Tuesday, 5 February 2013

Domestic Solar versus Domestic Wind ? Solar wins, every time....

I still see people on eBay bidding hundreds of pounds for 300W domestic wind turbines.  Some of the sales sites use terms such as '..free energy...' and '...save money...'. but these claims simply don't stack up....

Given that you can buy 170W solar panels on eBay for around £80 or so each, let's do a very simple comparison based on real data from my own experimental installations of both solar and wind (see my previous posts for more details on each).

Since 300W is a common-enough domestic turbine rating (based on a 1.4 m blade sweep), we'll do the numbers based on 300W. 

Let's assume that whatever installation materials / batteries / controllers / inverters / instrumentation / cabling etc you'd need for one system would cost exactly the same as for the other.

Let's also assume that you've bought your 300W turbine on eBay for £160, the same price as two 170W panels.  To make it even simpler, we'll also de-rate these solar panels to a combined 300W watt-peak output.

Our particular solar system suffers as a result of shadows falling on the panels during the winter months, since they're set on a low-level roof and the sun only gets to around 10 degrees above the horizon at the winter solstice, which is not high enough to clear the trees at our southern boundary, resulting in very poor winter performance.

However, since the start of May 2012 up until the time of writing, our solar array has produced 181 kWhr of AC energy, but that's a 540W system, so pro-rata for a 300W system would be almost exactly 100 kWhr in the period.

Our wind turbine is open to all winds from the south-west to the north-west, this quadrant being by far the most frequent wind direction at our location and probably also for most of the UK.   There are no buildings to the west for hundreds of metres, and only a very few trees which could possibly influence the westerly winds.

I think therefore we have a far better site for a domestic wind turbine than the majority of the UK population. 

Despite the decent site, since the start of May 2012 up until the time of writing, our wind turbine has produced just 15.3 kWhr of AC energy.  To be conservative, we'll say our own turbine is rated at 200W, so pro-rata for a 300W system would be 23 kWhr in the period.

So, at our location, the 300W solar system is four times more productive than the 300W turbine system.    And that's despite the solar panel location being sub-optimal and the turbine location being well above average.

Put it into cash terms, and you can see how terrible they both really are... at an electricity tariff of say 14p per kWhr, then the 300W solar system has returned just £14 worth of energy in the period.

However, if that wasn't bad enough, the 300W wind turbine has only returned £3, and that's actually a gross figure. 

The turbine of course is mechanical equipment and requires periodic maintenance.  This year, I've bought a set of three new rubber mountings and replaced the slip-ring carbon brushes.  Although these items only came to around £6 in total, and ignoring the cost of a couple of hours of maintenance work, that's a negative return on just the operating costs, without even considering the initial capital investment !

So unless you live in a croft on a hill in the Scottish islands where the winds are consistently stronger and more predictable, or you've nowhere at all on your property that allows a couple of panels to face south with a relatively unobstructed aspect, then a domestic wind turbine seems a very poor alternative to a couple of solar panels.

In conclusion, although neither is a good investment without greatly enhanced feed-in tariffs, it appears that solar will win hands down almost every time.....

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