we have 33 kWhr heat per kg hydrogen. It takes 5 bags (96 lb each to make a yard. Thus, we need 10 kg hydrogen per yard of concrete. This is quite portable. Each kg of hydrogen makes about 15 kg portland. We can start reframing for the next economy of distributed production as the energy required to do things. This has always been the case.

  • We have discussed that village scale production needs 200kW.
  • Here we need to develop a schedule of energy usage to tap available power as needed. Perhaps a good idea is 100kW solar, rest being wind.
  • 200kW gets us 1600 lb cement per day. 3 days to get to 5000 block for a new house. So cement for 100 houses per year, which is village scale development.
  • If we have 50 kW solar, and 50kW effective wind - we can produce 2000 lb concrete per day. This is a good deal, so investing in 50kW wind turbines is a good idea.
  • Does this verify with concrete calculations? Wikipedia sez 4700MJ/ton of concrete, or 1300 kWhr per ton. [12]
    • We have 50kw*6 hr + 50kW*24 hr = 1500 kWhr in our system - yes, it checks out.
  • Does lime have lower embodied energy? Doesn't appear so. See Embodied Energy.


  • Energy to calcine limestone - 755 Mcal per ton = 0.755 Mcal / kg. [13]
  • 1 Mcal = 4.18 MJ [14]
  • Thus, 1 kg of lime takes 3.3 MJ/kg
  • 40 lb bag is 0.01 cu yd [15]
  • Thus - one day of lime cement gives 0.03 cu yd of cement - or 0.3 cu yd of concrete. So 3 days of solar cement for a Microhouse foundation which is 6" tall and 14 feet on each side - which is about a cubic yard.
  • Roman Concrete
  • Construction Trailer

Geopolymer Cement

Concrete Howto