Hydroelectricity

Hydroelectricity is derived from the power harnessed from the flow of falling water, typically from fast-flowing streams and rivers. Presently about 6% of Ireland’s electricity generating capacity is in the form of hydropower. The Ardnacrusha hydroelectric station built in the 1920′s is still the country’s largest renewable energy generating unit.

It can be a useful way of providing power to houses or workshops at the micro-scale level. The electricity generated can be used in-house and surplus electricity can be sold to the national grid. Hydro electricity can be one of the cheapest methods of providing off-grid renewable electricity, but it is also very site specific.
The best sites are on steep hills, with fast flowing water. One advantage is that on a good site you may not need batteries or alternators as the turbine will produce 240 volts AC and can just be turned on when needed. A good hydro site depends on the ‘head’ of water (the vertical drop) and the flow rate.

How much energy can we get from small-scale hydroelectrcity?
To estimate the energy in a water source, multiply the flow (in litres per second) by the head (in metres) by 10 (acceleration due to gravity). Halve the result, to account for losses and inefficiencies, to get an idea of potential power generation (in watts).
Most micro-hydro schemes are ‘run-of river’ – they don’t have a reservoir and only take water from the stream when it is available. You usually need a drop of over 10 metres for a scheme to be viable.

The Turbines
Highhead ‘Pelton’ turbines are comparatively cheap, easy to install and work well in fluctuating flow. Crossflow turbines are more suitable for lower heads. Other turbines are available; suitability depends on a combination of the available head and flow of water.

What it Costs
Hydro installations and their costs are extremely site specific and thus prices vary widely depending on the type and size of system and how much work you are willing to put in yourself. The basic equipment for a 1kW off-grid battery charging system might cost € 6,000 to €8,000 plus installation costs. It might be possible to DIY a small scheme for under €12,000. In some situations this will be cheaper than paying grid-connection costs.
On the other hand the total cost of a Pelton turbine producing 5kW on a 25m head site might be around €30,000 professionally installed, less on a DIY basis. Larger systems can cost tens of thousands of pounds. There is an economy of scale – a 5kW system may only cost 50% more than a 2kW system. Because of the investment required, it makes sense to minimise energy use first; efficiency measures are a more cost effective way to reduce domestic carbon emissions.

Integration with the Local Power Grid
If your site produces a large amount of excess energy, some power companies will buy back your electricity overflow. You also have the ability to supplement your level of micro power with intake from the power grid. If it is possible to export excess power to the grid it is likely that we have moved from micro to the small scale hydroelectricity generation. More information can be found here and downloaded here in relation to this. Effectively these links discuss issues such as planning permission, Power Purchase Agreement, permission to connect to the electrical grid and any License issues. Issues such as environmental impact can arise witin the panning permission process.

Environmental impact
The ecological impact of small-scale hydro is minimal; however the low-level environmental effects must be taken into consideration before construction begins. Stream water will be diverted away from a portion of the stream, and proper caution must be exercised to ensure there will be no damaging impact on the local ecology or civil infrastructure.

Reliable Electricity Source
Hydroelectricity can produce a continuous supply of electrical energy in comparison to other small-scale renewable technologies. The peak energy season is during the winter months when large quantities of electricity are required.
Suitable site characteristics required
In order to take full advantage of the electrical potential of small streams, a suitable site is needed. Factors discussed above which you need to consider are: distance from the power source to the location where energy is required, stream size (including flow rate, output and drop), and a balance of system components — inverter, batteries, controller, transmission line and pipelines.

Low-power in the summer months
In many locations stream size will fluctuate seasonally. During the summer months there will likely be lessrainfall, flow and therefore less power output. Advanced planning and research will be needed to ensure adequate energy requirements are met.
How to design your project
The Dept of Communications Marine and Natural Resources and the Central Fisheries Board have released a report entitled “Guidelines on the Construction and Operation of Small Scale Hydro Electric Schemes and Fisheries” which can be downloaded from the Central Fisheries Board website as follows:

http://www.cfb.ie/pdf/hydro.pdf

Case Study: Restoration of Cahir Mills, Co. Tipperary.

http://www.sei.ie/Renewables/REIO_Library/Case_Studies_and_Other_Reading/cahirmillsrestoration.pdf

Case Studies
A number of case studies, listed by name, for small scale hydroelectricity can be found below and a map of the known generation sites in Ireland can be found here:

Ballinrobe
cahirmillsrestoration
anargethydropower
kenmarehydropower
bantry
celbridge

Further Information
For futher information you can refer to the attached links:
Download TEA Hydro Resource Report (PDF 608 Kb)
Download Teagasc Small Scale Hydro fact sheet (PDF 111 Kb)
http://www.alternative-energy-news.info/micro-hydro-power-pros-and-cons/