Installation manual

3.1.3. Worked example

If for example the head is 20 metres and the flow is 10 litres per second then the power

generated is about 1000 watts or 1 kW continuously (20 x 10 x 5 = 1000). The turbine will

therefore produce 24 kWh of energy per day and over 700 kWh units of energy per month.

This exceeds typical household energy consumption in most countries. If the power output

is only 500 watts then you would get half as many units per month, which would still suffice

in many cases. (The same arithmetic applies to solar PV although obviously that will only

work in daytime hours so that a 1kW PV array is unlikely to produce more than 6 units of

energy per day in summer and may average 4/day or less over a typical the year.)

3.1.4. Supply and Demand issues

Renewable energy is different from (for example) a diesel generator. In the case of a

generator, you can run your house (or whatever, known as the "load") directly from its AC

output. The governor in the generator will adjust the fuel consumption to meet your needs. If

you run it continuously then you will get through a huge amount of fuel.

In the case of renewable energy, the fuel is free, so you will not want the turbine to reduce its

output to suit the load. You will probably want it to produce as much energy as possible all

the time. That way you make best use of the investment in money and effort that went into

setting up the turbine. The only problem is that at any given moment you will often need

more power than the turbine is producing and you will often need less.

3.2. How to match the constant power supply to our changing demands?

The solution is to store the energy produced by the turbine in a battery, or to feed it into the

electricity grid. When you need more than the turbine can give you then you will draw the

extra from the battery or from the grid. This is how we build a renewable energy "system"

with a PowerSpout turbine (and perhaps also some solar PV panels) and a battery or grid-tie

backup. If the grid is available then this will normally be the more cost-effective way to store

the unused energy.

3.3. What happens if there is not enough water for the turbine?

The flow of water through the PLT or TRG turbines depends on the head of pressure and on

the size and number of jets that direct the water onto the Pelton or turgo runner. If there is

not enough water entering the penstock at the intake to keep this flow supplied then air will

enter and the pipe will gradually empty. This reduces the head and consequently the flow in

the jets is reduced and an equilibrium is found. However this will not produce the best power

output due to reduced head. If the power output is observed to decline then the user

should intervene and adjust the turbine jets to match the new flow. Closing one of the

turbine's valves may be enough to reduce the demand enough that the penstock refills and

full pressure is restored. Power output will be less than full power but at least with a full pipe

the best use is being made of the available water.

The user should check the pressure gauge and make sure that the pipe is always full by

choice of the number and size of jets in use. If the pressure is low then it may be a good

idea to close all the valves and wait until the pipe refills before opening a reduced number of

jets or changing to smaller jets to match the prevailing flow conditions.

On a good site this adjustment may rarely if ever be needed as there will always be sufficient

flow of water to produce full power. But where necessary the PowerSpout can make good

use of partial flows provided that the jets are adjusted to suit.