Solstice Energy
About Grid-Connected Photovoltaics
Overview
Since the 1970's PV's have been developed to work as an alternative energy source to fossil fuels. Now, every un-shaded southerly facing roof has the potential to produce electricity.
Rather than having just a handful of ageing and polluting power stations we now have the possibility of decentralisation; millions of small generators producing power where it is needed, also solving the problem of large energy losses during transmission.
Although photovoltaics work better in direct sunlight, they are not reliant on it. They only need daylight to produce electricity.
Photovoltaics have no moving parts and are very reliable. Most PV modules are guaranteed for 20/25 years, with a life expectancy far exceeding this.
PV's are silent and unobtrusive, they are designed to withstand the elements and weather very little with age.
Roof Suitability
Positioning
Photovoltaic modules will usually be mounted on a Southerly facing, pitched roof.
The "solar sundial" below shows that a fair bit of deviation in the positioning of a PV array will still yield a large percentage of the energy expected from an optimum orientation (a pitch of 30/40 degrees facing due South).
Shading
Whenever shading decreases the power output of any one module in an array, then the output of the whole array is similarly decreased. It is therefore very important to avoid shading (from trees, other buildings etc) when siting a PV array. However, if, for example, the shading only occurs late on winter afternoons then it will have less impact on the annual output of the array than shading that occurs every morning until 11:00.
Roof Area Required
Allow approximately 8m2 of pitched roof area (16m2 of flat roof) for every 1kWp of PV.
Obstructions like dormer windows and roof vents need to be considered when surveying the site.
Planning Permission
Planning permission is not normally required unless it is a listed building or in a conservation area. You should check with your local council.
Terminology
- Module
- A PV (photovoltaic) panel, which is made up of a number of 'cells',each of which produces a small electrical charge under light.
- kWp (kilo-watt peak)
- The number of thousand watts a photovoltaic system will produce in peak conditions.
- kWh (kilo watt hours)
- A unit of electricity. This is defined as power of 1000 watts (being consumed or produced) over the period of one hour. e.g. 2000w over 1/2 hour or 100w over 10 hours.
For example: A PV module could have a rating of 200 Wp (produces 200 watts in peak conditions). 12 modules are connected together on a roof to form a 2.4 kWp array.
(200 * 12 = 2400 Wp or 2.4kWp)
Electricity Produced
Daylight levels in the UK mean that PV will produce an average of 820 kWh of electricity per kWp system size, per year (South-facing & un-shaded).
As an example, an average household uses around 3000 kWh per year (so a 1kWp system would supply a quarter of the yearly use). Simple energy efficiency measures in the building will increase the proportion of energy coming from the Photovoltaics.
Exporting your electricity
There are two ways of storing the electrical energy produced by a photovoltaic array. One is by using batteries in a "stand alone" system (the remote village, boat, caravan etc); the other is by connecting to the national grid.
In a "grid connect" system, the grid works in effect as a battery. During the day the PV array might produce more energy than is required by the building it serves. This excess can be exported to the building next door or down the road via the mains. In the evening, or any other time of high use / low sun, electricity is drawn in the usual way from the grid.
At times of high production / low use the electricity you have produced will leave you in credit with your supplier and you can expect payment for this. Electricity suppliers getting their chequebooks out for their customers is a photovoltaic phenomenon! The electricity companies all run different buyback schemes which suit different patterns of use. We can advise you on your options, and you may want to switch electricity supplier to get the best deal for you. This can be done at any time before or after our installation.
If for any reason the mains electricity fails, the PV system will shut off. This is a safety requirement designed to protect workers on the (supposedly dead) grid from getting a shock. The system will restart 3 minutes after restoration of power.
Grant Funding
An example 5kWp retro-fit system will typically cost around £26000. This is excluding VAT which is set at 5% for domestic or not-for-profit organisations. Integrated PV systems cost around a third more than retro-fitted systems.
Low Carbon Buildings Programme domestic grants are available up to £2500. This grant funding is given on the condition that you reduce your electricity and heat demand as far as possible and practicable through cost-effective energy efficiency measures. These measures include low energy light bulbs and energy efficient appliances; or your loft and cavity walls (where they exist) are insulated accordingly.
Public and community buildings are also eligible for 50% funding, through Phase 2. Phase 2 is an 18 month programme with £50m of funds earmarked for the installation of renewable energy on public and community buildings.
The Financial Argument
PV generated electricity is inflation proof, and few observers of the worlds fuel situation and of our own dilapidated power stations would expect electricity prices to just stay in line with inflation. As electricity prices increase, the PV's become more valuable and will pay for themselves at an increasing rate.
With environmental concerns becoming more politically relevant, future legislation is likely to work more in favour of electricity from 'clean' generation, and increase the cost of electricity from polluting sources. Already, Renewable Obligation Certificates (ROC's) have paved the way for some electricity companies to offer payment for PV generation even if this power is used on site by the owner of the system. This means PV system owners can earn and save money at the same time just by using power during the day. See our case study for a more detailed analysis
A PV installation is an addition to the value of the building.
PV modules are normally guaranteed for 25 years. However, there are no degradable parts and no reason why they will not carry on working for 50 years.
The Environmental Argument
There is a growing awareness that the release of carbon into the atmosphere by burning fossil fuels causes global warming. The graph below shows the time frame that this is happening in:
- 580 billion tonnes of CO2 was naturally present in the atmosphere until around the time of the industrial revolution. This is known from the study of ice core samples.
- Present day levels are just under 800 billion tonnes, largely through accelerated fossil fuel burning since the Second World War.
- 980 billion tonnes is the level by which a 2-degree increase in global temperature is expected to have occurred. This would have a disastrous effect on climate, sea levels, etc.
- 1050 billion tonnes is regarded by many scientists as an intolerable level that will result in ecological catastrophe.
- The increase from the present day, as shown on the graph, is based on the present emissions of 6 bn tonnes of CO2 per year due to burning fossil fuels.
- Figures from "The Carbon War" by Jeremy Legget and the IPCC (Intergovernmental Panel on Climate Change.
For every kWh of energy generated by a renewable source, there is a carbon saving of 0.43 kg (Energy Savings Trust). This may seem a drop in the ocean compared to the figures in the graph above, but the real difference is the effect on attitudes that your system will have. We will all have to turn to renewable energy sooner rather than later, and your PV system will be an encouragement to others to do the same. For installations on commercial and public buildings it is always a good idea to install a large display meter - as well as bringing excellent PR, it is a source of education.