Solar
Solar power comes in several forms. One type of solar panel heats water, another type creates electricity (PV) and a third type of energy can provide warm (or cold) air to heat a building (In Ireland these are suitable for a workshop or holiday home).
The direction your roof is facing (orientation), the slope of the roof and shading are important factors, regardless of the type of panel you are interested in:
Orientation & Tilt angle
In the Northern Hemisphere the sun travels across the Southern sky, from East to West.
Your panels should be facing somewhere between South-east and South-West or else you will need panels on your East and West rooves.
The diagram on the left shows the best orientation for solar panels in green, yellow and red. With the angle of most rooves, a roof facing anywhere between Southwest and Southeast will only have 10% less efficiency, at worst, than the best or optimum southerly location. Click on this diagram, to zoom in more.
In a perfect world, people would tilt their solar panels differently at different times of the year to maximize solar radiation. For an Irish house, the perfect angles for your panels would be around 63º in the Winter and 43º in the Summer. However, as most sun arrives in Summer, a roof of 45º or so, makes sense. (An angle of 60º will get more benefit from panels during the Winter) The annual energy collection only varies by a maximum of 10% for rooves between 20º and 40º, if between 30 degrees east of south and southwest.
Shading
You may have the perfect orientation and tilt angle on your roof but if there are several large trees blocking the sun, then the efficiency of the panels could be reduced. Shading is an important thing to consider, when installing panels. Trees are not the only concern; chimneys and other buildings could also have an impact.
How do Solar Panels work in Ireland?
The reason that solar panels work well here is that there are two types of solar radiation; diffuse and direct. Direct happens on cloud free days, when the sun is beaming. Diffuse radiation accounts for about 60% of the solar radiation that we receive in Ireland and occurs on cloudy days. Both types of radiation allow solar panels to operate.
Solar panels that generate electricity are called Photovoltaic or PV for short. Solar power that heats water is usually referred to as Solar Thermal. For more detailed technical information on how each of these solar energy systems work, click here.
On a bright, sunny day the sun shines approximately 1kW or 1000W of energy per m² on the planet’s surface. The table below shows the monthly solar irradiation (kWh/m²per day). In Dublin this varies from 450W in winter to 4.77 kW in the summer sun. For further information on solar radiation around the world, see the table below.
Solar Panels for domestic hot water heating is the most common use of solar panels in Europe, at present. Part of the reason for this is is that PV panels are currently more expensive than solar thermal panels.
The two most common types of thermal panels in Ireland and Northern Europe are;
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Flat-plate panels
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Evacuated tubes.
A flat-plate panel essentially consists of a layer of glazing, an absorber plate and insulation in a box.
Evacuated tubes use tubes that look similar to fluorescent bulbs. They contain a strip of absorber plate in a vacuum, which acts an insulator.
There is much debate about which panel is better suited to the Irish climate. Evacuated tubes are in vogue at present. The efficiency of the absorber area in evacuated tubes is about 15% better but there is less of it than on a flat-plate. So a good flat plate can often be more efficient. The flat-plate panel is also less complicated and is likely to last longer without problems.
At BEO, we sell both types of panel. For objective information on the evacuated tube Vs flat-plate discussion, click here.
Finance and Pollution.
"Off-the-shelf" solar panels are one of the most cost-effective renewable energy solutions out there. Many people ask about payback on solar panels. It is funny how this question is never asked about cars, for example. The lifetime of a good flat-plate panel (in-roof installation) could be estimated at 25 years plus. For a building that uses hot-water predominantly in the summer time (e.g GAA club or B&B), the payback may be less than 10 years. For the average domestic house, I estimate the payback to be at least 10 years. For people who like baths and take two showers a day, the payback will be less. For those who don't use as much hot water, the payback will be longer. People that are good with their hands, might consider a DIY solar course which could be the most cost-effective solution of all.
In Ireland most electricity generation pollutes. Because of agreements made years ago (e.g the Kyoto protocol in 1997), pollution now equals expense. In future, electricity will rise in price. In the coming years, the more (non-renewable) electricity and fossil-fuels you use, the more you will foot the pollution bill.
Government grants are available in Northern and the Republic of Ireland. In the Republic, a recent scheme called Greener Homes Scheme from SEI (Sustainable Energy Ireland) makes a grant of several hundred per m² of solar panel available. In the North, the following information from the Action Renewables website maybe useful ”On 24th July 2006, the Household Programme officially opened for applications. The aim of the programme is to enable at least 4,000 private households to install solar thermal, PV, wood fuelled heating, ground source heating, or wind energy systems. The total funding allocated to this programme, over two years, is £8m.”
For further information on domestic grants contact SEI or Action Renewables.
For commercial buildings, see here.
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