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Solar Power, what is it and how Solar Power works

Solar Power refers to the process of harvesting the Sun's energy (transmitted via light as solar energy) into an energy source, such as electricity. Solar power can be converted into other energy forms, like steam,  but often in the residential setting direct conversion into electrical energy is used.

Solar powered systems, the key parts

Whether bought and installed at home or at the office, most solar powered systems consist of up to three main parts: a solar collector (i.e. the solar panels), an inverter and optionally a charge controller and battery set if you are operating 'off the grid'; i.e. without mains power supply. The diagrammatic form of this is shown below.

solar power system diagram
The solar collector, usually photo voltaic (PV), otherwise known as solar panels, convert the solar energy from the Sun into electricity. The solar panels are rated by peak power output measured in Watts.

Solar Panels come in many different forms, often varying in efficiency in relation to the initial cost outlay. The three main types of solar panel are described below:

1) Amorphous solar panels

Amorphous based solar cells are often used for small solar panels, such as in calculators. The individual cells are not distinctly visible as they form part of a thin film on another material. Amorphous cells are less power efficient (up to 6.5%) then mono- and polycrystalline cells but their quality is constantly improving, so at the moment their big advantage is lower cost.

2) Mono-crystalline solar panels

Mono-crystalline solar panels are based on individual 'cells' each a slice of a silicon crystal processed to act as a solar collector. These individual cells are wired together as a set to make the overall rated wattage for the whole panel. You can often tell a mono-crystal by the circular nature of the individual cells, leading to gaps between them at the corners.

The recorded highest power efficiency for mono-crystalline solar panels was set in February 2009 by Mitsubishi Electric Corporation at 18.9%. This type of panel is also the most reliable and often the solar panel used for homes.

3) Poly-crystalline solar panels

Poly-crystalline solar panels are made from cast square ingots, so the gaps in the corners of the mono type do not exist. Poly-crystalline solar panels are cheaper to produce than mono panels but are also less power efficient (up to 12.5%)

Solar Panel Ouput voltage

Solar panels most often produce a 'nominal' 12v DC output or multiples there of (i.e. 12 volt solar panels, 24 volt solar panels, etc) - the actual stated peak voltage will be about 40% higher than this at peak watt power output - assuming ideal solar conditions. Such a varying voltage depending on the solar conditions is not that useful for today's devices that often require a precise AC supply at much high voltages, usually either 240 volt or 120 volt.. Now you can put solar panels together in series to get to around this voltage, but it would be in DC and highly unstable as to the exact voltage at any given time...

So, this is where the inverter comes in. Its job is to take a 'nominal' 12 volt (or maybe 24 volt) from the solar panels (with a high Current level) and converts and 'smooths' it into a regular AC voltage output for mains devices..  What basically happens inside it is that the voltage is stepped up in return for reducing the current (Power equals voltage times current, or P=IV); usually with a small loss of power efficiency along the way. If you are connected to the mains grid, the other function the inverter can do is to synchronize the AC produced from the inverter with the AC of the mains supply.

Off the grid installations

When you are solely using solar power to operate your electrical devices, when the Sun goes down you have no power! So to get round this an off the grid installation is so scaled so that enough power is harvested during the day to provide power to your mains devices and enough is spare to charge up a rack of batteries to provide power at night.

Although this is not as simple as it sounds. Typically lead acid batteries are used to provide the storage, these as well as being expensive & heavy need to be charged in a very precise way. If overcharged they tend to 'gas off' and corrode internally, which shortens their lifespan and capacity. If undercharged or overdrawn, they tend to loose capacity also..  So often a dedicated battery charger unit (often known as a controller) is required to 'manage' the batteries for you and provide safeguards against such bad charging.

You can also get solar controllers which will deal with managing the power from the solar panels and where to route it depending on demand. These can also often deal with battery charging, and possibly be configured to 'fire up' a back-up generator if the solar panels or batteries prove unable to meet the demand.

Grid Connected Residential Solar Systems

In most residential situations a grid connected system would be most suitable, for several reasons:
  • Financial return. Solar often provides power when the grid power is expensive. Usually power supply companies will operate different tariffs during the day, with the most expensive usually being during afternoon office hours to the evening - this is exactly the time that you have highest chance of it being Sunny!
  • Feed in tariffs. Quite often it is possible for your 'excess' solar power to be fed back into the grid for a premium of the normal tariff (i.e. you are being paid to produce electricity). Now given it is likely that you will not be home when its sunny, this is a great way for the solar panels to pay for themselves by offsetting your electricity costs. Although do be very careful in doing your maths and remember your power consumption over time will tend to increase, so the amount you sell back will keep getting less.
  • Gross feed in tariffs. This is like the feed in tariff above but you get paid for all the solar power you generate and not just the excess. For instance the NSW government is putting in place in Jan 2010 a 60c a KwH gross feed in tariff..
  • Low maintenance. Once the system is installed it requires no real maintenance as such. The electronics is all automatic.
Sometimes people operate grid connected systems with batteries, on the basis that the excess power is first used to charge the batteries, then is fed into the grid. The only real benefit with this is if you suffer a power grid outage at night, you will still have power. Although do be careful to make sure the batteries are rated for such work (i.e. being left fully charged the majority of the time).

Should I trade in my RECs?

Most countries now have RECs (Renewable Energy Certificates) or equivalent schemes. Basically it is a mechanism for attributing the cost of greenhouse gas emissions to be offset against a none or lesser greenhouse gas producing energy source - such as solar panels or wind power which produce renewable energy. The idea is that green house gas producers need to buy REC's to keep their net pollution below their allocated threshold. So if you sell all your REC's in effect, from the environments point of view, its a zero sum game (i.e. pollution generated balances against pollution stopped). So instead of making a net 'green' contribution to the environment you just keeping the status quo...

Also with this REC scheme there is a lot of what could be termed 'perfect market assumptions'; i.e. we know precisely what is an acceptable level of pollution and we know precisely how to 'value' that pollution against what offsets it.

Now if you do not trade in your REC's, what happens? Well for starters, the buyers of REC's will need to go elsewhere - so by you keeping those REC's you change the game from being zero sum to pollution negative (i.e. you have voted against allowing your green power to be offset against the pollution generated). Also by reducing the number of REC's in the market, supply and demand dictates that for the buyers the cost of those REC's are more likely to go up.. Of course by not trading in your REC's your initial cost will be much higher. Or look at this another way, the amount you paid after trading in your REC's is in effect a subsidy cost benefiting the pollution producer, i.e. its your 'sunk cost' to allow them to pollute!

Also in Australia there is now a multiplier scheme in place, i.e. 5x the normal number of REC's on a qualifying system - what this means is that for the same 'physical' amount of carbon reduction its having 5 times the offset effect in the market! So basically the REC market is getting flooded with cheap RECs, distorting the whole process for years to come... Which indicates two things: 1) how little people really understand whats going on with the REC marketplace, and 2) that the government has been 'hoodwinked' by big business into making polluting cheap for them.

At the moment bug business is busy doing what ever it can to buy up these cheap REC's; as with an increasing focus on green house gas emissions and the REC scheme being applied to more market sectors, the financial value of these REC's can only really go up in the longer term... REC's are completely tradable in a global market remember..

The other thing with REC's that is actually quite nasty, is that it allows the pollution producers to 'defer' to some late time actually changing their ways to pollute less directly - in effect it gives them a license to pollute to how many REC's they can purchase from the market. In effect they have no real 'incentive' to directly change...

News Update (27/10/09)

Apparently it has been reported in the main stream press (AFR) that the REC market is now flooded with cheap REC's ($50 per Mega Watt down to $30) due to the $1600 solar hot water subsidy causing a spike in demand. This has perturbed the market so much that large scale wind power projects are unable to compete in the energy market and are not being built. The end result is that the current energy producers have less 'green' competition to deal with; and this was not foreseen...

Solar panel installation considerations

How solar panels are configured to provide the most power output is quite important, you need to think about the following:
  • Good visibility to the Sun. Having lots of trees and buildings in the way of your solar panel and the Sun as it tracks across the sky is not going to be good for producing reliable power you can do something with. Therefore check for good solar access, its critical. Must people mount their solar panels on their roof, but do ensure the roof surface runs 'true' East-West and not just magnetic East-West
  • Ideal mounting angle. You want to have the solar panel as 'square on' to the Sun as possible. This is both the vertical and horizontal angle. The vertical angle slowly changes over the sessions as in Summer the Sun is higher in the sky than in Winter. The horizontal angle cycles from facing East to West every day as the Sun passes overhead (15 degress each hour)
  • Maintenance access. You will need to make sure that the solar panels are cleaned about twice a year to remove dirt and bird droppings on the panels to ensure they operate at their best. Therefore either being able to get up to them directly, or at least remotely reach them with some spray or cleaner, needs to be taken into account.
As regards how the solar panels are mounted they usually come in three forms:
  • Fixed mount - the vertical and horizontal angles are set to a sort of average over the year for picking up solar power. Not great but if you have a limited budget better than nothing. The panels need to be aligned to 'true' solar North (i.e. on a true East/West line) and not the magnetic North as this will skew your alignment out by around 11 degrees and reduce your power output. if the property they are being put on has been designed to benefit from Passive Solar the whole roof could well be in the correct alignment.
  • Adjustable mount - with these the vertical angle can be easily adjusted by hand, so depending on the sessions you can change the tilt to improve the power collection. Again align to true solar North.
  • Powered tracking mount - these mounts are essentially on a powered mechanical gimbal that tracks the sun across the sky. Maximizing the power harvested, but also requiring occasional maintenance as you now have moving parts.
One important consideration when mounting on a roof is to make sure that the back of panels have adequate clearance to cool - if the panel itself gets too hot it progressively losses efficiency. You will need a minimum of 100mm clearance behind the panels to ensure sufficient cooling. Also having this clearance is a good idea anyways, as it stops leaves and other 'junk' accumulating behind the panels and becoming a fire risk (bad news in Australia!).

NEW We have just put together an online solar calculator to help you work out the number of panels you will need.

NEW We have also just put together a cable gauge calculator to help working out the size of wiring required from your solar panels to either the battery or inverter.

NEW We also have a Financial Calaculator for working out the potential gain from a quote on the installation of a solar system.

Using an Installer - read the contract small print..

Something to be very careful with is that a lot of installers are saying their systems are 'guaranteed' for 25 or 30 years. Do please check the following:
  • Exactly 'who' is the guarantee with when finally installed, i.e. what happens if the installer goes bust, does the guarantee fall back to the original manufacturer?
  • Whats the guarantee on the other components in the solar system, in particular the inverter - these often have a working life of around 5 years tops and cost anywhere from $800 upwards to replace (i.e. 25/5 * 800 = $4000 to keep running over 25 years).
  • Check on your house insurance to make sure 'acts of nature' do cover the solar panels.

Solar power energy consumption

One thing you will soon notice doing the maths on your power consumption is how much power does get consumed without you noticing! This comes from several sources:
  • So called 'phantom power', basically all those consumer devices left on standby.
  • Answering machines, wireless phones, chargers, etc
  • Alarm systems, timer switches, irrigation controls, etc
We suggest you have a good look around your house and before making a decision on whether to go solar, see what you can just turn off and measure your power consumption then..

Other Solar options

You don't need to go the 'whole hog' to get benefit from solar power, especially when trying to use solar around the home. Consider these usage cases:
  • Solar powered garden lights - these are ideal for running off solar either using standalone lights with built-in solar panels, or a common solar panel running a series of lights. Both systems require some form of battery storage to allow the lights to operate at night. The big plus with the standalone lights is that if you suffer a power cut you have easy access to lights you can bring in and use. Often use is made of LED lights to keep the power consumption down, you get slightly less light with these, but they last many times longer.
  • Solar powered water features - there is a lot of pump technology designed to run off 12v supplies, so ideal to use for to power water features or just to pump water to a higher storage place in your garden, so you can do gravity fed watering.

Why go Solar?

Big question - it really comes down to two things:
  • The value you place on the financial return, and,
  • The value you place on the damage to the environment being caused.
Everybody is very focused at the moment on green house gas emissions but we think this is missing the point - there is a very large 'embedded cost' element in having services, like electricity, supplied to your house or business. This has a general environmental impact in consumption of materials. Therefore if one is able to operate 'without' the grid that cost does not get incurred, but if you already have the grid to your house, the cost has already been incurred, so going solar will not change that one bit.

Essentially the best way you can help the environment is to reduce your general energy consumption first, then look at using solar if you energy consumption pattern would benefit from it.

Note: Solar panels in of themselves should not be considered to increase the value of your property; given the rate of improvement in the underlying technology (and the reducing cost base) the current generation of solar panels are likely to be superseded by cheaper and more effective panels in the future. It is very likely the intrinsic value of the panels will decrease over time, you should factor this into your financial calculations.

Related Books

  • Photovoltaics: Design and Installation Manual
    With this book a world-class solar energy training and education provider-Solar Energy International (SEI)-has made available the critical information to successfully design, install and maintain PV systems. The book contains an overview of photovoltaic electricity and a detailed description of PV system components, including PV modules, batteries, controllers and inverters. It also includes chapters on sizing photovoltaic systems, analyzing sites and installing PV systems, as well as detailed appendices on PV system maintenance, troubleshooting and solar insolation data for over 300 sites around the world. Used worldwide as the textbook in SEI's PV Design & Installation workshops.
  • The Renewable Energy Handbook: A Guide to Rural Energy Independence, Off-Grid and Sustainable Living
    Author/engineer William H. Kemp, who is a leading expert in small- and mid-scale renewable energy technologies, designed and built his own off-grid home. The result is a house that has all the standard “middle-class” creature comforts while using less than five times the total fossil-fuel energy of the average North American house.
    The Renewable Energy Handbook focuses on the unique requirements of off-grid living and contains chapters on energy conservation; heating and cooling; backup power; domestic water heating; wireless communications; photovoltaic, wind, and microhydro energy generation; battery selection; and inverters.

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