Photovoltaic (PV) Panels
1) What are PV panels and how do they work?
Photovoltaic Panels convert sunlight directly into electricity with no polluting emissions and no noise. The electricity is in the form of direct current (DC) at 12, 24 or 48 volts.
PV cells are most commonly made from silicon. When the cell is exposed to light, electrical charges are liberated and are conducted away by metal contacts. The electrical output from a single cell is small, and so multiple cells are connected together. The cells are then encapsulated to form a weatherproof panel.
2) How big are the panels and would my roof be strong enough for a PV array?
A panel of 100 W peak power has an area of about 0.8 m2 and the mass is about 10kg. Therefore an array of 10 panels providing about 1kW peak-power would have a mass of about 100kg. The weight would be distributed over an area of about 8m2 and thus there would normally be no problems concerning roof strength.
3) How much energy can be expected from a PV array over a period of one year?
An array of 1kW peak power optimally installed should provide 700 – 800 kWh/year in central UK. Assuming a mean forward cost of domestic electrical energy of £0.2 /kWh, this would give a saving of up to £160 / year or £800 over 5 years.
4) What is a suitable location for an array of PV panels?
An unshaded south facing roof inclined from 30- 50 degrees to the horizontal will give the best results. Panels facing from southeast to southwest will provide 80 % -90% of the optimum power. Panels can also be mounted on inclined stands in unshaded locations near to ground level.
5) What other equipment is required to make a complete PV system?
A charge controller and deep-cycle batteries are required to store the energy. To power low current mains voltage appliances, an inverter would also be needed. A suitable PV array and charge controller could also be used to charge your electric bicycle or car.
6) Do PV panels require bright sunlight to produce electrical power?
The power output of a PV cell depends upon the intensity of the light. So PV panels will generate more power on bright days than overcast days. The human eye compensates for the very large difference in solar intensity between a bright and an overcast day. Solar panels cannot do this however, and their output is much reduced under cloud. But they do not need to be in direct sunlight to work and provide some useful power.
7) What is the useful lifetime of a photovoltaic panel?
The lifetime of a PV panel can exceed 25 years without an appreciable loss of effectiveness. Monocrystalline silicon modules in particular have a very long life span. Other system components will have a more limited lifespan. For example batteries in stand-alone systems can last from 5 -15, years depending on type.
8) Is planning permission required in order to install a PV array on a house roof?
Roof mounted systems do not normally need planning permission unless the property is listed or in a conservation area. However it is wise to refer to the local planning authority when you are planning an installation. Planning permission is usually sought for larger systems that are eligible for a grant.
9) Are solar PV arrays suitable for DIY installation?
A stand-alone system (not connected to the grid), is suitable for DIY installation, provided that you have the appropriate building and electrical skills. The relevant codes of practice and legislation are contained within:
British Standards, BS EN 61215 and BS EN 61646
The Electric Supply Regulations 1988
The Building Regulations 1991 (and amendments)
The Construction (Design and Management) Regulations 1994
There are a number organisations that provide both advice and/or short courses to help DIY installers.
10) What is the energy and cost payback time for a PV array?
The time for a PV panel to payback the energy used in its manufacture is at present 1-3 years. The significance of this fact depends, of course, on the source of the energy used in the manufacturing process. The cost payback time for the panels themselves would be about 10 years at a price of £2,000/ kW peak and 5 years if the price were £1,000/ kW peak.
11) Are PV panels easily damaged and do they require regular maintenance?
The panels are very strong and they are not usually damaged by environmental forces such as hail or high winds. Being mounted inclined they tend to be self-cleaning, but they may be washed with a hose or soft brush if it is necessary. No regular maintenance is required for a PV system.
12) Are grants available for installed PV systems?
A grant of up to £2,500 or 50% of the installed cost may be available through the Low Carbon Buildings Programme. The property must reach a minimum level of energy efficiency and you must have any required planning permission before a grant is applied for.
Ground Source Heat Pumps
1) What use can be made of a ground source heat pump (GSHP)?
A GSHP absorbs heat energy from the ground and this can be used to warm water for radiators or under floor heating. Alternatively it can be used to pre-heat domestic hot water. A GSHP usually requires an external source of electricity to power a compressor. At least for smaller heat pumps, solar photovoltaic panels can be used for this purpose, thus making a GSHP potentially autonomous.
2) Is my property suitable to install a GSHP?
Internally, the equipment needs only about the same space as a domestic appliance, such as a refrigerator. Externally, a garden or stretch of land suitable for digging a trench or a borehole is required. The land area does not need to be very large. For example, for under floor heating about twice the heated area is needed to lay the ground loop coils.
3) Can a GSHP satisfy all of the space heating or hot water demands for an average household?
This is possible, provided that a device of sufficient capacity is installed and that a large enough area of suitable land is available. In most cases however it is preferable to use a GSHP in conjunction with another system so that a backup is always available. For example to periodically raise the temperature of a domestic hot water tank above 60 deg. C in order to sterilise any legionella bacteria.
4) To provide domestic hot water will I need to replace my (vented) hot water cylinder?
A GSHP is used as part of an indirect system; therefore a twin or triple-coil cylinder is required. As an alternative to replacing your existing cylinder, one can install a separate cylinder to hold the pre-heated water.
A GSHP can be used together with a solar thermal panel (and also perhaps a wind turbine) as part of a year round zero carbon hybrid system. (In fact, this is one of Solar Collect’s project goals.)
5) How does a GSHP actually work?
A mixture of water and antifreeze is circulated at low pressure through a loop of pipe buried in a trench 1-2 m below the surface of the ground. Heat energy is absorbed from the ground and stored in the fluid as latent heat of vaporisation. The vapour is compressed and the temperature is raised to about 50 deg C so that the heat energy can be delivered to the building or hot water tank.
6) Are ground source heat pumps freeze resistant?
In the UK the temperature of the ground more than 1 m deep is, on average, about 12 deg. C and it does not vary by much all the year round. Therefore variations in the air temperature have very little effect on the performance of the device. Most GSHPs have an environmental operating range of about -20 deg C to +40 deg. C, which is greatly in excess of the normal seasonal variation in air temperature.
7) Can a GSHP be used with a combination boiler?
Renewable energy devices usually require an energy store, hence the need for some form of hot water tank. Older “combi” boilers would need to be replaced, but newer types may accept pre-heated water from a storage tank.
8) Can GSHPs be used for space heating?
Traditionally, larger GSHPs have been used to power under floor heating systems where a flow temperature of only 45-50 deg. C is required. More modern heat pumps will provide an output at temperatures in excess of 65 deg. C (but with some reduction in efficiency) and therefore can be used with radiators. These systems are, of course, more expensive and have a longer payback time.
9) Is planning permission required for a ground source heat pump?
Planning permission is not normally required in the UK. There are no external visible works once the device is installed. However it is advisable to check to find out if any special local regulations apply.
10) Are ground source heat pumps suitable for a DIY installation?
Basic plumbing, building and electrical skills are all that is required for a successful DIY installation. Our GSHPs are sold with comprehensive installer manual and operating instructions.
11) How long will the GSHP last and what maintenance is required?
GSHPs have an expected working life of 25 years with a minimum of maintenance. Some products require a simple annual visual check and a cleaning of filters, but there is no scheduled servicing. The performance of the device does not deteriorate over its lifetime.
12) What energy savings can be made with a GSHP?
The savings are measured by the Coefficient of Performance (COP). This is the ratio of heat output to energy input (used to power the compressor). It is expected that an appropriately installed heat pump would have an operating COP of 3-4. This means that it would deliver 3 to 4 times as much energy as it consumes.
13) What energy cost savings can be expected for a GSHP?
A GSHP, used to provide domestic hot water, and supplying 1500 kWh / year of energy would consume about 450 kWh / year of electrical energy. This would save the householder about 1000 kWh / year in electrical energy costs. At a forward price of £0.2 /kWh, this would amount to a saving of £1000 over 5 years.
A PV array of about 1 kW peak power could provide 700 kWh / year of electrical energy for the compressor. The potential savings on electricity costs could then amount to £1500 over 5 years.
14) Are grants available for installed GSHP systems?
A grant may be available through the Low Carbon Buildings Programme. The property must reach a minimum level of energy efficiency and you must have any required planning permission before a grant is applied for.