However, like all renewable technologies one should be very careful to become aware of it's abilities and shortcomings, and design accordingly. There is no doubt that at the moment it is one of the most expensive forms of renewable energy, and classically will take 25-30 years to repay the original outlay.

They really come into their own for low-power uses where other technologies are unsuitable - boats, caravans, remote areas for waterpumps, stables etc.....

The best way to implement power from them is to "start backwards" - decide what your power requirements are (and minimise them as far as possible), then design to supply those needs.

Unfortunately, it's all down to "sums" - I've appended below a couple of simple examples which give an idea of simple battery-storage uses of pv panels - it should help give an idea of scale and costs -

I'll start with the very simplest use of pvs -

a simple fan arrangement to help ventilate something like a conservatory in summer, the power requirement and it's availability from the sun concur nicely -
(at it's simplest you have a 12v fan fed directly from a pv panel - when the sun shines, the fan revolves) - 20w fan, 20w panel etc.............

However, if you want to power a simple lighting circuit, a whole lot of other factors have to be taken into account - say for instance you want to power an 18w energy saving bulb for 4 hours an evening - you need to draw 1.5 amps for 4 hours - 6 amp/hrs - classically, you should aim to drain no more than 10% of a battery's capacity per day, so you'd need at minimum a 60amp/hr battery - then you have to decide how to put that much into the battery every day........

On a bright summer day, a pv panel will gather roughly 6 times it's rated power per day - so the sums are simple - one 12w panel should give you your 6 amp/hrs (12v @12w = 1amp for 6 hours).........BUT if you only use a 12w panel, if you have a dull day, you may only get a sixth of that.........so you really need to quadruple the size of the panel to be reasonably sure of putting in sufficient each day............

Then "sod's law" kicks in - the time you probably need most lighting is midwinter, when there is least light available to power the panels - so instead of 12 watts of panel, you'd be talking 100 watts or more (and probably a tripling of battery capacity.......)

How many people get over the problem of low winter output is to go for a combined wind/pv system - you tend to get more wind in winter, and the output from a small turbine can supplement the shortcomings of the panels.........(but you need a good rural position - urban sites are not good for wind)

I hope that has given you a rough idea of the sums that need doing - and I'm pretty sure I've talked myself out of a lot of sales - pvs in the right place are superb, but if you want to provide substantial amounts of power are very expensive (even at our prices)

As another quick example, we were asked about the practicability of providing renewable energy to security cameras at festivals - the cameras needed to be on 24/7, and would draw around 1amp per hour - so we needed 24 amp /hrs to be reliably available per day (just for the 6 months of spring/summer - if for winter too, we'd have had to "up" the requirements substantially) - we decided we'd need 4x110 amp/hr deep cycle gel batteries (at £150 a pop!), 2x110 watt panels @ £410 each, one small turbine at around £500, and suitable controllers at around £100............

]]> http://solarwind.org.uk/myfaq/index.php?action=artikel&cat=4&id=3&artlang=en Thu, 14 Feb 2008 12:17:29 GMT A typical domestic solar installation

A solar system needs to absorb, retain, transfer and store the sun's energy as efficiently as possible. In order to do this the system requires a collector, a controller, a pump, and a store (cylinder).

In addition there will be a controller that measures the temperature in the panel and compares this to the cylinder temperature, and turns on a circulating pump to transfer the heat from the collector to the hot water storage cylinder, if there is sufficient solar gain.

There will need to be some form of frost protection, this is usually achieved using antifreeze though there is one system on the market which is freeze tolerant; using flexible plumbing which can freeze with out damage to the panel. This is a direct system and to prevent lime scale build up requires some form of water softening measure to be installed.

There have been huge advances to solar systems in recent years and leading edge technology ensures maximum performance and reliability. This is a huge industry in Europe especially in Germany and Austria where many of the best systems are made and many houses benefit from free solar hot water. Systems can be designed to suit all heating systems, and on a new build can provide an element to space heating, working particularly well with underfloor heating.

In simple terms
a)there just isn't enough useable wind over a roof - it is low speed and turbulent (you need a VERY tall mast in an urban environment)
b)they WILL be noisy - the noise will transmit into the structure
c)it will likely cause structural damage

further reading -
http://observer.guardian.co.uk/cash/story/0,,1805154,00.html

http://www.wind-works.org/articles/RoofTopOvertheTopinBritain.html

To put things in perspective - a £1.99 energy-saving lightbulb, if substituted for a 100w conventional bulb WILL save probably 3 TIMES as much energy over a year!

]]> http://solarwind.org.uk/myfaq/index.php?action=artikel&cat=1&id=1&artlang=en Tue, 17 Oct 2006 11:59:36 GMT