Raine or Shine

Frequently Asked Questions

PRACTICAL RENEWABLE ENERGY

How to design and implement your own renewable energy systems in the real world

Customers often ask us to advise them what renewable systems they require, such as how many solar tubes they need to provide their hot water. It is important to realise that as well as the differing environmental factors that may apply to a particular site, there are also personal considerations that need to be taken into account.

If the following text does not answer your question, please call 01978 664114 or email info@raine-or-shine.com

Solar Photovoltaics (electric-generating panels)

What is PV?

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.

How long has Solar PV technology been around?

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.

Are photovoltaic panels expensive?

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.

Doesn't PV technology need bright sunshine to work properly?

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.

Is PV suitable for use in the UK?

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.

What applications are there for PV?

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.

How long will a system last?

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.

How much will I need to power my home?

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.

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.

How much Power can I expect to get from my PVs?

Typically a 1kWp array will produce 750kWh/year.

Why are PVs rated in Wp rather than watts?

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.

Can I connect my system to the grid and be paid for the electricity I generate?

Yes you can! Under the new feed-in tariffs passed by the government at the beginning of April 2010 you can now be paid back for photovoltaic power you generate. In order to benefit from the feed-in tariffs, you will need to have MCS (Microgeneration Certification Scheme) approved equipment installed by Raine or Shine as MCS approved installers. Raine or Shine supplies complete MCS Approved kits in our online shop or at our showroom.

Is it true that I can get my electricity meter to spin backwards?

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.

How much will I get paid for the electricity I feed into the grid?

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.

Why install a PV system?

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.

Are there any planning issues?

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.

Solar Water Heating

There are various solar water heating technologies. Flat plates are very effective in the summer, not not so good during the other seasons. Vacuum tubes will perform with similar results in the summer, but will vastly exceed the performance of flat plates during the rest of the year. Ideally a vacuum tube system should be orientated facing South, although SW or SE is almost as good, losing only around 15% of the available heat. If you are forced to use an East or West roof slope, then you will need to double the number of tubes to get the same output as a south facing system. The panels should be angled at your angle of latitude - so for example in the UK, it would be around 53°. In fact, up to 15% deviation from this will only result in a small reduction in efficiency (~5%), so it usually makes more sense to mount the panel at the same angle as the roof.

Off-grid systems

The constant power requirement of the controller, and the 40watts required by the pump is often viewed as excessive by off-grid system designers. Many have seen a system where the pump is powered by a solar PV panel. This is a bad idea for two reasons:

1.Solar-powered pumps do not work in low-sunshine conditions...whereas the vacuum tubes can still get very hot even in overcast weather.

2. The low voltage DC pumps are too low a wattage for solar vacuum tubes. A 20tube panel requires a minimum of 20-30watts of pump power in hot weather, and a 30tube system really requires 40watts.

An alternative is to power the system using a UPS (uninteruptible power supply) which can in turn be charged by solar PVs. This way, it is possible to run a full 40watt pumped system, without relying on mains power.

Be careful - some UPS systems use a lot of power in standby mode - 70-80watts minimum power consumption is quite common. We have selected a french system which requires only 3-4watts whilst powering the solar controller - which we can supply if required.

How many Solar Thermal panels are needed?

Even a small number of solar vacuum tubes will make a difference to your hot water heating requirements, regardless of cylinder size or demand. For small households, a single 20tube south facing panel should be sufficient. For larger households, a 30tube panel is a better option. For swimming pools, you should use 25-30% of the pools surface area (eg 4 panels for a 10x4m pool).

Cylinder size

If you do not use vast quantities of water, then a smaller cylinder will yield hotter water (albeit lower quantities). a 1200x400 cylinder (135litres) is usually sufficient. Many people chose larger cylinders - up to 175litres for a standard 20 tube south-facing panel. Larger cylinders up to 260litres can be accommodated by a 30tube standard panel. If you want to fit a mains pressure hot water system, now is a good time to do it. Solar water heating will work with mains pressure hot water. Use 'Thermal store' option to provide mains pressure hot water without the expense of a stainless steel pressurised cylinder.

Underfloor heating

Large panel arrays (4-8) can provide a useful addition to heating a house in the winter. However, they will generally produce heat at the wrong time - excessive heat in the summer, and little or no heat during overcast winter weather or at night. Conclusion: Very cost-effective, massive energy return for your capital, relatively short pay-back period, virtually every house can benefit from solar water heating.

Wind Turbines

Two things determine wind turbine choice

1. Amount of wind energy available at the site

2. Amount of energy required

Both are very difficult to measure. If you have no idea - then chances are that no-one else does either! You can check the average wind speed at your location at the BWEA website. This will give you the wind speed high-up, where there are no obstacles to cause turbulence. This will NOT tell you how well a wind turbine at low height will perform. Generally, if you consider the site to be windy, then you will get good results with our turbines. However, even a distance of a few metres on the ground can make a huge difference to turbine performance, and it can be quite amazing how significant the disruption can be, caused by trees and buildings.

What size turbine should I buy? If this question was accompanied by a cheque for £10, we would no longer need to sell turbines! It is not a question that can be answered. However here are a few pointers: * A 200W turbine is capable of running all of the household lighting circuits, if in a suitably windy location * Sometimes the decision can be based on battery voltage, if it is to be integrated into an existing battery system * wind turbines can be used as direct-heating with suitable controllers. This is an excellent way to heat a house, as wind tends to accompany bad weather, and is especially prevalent in the winter. Remember that wind turbines can potentially operate 24hours per day, so even a modest 1kW wind turbine, can provide a significant amount of heat required for a house. A larger turbine - 2kW -5kW may produce most of the heat, if in the right location. Please note that the wind turbine will provide no heat on a cold frosty night - so there is always the need for back-up heat. * wind turbines make excellent grid-connect power systems. However the cost of the grid-connect equipment is high, making it a longer term investment. No wind turbine can be connected directly to electrical loads (except for direct heating systems). This is because the wind power varies constantly, and if connected directly, the voltage/frequency would be constantly changing. You must either use a grid-connect system - which basically uses the national grid as a battery - feeding excess power into it, through an export meter. To work out what size wind turbine you require, you firstly have to identify your demands. If you average out household demand over 24hours, most houses use around 500-750watts. However, peak demand can exceed 10kW. If you want to be dependant on wind power, you will need to reduce your peak demand to a level that can be sustained by your inverter. Wind turbines are generally assumed to produce around 30% of their rated power, if you average things out - so to provide for a constant load of 500W, you would need a 1.5kW wind turbine. Of course, this assumes 100% efficiency and that storage issues are not a problem.

Grid-connection systems are the best way to run your entire house on wind power, but the grid-connect equipment cost exceeds the cost of the wind turbine by some margin. Conclusion: Great energy return on the investment.

Very effective for off-grid applications. Simplest solution is to use a battery bank/inverter, but this cannot be connected directly to household wiring. Alternative is grid-connect system, which can be directly interfaced with domestic wiring (ie no batteries). This is an excellent option, but grid-connection equipment is costly (will exceed the cost of the wind turbine kit by some margin).

Water Turbines

If you have a potential water turbine site, then there is no question that it will be a worthwhile investment. We provide very competitive prices on small scale hydro generation - so payback times can range from 2-6months - much faster than any other form of renewable energy. You will need a good flow and/or a good head of water. You can easily calculate the potential power of a water resource using the formula given on our water power webpage. Our water turbines have a built in dump load, which will soak up any excess power to prevent the water turbine over-spinning (important for voltage/frequency regulation). Conclusion: Exceptionally fast payback time. Very cost-effective, dependable power source. If you have a suitable water course, make use of it!

Ground Source Heat Pumps

Heat pumps produce more heat energy than the electric energy used to drive them. In fact, heat pumps will often provide 4 units of heat for each unit of electricity that is fed into the system. This is called the COP (coefficient of performance). For very small temperature differences (possible with a good heat source and underfloor heating), it is possible to achieve COPs greater than six. Ground source heat pumps can utlise heat from: 1.pipes buried in the ground 2.well water 3. a pair of bore holes (one flow, one return), 4. streams 5. lakes For the 9kW heat pump using buried pipes, you will need to run 3 loops (each 150m). You should make up a manifold, and use restrictors to balance the three loops, making sure that each loop has the same temperature differential. You will need quite an area of land to do this, so this is really only an option for small-holders and farmers. It is possible to install a heat pump in a conventional home, but this requires a water heat-source - such as a well, bore holes or a running stream. Conclusion: Very effective and dependable source of heat. Requires major earthworks unless a water source available as a ground heat source.

Microgeneration Certification Scheme

Supported by the Department of Energy & Climate Change

The Microgeneration Certification Scheme (MCS) is an independent certfication scheme designed to ensure microgeneration products and installers consistently meet strict European technical standards.

MCS is designed to raise standards.

The MCS is designed to raise standards, protect the consumers and offer information through the certification award.

For FITs and RHIs your installer must be MCS approved.

Your renewable energy system installer must be MCS accredited for you to take advantage of the various renewable energy incentives (RHIs and FITs).

Feed In Tariff (FIT)

What is the Feed In Tariff?

FITs are an incentive scheme that pays people for generating their own green electricity. Introduced in April 2010, the tariffs give 3 financial benefits

a) A payment for ALL the electricity you produce, even if you use it yourself.

b) Additional bonus payments for any power you feed back into the grid.

c) A reduction in your standard electricity bill.

Are they guarenteed?

Currently (August 2010), these incentives are guarenteed for 25 years. A review on the incentive level is due in 2012.

Any further details required are available on the FITs website www.fitariffs.co.uk

Renewable Heat Incentive (RHI)

What is the Renewable Heat Incentive?

The RHI is a fixed payment for the renewable heat you generate yourself.

Who is eligible?

RHI is eligible to anyone who has installed a heat producing renewable energy system since 15 June 2009. The system has to have been installed by an MCS accredited installer to qualify.

When can it be claimed?

The RHI tariff takes effect as of April 2011.

Any further details required are available on the RHIs website www.rhincentive.co.uk