Photovoltaic

Photovoltaic cells (PVs) use light to generate electricity and up until now have generally been used on sites where a grid connection would be difficult or expensive or that are only used in the summer but this is now changing with the advent of grid-tie. For an independent power supply, solar works well with wind as there is a good balance of both over the year. Solar electricity, like electricity from other renewable energy sources, doesn't produce carbon dioxide or harm the environment. Therefore the payback is twofold one is the saving on purchasing electricity from the producer, the other is a cleaner environment and a reduction in 'green house gases'.

Although start-up costs are higher than other renewable technologies, PVs have key advantages:

• There are no moving parts to fix so they are relatively easy to install and maintain.
• They can be sited in urban areas and are not restricted in the same way wind and hydro-power systems are.
• They can replace other roofing materials.
• They need not take up any additional land.

Solar modules are made up of many "cells" manufactured from various forms of silicon. The greater the light intensity falling on these cells the greater the current produced (light intensity and output current are proportional). However, the voltage produced is not proportional to light intensity but rises very quickly in low light ensuring that charging can take place.

Partial shadowing of a module should be avoided at all costs as the effect is a disproportionate reduction in power output. The cells in a module are in long series strings, where the current passing through each cell is the same; the cell with the lowest output thus determines the effective output.

Types of photovoltaic cell

Crystalline

These cellsl must be incredibly pure, are very efficient but generally more expensive than other types to produce.

Some Solar Panels (PV's) providing Power for Heating

Not a good idea!!! PV's are best suited for operating small motors, pumps, electronic equipment, lighting and similar apparatus. They can also handle the loads produced by toasters and microwaves because the demand is short lived. However, don't contemplate any form of heating whether it is for space or cooking its just not economical due to the very significant loads produced by such appliances.

All is not lost as solar thermal can be used for both hot water and space heating so please take a look at the solar thermal section of this web site.

Holistic Approach

Often people consider alternative means of energy production when they are building a new house, this is the easiest way to make a very significant difference to future bills for energy. Retrofit is equally valid and don't be put off because you are not about to build a new home. First you should consider the home as a system as many of the energy loads will be related to each other. Reduce the need for excessive amounts of power. Heating and cooling cost's money check the attic (or loft - depends what sort of English you speak :¬) is it properly insulated - adding to the insulation will both reduce the amount of power needed for both heating and cooling. Whatever the appliance may be - ask the question "Does this need to be turned on?" If the answer is no! You know what to do. Consider changing to low energy equipment - from compact florescent light bulbs to energy star appliances. Take control, don't take electricity for granted consider carefully what your needs are. A subtle change in life style could have a dramatic effect while saving you money in the long run and giving you considerable satisfaction of being in control.

How do PV's compare to other means of production

PV's can produce electricity anywhere under the sun, they have no moving parts to wear out or have serviced! Both wind and hydroelectric means of generating are constrained by the location. The amount of wind or water will vary depending on the season. A combination of systems can work exceedingly well as the wind is usually stronger in the winter and the sun is stronger or less obscured by clouds in the summer.

Conservation and Design

How much load will there be? The load relates to what will be powered, when and for how long. This is important but not so critical in a grid-tie situation because you can just purchase more power from the utility company. However if you are off grid then your production and consumption needs to be balanced. If you can minimise your consumption then the cost of equipment to produce your own power will also be reduced.

Carry out an energy audit, use a computer spreadsheet or a large piece of paper. List every room in the house then identify all the electrical appliances. You need to note down their actual power consumption in watts per hour. So if it is only used for a few minutes a day adjust your figures appropriately. At the end of the exercise you will know exactly where your energy is being consumed and it will help you to decide if and where changes can be made.

Watch out for ghost loads, these are not easily detected but equipment such as a television or VCR on standby will consume power. You need to identify all the potential ghost loads and make a decision, pay up or make changes to some or all of them.

Components of a PV system

Most professionals in this industry will shy away from describing an average system because there isn't one. The challenge is matching the client's expectations to a system that can fulfil them whilst keeping within a prescribed budget. Basically if you neither want nor need much then the solution will be simple and cheap and it goes up from there!

Power Panel

The choice of voltage will depend on what you want from the system. If it is small, i.e cabin, RV or marine application the 12 volts will be ample and a large selection of small appliances is available in this voltage. The problems associated with 12 volts are that of high line loss, so no long cable runs. This can be overcome by using either 24 or 48 volts in conjunction with an inverter to supply the standard household voltage (be it 120 volts @ 60 Hertz in North America or 220/240 @ 50 Hertz in Europe).

Portable systems are available which at an entry level start with a solar panel and a power pack and then grow in size and complexity until the next level which is basically for a cabin or vacation (holiday) property.

The example of a basic cabin system shown above would provide a combination of 12 volts DC and 120 volts AC. The 'bottleneck' in any system is always the inverter hence the need for carefully assessing what is needed in the analysis stage. The size and number of both batteries and PV panels will govern what is available in terms of power and how quickly the batteries may be recharged.

In place of the 'cabin' components' bigger 'everything' can then be substituted and systems developed to suite most power needs whether off-grid or grid-tie, the controlling factor is usually your bank balance! The needs of most energy conscious home owners and businesses wishing to have some control over their power production can be accommodated. This is particularly true when it is possible to integrate a windmill and or solar thermal components into the system.