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Q. Where can Solar PV be used?
A. Photovoltaic systems are arranged in modular panels which can be fitted to the top of roofs (looking similar to a Velux roof-light) and in slates or shingles which are an integral part of the roof covering (looking similar to normal roof tiles). Photovoltaic cells can be incorporated into glass for atria walls and roofs or used as cladding or rain screen on a building wall - this is particularly suitable for prestige offices. They can also be attached to individual items such as street lights, parking meters, motorway noise barriers or the sides of bridges. Photovoltaic systems can be discreet through being designed as an integral part of the roof. An ‘invisible’ design using slates or shingles as opposed to an architectural statement is likely to be preferable if in a sensitive area. Ideally photovoltaics should face between south-east and south-west, at an elevation of about 30-40°. However, in the UK even flat roofs receive 90% of the energy of an optimum system.

Q. What is PV?
A. The photovoltaic (PV) process converts sunlight, the most abundant energy source on the planet directly into electricity. The equipment required for this process has no moving parts and as a result requires minimal maintenance. In addition, the electricity is generated with no emissions and no noise.

A PV cell consists of two or more thin layers of semiconducting material, most commonly silicon. When the cell is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC).

The electrical output from a single cell is small, therefore multiple cells are connected together to provide a more useful output. Cells connected in this way are encapsulated (usually behind glass) to form a weatherproof module or panel. Multiple modules can likewise be connected together in order to provide sufficient power for common electrical appliances.

Q.How long has Solar PV technology been around?
A. In 1838 the photoelectric effect was discovered by physicist Edmund Becquerel although it wasn't until the 1950's that the technology was developed enough to produce efficient working cells. During the 50's and 60's Solar PV was put on satellites and sent into orbit but it was still too expensive for general use. The next few decades brought better technology with lower prices and Solar PV was installed in world-wide remote villages to provide electricity for where there was no supply. Grid-connected Solar PV has had a massive growth since 1990's in the more developed countries of the world.

Q. Are photovoltaic panels expensive?
A. Over the last 20 years the price of PV modules have fallen dramatically, from around £15 per Wp in 1980 to current prices of around £3.50 per Wp. That means that a single module, typically generating 60W of power under standard test conditions, now costs around £200 Solar PV is still a more expensive technology than most other forms of renewable energy, but it has many advantages over other systems.

Q. Doesn't PV technology need ’right sunshine to work properly?
A. The electrical output of a PV cell is dependent upon the intensity of the light to which it is exposed. So PV cells will tend to generate more electricity on bright days than when skies are overcast. However, photovoltaics do not need to be in direct sunlight to work, so even on overcast days a PV cell will be generating some electricity.

Q. Is PV suitable for use in the UK?
A. In the UK, we get 60% of the sunlight received at the equator - so there is still a lot of potential energy available! PV has been used in the UK over the last 20 years or more for many applications, particularly in remote areas where grid connection is impractical, such as weather monitoring stations, marine navigation aids, etc. Over the last few years PV technology has also started to be introduced into urban areas, incorporated into the roofs and facades of homes, offices and factories.

A modest sized domestic grid connect system will provide a substantial portion of a households electricity needs for over 6 months of the year and installations on commercial buildings are particularly suitable, meeting the daytime demands of an office. Over 1.5 MW of building integrated PV is already installed in the UK.

Q. What applications are suitable for solar PV?
A. PV technology has many applications in the UK, both for stand-alone systems and for integration onto buildings. PV has been used for many years in the UK in applications such as monitoring stations, radio repeater stations, telephone kiosks and street lighting to name just a few examples. There is also a substantial market for PV technology in the leisure industry, with battery chargers for boats and caravans, as well as for powering garden equipment such as solar fountains.

In more recent years in the UK, PV has become more widely used in urban areas, where it can be integrated into new buildings or mounted onto existing buildings. This is a rapidly growing market in the UK and throughout Europe. PV technology is ideally suited to the urban environment, providing pollution and noise free electricity without using extra space. PV technology is also widely used in the developing world. The technology is particularly suited here, where electricity grids are unreliable or non-existent, with remote locations often making PV power supply the most economic option. In addition, many developing countries have a high level of solar radiation levels year round.

Q. How long will a system last?
A.The average lifetime of a PV module can be in excess of 20 years, crystalline silicon modules in particular have a very long life span. In addition, they require very little maintenance. Other system components will have a varied lifespan, for example batteries in stand-alone systems can last between 2 and 15 years depending on type.

Q. How much will I need to power my home?
A. A typical domestic system of 1.5 kW in the UK would produce around a third of the annual demand of an average family household (taking the average demand to be around 10 kWh per day). However, calculating the system size depends on many factors, for example whether the system is grid connected, energy demand of the household etc.

Q. What is the efficiency of the Solar panels?
There are different types of solar panel technology and the size of available roof space, angle to the sun, pitch of the roof and budget will have an effect of how much solar electricity you can produce. Below is an overview of the different solar panel technology.

Monocrystalline

• High efficiency and fairly expensive
• Prefers high-light conditions
• Power output c780 units/kWp/year
• Power density = 120 Wp/m2
• Charcoal ordark blue

Polycrystalline (‘multicrystalline’ or ‘thickfilm’)

• Lower efficiency and less expensive
• Prefers high-light conditions
• Power output c720 units/kWp/year
• Power density = 120 Wp/m2
• Shiny and spangly blue

Amorphous ('thinflim')

• Loves low light conditions and cheap but you need a very big area to put it on.
• Power output c900 units/kWp/year
• Power density = 62 Wp/m2
• Dark brown or dark blue

Hybrid

• Combines monocrystalline and Charcoal amorphous technology.
• High efficiency in both high and low-light conditions
• Power output c900 units/kWp/year
• Power density = 156 Wp/m2
• How much Power can I expect to get from my PVs?
• Typically a 1kWp array will produce 750kWh/year

Q. Why are PVs rated in Wp rather than watts?
A. Wp means peak Watts. In other words, a 100Wp panel will produce a maximum of 100W in peak conditions (1kW/m2 solar irradiation) - this is equivalent to a bright sunny midsummer day in the UK

Q. How can I connect my system to the grid?
A. You will need to use a grid-tie inverter. If you wish to get paid for the electricity you produce, you will need to ensure a G83-certified inverter is used. However, many people use non-G83 certified inverters, and simply do not bother with an export account. In many cases the household will always be consuming more electricty than that being fed into the grid, therefore, the net effect is zero export

Q. Is it true that I can get my electricity meter to spin backwards?
A. Not usually, nor is it legal to do this. The very old meters may cause this to happen, but most have a rachet-type mechanism to prevent this from occuring.

Q. How much will I get paid for the electricity I feed into the grid?
A. If you shop around you can expect 8-10p per kWh plus another 4p/kWh for the ROC entitlement, although the necessary paperwork may not warrant the effort for the ROC payment.

Q. Why install a PV system?
A. There are many reasons to install a PV system:

• It is the most practical and economically viable option for many applications in remote areas
• It is completely pollution free. Installing a small domestic system of around 1.5 kW would provide around 1000 kWh of electricity every year, this would save around half a tonne of CO2 annually
• PV can be integrated into the fabric of a building
• Electricity can be supplied at the point of use
• The system will run silently
• There is very little maintenance required for a PV system
• After the initial installation costs, there are no further fuel costs
• PV systems are modular, and can be added to at any time

Q. Are there any planning issues?
A. One of the conditions of the grant scheme is that you have received planning consent from your local council - please note, this is different from planning permission. For the majority of homeowners the addition of solar PV panels fall within 'permitted development rights', which means that the panels will be more or less flush with the roof. If your property is in a conservation area, Area of Outstanding Natural Beauty or is a listed building you may need to apply for full planning permission. We recommend checking with your local council to see what their stance is on solar PV panels, although most people install PVs without doing this.

Q. Will a solar panel produce electricity on a cloudy day?
A. Yes, a solar panel does produce electricity even when it is not placed in bright sunlight. On a normal cloudy day there is always enough so-called diffuse light, by which the panel will produce electricity. However, the production of electricity is not as high as when the panels are placed in bright sunlight.

Q. Will solar panels work in the winter?
A. Yes, solar panels work on light not heat. The amount of sun hours will be less in the winter, as the sun rises later and sets earlier.

Q. Will a solar panel supply electricity 24 hours a day?
A. No, solar panels convert light into electricity. So as the light reduces in the day so does the output of the solar panel.

Q. What size solar panel do I need?
A. This depends on the load you have connected to the battery. You will need to calculate the watt-hour or amp-hours you are using in a period of time (see FAQ How to calculate your solar panel needs), then having a rough idea of the amount of direct sunlight your solar panel will receive each day. The solar panel needs to supply approximately 20% more than your needs to compensate for variables, such as cloudy days etc. Obviously the winter will have shorter sunlight hours per day than the summer, but you can work on an average of approximately 4 hours sunshine a day in the UK over a year.

Q. What is a blocking diode?
A. This is a component connected within the cable that prevents the solar panel discharging the battery when there is no sunlight.

Q. What is a charge controller?
A. This device controls the charge to the battery. When the battery is fully charged the controller disconnects the solar panel from the battery.

Q. Do I need a charge controller?
A. We recommend that charge controllers are used with 15watt solar panels and above.

Q. What is an inverter?
A. An inverter takes the DC (direct current) from the solar panel and creates a useable form of AC (Alternating current). Inverters are power hungry, so it is best to purchase (if possible) a product that operates on 12vdc.

Q. Can equipment be used directly from solar panels?
A. Yes, solar panels will run equipment direct, these could be loads such as fans & pumps, but make sure the load of the equipment is not equal to the output of the solar panel, as overcast or cloudy days will reduce the output. Solar panels with not run TV's or radio's (without battery backup), as they require a more stable voltage.

Q. Is maintenance required on solar panels?
A. Clean using a non-abrasive cleaner. In the long term check the sealing especially in marine use and reseal with a silicon sealant if damage is suspected. Check battery connections periodically when you check battery levels. Fuse holders and connections should be kept dry and clean.

Q. What are the possible problems?
A. Failure of a solar panel is normally due to water damage to the panel itself or the connections. Also damage to the sealant around the frame could cause failure. Mounting the panel incorrectly. If it is fixed horizontally it may be able to collect water. Not a sufficient air gap beneath the panel can also cause damage.

Q. What problems might there be with mounting a solar panel?
A. Try not to fix panels horizontally as rain will collect in the frame and not cleaning the panels will reduce the output. Make sure there is an air gap beneath the panel.

Q. How to calculate your solar panel needs?
A. Battery Ampere Hour: The amp hour (ah) rating of a battery tells you how much amperage is available when discharged evenly over a period of time. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for a given period, you have to divide the amp hour rating by the amount of hours the load will be used.

Example: If a battery has an amp hour rating of 85, and it will be used for 20 hours dividing 85 (ah rating of battery) by 20(hours of load) = 4.25. Such a battery can carry a 4.25 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) Please be aware that it is not a good thing to discharge the battery fully. If the battery is fully discharged the solar panel may not be able to start the recharge, so add at least 15% more to you battery needs.

Please remember that these examples are for guidance only. The ratings of Solar panels are calculated in bright direct sunlight. Conditions such as indirect sunlight, cloudy, hazy conditions and partial shade will decrease the output. Also the length of daylight i.e.: summer vs. winter.

Calculating power using current and voltage
There are three ways of writing an equation for power, current and voltage:

Power = Current x Voltage so:

P = I x V
or
I = P divided by V
or
V = P divided by I

Where:
P = power in watts (W) P = power in milliwatts (mW)
V = voltage in volts (V) V = voltage in volts (V)
I = current in amps (A) I = current in milliamps (mA)
A milliwatt is a 1000th of 1 watt
A milliamp is a 1000th of 1 amp

Example: A 12 volt 15 watt solar panel in peak light conditions will give approximately the following current using one of the above equations. We have the 2 variables, volts and watts so the following equation can be used:

I = P divided by V
I = 15 divided by 12 =1.25 amps

So as the formula states that a 12 volt 15 watt solar panel in peak light conditions will supply a current of 1.25 amps.

Example: If we say that a 12 volt 15 watt solar panel will supply 1amp-hour (average) for a period of 6 hours (in the summer) it will replenish the battery with 6amps in a day. If you have equipment which is connected to the battery that use more than 6amps per day then the solar panel you have may not be sufficient for your needs, as it will eventually drain your battery.

Please remember that these examples are for guidance only. The ratings of Solar panels are calculated in bright direct sunlight. Conditions such as indirect sunlight, cloudy, hazy conditions and partial shade will decrease the output. Also the length of daylight i.e.: summer vs. winter.

Appliance Test Information

The following 240V appliances were tested using a 12v leisure battery and a Power Inverter High Quality 400-800 Watt to find out their approximate power consumption when using an inverter, as a guide for our customers when working out what solar panels and equipment to use:

• 240V Radio Cassette Player = 700mA
• 240V Home Computer (base unit) = 8 amps
• 240V Computer Monitor = 6 amps
• 240V Light Bulbs - for every 10 watts allow 800mA
• 240V Small Marshall practice amp & electric guitar = 900mA

 

Please feel free to get in contact with us by email or call 0845 189 9894 to discuss any of your requirements.