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.

Tuesday, 17 November 2015

Making use of what you generate

In the course of the last ten days, as the flow from the spring has picked up, output has doubled from 225 W to 518 W .

At 518 W, more than enough power is being generated to meet the 'base load' of our house, by which I mean the total load of all those electrical gadgets which are taking power in the background most of the time.  For us, 'base load' is made up of fridge and freezers, central heating pumps, lights, computers and a good number of small devices connected through mains rectified power units.  The total load comes to about 350 W, but it fluctuates, particularly depending on whether fridge and freezers happen to coincide their 'on' times.

So there is a surplus of generated power much of the time, and as water flow picks up further, this surplus will get greater.  What to do with it ?

Back in August this year, I had some solar PV panels put in, 3.25 kWp in total, and at the same time installed a Solar Cache, which is a device to divert surplus home generated power to useful loads 'in-house'.  The greater benefit of Solar Cache comes from diverting the huge amounts of surplus power arising from a sunny day, but it works just as well in diverting the smaller amounts of surplus hydro power.  By so wiring it that it registers the total of home generated power, it works seamlessly to divert power whether it is solar, hydro or a combination of both.

Here is a picture of the Solar Cache screen taken last night:

Taken as it was at 22.50, there was no solar generation and the 518 W indicated to be solar all comes from the Powerspout.  House 'base load' at the time is recorded as 197 W so there was a surplus available of 321 W.  The cleverness of Solar Cache is that it diverts as much of this surplus as it can to a useful load, whilst just maintaining a trickle of export to the grid.  From the screen, it is trickling 95 W to grid and sending 230 W to the immersion heater in our domestic hot water tank.

Under the feed-in tariff scheme implemented in the UK, payment for 'exported' energy is not calculated from a metered export reading but from a 'deemed' amount, which for hydro is 75% of energy generated.  Thus the way Solar Cache works which is to keep exported energy to a minimum (the makers claim around 50 W) does not mean that the revenue one receives for exported energy is reduced.

This, however, may be about to change.  In the UK, the government are embarked on a public consultation regarding changes to the feed in tariff scheme, and one of the questions in the consultation is:
"Given our intention to move to fully metered exports for all generators, do you agree with the proposal that new and existing generators should be obliged to accept the offer of a smart meter when it is made by their supplier?"

The effect of this change, were it to be implemented, would certainly reduce the income coming from a Powerspout, and this would be the case whether one had a Solar Cache or not.  A Powerspout installation, by the smallness of its output, will never generate sufficient for 75% to be exported, so any change from the present calculation method based on '75% deemed' will reduce income and prolong the 'payback time'.

But hey ! - it's not about the finances but the fun of having such an elegant source of home power.

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