To do any kind of off-grid tiny house living with the comforts of civilization, power will be needed to run your devices. Instead of relying on utility companies, you can instead utilize off-grid power systems.
Because tiny homes have fewer electrical devices and less wiring compared to the usual mortgage homes, it’s feasible to make tiny homes run completely on renewable power via off-grid power systems. Also, making a tiny house run completely on an off-grid power system becomes easier if efficient electrical wiring and appliances are used.
First, the functioning and the principles of wind, hydro, and solar power off-grid power systems will be covered first. Then the common electrical components and wiring of off-grid power systems will be explained in-depth.
Wind is created via unequal heating of the earth. Wind turbines are then used to convert the wind’s kinetic energy into rotary motion to drive the alternator and produce clean electrical power. Before deciding whether wind is suitable, it’s important to know that wind power is most variable and potentially has the most costly installation and maintenance of the three renewable power sources.
For one small wind tower, the wind turbine can cost $300-$1500+ and the mounting tower (60-80 ft) can cost $3000 to $10,000+. If you are still interested, there are few things to know regarding what is needed at a site for good power generation:
- How high the turbine needs to be: First thing to know is that wind power is related to the turbine/tower height cubed. This means that the higher the turbine/tower, the better; this is also because the further away the turbine is from the ground, the less wind shear and turbulence will occur as a result of surface obstacles like buildings and trees. A common rule of thumb is that the bottom of the turbine blade(s) is at least 30 feet from obstacles. For example, if there are wide open spaces without trees or buildings within about 500 ft. a tower about 30 ft from surface to the wind blades’ bottom should suffice. If there were trees and buildings around with the tallest tree/building about 40 ft within 500 ft, then the height of the wind blades’ bottom from the surface should be 70 ft(30 ft + 40 ft) at minimum. Also take into account that the taller the tower, the more the installation and maintenance will cost.
- Wind speed and direction(s): This means that the windiness of the site of choice needs to be determined if its appropriate. Unless you have proper experience in this, you should leave the accurate determining of the wind speed and its direction(s) to professionals. Even if you aren’t a professional, you can at least make approximations about a site’s viability before deciding to consult a professional for further planning. One way is to take some wind data with an anemometer(for wind speed) and a weather vane(wind direction) over a period of time. Another way is to use wind maps or wind calculators from online references. The maps can show average wind speeds at different heights. Calculators can ask for location(latitude and longitude) and height and the output is approximate wind speed for that spot. Regarding minimum wind speed, the site’s minimum at a decent height should be 5 m/s on average otherwise the power generated won’t be anything significant.
- Air Density: this refers to the mass of air per volume unit. Compare wind #1 with air density A and wind#2 with air density B with same wind speed; density A is greater than density B. The wind turbine propeller would turn faster(thus more power) with wind #1 over wind #2 because there is more “moving mass” from wind #1 due to its higher wind density over wind #2. According to the ISA(International Standard Atmosphere), at sea level and at 15°C, the air density is at approximately 1.225 kg/m3. Factors that affect air density are humidity and temperature.
- Legal Considerations: some local laws and H.O.A.(home owner association) regulation may restrict/prohibit a tall structure due to wind blades due to safety issues. Regarding safety issues, birds can be injured by a spinning blade. Also, the tower can injure nearby people like the blade can fall off and hit someone, or a tower with poor foundation can tilt and crash, and there is also danger with climbing up a high tower to do maintenance. Another concern to authorities is that wind towers are a detriment to property values due to standing out. Luckily, some authorities/realtors consider wind towers beneficial to property values due to the appeal of personally generated electricity and some authorities/realtors like the aesthetics of a large wind turbine tower.
Along with site considerations, there are considerations regarding the wind turbine/tower to account for:
- Sweep Area: other than tower height, air density, and wind speed; the propeller size also affects how much theoretical power can be generated. The larger the wind turbine blades, the more air can press against the wind blades causing it to turn. However, in some cases, the RPMs have to be increased and this can be done by shrinking the propeller size(thus sweep area); this is for turbines that require high RPMs.
- Type of Turbine: The turbines of choices are usually dependent on wind speed. On lower wind speeds, Permanent Magnet Alternators/Generators(PMA/PMG) are suitable because they can produce power at lower RPMs(thus lower wind speeds). The other turbine of choice are electrostatic alternators(ex: car alternators); these don’t work well unless there are high RPMs(thus higher wind speeds); however, at higher RPMs, produced watts exceeds that of PMAs/PMGs at similar RPMs. While the former is preferred over the latter generally, the latter is better if there are consistently strong winds to provide high RPMs.
- Type of Tower: There are three main variations of towers. They are free standing (self-supporting), guyed towers, and tilt-up towers. Free standing towers need to have strong foundation because they are tall and without supports. Guyed towers are towers supported via wires bolted to the ground and thus doesn’t rely on as strong a foundation as free standing towers. Last are tilt-up towers which are towers that can be tilted to the ground off its foundation in order to repair the turbine; then the tower can be tilted up back onto its post and fully erect again after repairs. Tilt-up towers are often kept erect via strong wire like guyed towers. Regarding the $3000-$10,000+ cost of towers, guyed towers are priced on the lower end ($3000-$5000) and free standing towers can easily reach $10,000+. Tilt-up towers are probably on the lower to mid-end of the price range unless it’s motorized to automate the tilting.
Another thing to discuss is the difference between two types of Wind Turbines. The two known types of wind turbines are VAWT(Vertical Axis Wind Turbine) and HAWT(Horizontal Axis Wind Turbine). They can be distinguished with a glance because the a HAWT’s wind blades and axis is parallel to the ground while the VAWT’s wind blades and axis if perpendicular to the ground. See the comparison below:
Although there are differences between HAWTs and VAWTs. For tiny house owners who want to obtain a sizable amount of wind power, the verdict is to use HAWTs over VAWTs. Despite VAWTs being able to take in wind from any direction, there are some significant limitations holding VAWTs back. Due to its shape, VAWTs can mostly be mounted near the ground which is detrimental to power generation. Also, because of its airfoil shape, part of the rotating foil will always ‘cut-back’ against the wind when rotating reducing efficiency.
Due to the potentially huge expenses associated with wind power, all the above things have to be considered before deciding, with professional consultation, on a wind power system and installation; otherwise, you will get little in return for for your investments. On last note, despite solar power and micro hydro power being cheaper and more reliable than small wind power, there are reasons to use small wind power. Small wind is often used complementary with solar power. On sunny days, which tend to have little wind, solar panels will produce power. On days with little sun, wind turbines can produce power. Cloudy days, rainy days, stormy days, and the winter season tend to have a decent wind suitable for small wind power.
Hydroelectric power is not just available from the giant turbines powered by water held back behind a dam. Hydroelectric power can also be made for personal power generation. This is called micro hydro power as the natural flow of water is used to drive a small turbine to generate enough power for a small community or a single house.
Similar to wind turbines, alternators are also essential to micro hydro turbines. If the water flow is fast, micro hydro turbines with electrostatic alternators may be considered. This is because water going through a narrow pipe can be travelling very fast if the head (see below diagram) is high and if there is decent water pressure. If that concentrated high pressure water hits the small turbine wheel of a micro hydro turbine, high enough RPM can be produced for an electrostatic alternators.
However, if a water mill is used for power, the RPM will be much lower because water mills are generally used for slower streams and the large wheel size also contributes to a lower RPM. In that case, a magnet-based alternator is preferable to accommodate the lower RPM rates.
Compared to solar and wind, micro hydro can arguable the biggest power generator of them all for all four seasons. This is because as long as there is a flowing water source, a micro-hydro can run 24-hours per day all year; even in the winter as long as the stream (and its water source) is not frozen. The diagram below is an example of a possible micro hydro installation along with its components:
To start off, before explaining the above diagram, is to note that there are 2 main things needed to install any kind of micro hydro system.
There first has to be a head, as shown in the above diagram. The head is the height from where the water taken/diverted from and down to where the turbine wheel is. The reason for the head is that gravity will convert the potential energy from the water to kinetic energy as the water flows downward. The kinetic energy drives the turbine.
The other necessary thing is a good flow. The flow is the quantity of water that is “falling”. If the flow is too little, there wont be enough moving water mass to make the turbine spin. If the water flow is too much, the water can fill the turbine chamber faster than it can release the excess water.
Here are the parts found in typical micro hydro off-grid power systems as shown in the above diagram:
- Intake Diversion with Screen and/or Filter: here water is first diverted for use for micro hydro power. The screen and/or filter is used to keep out small particles and wild life. Lastly, the diversion should not take out too much of the water as one as it should not disturb nature unnecessarily.
- Forebay Tank: this part can be optional if the intake diversion already has screens and/or filters to block particles. If there are no screens nor filter is used, this should be used. After the water has been diverted, this pond-like structure allows particles in the water to settle before allowing the water through the penstock.
- Penstock: this pipe carries the water from the forebay tank to the turbine. The penstock is inclined downward so the water can generate enough kinetic energy to drive the turbine. The distance the water vertically “drops” within the downward incline is called the head(labeled in diagram). There maybe a pressure regulator attached between the penstock pipe and turbine chamber to prevent too much water from shooting into the turbine at once.
- Generator: by definition, this device converts mechanical energy into electrical power. The falling water at the bottom of the penstock has enough kinetic energy to exert mechanical power onto the turbine wheel. The power created can either be AC or DC. Like with wind turbines, the choice of turbine here will be between whether its base is PMA/PMG vs electrostatic alternator.
- Wires: these carry the power to the battery bank, via charge controller, or even to a load to dissipate the excess power.
- Tail Race: this is simply where the water is returned to nature.
Besides micro-hydro water turbines, water wheels(or water mills) are also an option. Below is an example:
First, there are some differences between micro-hydro and the larger water wheels in terms of mechanics. Head and flow are still necessary just as in the previous micro hydro system along with nearly the same components.
However, one major difference between water wheels and micro-hydro turbines is the different utilization of the head. In case of waterwheels, the start/top of the head is when the water exits the flume. The falling water then falls into the water wheels’ rudders causing it to turn; the conversion of kinetic energy from potential energy as the water falls onto the water wheel causes the wheel to turn.
The bottom of the head is when the water hits the water or the surface under the wheel. This is different from micro-hydro turbine systems where the start of the head was at the top of the inclined penstock where water was to let to “fall” inside the penstock to build up kinetic energy before exiting the penstock(bottom of head) in concentrated form to make the micro-hydro turbine spin.
Also, instead of a penstock, which is a closed and narrow pipe, flumes are used for water wheels instead because these are wider which enable more water to fall and thus make the water wheel(larger than water turbine blades) spin. Flumes are open or closed-air as necessary. In the image above, you can see the flume above the water wheel.
While it is generally better to install turbines because turbine wheel and generators are more compact, there are reasons to resort to a water wheel over a conventional turbine:
- Micro turbines at time can have a lower output due to screen blockage via intake screen. Because water wheels are bigger and thus the needed penstock would have to be larger, clogging is less of an issue. So an intake screen may not be required.
- The head of a waterwheel system often doesn’t need to be as high as the head of a micro hydro turbine system as long as there is appropriate flow with respect to how much water is needed to make the water wheel spin.
- Because watermills have been around much longer than micro hydro turbine systems, it’s possible to find sites with a waterwheel or a former site(with a vacant water mill pit) which can require minimal building for personal use.
- The costs of a water wheel over a water turbine system can be lower at times because water wheels and flume can be constructed by hand using something like wood instead of purchasing small parts for a micro-hydro system which often need to be manufactured.
- Aesthetics is a major selling point of water wheels as it attracts attention and visitors
Regarding tiny houses, hydroelectric power is best used for tiny houses that are settled upon land(not on the move with wheels) that has a source along with obtainable water rights. The water source should be somewhat elevated higher than the tiny house location so there can be a sizable head to drive a micro hydro turbine or a water wheel. There should also be a way to divert the water used to make the wheel spin back to nature. If the location is right, micro hydro power can be the biggest & most consistent power producer of the 3 types of renewable energy off-grid power systems.
While there are many applications of solar energy like solar thermal & solar distillation, the usage of solar as a renewable energy is called photovoltaics(PV). Solar power is arguably the most used of the three renewable resources because you can hear about it everywhere; it can be set up anywhere with sunlight like on top of tiny houses(with or without wheels); and the electricity produced is sizable and consistent most of the year round. Before going any further, how Photovoltaic(PV) Cells work:
To the right is a diagram of a typical solar cell. The basics of the solar cell lies in its N- type and P-type semiconductor layers.
Both the N-type and P-type layers are made of silicon. Silicon is used because it is has four valance electrons which allow strong bonding; silicon is abundant; and is a semi-conductor which allows the flow of electrons.
The N-type and P-type layers are not made of pure silicon, but they are doped with tiny concentrations(as little as 1 atom per million) of other elements.
The N-type layer silicon is doped with trace amounts of atoms with 5 or greater valance electrons like phosphorus(5 valance electrons). In the N-type layer, after the doping atoms each form 4 covalent bonds with the surrounding silicon atoms, there will be free electron(s)(the (-) yellow balls in diagram) unable to form covalent bonds but are held in place due to positive charge(s) needing to balance out. Thus, the N-type layer will be of neutral charge due to total proton and electrons balancing out.
In the P-type layer, the trace elements used all have 3 valance electrons or less like boron(3 valance electrons). When the P-type layer is doped, the doping atoms will form three or less covalent bonds with neighboring silicon atoms. Due to this, the positively-charged bonding spaces with a missing electron(s) are addressed as a “holes”(the (+) bluish balls in the diagram). Because there are equal number of electrons to match the number of protons, the P-type layer is also of neutral charge like the N-type layer.
Also know that because electrons in the covalent bonds can move within their respective orbits, the shifting negative charge causes the holes to “move”. Then, the PV cell works when the N-type layer makes contact with the the P-type layer like in the above diagram. When this happens, the free electrons from the N-type layer begins to rush to the P-type layer to fill in the holes.
If the electrons didn’t have charge, the P-N layers would evenly distribute electrons and “holes”; however, this doesn’t happen. When the P-type layer gains electrons, the layer becomes negatively charged. When the N-type layer loses electrons, the N-type layer becomes positively charged. This creates a voltage potential difference between the two layers. The voltage pressure tries to push the free electrons back into the N-type layer. The diffusion “force” and the voltage pressure eventually balances out creating the depletion zone.
After the PV panel array is connected to a load, it’s placed under sunlight. When sunlight hits the PV panel on the N-type side, the sunlight(via photovoltaic effect) knocks the free electrons from its positive and negative attraction. Because the free electrons cannot pass the depletion zone, the free electrons instead travel through the wire and through the load to the P-type layer. The migration of the free electrons from the N-type layer to the P-type layer via wire and load causes a voltage potential difference due to change in charge balance. The free electrons in the P-type layer traverse through the depletion zone and back to the N-type layer. As long as there is sunlight and a closed circuit, the useful moving charge(current) will flow though the load whether its a device or an appliance.
Aside from knowing how solar panels work, there are few things to know when deciding which solar panels to use:
- Efficiency: This refers to the efficiency of the solar panel in converting solar energy into power(watts). With any commercial solar panel, it should be identified approximately how much wattage is produced under tested conditions. The 2 main kinds of solar panels are mono-crystalline and poly-crystalline. Mono-crystalline means purer silicon(before adding impurities) and poly-crystalline means silicon bonded with other elements(before adding impurities). While mono-crystalline is more expensive than the latter, it is also much more efficient because efficiency is related to silicon purity. Try to get mono-crystalline solar panels when possible to get the most out of solar energy on the long run.
- Size: It has to fit where you want to put the solar panel(s) or the location has to be made to conform to the solar panel(s) size and shape. Also take into account that larger the solar panel, the more solar cells it will have to take in solar energy.
- Location: This is important because the location has to give the solar panel optimum sunlight. Places where light can get occluded like under the shade, clouds, snow, and etc should be avoid. Most common spots to place solar panels are the roofs and/or near the tiny house in an open area to avoid obstacles. Also, consider the sunlight strength of the locality.
- Angle: Important to know is that a panels get maximum wattage from solar energy if the solar rays hit the surface of the PV panel(s) in a perpendicular manner. The PV panel(s) should be angled to “face” the sun as much as possible. sun trackers fitted to the PV panel(s) are also an option, but the maintenance trouble usually isn’t worth it.
Because sunlight is found nearly everywhere, nearly anyone can gain some benefit from PV panels. Although it was expensive before in nearly the same league as small wind power, the price of PV panels have gone down over the years even for a full-time use.
IV.Wiring of Off-Grid Power Systems
Even if you have decided on which of the renewable energy sources you want to use after several considerations, you will still need an electrical system to distribute and/or store power. Here is a diagram to show what kinds of components are seen in off-grid power systems:
The above is general and should not be taken as absolute; this diagram is mainly to give a good introduction and a basic understanding to how off-grid power systems work. Here are what the parts generally do:
- Rectifier: this device converts current from AC(alternating current) to DC(direct current). While there are a few places in the circuit which may require rectifiers, the most likely place is right after the alternator from the wind and hydro power turbines which often use alternators to produce AC. The AC has to be converted to DC because battery packs can only absorb DC voltage. Sometimes, however, a rectifier may not be needed because the right charge controller can have a built-in rectifier to convert AC to DC volts.
- Battery: this is where the power generated by the renewable energy devices are stored and utilized from. The battery can only store and emit DC. In a renewable off-grid power system, several batteries are used and wired together into a battery bank. Most commonly used are 12 volts lead-acid batteries. There are other voltage types like 24 volts, 36 volts, and even 48 volts. Of major importance is sizing the battery bank appropriately with regards to the system; this post shows how to do it.
- Charge controller: A charge controller is a device that regulates how the voltage and the current from the renewable power device enters the battery. For instance, if there is a micro hydro power turbine that can produce 40 volts, it would damage the battery bank if the 40 volts was forced into it without any charge conversion/regulation. A charge controller would convert the 40 volts to about 13.6- 14.4 volts. Note that an actual “12 volt” battery is actually about 12.7 volts at rest and the charge controller converts the 40 volts to 13.6-14.4 volts as it is slightly higher than 12.7 volts; this is due to the fact that charge flows from high voltage to low voltage and this is needed to charge a battery bank. 13.6-14.4 volts being slightly higher than 12.7 volts won’t cause battery damage like 40 volts would. Another thing to know is that if the renewable power source is hydro or wind, there are charge controllers that can convert AC voltage to 12 volts DC. Also, the charge controller prevents slight reverse current discharge of power from the battery bank circuit over time. Thus, a charge controller is very important to renewable power systems. Lastly, like I said before, a charge controller can have a built-in rectifier to convert an AC voltage to DC 12/24/48 volts. The two major types of charge controller are PWM and MPPT; more on this is found on this post.
- Dump Load & Dump Load Controller/Diverter: In the case where the battery bank is completely full and there is still more power coming from the renewable energy device, the excess charge has to be diverted somewhere. That somewhere is the dump load. The dump load can be as simple as a bunch of resistors which release the excess as heat; or the dump load can be something useful like a heating element which can use the excess heat to boil water. The dump load is connected to a dump load controller which senses when the battery bank is about to overfill and directs the excess charge to the dump load. The dump controller may be built into the charge controller, and thus the dump load would be connected to the charge controller. Other times, the dump controller is connected to the battery bank with the dump load attached separately from the charge controller. The benefit of the latter setup is that the load controller doesn’t share the same point of failure as the charge controller.
- Battery/System Monitor: This device as it name implies monitors the battery bank. Read values include instantaneous current and voltage,net energy into and out of battery, remaining amp-hours, and etc.
- Inverter: this device converts DC to AC. While this may be needed in a few places, inverters are needed mainly to convert the DC power from the battery bank into AC power for the various devices and tiny house systems that require AC power. The wires can bring the converted AC power directly to the AC devices or through a AC panel grid which distributes the AC power through outlets. As the inverter is an important component, here is a post detailing how to select one.
- Fuses: It is a device that consists of a strip of wire that melts and breaks an electric circuit if there is over-current. Mismatched loads, device/component failures, overloading, and short circuiting are common reasons for over-current. Fuses are inserted on to wires as safety devices. There are both AC and DC fuses. AC fuses are usually one component and are easy to set off(have high interrupt ratings). DC fuses are more complex(more components) and are harder to set off(have lower interrupt ratings). Fuses are one time use.
- Circuit Breakers: Similar to fuses, circuit breakers interrupts current flow if a ‘fault condition’ is detected. However, unlike fuses which are one-time use devices, circuit breakers can reused by resetting it manually or automatically.
- AC Breaker Panel: It’s a device that distributes AC current to all the devices in the house via auxiliary circuits which each connects to the sockets/appliances. Each of these auxiliary circuits also have a built-in fuse or circuit breaker. DC breaker panels also exist, but because DC devices are not common, it’s not worth investing in one and it would be better to get DC power directly from the battery instead.
- Kilowatt-Hour(kWh) Meter: It measures the amount of electrical energy(or kilo-watt hours) consumed. A kWh meter has a counter or digital display that counts the units of kWh. The total energy consumed is equal to the difference in counter values from beginning to end of a time period. Another feature of kWh meter is if the net units of kWh goes backwards for an entire month(done via power generation), the excess power is sent back into the grid and to the power company where excess electricity is credited for future use for exchange for cash.
When wiring up your tiny house with a renewable power system, there are 4 variations of the above system diagram you can choose from:
- Grid-Tied without Batteries: This is the type of system where the renewable power is used immediately for the various uses. Surplus energy is sent back into the grid to be credited for you to use at other times or exchange the credit for money. Unless your renewable power is provided 24 hours a day, it’s impossible to be self sufficient power-wise. This system isn’t suited for off-grid enthusiasts and is better suited for those who still rely on grid-tied power and want to cut down on the electric bill or make some money using renewable power.
- Grid-Tied with Batteries: This configuration is suited for both off-grid enthusiasts and those who only want to be partially off-grid. Off-Grid enthusiasts can aim to get all their energy from renewable power and use batteries for storage. Those who want to be partially off grid can use this configuration to generate back-up power from renewable energy while mainly relying on grid-tied power. Via grid-tie, excess renewable power can also be exchanged for credit for you to use at other times or exchange the credit for money.
- Off-Grid without Batteries: This is only possible if large amounts of renewable power is produced 24 hours a day. This is to account for the fact that there is no storage nor a grid-tie connection if renewable power is unavailable.I say NEVER go for this configuration.
- Off-Grid with Batteries: This system is purely for off-grid enthusiasts. Also, this is suited for tiny houses which are unable to be connected to the grid due to any location disadvantages; off-gridders usually settle in these kinds of locations to get some distance from civilization. Because there is no grid-tie, the produced power has to be consistently available for home use. Energy conservation practices are necessary here.
Lastly, here are some basic electrical terminology as these words may be seen in some of my more technical off-grid power systems related posts. I will explain these using an anology:
- Amps(A): This is the measure of the number of electrons that pass a specific point over a time period.
- Volts(V): This is a measure of the force or pressure that makes electrons move. Without voltage, the electrons wouldn’t move. A battery’s voltage rating is how much pressure is used to move electrons from power source to the circuit.
- Watts(W): This is a measure of work done by the current.
- Ohms(Ω): This is a measure of electrical resistance. Here is an analogy: a fast flowing river has low “resistance” and it hits a dam with a small outing. The water that comes of the outing has much less speed and force. The dam with the small pipe/outing acts as resistance to the water flow.
- Amp-Hour(A-hr): This unit is the amount of energy charge in a battery that will allow one ampere of current to flow for 1 hour. This is commonly used to describe the energy capacity of a battery bank.
If you liked this in-depth guide, be sure to share(via social media bar) and subscribe for email updates(if you already haven’t). Leave a comment below regarding your thoughts, ideas, and experiences regarding the wind, hydro, and solar off-grid power systems I covered as well as the wiring and system setup.
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- Header Image: “bigstock-solar-energy-panels-and-wind-t-” (CC BY 2.0) by aqua.mech
- HAWT vs VAWT Wind Turbines GIF: by Ssgxnh (Own work) [Public domain], via Wikimedia Commons
- Water Turbine System Diagram: Original Image created and owned by this website. You may use if you give proper attribution as explained in this site’s “Content Reuse & Attribution Policy” from the bottom.
- Overshot Water Wheel Image: By DanMS [CC BY-SA 2.5], via Wikimedia Commons
- Solar Cell Diagram: Exact same policy as above #3
- Off-Grid Power System Electrical Diagram: Also exact same policy as above #3
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