The set up

The set up
5.46mm jet delivering 0.68 l/s to the pelton which is rotating at 900 rpm and generating 135 watts into the grid.

Thursday, 25 February 2016

How significant is the contribution from a Powerspout ?

There are, by my reckoning, at least eight small hydro installations within a radius of 5 miles from where I live.  Most are in the 10 to 20 kW range and most are owned by farmers who have seen the economic sense of generating their own electricity.  Here are two of them:
This one is a twin jet Hydrolite turgo unit driving a vertically mounted induction motor giving 8 kW into the grid.


And this is an Ossberger crossflow turbine, again driving an induction motor as generator, with a full flow capability of 30 kW.

These machines have been put in for one reason: to earn money. The income they earn from the favourable government scheme which, until recently, we have had in the UK, means that such 10 to 20 kW installations can provide a very useful new income stream, - a source of farm revenue which is diversified away from the main source of agricultural income.

By comparison with these machines, my Powerspout looks almost like a plastic toy, and being rated at just 0.75 kW at full flow, it is not surprising that many people cannot believe it makes a useful financial contribution. Certainly in terms of income arising from the government 'Feed in Tariff' scheme, it is true the cash return is nothing like what my neighbours are getting.  But a very small turbine has a hidden advantage over its bigger cousins.

This week I received my electricity bill for the last quarter, the quarter which runs from Nov 19th to Feb 19th.   Here it is:






As you can see the total energy consumed was 289 units of day-rated energy and 89 of night-rated, making a total of 378 kWh.

I know its rather sad I do this but I've been keeping records of electricity consumption since we moved here in 1992. Plotting the consumption for each first quarter since 1994 gives this graph:


The figure for the latest quarter, 378 kWh, is seen at bottom right, and is the lowest first quarter consumption ever, lower even than the two previous years during which the Powerspout was operational.  (in case you're wondering why the consumption was so high from 1998 onward, the reason is a combination of having children of teenage years in the house combined with having elderly parents from 2003 onwards. One elderly parent is still with us in 2016.  Without her, the Powerspout years 2014, 2015 and 2016 would show even less grid consumption).

The hidden advantage of a small turbine is that its output is so small that all of it, or virtually all of it, gets to be used 'in-house'.  The same cannot be said of a larger turbine because a normal house would struggle to consume the continuous higher level of power output it can put out. So all of the small turbine's output earns a return twice over: once from the feed-in-tariff payments and again from offset of grid energy. Only a small proportion of a larger turbine's output earns 'twice over' in this way.
    
So whilst the financial benefit from feed-in-tariff income might be small for a Powerspout, the financial benefit from 'offset' grid energy is significant: as the bill above relates, this quarter has cost £71.72; the bill for a first quarter in a typical pre-Powerspout year such as 2013 (when electricity prices were very slightly cheaper) was £261.14, giving an offset value for this quarter of £190 (calc: 261- 71).

Factor in the much higher installation cost for a big turbine, which can be approximated at being £7,000 - £10,000 per installed kW, and the maths for a small turbine become even more attractive.

How significant is the contribution from a Powerspout then ? - I would say very.

Added later: for the sake of completeness, the Powerspout's generation for the same quarter was 1,697 kWh.  If all of this was used in-house, total consumption for the quarter was 2,075 kWh (calc: 1,697 + 378). The gain from offset was therefore greater than as calculated above, which used consumption in 2013 when the total was 1,736 kWh.

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