In 2020, our solar powered website obtained an uptime of 95%, meaning that it was offline for 444 hours or 20 days. Unsurprisingly, most of the downtime is concentrated in the winter months.

The graph above (click to enlarge) shows battery storage capacity in relation to the weather in Barcelona from January to December 2020. Yellow is sunny, grey is cloudy, blue is rain. From May to November, we were online without interruption for almost 6 months.

The data were collected and visualised by Roel Roscam Abbing and David Benqué.

During a global catastrophe such as a nuclear winter, in which sunlight and temperatures are reduced across every latitude, to maintain global agricultural output it is necessary to grow some crops under structures.

Either a small regional nuclear war, such as India vs. Pakistan or a minor one-sided nuclear assault on population centers could catalyze a global nuclear autumn, which would starve millions of people.

This study designs a method for scaling up crop production in low-tech greenhouses to contribute to global food sustainability during global catastrophic conditions. Constructing low-tech greenhouses would obviate growing crops using more expensive and energy intensive artificial light. To significantly contribute to world-wide food demand, these greenhouses must be constructed quickly, cost-effectively, and in extreme quantity.

The greenhouse structures are designed to utilize global markets of timber, polymer film, construction aggregates, and steel nails. The limiting market that determines the growth rate of the greenhouses is the rate at which polymer film and sheet are currently extruded.

In an event that causes sunlight and temperatures to decrease over the entirety of earth, most crops would be too frost sensitive to be grown outside the tropics, and even the tropics would require an alternative method to growing crops than simply conventional growth outdoors. Conditions under low-tech greenhouses in the tropics would feasibly accommodate the production of nearly all crops. Some supplemental lighting would be required for long day crops.

The analysis shows that the added cost of low-tech greenhouses is about two orders of magnitude lower than the added cost of artificial light growth. The retail cost of food from these low-tech greenhouses will be ~2.30 USD/kg dry food higher than current costs; for instance, a 160% retail cost increase for rice. According to the proposed scaling method, the greenhouses will provide 36% of food requirements for everyone by the end of the first year, and feed everyone after 30 months. (Population is considered constant at currrent values).

Source: Alvarado, Kyle A., et al. “Scaling of greenhouse crop production in low sunlight scenarios.” Science of The Total Environment (2019): 136012. Open access.

Joey Hess has designed, built and tested an off-grid, solar powered fridge, with no battery bank. Using an inexpensive chest freezer with a few modifications, the fridge retains cold overnight and through rainy periods. The set-up consists of a standard chest freezer, an added thermal mass, an inverter, and computer control. He writes:

The battery bank is a large part of the cost of a typical off-grid fridge installation. It needs to be sized to run the fridge overnight, as well as for several days of poor weather. Cheaper batteries only last 3-5 years, and longer lasting batteries are correspondingly expensive; either way a battery bank for an off-grid fridge is extremely expensive over the lifetime of the fridge. By storing solar power in the form of cold, I can avoid the battery bank expense and environmental footprint. The only battery power it needs is enough to turn it off cleanly when the solar panels stop producing — a few minutes of power instead of days — and a small amount for its computer control.

Joey’s off-grid, solar powered, zero-battery-use fridge has successfully made it through spring, summer, fall, and winter:

I’ve proven that it works. I’ve not gotten food poisoning, though I did lose half a gallon of milk on one super rainy week. I have piles of data, and a whole wiki documenting how I built it. I’ve developed 3 thousand lines of control software. It purrs along without any assistance.

Read more:

• Fridge 0.1
• Fridge 0.2
• Fridge data
• Fridge Wiki

Related:

• “Daylight Drive” DC Solar Power at the Living Energy Farm

Thanks to Roel Roscam Abbing.

Reader Goran Christiansson sends us a link to Living Energy Farm, a research and community project in Virginia, USA. Most notable is their use of “Daylight Drive” DC solar power without batteries for workshop tools — reminiscent of the ideas outlined in How to run the economy on the weather. Also of note is their choice for less efficient but more durable Nickel Iron batteries for lighting.

Below is an excerpt from the introduction page:

“The vision of Living Energy Farm (LEF) is envisioned to be a community that is food and energy self-sufficient. We are off-grid, and we are putting together the means to run our farm without fossil fuel. Our intent is for Living Energy Farm to operate on a modest, globally applicable, renewable energy budget. We have found that this global perspective differentiates us from most other projects working on sustainable technologies.”

All of LEF’s DC shop tools and most of our appliances run “daylight drive” straight from the solar electric (PV) panels. We run high-voltage industrial DC motors with no batteries, no inverters, no costly or fragile electronics whatsoever. This is a MUCH cheaper, simpler, and more durable way of utilizing solar energy.

“In starting Living Energy Farm, our plan was to pull together renewable energy technologies already in existence rather than “re-inventing the wheel.” We have found that we cannot buy a lot of what we need, and thus we are having to build some of the tools and machines we need. We live, day by day, off-grid and (mostly) without fossil fuel. We experience the benefits and limitations of our own ideas every day.”

“We have assembled a set of documents to explain how our unique, off-grid systems operate. We suggest you review “Longterm Integrated Village Energy (LIVE) — community energy systems that make centralized power grids unnecessary” before proceeding to the other documents. That will give you an overview of the design process at LEF.”

At Living Energy Farm, our conservationist design means we need very little stored electricity. We store electricity with nickel iron (NiFe) batteries, a very old, very durable battery technology. Nickel iron batteries tolerate tremedous swings of voltage input and discharge rates that would destroy any other kind of battery.

“We have been pleasantly surprised by how well our DC Microgrid has worked. We have found a much, much better way to live off-grid. The widespread adoption of the tools developed at LEF could widen access to energy services for people all over the world while radically decreasing our environmental footprint. We are trying to spread these tools far and wide, and looking for support in that work.”

Living Energy Farm. Overview of all technologies (pdf).

We are reaching an important milestone in the Testfield: the high-precision membrane mirror that we have been working on for the last two years, is standing. A team within the technology group has designed and built a prototype solar concentrator by innovating and developing the inflatable membrane mirror technology first introduced by father and son Hans and Jürgen Kleinwächter several decades ago. The present advances are the result of a dedicated team within Tamera working in cooperation with Jürgen Kleinwächter, SunOrbit (Germany) and supporters in India and Australia.

Our prototype mirror uses 0.1mm thick reflective polymer films inflated with air pressure, over a lightweight aluminium frame, achieving high optical precision cheaply and with very low embodied energy. It has an effective optical aperture of 4m2, concentration of over 1000 times, reaching over 1000 degrees Celsius, and has applications ranging from round-the-clock cooking with storage, through ceramics, metalwork and lime burning for waterproof clay buildings, to photo-catalytic fuel production from water and CO2. Future concentrators will undoubtedly take the technology further.

Many challenges in the components and sub-systems have been overcome over the last two years. Now we will start to see how the system really functions as a whole. We have progressed from unstable wooden experiments to a simple, lightweight aluminium framework, developed a deflectometric mirror analysis technique using computational photography, built a tool to weld flouropolymers together (basically welding Teflon to Teflon), designed and fabricated a dual-axis tracking construction, and invented a robust technique to evenly tension membrane films. We are looking forward to testing and tuning the complete system. System tests will start now, as we continue to complete the details.

Quoted from: High-precision Membrane Mirror Research in the SolarVillage Testfield of Tamera, August 2016.

Previously: The bright future of solar powered factories.

The SunSaluter is an ultra low-cost, passive, single-axis solar panel rotator (called a tracker) designed for the developing world. Using only the power of gravity and water, the SunSaluter enables a solar panel to follow the sun throughout the day, boosting efficiency by 30% and producing four liters of clean drinking water.

It is 30 times less expensive than conventional motorized solar panel rotators (which use complex electronics), much more reliable, and consumes no electricity itself. With improved efficiency, fewer solar panels are needed, and the overall cost per watt of solar energy is reduced.

The SunSaluter features an adjustable design which allows it to integrate with any solar panel – no special tools needed. The solar panels are mounted on the rotating frame, a weight is suspended from one end, and a special waterclock is suspended from the other. As the water empties and the container gets lighter, the panel slowly rotates. The user can set the rate at which the waterclock empties, which controls the SunSaluter’s rate of rotation.

The SunSaluter also contains a water purifier so that each day it produces four liters of clean drinking water. By combining energy and water collection into one simple device, the SunSaluter improves consistent usage of the purifier, which is the Achilles heel of clean water programs. SunSaluters are available for purchase anywhere in the world as a DIY-kit, or in India as prefabricated systems.

More information: SunSaluter. Via Makeshift, who made a video about the technology.

“Graining cereal crops is a basic, century old business and it will continue to be as important as ever before for centuries to come. Before the age of oil grain milling was entirely based on renewable energy. It was either done by wind energy, hydropower, animals or manpower. For the last century the traditional grain milling has been mainly replaced by electricity and fuel driven milling.”

“The Solar PV Grain Mill works to the same principle like any conventional, electrically driven mill. The mill has a very efficient 3-phase AC motor which is directly coupled to the graining system. The main invention of the system is, and that makes it unique among PV systems, that it is a “direct drive system” without the need of batteries. The Solar PV generator converts solar radiation into electricity, and the generated electricity is directly feeding the motor drive. There are no additional conversion losses, such as energy storage losses in batteries, battery maintenance or replacement costs, which are a common problem in conventional Solar PV off-grid systems.”

Read More: Solar Milling. Via Engineering for Change.

I would like to add that the direct drive system also eliminates the high energy use caused by the production of the batteries, which can make solar PV off-grid systems everything but sustainable. Therefore, storing work instead of energy — the solar mill only operates when the sun shines — is a very interesting strategy in sunny regions.

Related:

• The Bright Future of Solar Thermal Powered Factories
• Back to Basics: Direct Hydropower
• Wind Powered Factories: History (and Future) of Industrial Windmills
• Pedal Powered Farms and Factories: The Forgotten Future of the Stationary Bicycle

Build-It-Solar blog writes:

Kotaro Nishiki built a passively cooled home in Leyte Philippines at 11 degs north latitude that incorporates a number of unique cooling features that allow the home to be cooled passively and without electricity…

In this area, most homes are constructed of concrete, and the concrete structures tend to absorb solar heat during the daytime, and then retain that heat through the night making the homes uncomfortable.

Kotaro’s design is centered on eliminating these daytime solar gains. He keeps the whole house shaded using these techniques:

• The south facing single slope roof has on overhang on the south that keeps the south wall in shade most of the day.
• The north side of the house is shaded by an roof extension sloped down to the north that shades the north side of the house most of the day.
• The roof is double layered with airflow between the well spaced layers.  This greatly reduces solar heat gain through the roof.
• The east and west walls of the house are double wall construction with a couple feet between the walls.  The shading that the outer wall offers plus airflow between the double walls keep the wall temperatures low.
• In addition, he has worked out ways to take advantage of the night
  temperature drop and to use thermal mass on the basement to provide some
  cooling.

More: A unique, passively cooled home in the Tropics (Build-It-Solar), Passive Solar House in Tropical Areas (Kotaro Nishiki). Build-It-Solar has more examples of passively cooled houses.

If anyone has more information, comments are open.

“The solar kiln described was designed, constructed, and tested at Virginia Tech. This design is based on 25 years of research and development on the solar drying of lumber in the United States and foreign countries. Drawings for two versions of this kiln are available; one for 800-1,000 bd ft and the other for 1,500-2,000 board feet of lumber. Both kilns will dry a load of lumber in approximately one month of moderately sunny weather at its location in Blacksburg, VA.”

“Drying lumber can be a complex process where accelerating drying without having quality loss often requires extensive knowledge and experience. The design of the Virginia Tech solar kiln is such that extensive knowledge, experience and control are not required. The size of the collector keeps the kiln from over-heating and causing checking and splitting of the wood. The kiln is simple to construct and utilizes a passive solar collector, four insulated walls and an insulated floor. The roof is made of clear, greenhouse rated, corrugated polyethylene.”

Virginia Tech Solar Kiln. Via Build It Solar.

“The Earthern Solar Cooker is a large parabolicly shaped hole in the ground lined with reflective materials such as salvaged pieces of broken mirrors or reflective can lids. The mirrors reflect and concentrate sunlight to the base of the hole where ten one gallon black containers of water can be boiled per hour and used for drinking or food preparation. Cooking/water boiling containers are accessed via steps carved into the side of the Earthen Solar Cooker.”

“A 2.5m diameter hole, 1.5m deep cooks 10 gal of rice/hr from 11am to 3pm on an 85f summer day in south central Oregon. Since the power of a parabolic concentrator is proportional to the surface area of it’s aperature (A = 3.14 x r^2), doubling the radius of the hole increases the power of the Earthen Solar Cooker by a factor of four.”

“An Earthen Solar Concentrator the size of a small amphitheater might be capable of casting bronze or boiling the water near the surface of a shallow well located at the vertex, thus making possible the creation of a solar bubble pump that could lift pasteurized water to a tank above ground level.” Read more about the project at Appropedia.

Previously:

• Parabolic Basket and Tin Can Solar Cooker
• Solar Cookers that Work at Night
• Build a Solar Powered (Interior) Kitchen

The Solar Spark Lighter is a pocket-size solar firestarter and lighter. It is a stainless steel parabolic mirror, like the one used to light the Olympic torch. It is designed to focus the sun’s radiant energy to a precise focal point that can reach hundreds of degrees. Just point it at the sun and it lights in seconds. Measures about 4.5″ diameter.

The Britons worked out how the heavens move thousands of years before the Greeks started thinking about it. That is, in a nutshell, the story of engineer and author  Jonathan Morris.

His hypothesis originated from a solar renewable energy concentration system which he developed, using small fixed pieces of flat reflectors.

By chance, he discovered that the structural support of the solar energy system appears to be duplicated at Stonehenge, the enigmatic monument built 4,000 to 5,000 years ago. Every single one of the technical features required are precisely duplicated in size, height, location and orientation at Stonehenge.

Morris outlines his ideas in a novel (“The Broken Stone”) and a technical outline, available via his website: “Heavens’ Henge: A geocentric worldview“.

Unfortunately, it is the other way around. Solar cells are produced in China, and shipped to countries with relatively clean electric grids.

The quote is from: “Towards real energy economics: energy policy driven by life-cycle carbon emission“, Energy Policy 38, 2010.

“The town I live in is located near the Alberta-BC border, about 100 miles north of the US Canada border. Winters here are long and cold, but many days are crystal clear and sunny.”

“Our tool shed has a south-facing wall which was ideal to mount a solar thermal direct-air collector panel. The collector panel exterior dimensions are 48” high x 49.5” wide. Total budget: $200.00 Result: 16 sq ft harvest up to 6 kWh/day.”

Build a Solar-Thermal Direct-Air Heater (PDF). Introduction (and another project) here.

“The electric bicycle has become a very long way in recent years. However, the lack of luggage space and limited range of the battery makes the electric bike less suited to long distances. Solarwind, designed by architect Raf Van Hulle, offers a solution.

The trailer provides extra luggage space and is fitted with a solar panel to keep the electric bicycle’s battery charged.”

Solarwind.

Solar Fire is currently testing a larger version of its low-tech solar concentrator; the Solar Fire P90. Just like its smaller predecessor the Solar Fire P32 (which we covered before), the machine can produce heat, electricity and direct mechanical energy, making it suitable to manufacture almost anything on your roof or in the garden.

The Solar Fire P90 delivers up to 5 kW of electricity and 40 kW of thermal energy, is built using simple, abundant and non-toxic materials, and requires no foundation in the ground. The frame size is 11.5 x 11.5 metres and the machine requires an area of 16 x 16 metres for revolving.

Tracking is done by hand using a simple but ingenious system — one person can operate up to five of these solar concentrators at the same time. The Solar Fire P90 is an open source design, but it can also be bought for about $ 12,000, excluding transport costs.

A video of the tests can be found here. For more information on the workings and applications of these kinds of machines, see the article “The bright future of solar thermal powered factories“.

Picture: Solar Fire.