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Is Solar for you?
A summary and comparison of Solar PV and Solar thermal systems
| SOLAR PV | SOLAR THERMAL | ||
| What is Solar? How does it work? | PV stands for photovoltaic, a technology that converts the sun’s radiation directly into DC electricity. They do this by using a thin layer of semi-conducting material. When the material is exposed to daylight, electrons in the material become energised and are able to flow through the material, generating a DC current. This current is then directed through an inverter to convert it into AC current, which can be used in the home. |
There are two types of solar thermal panels: flat plate panels or evacuated tubes. The collectors absorb solar radiation from the sun, which heats up a working liquid. The solar panels are connected to a hot water cylinder via insulated pipes which allows the heat to be transported. When heat is gathered in the water cylinder it can then be used by the boiler for distribution. A small pump distributes the liquid back to the solar panel for re-heating. |
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| Is my home suitable for a solar installation? | PV panels may require up to 20 m2of roof space, with systems installed on south-facing roofs will yield the best results. If there are no suitable roofs a system can be fitted on the ground or a wall hanging. It is not recommended to install PV panels on north facing roofs. | For conventional solar thermal systems, you’ll need around 2-4 m2of roof space. A solar thermal system requires a hot water cylinder, which stores the hot water for later use, so you will need to install one of these if you do not have one. Connections also need to be made with the existing heating system. | |
| Is it easy to install? | Installation will involve the bolting the PV array onto the roof. A Solar PV is simple to install, usually taking a day or two and with minimum disruption to the household. | Installing a solar thermal system can take from 2-3 days. You should expect some internal and external disruption for installation of panels and the cylinder. You may be without hot water for a day. | |
| Will my system be grid connected? | If the system is grid connected, this means that when the system is producing electricity, but the household is not consuming it, it will be sold back to the grid. Domestic PV systems are such, so as to benefit from export tariffs. Solar thermal systems are not grid-connected; they only produce and store hot water in a household. | ||
| The UK doesn’t get enough sunshine for PV to make sense | A common misconception is that a solar cell needs direct sunlight in order to create electricity. It’s not so much about the amount of sunshine, rather the intensity of the light. So even on a cloudy day, PV cells will still create electricity, and solar thermal panels will still contribute to heating up the water, albeit to a lesser degree. Ultimately, the systems performance should be based on its average performance over the year, and its total yearly output will provide a significant contribution to your household. | ||
| The following calculations are based on a 4kW system, tilt angle 30⁰, facing directly south. | The following calculations are based on a typical £4500 system generating 1500kWh per year. | ||
| What size of system will I need? | This depends on your household energy demands, how much you are willing to spend in installation costs, and what projected savings you wish to fulfil. A typical PV system will between 2.8kWp and 4kWp. Solar thermal systems do not tend to vary too much. | ||
| Carbon emissions saved | Solar PV systems replace grid electricity. A gas boiler is highly efficient, and this is the energy that your solar thermal system will be replacing. So per unit generated, power from PV will save up to twice the amount of carbon emissions than solar thermal. | ||
| Energy Savings | A typical solar PV system in the UK will produce around 850kWh per year per kWp. However, as the energy that isn’t used is exported to the grid, energy savings depend on your electricity usage patterns. Energy bought from the grid costs 15p/kWh, but energy exported is currently only worth 3.2p. The biggest saving are made by systems timed to heavily use electricity during daytime hours during the daytime rather than exporting it back to the grid. | A typical solar thermal system will meet 50-60% of a households hot water needs translating to an average savings of 1,500 kWh/year. Savings depend on what sort of resource is being replaced; typical savings are £80/year when replacing gas and £230/year when replacing electric immersion heating. The timing of back-up heater relative to water use is the main factor as to how much solar energy the system intakes. | |
| Are there government incentives for solar systems? | The Feed-In Tariff (FIT), is paid by the Government as an incentive for people to generate their own electricity. From 1st August: 0-4kWp installation will have a generation tariff 16p and an export tariff of 4.5p with a guaranteed lifetime for 20 years, index linked with the RPI. | The Renewable Heat Premium Payment is a one-off £300 grant designed to help towards meeting the costs of installing renewable technologies in your home. The second phase of the RHI, which will offer payments to domestic users, is scheduled for consultation on October 2012, for deployment in 2013. | |
| Installation costs | A typical 4kWp system should cost around £8,000. From 1st August 2012 with a FiT of 16p, this will give a return on investment of 9.2%, after taking into account incomes from generation and export tariffs as well as energy savings. This is guaranteed for 20 years and is index linked to RPI. The payback period would be 10 years. | The cost of installing a typical solar water heating system is around £4,500 (including VAT), depending on the size and type of the system. It is anticipated that there will be a domestic Renewable Heat Incentive (RHI) which would offset some of the cost of installation. | |
| Is a solar system easy to maintain? | Little to no maintenance is required for a PV system, though you’ll just need to make sure trees don’t begin to overshadow them. It is advised that the installation is checked once every 3 years to ensure peak performance. | From time to time, you should check whether there are any leaks in the system. It is generally recommended to replace the anti-freeze every 3-7 years, costing approximately £100. The pump in these systems normally last for over 10 years, and then can be replaced for about £90. | |
| How long will the system be fully functional? | The panels will last beyond 25 years and the only item that needs to be replaced is the inverter, every 10 years or so, at approximately £1200. | Once installed, solar thermal systems can operate for 10 more years without having to change any components, and entire systems last for up to 25 years. | |
| Will I require planning permission? | Although planning permission for domestic solar installations is not generally required, there are still occasions when either general planning permission or listed building consents must be sought. Always check with your local planning department planning requirements. | ||
| I have decided i want to install a solar system. What should I do now? | To ensure your installer is reputable and for you to obtain government incentives, you must verify that they are acknowledged by the certified by the two government schemes approved for renewable installations: the Microgeneration Certification Scheme (MCS) and Renewable Energy Association Scheme Ltd (REAL) Assurance Scheme. To verify that any installers you contact are MCS certified by visiting the official websites at microgenerationcertification.org and realassurance.org.uk. | ||
| So which is better….? | If your household uses a lot of hot water and not too much electricity during the daytime, you may get better savings from a solar thermal system. If you use electricity heavily during the dayime, then PV will be a better investment. Ultimately, it all depends on your usage passage patterns. | ||
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