Planning an off-grid solar system.

Estimating Energy Generated by your PV System

Using the equation below, you can estimate the annual electricity production and electric bill savings for a grid-connected home solar electric system with a net metering arrangement.

Determine the PV system’s size in kilowatts (kW).

A typical range is from 1 to 5 kW. This value is the “kW of PV” input for the equation below.
Based on your geographic location, select the energy production factor from the map below for the “kWh/kW-year” input for the following equation.

Electricity production from the PV system

kWh/year = (kW of PV) × (kWh/kW-year)

Calculate the watts if you know the voltage and amperage of a device.

Watts = Volts x Amps

If your T.V. plugs into a standard 120 volt receptacle and uses 4 amps, the total watts is calculated by multiplying 120 volts x 4 amps. That equals 480 watts.

120 Volts x 4 Amps = 480 Watts

Diagram of a simple solar stand-alone PV system

Meagle Sun

Some simple examples of rural off-grid power provision.

Straw bale gardening

It’s time to devote some time to learning (and practicing) straw bale gardening. I’ve been aware of this technique/system for a while but have not paid much more attention.

Here’s a great starting point, an article from The Dirt I Occupy “The Amazing Straw Bale Garden“.

And another from No Dig Vegetable Garden.

Here’s an article, “Human urine: An excellent and safe liquid fertiliser for your vegetable garden“, about human urine from Otepoti Urban Organics. It’s a great source of urea (the sraw bales need this added to help with decomposition).

Masonry heaters & stoves


Many people currently cook in a microwave oven. It’s called “micro” because the high-frequency radio energy used to jiggle the food’s water molecules has a very short wavelength. We call our stove the macrowave because, even though it utilizes radiated infrared energy (heat) which has a much higher frequency and even shorter wavelength, the stove itself is so much larger.

Read more about masonry stoves, and homesteading in general at the Geopathfinder ( site.

A collection of straw bale resources

Straw bale building guidelines for wet and humid climates
Climate and Straw bale construction
Five tips for keeping straw bale walls dry in a wet climate
Yes you can! Build with Strawbale in Wet Climates
Moisture and straw bale walls.
Sun Plans
Strawdio Template
Straw Bale Futures
Passive Solar Design
Lime paint, lime wash and paint lime wash in Edinburgh Scotland
IronStraw – Calculating How Many Bales of Straw You Need
Harvest Homes: Straw Bale Material Calculator
Green Building: From the Basement to the Roof
50 straw bale house plans
Descriptions of solar homes from the owners
International Straw Bale Registry Project
Straw House – Home
Straw Bale Articles |
Magyar Szalmaépítők Egyesülete
Solar Haven – self sufficient living without utility costs or a big mortgage … straw bales resources [Austrian/German site]


Common-Sense Compost Making by the Quick Return Method

by Maye E. Bruce


This book describes a way of making compost, i.e. humus, which is simply, labour saving (no turning) and quick, both in ripening the compost and in getting results in the soil. It is adaptible to all conditions and to every size and type of garden, allotment or farm, the process being based on nature’s own methods.

Miss Bruce tells how to make use of the natural heat of disintegration, which liberates the vitality of the plants; how to retain that vitality within the heap, and how to quicken both the disintegration of plants and the energizing of humus by treating the heap with a simple activator. This is a herbal solution which contains in living plant form the chief elements necessary to plant life; formulae are given.

From Vegetable Waste to Fertile Soil affirms a belief in the universality of Life, this Life being manifest in varying ‘rhythms’ in the mineral, vegetable, animal and human kingdoms. Health, productivity and perfection of growth in the vegetable kingdom, says the author, can best be achieved by feeding plants within the ‘rhythm’ of this kingdom.

Common-Sense Compost Making by the Quick Return Method

Checking straw bale wall moisture levels & all things monitoring

Moisture meter

I have the opportunity to add “smart” technology to my house as I’m building. I’m considering using either, or both, arduino boards & Raspberry Pi computers as the main processors to which I’ll attach various sensors and switches.

Primary considerations will be power consumption, heat production & cooling, and reliability. Both Arduino and Raspberry Pi units use very little power, especially when compared to their utility. I’m not sure about how much heat they produce however, hopefully, I’ll be able to position them within the house in a place where they can be easily and consistently cooled. Maybe the heat can be re-used somehow?

Moisture sensors are an obvious requirement – dampness & water being the worst problems for straw bale walls.

If we have the budget I’ll add controls for automation of lights and other electrical appliances that we can run to a central control


  1. Arduino
  2. Arduino at Wikipedia
  3. Arduino User Community
  4. Top 40 Arduino Projects at Hack N Mod
Raspberry Pi
  1. Raspberry Pi
  2. Raspberry Pi at Wikipedia
  3. Raspberry Pi Community site
  4. R-Pi Hub at eLinux
Moisture Sensors
  1. Moisture sensor circuit at Rob Faludi
  2. botanicalls
Home Automation
  1. Home Automation Tutorial at Hack N Mod

Rainwater harvesting calculator.

One millimeter of rain on one square metre of roof equals one litre of water run-off

To calculate the approximate amount of rainwater you are likely to harvest, use the following formula:

Estimated Net Runoff from an Impervious Catchment Surface Adjusted by its Runoff Coefficient

catchment area (m2) x rainfall (mm) x runoff coefficient = net runoff (litres)

Run-off (litres) = A x (Rainfall - B) x Roof Area

A is the efficiency of collection and values of 0.8-0.85 (i.e. 80-85% efficiency) have been used (eg Martin, 1980).

B is the loss associated with adsorption and wetting of surfaces and a value of 2 mm
per month
(24 mm per year) has been used (eg Martin, 1980).

Rainfall should be expressed in mm and Roof Area in square metres (m2)


In an area receiving 600 millimetres of rain a year with a rooftop catchment surface that is 11 metres long and 4.55 metres wide, and you want to know how much rainfall can realistically be collected off that roof in an average year. You want a conservative estimate of annual net runoff, so you use a runoff coefficient of 80% or 0.80.

catchment area (m2) = length (m) x width (m)

2 x (length (m) x width (m)) x rainfall (mm) x 0.80 = net runoff (litres)
2 x (11 m x 4.55 m) x 600mm x 0.80 = net runoff (litres)

100m2 x 600mm x 0.80 = 48,112 litres

48,112 litres = net runoff

A realistic estimate of the volume of water that could be collected off this 11 meter by 4.55 meter roof in a year of average rainfall is 48,112 litres.

Dimensions of straw bales

Straw-bales can be made from a range of plant fibres not only grass-family species like wheat, rye, barley, blue-grass, and rice, but also flax, and hemp. Bales of recycled materials like paper, pasteboard, waxed cardboard, crushed plastics, whole tires, and used carpeting have also been used or are currently being explored for building.

Basic straw-bales are produced on farms and referred to as “field-bales”. These come in a range of sizes from small “two-string” bales (W460mm x H350mm – H400mm x L800mm – L1200mm) to three-string “commercial bales” (W540mm x H410mm x L1200mm). These sizes range in weight from 18kg to 45kg.

Larger “bulk” bales are now becoming common, H1000mm x W1000mm – W1200mm x L2000mm and even W1200mm x H1200mm x L2400mm, weighing up to a ton. All of these “economy-size” units also offer unique potential for imaginative designers.

A newer trend is the use of high-density recompressed bales, sometimes called strawblocks, offering far higher compression strength. These bales “remade” from field bales in massive stationary presses, producing up to 4 MN of force, were originally developed for cargo-container transport to over-seas markets.

Innovators soon discovered that, where a wall of “conventional field bales” is able to support a roof load of 900 kg/m, the high-density bales can support up to 4500kg/m to 7000 kg/m. This makes them particularly suited to load-bearing multi-storey or “living-roofed” designs.

They are available in a range of sizes from different companies’ presses but L600mm x H600mm x W450mm might be considered “typical”; because they are bound with horizontally ties or straps, at 10mm or 12mm intervals vertically, they may be recut with a chain-saw at a range of heights. They are usually used in “stacked bond”, with the straws running vertically for greatest strength and tied with “re-mesh” on both sides before stucco application.

A 1-acre self-sufficient small-holding


We’re shopping for land in Hungary and while prices are relatively low, when compared to those in Scotland, it’s possible that our budget will only stretch to a 1-, or 2-acre plot. Ideally we’re looking for 4 or 5 acres minimum however 1 or 2 acres will be suitable.

With this in mind I’m collecting information and learning how to “survive” on smaller plots.

Download: Start-a-1-acre-self-sufficient-homestead

Optimum orientation of solar panels

To get the most from solar panels you need to point them in the direction that captures the most sun. But there are a number of variables in figuring out the best direction. This page is designed to help you find the best placement for your solar panels in your situation.

This advice applies to any type of panel that gets energy from the sun; photovoltaic, solar hot water, etc. We assume that the panel is fixed, or has a tilt that can be adjusted seasonally. (Panels that track the movement of the sun throughout the day can receive 10% (in winter) to 40% (in summer) more energy than fixed panels. This page doesn’t discuss tracking panels.)

Solar panels should always face true south if you are in the northern hemisphere, or true north if you are in the southern hemisphere. True north is not the same as magnetic north. If you are using a compass to orient your panels, you need to correct for the difference, which varies from place to place. Search the web for “magnetic declination” to find the correction for your location.

The next question is, at what angle from horizontal should the panels be tilted? Books and articles on solar energy often give the advice that the tilt should be equal to your latitude, plus 15 degrees in winter, or minus 15 degrees in summer. It turns out that you can do better than this – about 4% better.

Optimum Tilt of Solar Panels

Equation: If your latitude is between 25° and 50°, use the latitude, times 0.76, plus 3.1 degrees.

Solar panel pitch for Budapest (47.4547N, 19.0498E)

Winter: (47.4547 * 0.89) + 24 = 66.2347ᵒ
Summer: (47.4547 * 0.92) – 24.3 = 19.3583ᵒ
Spring/Autumn: (47.4547 * 0.98) – 2.3 = 44.2056ᵒ
Full year (no adjustment): (47.4547 * 0.76) + 3.1 = 39.1656ᵒ

Solar panel pitch for Mezőszentgyörgy (46.9969N 18.2752E)

Winter: (46.9969 * 0.89) + 24 = 65.8272ᵒ
Summer: (46.9969 * 0.92) – 24.3 = 18.9371ᵒ
Spring/Autumn: (46.9969 * 0.98) – 2.3 = 43.757ᵒ
Full year (no adjustment): (46.9969 * 0.76) + 3.1 = 38.8176ᵒ

Tools to assist in sun calculations

Solar panel pitch for Daruszentmiklós (46.8363N, 18.8594E)

Winter: (46.8363 * 0.89) + 24 = 65.6843ᵒ
Summer: (46.8363 * 0.92) – 24.3 = 18.7894ᵒ
Spring/Autumn: (46.8363 * 0.98) – 2.3 = 43.5996ᵒ
Full year (no adjustment): (46.8363 * 0.76) + 3.1 = 38.6956ᵒ