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INFORMATION:

Solar Option is eager that purchase and installation of any solar product should be treated as an investment, be as cost effective as possible, and therefore give a Return On Investment (ROI). To have reached this page indicates you are eager to find information that may clarify some of the hype or misconceptions about solar.

Only 'Go Solar' if you are prepared to have it installed in the correct manner for it to function efficiently. There are already far to many 'pretend' solar installations around that look the part but fail to provide the desired benefit.

Solar products do not function the same for everyone! Installation determines the maximum efficiency it can attain (and at what time of year this occurs), dictated by solar access, orientation and the building (or imposed) constraints/limitations, at the location.


2016 Solar Option

The articles on this page are intended to present information about functionality.

Please send feedback if they tend to confuse, or you require further information.

Topics:

Why should anyone consider solar energy?
Solar Collector Tilt Angles.
Passive Sun Control.
Greenhouse Gas Calculator.
Passive Solar House/Block.
Photo-Voltiac (electricity generation) Basics.



Utilising or controlling Solar Energy requires knowledge of constants that do not change, which you can choose to adhere to (for correct operation) or ignore (a costly waste).

When cooking, would you use metal cookware in your microwave, or plastic microwave cookware on your gas/electric stove? The choice is yours, and result is immediate.

Efficiency of a solar device may only become obvious to you after at least a whole year of operation. A bit late to change your mind, or seek a refund.

Adhere to indisputable constants for the best result!

Why should anyone consider solar energy?

Energy from the sun is fundamental to all life on Earth, and available to anything exposed to it, free of charge. There is however a cost for devices designed to utilise/control that energy.

Solar energy (including resultant energy from wind, hydro and wave) is the only form of energy that is free for personal capture/use. Once the initial outlay for equipment is recouped, future energy is virtually free (apart from a relatively small cost for ongoing maintenance of the system).

This means at some point not only will the system have paid for itself but give an ongoing return on the investment. This is not a gamble like shares or other forms of investment, but a certainty (though time period is variable) dictated by installation efficiency.

Though all other energy saving appliances you purchase (fridge, washing machine or TV) may reduce your energy use (and only that), they will never return a profit.

There are two components to energy saving, financial and environmental. The financial saving primarily benefits the end-user, the environmental saving benefits all on our planet.

The most common solar energy systems are water heating, which have been available for many decades, and electricity generation using photo-voltiac (PV) panels, which have only become very widespread in more recent times.

The use of solar energy for water heating gives the most efficient conversion of solar energy for domestic use, and as hot water is a large component of home use it makes sense to consider installing this as a priority. Solar can provide close to all your year around hot water requirements, 'when done correctly'.

Electricity generation is a good way to offset energy use and cost (which will continue to increase over time), but in most cases will only provide a portion of your total energy use.

You will still need to include energy reducing practices to maximise benefits, which will also effect the period of time to achieve system payback and possible ROI.

Most energy suppliers offer 'feed in' schemes where they purchase excess energy developed by your (PV only) system. Though they pay a fraction of what they charge to supply. This can both reduce your energy costs and encourage further energy reduction through revised energy use (to maximise returns).

Tailoring your energy (time of day) usage can give a better 'return' (by minimising both export and import) than getting a 'monetary refund' for power exported to your energy supplier, unless your system can deliver more energy than you require 24/7.

Both Solar Water Heating and PV systems qualify for Renewable Energy Certificates (RECs), a refund which is a monetary value for the energy efficiency of the system calculated over a fixed time period. The value of these certificates is variable and may become more transparent (and possibly higher) when/if a fixed price for carbon is established.

Governments will determine if this scheme remains or is scrapped.

As battery storage becomes lower cost, it may encourage people to totally separate from the electricity grid. Though it is likely most people will remain connected (to guarantee 24/7 power) and take advantage of 'off-peak' power tariffs (though even this tariff will increase over time).

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Those within 200mtrs of the coast, be aware!

When installing either PV or water heating panels, something that most will not be aware of (or may not consider) is location. I am primarily concerned here with locations really close to the coast. The closer, the higher the consideration.

Salt laden air can travel far inland, depositing the salt along the way. Roofs are often places where some salt settles out of moisture laden air. Roofing materials are usually chosen to suit these conditions.

Most PV and water heating panels may be OK in these locations.

What helps lower the risk of salt effecting these products is rain. It washes the salt away. Without rain the salt will just sit there and can slowly (unknowingly) destroy the materials over the years.

Placing panels on a roof provides a protected environment under the panels. Though salt laden wind can still access the gap between the panels and roof, the rain can only wash the panels and roof troughs under these panels.

I have seen photos taken during renovations of a plain terracotta tiled roof (in South Fremantle) that had solar water panels installed on it many years ago. The roof around it was perfectly intact, as were other tiled roofs in the area.

However, when the panels were removed, the tile ridges which were protected from the rain (by the panels) had dissolved and disappeared, leaving only the troughs that were washed of salt whenever it rained, by water running down them from higher up the roof.

This may also have been assisted because of the plain terracotta surface being quite open, offering micro hollows for the salt to sit, protected from rain.

If evacuated tubular water heaters had been available and installed back then, this may not have occurred as rain can still pass between adjacent tubes, washing salt from the ridges.

Solar Collector Tilt Angles.

This information is assuming your collectors have good solar access (see SACI) and face due North.

Though both photo-voltiac (PV) panels and solar water heater (SWH) or air-heater collectors can look similar and require direct sunlight, each has its own ideal tilt angle for maximum efficiency, as they are designed for different purposes.

As photo-voltiac panels are expected to produce the maximum (total) kWhs throughout the year, they are best suited to a relatively flat tilt of about 20-25 degrees (most roof pitches). This is because the longest daylight hours are during summer, which is also when the sun is at its highest and solar energy (insolation) at its greatest. If you have air-conditioning it is also the best period to offset electricity usage. Whereas solar water heaters are required to function at their highest efficiency during winter, and therefore require a steeper angle.

Applicable rebates may 'sweeten' the move to solar, but do not offset efficiency lost through poor installation, or make it any more of an investment. Eventually any lack of efficiency will result in a cost to the end user (purchaser). Most 1.5kW PV systems will only reduce household electricity use and gain little (if any) from the present utility buy-back scheme. However, it is beneficial to the utility, as it delays their need to upgrade infrastructure for increased capacity.

The rest of this article is aimed at solar water heating collectors (see article #5 below, for photo-voltaic panels). Water heating is currently the most efficient use/conversion of solar energy, so don't lose that benefit through poor installation.

A correctly installed solar water heating system may cost the same overall (product+install+running) after twenty years, that a poorly installed system may have cost after only ten years (and may even require replacing around that time). In the second case would you go solar again for the replacement? I doubt it.

Solar water heaters are solely designed to deliver hot water. However a poorly installed electrically boosted solar water heater could more accurately be described as a 'solar augmented electric water heater', as the booster will do most of the heating in winter, when hot water requirement is greatest and the collectors should be functioning at their best.

A recently conducted energy audit I assisted with has shown that; if you currently have a serviceable gas water storage heater, you may still be better off (financially) sticking with it, than changing to an electric boosted solar water heater. Don't be swayed by a salesperson only interested in selling more product trying to convince you otherwise. Once the gas unit 'has to be replaced', changing to a correctly installed solar water heating system does become an investment.

There is a large difference between total annual input, and input corresponding to usage. The difference (apart from orientation) is mainly related to the collector tilt angle. You can find an additional pdf (0.4mb) describing tilt angles for solar water heating collectors here, though most details are covered in this article.

Though it is true that having water heating collectors on a shallow tilt does give the highest total (annual) input, it comes with a penalty. As you are probably not using the hot water as much during summer, it puts extra thermal stress on the system, shortening its expected useful life, unless you climb on the roof and cover part of the collectors during this period. Then during winter the sun is to low for useful input for most of the day, requiring excessive booster use to compensate, when hot water is more in demand.

The time of year that most hot water is used is during winter, therefore the collectors should be set on a steep tilt (about 55-60 degrees) for maximum input throughout this time of year. This maximises surface area exposure and reduces reflection, as the sun is always below the mid-day altitude. This will minimise the need for the booster to heat water on shorter daylight hour (and cloudy) days near the winter solstice. This results in a lower overall/annual input, but delivers a more appropriate, time of use input.

Tilt angles

On a steep tilt, efficiency drops during summer when considerably less hot water is used (while still providing more than enough), due to there being less surface area directly exposed and increased reflection, plus helping prolong system lifespan. With the sun higher in the sky, more daylight hours when the sun is more intense, loss of input is not a problem as hot water use is lowest during this period.

Overall a SWH collector tilt of 55-60 (in Perth) gives a more even input throughout the year,with significantly more input during colder months and lower input during hot months, than collectors at a low tilt angle. The system can be more accurately sized for its task in winter, though lower usage during summer should also be considered.

Solar energy is weakest close to sunrise/sunset, reaching maximum around mid-day. Collectors may be far colder than the tank temperature in the morning, so have to use the solar energy just to reach the tank temp, before any heat is available for input. In winter there may be no more than 0.9kW /m2 (maximum) energy available at midday, whereas the electric booster has around 2.4kW available immediately.

Boosters will always override solar input due to their immediate availability of energy, so should only be used manually, or work via a timer. Otherwise the booster heats the water quickly, and for the rest of the daylight hours the collectors have nothing to do. Any heat the collectors do contribute beyond the booster cut-out temp (most evident in summer), may just contribute to shortening the system lifespan.

The Solar Saver was a retrofit designed (by Jay MacFarlane) to automatically give preference to the collectors when it detects there is enough solar energy in the morning to heat the water (gradually) throughout the day, by turning the booster OFF. Whenever there is not enough solar energy available (cloudy days) the booster switches ON as normal. This simple device was never taken up by any SWH manufacturer.

It has become apparent that the lesser known Evacuated Tubular Collectors (ETCs) are far more efficient than standard flat plate collectors, for heating water. They start to contribute heating earlier in the day, have close to maximum input for the majority of the day which only drops later in the day. Whereas flat plate panels start more gradually, reaching maximum input around midday, and tapering off afterward (a regular bell curve). Prices may be slightly higher for ETCs but the efficiency benefit makes them cheaper overall, with an earlier ROI.

Raising the collector angle for maximum winter input is applicable to both flat plate and ETCs. However flat plates offer a solid surface (sail) to the wind, whereas ETCs allow the wind to pass through. It may also increase surface losses to flat plates (temperature dependent), which causes little effect to ETCs (due to their vacuum insulation).

SWH comparison

The graph shows that ETCs at a high angle produce less hot water in Summer than at a lower angle, when less hot water is used. It also shows that ETCs at a high angle produce a more extended input during winter than at a lower angle, when hot water use is greatest.

If you have a solar water heater on a low tilt angle that is under-performing during winter, don't be tempted to increase collector area unless you are prepared to place a partial cover on the system during hot months, or you will just reduce its lifespan even quicker.

Some people that do not wish to install on a north-facing roof (due to aesthetics), or do not have a suitable north-facing roof, attempt to rectify this by installing on a frame to restore correct orientation. Unfortunately almost all of these frames still use a low tilt angle. Not only does it cost extra to install, but it still doesn't provide maximum efficiency when needed most, or prolong system lifespan. If you do consider a frame, make the extra cost worthwhile by installing at the correct high tilt angle to ensure system efficiency and longevity.

Even a north facing wall (with good solar access) can be utilised, either using a frame to create a projection (shade) over a window, or fixed against the wall to provide additional winter only input.

If unable or unwilling to install SWH collectors in the correct manner, and your only alternative for heating water is electricity, the next best option is an 'air sourced' heat pump system. This works in an opposite manner (but same principle) to your refrigerator. It takes available heat from the air and transfers it to the hot water tank.

Though it still uses electricity for its operation it is approximately 3.5 times more efficient than the heating element normally used in an electric storage system. There may not seem to be much heat available in the air on a cold winters day or night, but the heat is not relative to the 0c to 100c range that we normally relate to, but relative to absolute zero (-273c).

An even more efficient version is a 'ground sourced' heat pump, as ground temperature is more consistent throughout the day/year, but would require trench excavation or a borehole, provided a suitable location/area is available.

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This article does not imply collectors will not work if advice is not fully complied with, just shows how to maximise performance for the collector type.

The article relates primarily to Perth, West Australia, though the overall premise applies throughout the southern half of the Australian continent.

Low tilt angle image

Low tilt angle

Steep tilt angle

Hot water usage.

There is one other aspect to consider in relation to solar water heaters, time of use. Conventional storage or instant water heaters are usable at any time of the day/night.

To get the greatest benefit from solar water heating you should consider when (solar) heat is available, and when heat is lost from the system. Tank losses are applicable to all storage types (solar/gas/electric).

It is far better to use the hot water in the evening than to expect it to still be available in the morning after many hours of losses and prior to any input from the sun, unless you are happy to use the booster.

Obviously heat input is only available when the sun shines (reduced by cloud or at night).

Heat loss is greatest at night and more so during winter. Heat is not only lost from the tank due to the temperature difference with the outside, but also from uninsulated pipes and the cold water replacing the hot water used.

If the tank temperature is set at 65c, during summer the overnight temp may drop to 20c so there is a differential of up to 45c. In winter the overnight temp may drop to 5c, with the differential increasing to 60c (33% greater).

The booster will turn ON whenever the tank temperature drops below that set point.

Don't have the tank/booster temperature set to high. As the set point is lowered, so will the differential, and therefore also the rate of loss. A set point of 55c is good as it minimises tank losses but is still hot enough for any purpose.

Only turn the booster ON if there is an urgent need for hot water, and only for a short period.

The temperature of the replacement water is also lower in winter, as the ground which the pipes are buried in is colder. And uninsulated cold water pipes above ground can cool to below the outside air temperature.

Most people do not insulate cold water pipes leading to the SWH, though it can save energy (reduce losses) in winter.

Any uninsulated copper pipe acts like a little radiator because copper is an excellent conductor of heat. The heat will travel along the pipe to the point where it can easily radiate. By insulating all pipes connected to the tank, losses are minimised.

In relation to evacuated tubular collector systems. No company in Australia has the capability to produce the glass tubes for these systems, at an affordable price.

All tubes available come from China. Therefore it is cheaper to source the whole systems in China. Virtually all systems, no matter what the name badge says, come totally from China.

There is however one company (Ark Solar) that manufacture part of the system in Australia. Ark Solar also recommend installing their collectors at the steeper tilt angle to best suit the (yearly) time of use, to minimise booster use, which also prolongs system life expectancy.

As with any system, the quality of the materials used in construction also have a large part to play in the life expectancy, to suit the local water quality.

Passive Sun Control.

Though Solar Option manufactures the SUNGOLA passive sun control, handy persons may like to try their hand at making their own version.

You will find a brief pdf (0.4mb) description of how such a structure is designed here. Actual angles and overlaps are not shown as they are more specific to the latitude of the location, and shade requirement.

The SUNGOLA has been supplied as completely knocked down (CKD) kits for those wishing to undertake their own construction. This has been the normal supply method used outside the Perth metro area (Three Springs to Esperance). The kits include all components, assembly drawings and instructions.

Corrugated metal sheeting gives 100% shade all year around, hit/miss battens and shade cloth create more shade in winter than summer. Only a correctly designed and oriented Passive Sun Control device provides a more appropriate shade, for the time of year.

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The document relates primarily to latitude for Perth (32s), Western Australia, but still viable +/- 2 degrees.

Winter sun through sungola Summer sun blocked by Sungola

A 'solar pergola' (generic term) is a fixed angle shade device, it does not generate electricity but passively adjusts shade throughout the year, in relation to the suns' inclination (above the horizon) and path across the sky.

Greenhouse Gas Calculator.

Steve has collaborated with Ben Rose to produce a Green House Gas emissions calculator (Windows only) for use by Australian households.

The project started when they both belonged to the Warren Districts Renewable Energy Group (WDREG). At which time the group was undertaking one of the 20 Cool Communities projects around Australia (3 in W.A.), aimed at encouraging households to reduce their energy consumption. The Cool Communities projects were funded by the Australian Greenhouse Office and supervised by the Conservation Council. The calculator was developed independently of that project.

Ben had already been developing a spreadsheet to calculate greenhouse gas emissions attributable to Australian households. Steve liked the information that it could show but (like others) was not sure that a spreadsheet was very user friendly, so as an amateur programmer attempted to develop a stand alone version.

After demonstrating the (very buggy) initial version at a WDREG meeting, the two decided to develop it further. Once most of the bugs were removed, the original version was made available on the WDREG website. Over time it has expanded to enable more data to be input, to give a more accurate result while still sticking with an easy to use interface. Initially designed to fill a 800 x 600 screen (to minimise scrolling), this has since been increased to 1024 x 768. Unfortunately programming skills still remain minimal.

The screen layout is arranged with the highest emitting section at the top, decreasing down the page. Most of the items are multiple choice, with input of quantities required. This can be done as a quick guesstimate for one section, or a sit and think total household estimate. Some sections contain sub-sections for more in-depth input.

Ben has stuck to his principal of giving the whole picture, rather than massaging results to promote any particular group agenda. The program also functions as an energy calculator.

Though quite logical to use as is, there is plenty of on screen information, supported by an extensive help file, giving more than just program help/instructions. By downloading and running the program, results are shown immediately, whereas online calculators have a short pause between actions, and are mostly aimed at a particular interest group rather than a more realistic overall picture.

More in depth information can be found at Ben's website.

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GHGcalc screen image

download GHGcalc5.zip (0.5MB)

After un-zipping, move the complete folder to a suitable location.
Go to Ben's website for more details on environmental sustainability.

GHGcalc1 screenshot
(Original version of GHGcalc)

Passive solar houses/blocks.

Orientation is crucial for a passive solar house design to function correctly, but siting a house on a block is usually dictated by the block/house size, orientation and local council requirements/set-backs.

Though councils are supposed to require that new developments are environmentally sound, just look at the layout of developments approved over the past few years, to see how few attempt to encourage this. Though these are primarily the layout of the developer. When looking through the street directory, it is easy to see how few councils are attempting to make passive solar housing more accessible.

When choosing a passive design, it can only function correctly with correct orientation. For ease of layout, the vast majority of blocks are rectangular and run parallel/perpendicular to the street. All councils have their own fixed set-backs parallel to block boundaries and as a result most houses also coincide with street direction.

Gone are the days of the 'quarter acre block' (about 1000sqm), where a large house could fit easily with plenty of distance from set-backs on almost any orientation. Most new houses struggle to fit within set-backs, forcing house orientation to exactly match that of the block. If your chosen design has to be re-aligned to comply with set-backs, it may no longer function at the designed rating.

A developers primary focus is to maximise their investment by getting as many blocks as possible out of a parcel of land, not provide ideal blocks. Councils just rubber stamp developments to maximise rates from the overall development containing the maximum number of rateable blocks.

It's not that parcels of land contained within poorly aligned streets can't be divided into blocks with good orientation, it's because there is no incentive to do so, people just buy what's on offer as that is all that is available. With greater information about the blocks available to the buyer (not just size), decisions on purchase would be made easier. It would also indicate to developers what the public are really looking for, as less desirable blocks would be hardest to sell.

Should you intend installing PV or a SWH (initially or in the future), correct roof orientation and area has to be available, or it may not be able to function efficiently (or to its maximum capacity). This will be (most likely) primarily determined by the block.

How to rectify this.

I submitted a proposal (to ABCB) that there should be a star rating for blocks, to enable purchasers the option to match the block with/to their house design. This would give confirmation that both block and house are compatible and able to fully utilise the house rating. A star rating would also indicate that the developer is environmentally responsible, by providing such information.

The block star rating would encompass; block size, aspect ratio, block orientation, topographical situation, shading (by permanent structures) and local council set-backs (which may not otherwise be obvious prior to purchase).

There are energy star ratings for washing machines and fridges, which can hardly be classified as major purchases, though they do have an ongoing energy requirement/cost. The house and land (package) is not only THE major purchase but also THE major ongoing energy consumer, required to provide lifestyle comfort (heating/cooling and lighting), and therefore far more important for assurance of efficiency. The house rating alone is only part of the package and can not exist/function correctly without a compatible block.

Though homes are now designed to comply with a minimum 6 star rating, this may be greatly reduced through incorrect orientation, due to poor block choice/availability. Therefore being able to match the house with a compatible block makes for good sense and an overall (lifetime) saving.

As more purchasers request 6 (or more) star blocks it should encourage developers to provide more ideal blocks (as they will probably sell for a premium). Getting less for low star rated blocks, should promote more environmentally friendly layouts, as a block with a low star rating would indicate to purchasers that problems are evident, prior to purchase. Making it difficult to 'off-load' bad blocks for good money.

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Ideal streets for best orientation either run North-South or East-West.

If you have already chosen a house design, select a block that allows it to fit easily inside of the set-backs, on the correct orientation for the house design.

A house placed diagonally on a block can sometimes be permitted to encroach on a set-back, if the local council allows the area near the boundary to be averaged.

If correct house orientation doesn't fit, look for another block rather than suffer the consequences, for the whole life of the building.

When looking for a block to purchase, a compass is an essential tool to take along, and copy of the local council building set-back rules.

Though the view may be picturesque, the most important view to consider is that directly North of the proposed building, in order to position it for maximum efficiency.

Is it free from objects (tall trees/buildings) that may reduce solar access in winter?

A solar access assessment will be of benefit if you intend utilising solar products (see SACI) or passive solar design.

In the future, existing house sales will likely require the seller to provide building details (star rating) on efficiency, in order for the/any sale to proceed. Effecting the sale price.

Therefore getting it right initially will make it easier to sell and get the best price, down the track.

Photo-voltaic panels - the basics.

Solar water heating panels and photo-voltaic panels (despite using the sun) are entirely different in their operation, though from a distance they may look similar (as do solar air heating panels). Water heating panels (see article #1 above) transfer heat energy from the sun directly to the water in the panels, whereas photo-voltaic (PV) panels convert the light energy (photons) into electricity. The following article looks at photo-voltaic panels.

In the article on solar water heating I mentioned installing at a high tilt angle, the opposite applies to PV. Though it is still beneficial for input during winter you get the highest input during summer, which is the ideal time to offset your energy use/cost or maximise return if you are on a buy back scheme (especially if you use an air-conditioner).

To lessen confusion by consumers, PVs are 'packaged', as there are lots of variables to be considered. As they relate to electricity, the panels are rated in Watts (W). The rating is the peak power output of the panel under a fixed set of conditions, and is generally a world accepted standard. This does not mean they will function exactly the same anywhere in the world, as the weather conditions they are exposed to will be different.

Sticking with electricity, everyone can relate to the old light globes that have existed for most/all of their lives. You generally choose a low wattage (25w) globe for a small room, up to a high wattage (100w) globe for a large room, or multiple globes for a very large room. The consumer does not need to know how that figure is arrived at, only that it is a figure that can be related to, when purchasing a globe. Thankfully the old style globes have been replaced by more efficient CFL and LED lighting.

Likewise PV panels are sold on their rated wattage output, though most people will purchase multiple panels (an array) to give an overall output, usually in kilowatts (kW). You may notice that 1kW arrays have between four and seven panels, depending on the output of the individual panels. Each manufacture has their own selection of preferred sizes, for their production process.

Just as cars come in different types (sedan/4WD/formula-one) PVs are not all the same. There are basically three types: Mono-crystalline, Poly-crystalline and Amorphous (thin film). Mono-crystalline as the name suggests each cell is constructed from a single crystal. Poly-crystalline is composed of many crystals. Finally came Amorphous, which is composed of very small particles deposited in a thin film.

Each type has a different 'efficiency' (the amount of sunlight it can convert into electricity). Mono-crystalline are highest at around 20%, Poly-crystalline around 17% and Amorphous around 10%. As panels are sold by their output rating, the size of the panel is related to its efficiency. The higher the efficiency, the smaller the panel. Therefore a 1kW array of Mono-crystalline (20%) panels will require around half the area of Amorphous (10%) panels.

If available roof space is limited, or you may be considering adding more panels in the future, Mono-crystalline should be your first choice as they have the highest efficiency. Not all suppliers sell all types. Once you have committed to apanel type you are stuck with it, as different types should not be mixed.

You can usually pick the panel type by their appearance. Mono-crystalline are mostly black cells (round or square), Poly-crystalline are usually blueish square cells, and Amorphous are more of an overall (brownish) panel colour.

Generally panel efficiency is reflected in the price, but the difference is not great considering the overall cost of a system, be it grid connected or stand-alone (with battery storage). As with any product, there are quality differences between manufacturers and countries of origin.

Panel efficiency is reduced by dust on the panels and panel temperatures above 25C. Shallow tilt angles and lack of air flow around the panels increases the panel temperature in summer as well as the likelihood of dust build-up. An occasional clean with lightly soapy water helps to remove the dust (especially during long dry periods) and maintain efficiency.

Incorporating PV panels into the roof is not recommended, as roof cavity air can be well above the ambient outdoor temperature in summer, keeping the panel temperature artificially high and reducing efficiency even further. They should be raised clear of the roof to facilitate cooling, though this will possibly still be above the ambient outdoor temperature. This does however reduce the area of roof (beneath it) being heated by direct sunshine.

Another important item that has a bearing on efficiency is the inverter. This converts the DC voltage produced by the panels to the AC voltage used by the appliances within your home and the electricity grid you are probably connected to. The overall size/output of your panels should be close to the rated size of the inverter as it is designed to maximise output. Shading of any individual panel will reduce the output of a panel array if they are all connected (in series) prior to the inverter, determined by the lowest output producing panel.

Some newer panels have what is called a 'micro inverter' on each panel, which produces a regulated AC voltage from each panel. This means if one panel is effected by shade it does not reduce efficiency of the other panels in the array. This can give an improvement in efficiency of 10-15% over the year. Though not common presently, they may become the predominant type of panels in future.

Though micro inverter panels are presently more expensive than standard panels they can easily/individually be replaced or increase an array size, and can be safer, as it is easier to switch AC than DC.

As with solar hot water systems, time of use is a large part of how much value you get from it. When PV was first being promoted as an alternative form of domestic energy, many energy suppliers paid more (double) for energy exported to them than you paid for energy from them. It was therefore worthwhile sending them as much energy as you could, for a nice refund cheque.

Nowadays however the suppliers pay you far (as little as one third) below their charged tariff. Therefore to maximise the return on your investment, it is far better to use as much of the energy produced for your own purpose (air-conditioning, clothes washing) at the time the energy is being produced by the panels, and minimise that sent to the energy supplier. The larger your refund cheque, the lower return you are getting on your investment (longer the system will take to pay for itself).

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Photo-voltaic panels (modules) consist of a collection of individual cells, which are normally joined together in multiples (arrays) to achieve the desired output.

PV graphic

Cells are either joined together end-to-end (in series) or side-by-side (in parallel), or a combination of both, to achieve the desired panel (module) output. Panels are likewise connected within arrays.

Though the arrangement does not alter the total (voltage x current = watts) output of the panel/array, it changes the balance between voltage and current.

Series connection adds the cell/panel voltages together (10 x 12v =120v), at the panel current (2a). Multiple panels connected in this manner is called a 'series string'. Shade across a single cell/panel will effect output from the whole string.

Parallel connection retains the cell/panel voltage (12v) but adds the currents together (10 x 2a = 20a). Multiple panels connected in this manner forms a 'parallel string'. Shade across a single cell/panel only effects that item.

Both simple examples above produce the same (240w) amount of output. Though voltage is the prime property manipulated within the inverter.

The arrays are connected to an inverter, for conversion to power; standard 240v appliances, to batteries for storage on site (and use later), export to the grid.

Residential size arrays are NOT a fire risk!

As PV systems are aimed at producing the maximum output for the year, panels should be installed at around 20-25 tilt angle (facing North), to take advantage of the longer daylight hours during late spring, summer and early autumn.

Low tilt angle image

The main setback is that the higher intensity of summer sun striking the surface causes it to get hot. As panel temperature increases above 25C (easy due to their dark colour) panels drop efficiency. The higher the temperature, the less efficient they become.

In rural areas ground mounted arrays can be more efficient than roof mounted, due primarily to better air flow around panels, reducing heat buildup. However shading may be greater when mounting below the roof height. Check your solar access before committing!

A regular wash during dry periods will limit dust build-up from lowering efficiency. Easier to be done on a ground mounted array.