Hydropower for home : Is it an option?
Renewable energy is a big deal at the moment. For many people, it just makes sense to create energy from the sun or the wind. It saves resources and creates less pollution.
The push for renewables is so great that many states have created incentives in the form of tax rebates and electricity buyback to encourage the installation of solar electric PV.
Home wind turbines are also viable in certain locations and hybrid solar-wind systems are becoming more common. But what about hydro-energy?
Can hydropower be used in homes and businesses?
As a general rule homes, farms and small business can be powered by a hydroelectric turbine of between 5kw to 10kW. A 10kW rated turbine is termed a micro hydro system. The most common turbine for use with micro hydro power is the impulse type, such as the Pelton Wheel or Turgo Wheel designs.
How can water be used to generate electricity?
The basic principle is simple – water pressure in hydroeletric generator impacts the impeller of the turbine, which turns a generator to generate electricity.
Within that basic concept there are a lot of questions. Before we dive into the answers, the video below gives some very useful information about the hydroelectric power generation.
If you prefer to read, the video transcript can be found underneath. If you want to skip it altogether, just jump down to the next section.
Video – How do hydroelectric turbines work?
The terms hydropower or hydro-energy imply the extraction of energy from running or flowing water.
The terms are also used in reference to fresh water and not sea water. The process of hydropower generation requires creating a barrier in the path of flowing water. The water is then channelled and made to drop, when its potential energy is converted into kinetic energy.
This energy is then extracted by means of a turbine. The scale of hydropower is extremely broad. Energy can be generated from a few watts to several gigawatts. In fact, the world’s largest power plant is a hydro energy project called the Three Gorges Dam in China.
It has a nameplate capacity of a whopping 22 gigawatts. Large-scale hydro projects can not only power towns and cities, but a whole country!
The range hydropower projects are classified as follows:
- Pico hydro-energy comprises of projects which have a capacity of 5 kilowatts or less.
- Micro hydro means capacities of 5 kilowatts to 100 kilowatts
- Small-scale hydro means capacities of 10 megawatts or less
- Anything above 10 megawatts is classified as large-scale hydro
There are many countries that are heavily reliant on hydro power. For example, Norway gets more than 98% of its energy from hydropower. Even to this day hydropower is one of the cheapest modes of electricity generation.
Furthermore, the energy extracted is renewable energy. Water is constantly replenished by nature because of the water cycle. There are no co2 emissions when converting water’s kinetic energy into electricity.
This does not however mean that hydropower does not have any negative environmental impact, as will be explored later. Streams and rivers have different levels of water flow.
The flow rate of fresh water also varies across the year and therefore to extract energy there are different types of turbines, some more suitable than the others depending upon the head of water and the fluid.
The head of water is the measure of hydrostatic energy of water. It is simply the height of water above a certain point. For hydropower, it is the measure of the height that will be available above the turbine.
Then there is also the flow rate. The flow rate is the volume of water crossing a certain point in a second. Based on the head of water and the flow rate at a certain location, the turbine type is selected.
Home hydro generator – the hydroelectric power house
There are four major types of turbines, as follows:
- Kaplan turbine
- Francis turbine
- Cross flow turbines
- Pelton wheel
- Pelton Wheel – Specific Speed 5.0 rpm
- Francis Turbine – Specific Speed 30 rpm
- Francis Turbine – Specific Speed 70 rpm
- Kaplan Turbine – Specific Speed 113 rpm
The chart in the video shows shows the operating envelope of the turbines based on the flow rate and the head of water.
For example, when there is high head and low flow rate, the Pelton wheel is used. On the other hand, when the head of water is low and the flow rate is high, then Kaplan turbines are used.
The Pelton wheel is an impulse turbine, whereas Kaplan turbine is a reaction turbine. There is also Francis turbine which falls in the middle. Francis turbines are used for medium head levels and medium flow rates.
The operational envelope of Francis turbine is very wide. It is a hybrid turbine in that it utilizes both impulse of the force and the action of the force. Another advantage is that it can also act as a pump for pump storage systems, which will be discussed later.
It is interesting to note that both Kaplan and Francis turbines can reach operation efficiencies of over 90%, making them the most efficient renewable energy devices in the market.
Lastly, there is the cross flow turbine or the Bank II turbine. It is a slow-moving machine which is well-suited for locations with a low head of water but with high flow rate. Being a slow mover, the turbine is easier to maintain as the bearings don’t need to be replaced often.
Furthermore, the turbine is self-cleaning and gets clogged up less frequently compared to other turbines. The efficiency of cross flow turbines and the Pelton wheel is lower than that of Francis turbine and Kaplan turbine.
Water powered generator for home use
Now, there are other varieties of turbines also available, particularly at the micro scale. There are turbines with helical blades that can run in the shallowest and slowest of running water. For instance, the motor rotor turbine can utilize water at speeds as low as 2 miles per hour.
One of the advantages of hydro power is their usage in pump storage projects. The idea of these projects is to meet the high electricity demand during peak times.
It should be noted that our electricity requirements change through the day. Pump storage provides an energy buffer during the times of calm when electricity usage is low and there is excess electricity in the grid.
During those times water is pumped back from the lower elevation reservoir to the higher elevation reservoir. This is done by using grid electricity and running the turbine in reverse which allows it to act as a pump.
The pumping of water increases the reservoir capacity and the water head. This additional water is then used during the peak energy demand tines, which can occur during the day or during the evenings.
The water that was pumped back can then be utilized alongside existing and incoming water to run the turbines to their peak capacity. Outside the many positives of hydropower there are also a few negatives.
For example, to harness hydropower, particularly at large scales, dams have to be constructed that come at a huge cost. Creating a barrier across flowing water floods the upstream lands.
This means that the natural environment is destroyed and the habitat of not only plants and animals is affected but also people living in the vicinity have to be moved. There are many fish species that spawn upstream of the river.
The building of a dam blocks their migration path, although by providing a fish ladder this problem can be alleviated to a large extent. Similarly, there are many freshwater fish species that cannot migrate downstream because of the barrier.
Accumulation of silt, debris and dead wood can reduce the capacity of the dam over time. Furthermore, the decaying plantation that stagnates upstream of the barrier also produces emissions. Lastly, building a large dam can also alter the natural water table in downstream lands.
It should be noted that due to strict environmental legislations it is difficult to build large scale hydropower projects in modern times. The best practice is therefore to have several small-scale run-of-the-river schemes than a few large ones.
Home water turbine generator
In the run-of-the-river project a portion of water from a river or a stream is channelled into pipes that transport the water to a power house. A turbine is located in the powerhouse that utilizes this siphoned water to generate electricity.
The power house is located at a much lower elevation than the point where the water is bled from the river or the stream. Run-of-the-river schemes are relatively environmentally friendly, although their return on investment is lower than large-scale projects.
The other advantage of tunnel deliver scheme is that they are easy to build on commission and can be completed within days or weeks, as opposed to large-scale projects that can take several years to build.
Now let’s look at the estimation of hydropower at a given location. The total amount of power that can be extracted by a turbine can be determined by a simple formula.
The formula is:
P = Nu x Rho x Q x G x H
- where P is the power in watts
- nu is the dimensionless efficiency of the turbine (for Francis and Kaplan turbines it’s nearly 92%)
- Rho is the density of water in kg per meter cube
- Q is the flow rate in cubic meters per second
- G is the acceleration due to gravity and
- H is the height difference between the inlet and the outlet in meters.
Can a water turbine power a house?
All renewable ‘alternative’ energy generations systems can power a house, but sizing depends on your home’s energy consumption in kilowatt-hours (kWh). This is the first step, to determine how much energy a home uses over the year.
One way is to add up the power ratings of all household appliances and multiply the rating in watts by the estimated number of hours each appliance would be used throughout the year.
This isn’t a particularly good method for two reasons. First, usage is just an estimation and you might be out either way, either too much or not enough.
Secondly, some appliances are not easy to assess. For example, HVAC, fridges and freezers have compressor motors on-board, which start and stop in cycles according to temperature target settings.
Motor surge currents are to 3 times greater than a motor’s running current, a fact which isn’t reflected on the nameplate rating. In addition, a poor Power Factor can also mislead you into thinking that Volts x Amps always equals Watts. In AC circuits it often does not.
A better way is to refer to your utility bill for the previous year (see image below):
Once you know how many kilowatt hours your home used in the previous year, you can size your turbine rating needed (or solar, or wind turbine.)
The average amount of energy used by the average American household is about 11000 kWh per year.
A 5kW hydroelectric turbine with constant water head and flow will potentially generate:
5kWh x 8760 hours (in a year) = 43800 kWh
For comparison, a 5kWh solar panel system would generate approximately:
5kWh x 1825 (peak-sun-hours per year) = 9125 kWh
In theory, a home hydro power system far out-performs solar, even allowing for substantial system losses in cabling and fluctuations in water flow.
What is the similarity between hydroelectric power and solar energy?
The three main renewable electrical energy systems available for home use are:
- Solar electric PV panels
- Wind turbines
- Water turbines (small hydroelectric generator)
As you might imagine, solar panels are by far the most common. Wind turbines are not always viable in some areas, while hydropower is completely dependent on a supply of running water.
Basically, this means that water turbine use is mostly limited to country areas, homesteads and farms. However, when the conditions are right, hydroelectric power is very efficient.
It should be noted there are big differences between the three power sources – solar output depends of the irradiance (peak sun hours) for a location, while a wind turbine’s output can be very variable and need wind speeds in excess of 5m/s to work at all!
On the other hand, a water turbine operates at a constant speed (more or less), and therefore it’s electrical output is always maximum.
Is hydroelectricity cheaper than solar energy?
On the larger scale this is certainly true – solar comes in at 10 cents/kWh and hydroelectricity generates power at half the price at 5 cents/kWh. But is this true for all scales of power production?
Take a look at the chart below:
(Based on 5kW output rating)
Cost per kW installed
Cost per kW DIY
25-30 yr warranty
8 years average (U.S.)
11 average years
7 to 10 yrs
20% max (monocrystalline panels)
35% (high estimate for 5kW turbine)
No (shading, night, dust & low-light)
No – heavily wind speed dependent
Yes – full output (with constant flow)
Time to install
2 to 3 days
3 to 5 days
Can use off-grid?
There’s a couple of things to note from the above:
Output Capacity of Solar and Wind Is Variable
A solar panel’s output power depends on the sun’s energy, which is not constant. It is strongest in the middle of the day and lowest in the mornings and evenings. Obviously, at night there is no sun and no electricity production possible.
A wind turbine’s power output can vary enormously, as the output watts increase 8 times every time the wind speed doubles!
If either system is connected to the grid (grid-tie), then excess power feeds back to the utility company automatically. If it’s an off-grid system, then batteries are needed to ensure power supply at night time, or in the event of a power outage.
Home Hydropower Power Output
Assuming a constant head of water, or river flow, then a hydroelectric generator will always produce maximum watts. If the load is less than the hydro output, that excess power generation needs to go somewhere!
If the system is grid-tied, then it can flow back into the grid. If off-grid, then it must be diverted to a dummy load, often in the form of water or air heater elements.
Do you need batteries for hydro power?
Assuming constant water flow, no you do not. However, if the system is grid-tied, it may be advisable. In the case of power outage, the system is disconnected from the grid and is also not able to power the house.
This is done automatically to prevent ‘islanding’, which is when independent generation systems could feed back into the grid endangering any personnel working on the line.
What is micro pumped hydro storage?
This an intriguing idea that works at any scale. Imagine you lived by a lake or large pond with an incline to a higher level close to your house. Your goal is to live off-grid and you have 8kW of solar panels installed.
Being ecologically minded, you’re trying not to use a big battery bank, which are very expensive and only have a limited life anyway. In spite of this, you have no electricity from your solar panels at night.
One solution is to create a pumped hydro storage system.
When their is excess electricity available form solar in the daytime water is pumped from the lake up to a reservoir at a higher level.
At night-time, when their is no solar output, the water in the reservoir is let out and is gravity-fed through the turbine which now acts as a generator.
The arrangement is basically a replacement for a chemical battery bank, but is none polluting and uses no precious resources.
How much water flow is needed to produce electricity?
You may have a stream running through your land, but is there enough head and flow to generate enough electricity for your needs?
I’ll outline the simplest methods, but I suggest that a professional surveyor will give you the most accurate measurements. Probably a good idea if you’re spending several thousand dollars on a micro hydropower system for our home.
Measuring the stream or river water head
Run out a length of hose between the highest elevation where the stream comes from and the other end to the propose turbine location. Connect a pressure gage to the lower end and read off the psi.
2.31 feet of head can be assumed for 1 psi.
The simplest way (unless you have water flow bigger than a stream or small river) is to simply fill a bucket of known capacity and time the number of seconds it takes to fill it.
You need this in gallons/minute, so the question for flow becomes:
60/seconds x bucket capacity in gallons = flow in gallon/minute
Example: A 10 gallon bucket fills in 15 seconds:
Water flow = 60/15 x 10 = 40 gallons/minute
Micro hydro power calculator – find turbine watts from head and flow
Most micro hydro power systems have an efficiency between 50% and 60%, The equation below is a simplified way of calculating the power capacity possible using you head and flow values using an efficiency of 53%
(head (feet) × flow (gpm)) ÷ 10 = Power in Watts
Let’s substitute some figures and see how the numbers look:
Example: Head psi = 38 Flow = 76 gallons/min
Discover your solar saving potential
Head in feet from psi reading = 38 x 2.31 = 87.78 feet
Turbine power in watts = head x flow / 10 = 87.78 x 76 /10 = 667W
How to generate electricity from water at home
There are many standard sized micro hydro electric turbines on the marketplace. The generator below is supplied by Suneco and is an example of a typical 5kW unit.
The diagram underneath gives a great idea of the installation configuration and the kind of construction required.
Micro hydro power for off-grid houses
Even though I recommend a complete project from study, design through to completion is done by a professional installer, many home owners have built and installed their own systems. Everything is doable! It’s just that using a pro eliminates any costly mistakes.
Home micro hydro power systems are much more efficient than either solar or wind turbine. They have an equal life, if not longer,and provide a higher, steadier output.
Home Hydroelectric Related Questions
Can hydroelectric power be used in homes?
Home hydroelectric power is a great option for the home, with the obvious proviso that there is an adequate supply of water with enough head and flow to supply the power needs.
The average home energy consumption in the USA is 11000 kWh/yr. A 2 kW turbine would produce up to 2800 kWh per year, so would about cover about 20% the average home’s energy needs.
How much does a micro hydro system cost?
As a general rule, the cost of a micro hydro power system lies between $1000 and $3000 per kW. The variation is wide because the micro hydro power range is very wide – from 1kW to 100kW!
Different projects with various head and flow values, and the amount of piping/concrete also affect the overall price of a given project.
How much water does it take to power a house?
A simple formula can be used to determine how much water a turbine needs to power a house – (head in feet) × flow in gpm) ÷ 10 = Power in Watts. Assuming a 2 kW turbine is required to easily supply the average home, then the combination of flow and head must equal 2000 watts.
What is micro hydro electricity?
Micro hydro electricity is a system often using a stream or other water flow to generate relatively small amounts of power for feeding a home
How much energy does micro hydropower produce?
Micro hydropower systems generate between 5kW and 100kW of power and are typically used in homes with access to year-round running water.
Resources relating to home hydroelectric power