Micro Hydro

Hydro systems are accredited under the Microgeneration Certification Scheme as an MCS approved technology. This means as an MCS Accredited installer you are able to install MCS Accredited Hydro Equipment and offer consumers the Feed in Tariffs.

Hydroelectricity systems generate electricity from running water - usually a small stream. Small or "micro" hydroelectricity systems can produce enough electricity for lighting and electrical appliances in an average home. Hydroelectricity systems are also called hydro power systems or just hydro systems.

Hydro-power systems convert potential energy stored in water held at height to kinetic energy (or the energy used in movement) to turn a turbine to produce electricity.

A micro hydro plant is below 100kW. Improvements in small turbine and generator technology mean that micro hydro power schemes are an attractive means of producing electricity. Useful power may be produced from even a small stream. The likely range is from a few hundred watts (possibly for use with batteries) for domestic schemes, to a minimum 25kW for commercial schemes.

Small scale hydro and your home
 

Hydro power requires the water source to be relatively close to where the power will be used, or to a suitable grid connection. Hydro systems can be connected to the main electricity grid or as a part of a stand-alone (off-grid) power system. In a grid-connected system, any electricity generated but not used can be sold to electricity companies.

In an off-grid hydro system, electricity can be supplied directly to the devices powered or through a battery bank and inverter set up. A back-up power system or fuel source may be needed to compensate for seasonal variations in water flow.

The capital cost is high but the prospect of not having electricity bills or making money by selling energy back to a power supplier may tempt you!

Provided the resource is there, community hydro projects can also be a viable proposition. Potentially, there are great benefits in clubbing together to increase buying power or sharing expertise - although the work and costs involved should not be underestimated.

Small Scale Hydro Power
 

Energy available in a body of water depends on the water's flow rate (per second) and the height (or head) that the water falls. The scheme's actual output will depend on how efficiently it converts the power of the water into electrical power (maximum efficiencies of over 90% are possible but for small systems 50% is more realistic). Hydro electric systems are generally divided into two categories, low and high head.

Reliable and efficient equipment - and sound advice - is available from a large number of experienced UK suppliers and consultants.

Will it meet my energy needs?
 

This depends, of course, on your energy needs and the resource available. For houses with no mains connection but with access to a micro-hydro site, a good hydro system can generate a steady, more reliable electricity supply than other renewable technologies at a lower cost, however it may still require a backup.

Total system costs can be high but often less than the cost of a grid connection and with no electricity bills to follow. It should be noted that in off-grid applications the power is used for lighting and electrical appliances. However space and water heating can be supplied when available power exceeds demand.

Costs & Returns

Due to the different permutations possible of the different components of the total value for generated electricity, a few assumptions have to be made if a simple table of annual revenues is to be constructed. To keep things simple, in the table below no value for offsetting has been included, and the default export price of 3 p/kWh has been assumed. This would be the ‘worst case’ for revenue; the ‘best case’ with 100% offsetting could provide substantially more revenue. Therefore the generated electricity values used are:

Table 3 - Feed-in Tariff, export & LEC value for different sizes of hydropower system.

For a range of different sizes of micro hydro and small hydro system the annual revenue is shown below. These are all based on a typical UK capacity factor of 0.5.

Table 4 - Annual revenue for different sizes of micro hydro and small hydro systems.

Remember that different sizes of micro hydro and small hydro systems qualify for different Feed-in Tariffs, so even though larger hydro systems generate more energy, the annual revenue generated doesn’t always scale in line with the annual energy production because a larger system may fall into a lower Feed-in Tariff band. This means that in some situations a smaller hydro system may produce a greater revenue than a larger one. This is particularly true for hydro systems between 100 and 150 kW, where it is often economically better to reduce the size of the system to qualify for the higher 15 -100 kW Feed-in Tariff. This is an unfortunate anomaly caused by too-larger gap between the less than and greater than 100 kW Feed-in Tariffs.

How much do micro hydro and small hydro systems cost?
 

It is difficult to make generalisations about what micro hydro and small hydro systems cost because they are always designed to suit the particular site. Also the extent of civil engineering works is very site dependent, with some new-build sites requiring everything to be built from scratch, while other retrofit projects can make use of and adapt existing civil engineering structures. However, the table below is a vary rough ball-park estimate of typical project costs for systems requiring an ‘average’ amount of civil engineering works and grid connection upgrades, and assuming access to the site was reasonable. In all cases it is assumed that good quality hardware is used throughput (which is always the most cost effective option anyway in the long run).

Table 5 – Indicative total project costs and annual operational expenditure.

It is possible to install systems for a lower cost, particularly at the lower power outputs if the existing infrastructure at the site lends itself to easy adaption to a modern hydropower system so only modest or no civil engineering works would be needed. However even in the most favourable circumstances it is unlikely that the cost would reduce by more than 50%.

An indicative cost of annual operational expenditure (OpEx), which includes routine maintenance, is also provided. This assumes that willing and low-cost labour would be available to manually clean the intake screen for the smaller systems, but then as the systems get larger (50 kW+) someone would be paid on a part-time basis to keep an eye on the (automatically cleaned) intake screens. It also assumes that monthly greasing would be done by the same part-time attendant, and an annual service and system check would be carried out by a professional hydro company.

What would be the return-on-investment on a micro hydro or small hydro system?
 

Using all of the various assumptions, revenues and costs discussed above, and assuming a design life of 20 years (see ‘How long do they last’ below), the following table of Internal Rates of Return (IRRs) can be constructed.

Table 6 – Internal Rates of Return over 20 year for a range of typical hydro project sizes.

Table 6 clearly shows that the smallest micro hydropower systems struggle to make economic sense. We normally say that the smallest commercially viable hydro systems are minimum 25 kW, unless the site is a historic hydro site that lends itself to easy redevelopment.

It is worth mentioning that sometimes intangible benefits can be worth a lot, for example at sites frequented by tourists a micro hydro or small hydro system can add a lot of additional interest as a visitor attraction and in other cases the marketing benefit to a company from being able to say that their energy is generated on site from zero emission hydropower can be significant.

The best sites are generally larger, with higher heads, easy to adapt infrastructure, easy access and a good grid connection.

What is the physical size of a hydropower system?
 

Once again it is difficult to make generalisations. Low-head hydropower systems take up much more space than high-head hydropower systems because the turbine has to be physically large to get a higher flow rate through it with only a low water pressure across the turbine. On smaller (<25 kW) systems it is possible to not have a turbine house and instead have a steel-fabricated turbine enclosure with a weatherproof cladding, similar to the Cricklepit Mill enclosure, clad in cedar wood, shown at the top of this page. Penstock pipework is normally buried, so is out of sight. On low-head sites the intake and discharge channels can be covered over and turf laid, so are effectively invisible. Even though penstock pipes and channels can be invisible when the system is finished, bear in mind the size of the excavations required during the construction phase.

The table below gives indicative dimensions for the main system parts to give you an idea of turbine house sizes, diameters of pipes and cross sectional areas of channels and intake screens. In this example ‘low-head’ is assumed to have a net head of 2.5 metres and ‘high-head’ 50 metres.

Table 7 – Indicative sizes of main parts of low-head and high-head micro hydro and small hydro systems.

Environmental impact
 

Turbines can have visual impact and produce some noise, but these can be mitigated relatively easily. The main issue is to maintain the river's ecology by restricting the proportion of the total flow diverted through the turbine.

You will need to talk to the relevant planning & water authorities to ensure the site and design are acceptable and identify any other permissions required.

The estimated costs are often quickly covered by the Feed in Tariffs which can be offered by Microgeneration Certification Scheme (MCS Accredited) Installers who offer MCS Accredited Micro Hydro.

Call our MCS team on 0800 882 4308 to start your MCS for Micro Hydro.

Data Referenced from http://www.renewablesfirst.co.uk/introduction-to-micro-and_small-scale-hydro-power.html#link10