Off-grid Hydropower

Solar power is what comes to everyone’s mind when they think about clean off grid energy. However, there are additional options. You can harness the elements and produce electricity from other sources, not just the sun. In this guide, we will take a look at the off grid hydropower, producing energy from flowing water.

Before we proceed, an important warning. You must check with the local authorities whether or not the usage of the hydropower is allowed in your area.

What is a Micro Hydropower System?

If there is a river or even a small spring flowing through your land, then you’re in luck. You can use it to generate electricity. Just install a microhydropower system and enjoy hundreds of kW of free electrical energy. This can be enough to power up a large home or even a farm.

How does it work? Basically, in the centre of a hydropower system is a waterwheel, pump or turbine. This part is moved by the flowing water, and then the rotation is transformed into electricity. Additionally, a micro hydropower system includes a generator or alternator, where this rotating movement is actually translated into energy. The generator/alternator is controlled by a regulator. Wiring is the final part of this system, it delivers electricity wherever it’s needed.

It’s important to mention that while sometimes the waterwheel is partially submerged into the water stream, usually there is a channel or a pipeline that brings the water from the natural stream and onto the wheel, pump or turbine.

You can purchase generators and turbines in one package. If you buy them separately, remember to match the generator and turbine’s horsepower and speed with the greatest care possible. Then there is also the issue of DC/AC. You can either get appliances that run on DC electricity, since this is what the hydropower system produces, or add an inverter to the system. The inverter will transform the low-voltage DC electrical power into 240V of AC electricity. As for storing the produced electricity in batteries, it is less practical in the case of hydropower. Hydropower tends to be even more seasonal than solar or wind power. If you do choose to use batteries, install them in the turbine’s vicinity, since low voltage power has difficulties being transmitted over a distance.

Since a waterwheel, pump or turbine is a central part of the system, let’s quickly review them and list their advantages and disadvantages:

  • Waterwheel: A waterwheel is the original system component, it’s been around for many years. While waterwheels can still be obtained, they are not recommended. Their large size and slow velocity are less than ideal when it comes to producing electricity.
  • Pump: Pumps, on the other hand, are more mass produced than any turbine. They usually don’t cost much. When their functioning is reversed, they act just like a turbine. However, they are more breakable, less efficient and demand a constant flow of water in order to perform in a satisfactory manner.
  • Reaction turbine: This extremely efficient type of turbine produces energy by pressure, as its blades are directly pushed by the water at all times. The reaction turbines are frequently used in large hydropower systems and are less common in micro hydropower setups due to their cost.
    The only exception is a propeller turbine, which is more affordable. It works similarly to a boat’s propeller and has 3-6 blades. The blades are set on the runner at different angles. A Kaplan turbine is a subtype of a propeller turbine, it’s very adaptable and can be utilised in a micro hydropower system.
  • Impulse turbine: This type of a turbine has a relatively simple design and can be frequently found in high-head systems. They are operated by the water’s velocity, which moves the runner (the turbine’s wheel). There are several subtypes of the impulse turbine.
    • Jack Rabbit turbine: A small turbine, it actually requires only a foot of water depth. The output is 100W, so thoroughly check if this is sufficient to power your household.
    • Pelton wheel: The energy is created by the jet force principle. The water goes into a pipeline with a narrow exit opening, formed like a nozzle. The water comes out of the nozzle in a jet, hitting the wheel’s buckets. The buckets are formed to maximise the impact’s influence, and the jet rotates the Pelton wheel with about 80% of efficiency. A Pelton wheel can be found in a variety of sizes and it’s highly recommended for high-head, low-flow settings.
    • Turgo impulse wheel: This is an improved Pelton wheel. The jet is smaller and angled, and it hits 3 buckets at the same time (and not 2, like in Pelton’s case). This makes the wheel move at double speed. Turgo impulse wheel is known to be reliable and low-maintenance. It’s smaller and includes less gears, or none at all.

How to Measure Hydrosystems Head?

We mentioned “head” and “flow”, but what exactly do they mean? They are the factors that you need to check in order to determine whether or not you have a suitable micro hydropower site on your property. Just having a flowing water source is not enough, although, of course, it’s a great start. The water must fall, and its head and flow will tell you a lot about its energy-producing potential.

So, to put it simply:

Head is the vertical distance that the water falls.

Flow is how much water is falling.

Now, most micro hydropower systems have around 53% efficiency. A simple formula can calculate the output you will have for such a system given the head and flow of your site.

Net head (in metres) X Flow (in litres per minute) / 10 = System’s output (in Watts)

Let’s discuss the measurement of these deciding factors. As you probably understand, a higher head is preferable, since less water will be required to fall to produce enough energy, thus you’ll need to install a cheaper and smaller hydropower system. A high head is a vertical fall over 3 metres. Anything less is considered a low head. And finally, a drop of less than 0.5 metres makes a typical micro hydropower system completely impractical. In such cases you will need something like the aforementioned Jack Rabbit turbine, which is completely submerged into the water.

How do you get a rough estimate of head? Get someone to help you and pack a funnel, a measuring tape and at least 2.5 metres of a small-diameter garden hose or any other flexible tube.

  1. Stretch the tubing down the stream from the most practical elevation point for the penstock intake. Have your helper hold the upstream end of the hose underwater (with the funnel in it) as close to the surface as possible.
  2. At the same time, lift the downstream end until water no longer flows from it. Measure the vertical distance between your end of the tube and the surface of the water. This is the gross head for that section of the stream.
  3. Ask your helper to move to your current location and place the funnel there. Then walk downstream and repeat the procedure, measuring again. Continue taking measurements in this fashion until you reach the spot where you intend to situate your turbine.
  4. Summarise all these measurements, and you get the gross head available for your future hydropower system. If you’re satisfied with the number, perhaps you should get a professional survey.

How to Measure Hydrosystems Flow?

And what about flow? You can measure it as well. 

The bucket method is the simplest way imaginable. Dam the stream with some boards and divert into a bucket or a similar container. Time how long it takes for the water to fill the bucket. The bucket’s volume divided by the time it takes to completely fill it is the flow number.

A more advanced measurement method is performed with a weighted float. Be careful not to use it if the stream is too fast or too deep. Get someone to help you and pack a weighted float (for instance, a plastic bottle half-filled with water), some graph paper, a tape measure, a yardstick and a stopwatch. The method helps to estimate flow at the lowest level of the streambed.

  1. Select a section of stream with the straightest channel, and the most uniform width and depth.
  2. At the narrowest point, measure the stream’s width.
  3. Hold the yardstick vertically, cross the stream and measure the water depth at regular intervals. You can stretch a rope with increments marked on it.
  4. Use the graph paper to plot the depths. This is the cross-sectional profile of the stream.
  5. Determine the sections’ areas. To do this, calculate the areas of the rectangles (area = length X width) and triangles (area = base X height divided by 2). Do this for every section.
  6. Mark a point at least 6 metres upstream from the point where you measured the width.
  7. Set the weighted float free in the middle of the stream. Time with the stopwatch how long it takes for the float to reach the initial point downstream. If the float drags against the bottom, use a smaller one.
  8. Now you can divide the distance between the points by the time in seconds. You get the flow velocity in metres per second. Repeat this procedure several times to get even more precise measurement. Calculate the average velocity.
  9. Next, multiply this velocity by the cross-sectional area that you measured earlier.
  10. Finally, multiply the result by the factor of roughness. Different stream channels have different roughness factors: 0.8 for a sandy streambed, 0.7 for a bed with small to medium stones, 0.6 for a streambed with numerous large stones. This final result will give you the flow rate in cubic metres per second.

Keep in mind that the flow is often seasonal. When you design your system, take the lowest average flow, to be on the safe side. On the other hand, the local laws might restrict you on how much water you’re allowed to divert at different seasons. In this case, take the average flow rate from the period of the highest demand for electricity.

Final Words

Hydropower is a great option to produce alternative energy, especially if you are living off the grid. It’s eco-friendly and can be achieved, as long as the local terrain allows it.

Always keep in mind that if you’re unsure whether or not you have the proper conditions to produce enough electricity, there is nothing wrong with hiring a consultant.

Naturally, water is not the only element that can be harnessed to produce free energy. Check out our comprehensive guide on off grid wind power. The guide includes important information on how to test your property and decide whether it has the potential for wind energy.

Solar energy is, of course, the most common off grid energy type.