The set up

The set up
5.36mm jet delivering 0.63 l/s to the pelton which is rotating at 870 rpm and generating 127 watts into the grid.

Saturday, 6 March 2021

How I use the electricity my Powerspout generates - in summer months

In the previous post I showed how electricity from my Powerspout is used in winter; in this I show how it's used in summer.

The seasons are quite different; winter sees generous hydro and little solar; summer is the opposite with lots of solar and little hydro. 

There are other differences: in summer the fire in the house is not alight and the space (storage) heater for the priority 2 diversion load is switched off; together these differences create a quite different pattern for what happens to the electricity which is generated.

As with the previous post, I have taken data from one particular day, an unusually sunny day from the look of the solar generation record, to illustrate what happens in summer; the two plots below display the data.

Plot 1

Plot 2

Explanation of the plots

as before, the vertical axis of plot 1 is power in watts, of plot 2: watt hours, and the horizontal axis of both is the time of day.

the green line represents power being generated, - in the hours of darkness this is only the contribution from the Powerspout (283 W), but when the sun is up, it rises to 3000 W as the PV array adds its contribution; the PV comprises 12 panels, each rated at 275 W (ie 3.3 kW peak).

there being no input from a fire to heat the house hot water in summer, the first priority for any spare power is for this purpose; the diverted power appears as intermittent blocks of red bars, intermittent because a washing machine, dish washer and bread maker are programmed to come on during the night; when they draw power, none is available for diversion, especially since the Powerspout is only producing 283 W;

from Plot 2, a total of 2 kWh can be seen to have been diverted to house hot water by 08:20, - little of it coming from the Powerspout and most coming from the PV in the first 1.5 hours after sunrise.

after house water is up to temperature, power is then seen to be sent to the second priority load, signified by blue bars, until that too reaches its thermostat setting; 

the priority 2 load in summer is an immersion heater in the hot water tank of the annex;  when both annex and house hot water are up to temperature, no diversion loads are available and excess power is fed back into the grid; there are just short duration top-ups to one or other diversion load from time to time.

the total energy exported to the grid on this day was ~ 14.7 kWh 

imported energy from the grid was 2.7 kWh.


The big difference between summer and winter is the amount of energy which is spare; in summer, at least on a sunny day like the day studied, 14.7 kWh was put back into the grid, and to this can be added the 3 kWh which went to the priority 2 load because it is not usually necessary for us to have hot water in the annex;

in winter there is really none to spare; diversion to the annex which is optional in summer changes to being essential in winter; the 7 kWh which goes there is needed to take the chill off the rooms and stop water from freezing.

As I said in the previous blog post, the purpose behind analysing how our home generated electricity is used is to be able to make an informed decision about opting for home battery storage; I mentioned that one factor in that decision is what happens to the grid price of electricity.

This week I was notified of another increase ! 

On April 1st 2021 our off-peak energy moves up from 12.44p to 14.26p, standard day energy from 18.67 to 20.65 and the standing charge per day from 24.1p to 25p.

Now, I just need the price of batteries to come down !

Saturday, 9 January 2021

How I use the electricity my Powerspout generates - in winter months

In January and February my Powerspout produces more electricity than at any other time of year; its power output is usually a constant 924 Watts giving an energy yield of just over 22 kWh per day.

The question I want to answer in this blog post is: how does this electricity get used ?

Below are two plots which show how the power and energy was used on one, unexceptional day last year: the 20th February 2020; the data was captured by the diversion device I use (a Solarcache) which has the ability to record information every 6 seconds to an SD card.

Plot 1

Plot 2

Explanation of plot 1.

the vertical axis is power in watts; the horizontal axis is the time of day.

the green line represents power being generated; during the hours of darkness, fairly obviously this will only be from the Powerspout, but between 08:30 and 16:00 a variable contribution from solar panels is added giving the spiky appearance mid-way through the day.

power in excess of what is being consumed in the house as 'base load' is diverted by Solarcache to two 'non-essential loads'.

these two non-essential loads are prioritised so that one, a 3 kW immersion heater giving the main house its domestic hot water (DHW), receives power first until the water is up to the temperature of its thermostat;  when power is being fed to this load the plot represents it by the red bars.

when the thermostat opens, Solarcache senses there is no load to supply and starts sending power to the second priority load, represented by blue bars; 

this second load is comprised of another 3 kW immersion heater supplying hot water to our 'granny' annexe plus, in parallel with it, a 3 kW storage heater for space heating in the annexe; the storage heater is set to allow air to convect through it at all times so it never gets hot enough for its thermostat to open; in this way the priority 2 load never switches off and is always available to receive excess power.

'base load' consumption in the house at any moment can be determined from the plot fairly exactly by the number of watts by which generation exceeds the power being sent to one or other diversion load; I say fairly exactly because Solarcache always allows a trickle of power to flow back to the grid, of about 40 to 80 W; this amount will contribute to the difference between generated and diverted power and makes it difficult to be precise about base load consumption.

base load is made up mostly of lighting (LED or compact fluorescent) but includes also a Grundfoss central heating pump (48 W), a fridge and a freezer (111 W each) and innumerable switch-mode battery charging devices; we have no TV.

when a power hungry household appliance is switched on, requiring more power than is being generated by the sum of hydro and solar generation, the diversion loads automatically switch off and the extra power needed to supply the appliance is drawn from the outside grid. 

the household appliances which make up the power hungry category are: kettle, hob, oven, microwave, vacuum cleaner, washing machine and dishwasher, - the latter two only being power hungry when they are heating water which they have to do as each is only fitted with a cold water supply.

the discerning reader will detect the times when power hungry appliances were in use on 20th Feb 2020 by the white gaps within the red and blue bars.

the provision of DHW in the main house does not only rely on its immersion heater; the tank also has a heating coil which receives hot water from the back boiler of a log burner in our lounge and in winter this is burning 24/7; thus the water quite quickly gets hot enough to open the immersion heater thermostat and for this reason the cumulative energy taken by the priority 1 load is less than that of the second priority load in the annexe.

Explanation of plot 2.

the vertical axis is in watt hours (Wh); dividing by 1000 gives the more common unit for energy: the kilowatt hour, - kWh, - aka a unit of electricity for metering purposes.

the blue and red plot lines represent respectively the cumulative energy diverted to the house load and the annexe load;

as explained above the priority 2 (blue line) receives the greater share because DHW in the main house receives additional energy from a log burner and can switch off, whilst the priority 2 load can never switch off and is always available to soak up power.


this is how the system works in winter when winter conditions prevail: hydro power is plentiful, the lounge fire is alight and solar power is minimal.

the situation in summer is quite different and will be the subject of a later blog post;

the 'brains' of the system is the Solarcache and it is a huge pity this device is no longer available; mine has been bomb proof since installation 5 years ago and I am not aware of anything being marketed now which has quite the same functionality.

the SD card (8 GB size) which stores all the data has been quietly recording everything since August 2015 and last week covid lockdown stimulated yet another job to be tackled that had long been put off, - I ventured to download the accumulated data; there was 2.3 GB of it with each day accounting for 1.3 MB; considerable patience was needed because it took ages to get the data off the card to my desktop, and then MS Excel went into extra slow mode trying to crunch the figures.

such a huge amount of data is probably excessive but its usefulness is in being able to see how much surplus energy my combined hydro and solar installation yields at different times of the year; such information can help decide whether storing the energy in a battery, rather than use it for diversion load heating, might be a worthwhile road to take. 

For the moment, I don't think that is the way I want to go, but if battery prices come down and grid electricity prices go up, at least I'll have the hard data to help me make the decision.

A fuller description of Solarcache is in this blog post.

Saturday, 24 October 2020

Repairing and damp-proofing a V-Clamp board

A job, long delayed by uncertainty about how to proceed, has finally been taken off my "to do" list: how to restore Voltage clamp boards which have failed. Time to devote to it happened because of Covid, - a minor bonus in these otherwise difficult times.

Early Powerspout turbines had V-clamp boards to keep voltage within limits when the output from the turbine is to an open circuit; the function of the board is to divert power to a dump load and thereby hold the Powerspout's output to a voltage acceptable to whatever device the turbine is connected to: - either an MPPT controlled battery charger, or as in my case, a grid tied inverter.

When manufactured, the boards were covered with a conformal coating intended to keep the underlying electronics free of moisture, but the coating used was hot melt glue and at low temperatures this becomes brittle, separates from the underlying printed circuit board and develops cracks. Through these cracks, moisture could reach the live circuitry beneath and sooner or later this had terminally disastrous results.  

In the early months of my installation in 2013, two boards died in this way; but the years since have been completely trouble free through EcoInnovation having come up with a one-off special, - special in that the board was entirely encased in an epoxy resin block.

So the long delayed job has been to repair the two boards that died, and then to cast them in epoxy, as had been done for the special.  

Here, in pictures and captions, is the process:

An original board showing how the coating of hot melt glue cracks and separates from the underlying pcb, allowing moisture to enter.

Typical tell-tale evidence of underlying pcb damage with blackening visible through the conformal coating and molten glue running out. The white stuff is heat conducting paste applied to the heatsinks on the board where they attached to the bulk head of the turbine; the bulk head, being water cooled on the pelton side, creates a good means of dissipating heat from the power electronics on the board.
Initial view of the damage once glue had been removed; since hot melt glue becomes brittle at low temperature, cooling the pcb in the freezer to -18 deg C allowed the coating to be chipped off, but it is a very time consuming process and care is needed not to accidentally remove any surface mounted electronic components. (addendum 9 Feb 2021: see below for an alternative method.)
Later view of damaged area after further cleaning, showing the glass fibre substrate of the pcb has carbonised and copper tracks have been lost; carbon being a conductor, this all had to be removed using a precision rotary tool (Dremel) and the resulting cavity filled with non-conducting epoxy.
Top-side view of the same area of damage; from some components such as the surge protection thermistor in the centre, the hot melt glue could not be removed, so this device was de-soldered and replaced with new; flakes of hot melt glue are still visible around surface mounted components.
Damaged area after repair; the next stage is a final clean with isopropyl alcohol then casting in epoxy
Topside view after repair with a new surge protection thermistor and adjacent capacitor
This is the 'special' made for me by Andrew Smithies, who designed the board; it was with his advice I arrived at my method of casting; one key piece of advice concerned 'thermal runaway'; this is the intense heat generated by two part epoxy compounds as they cure; the heat was so much when he did it that it melted the mould and let some of the epoxy escape; the resulting void had to be filled later with more epoxy; but epoxy added later to already hard-cured epoxy does not unify into one block, so I was keen to avoid this happening.
Before proceeding to casting the repaired pcb I wanted to check it was fully functional; at this stage it was vulnerable to moisture with the bare soldered components having no protection, so testing had to be done on a dry day with low ambient humidity; the test shows volt meters on the two outputs when the turbine was operating without power being fed to the inverter: - the digital voltmeter reads 381v dc, which is the correct voltage for the 400v version of the V-Clamp board, and the AVO analogue meter is reading the voltage being fed to the dump load. The turbine was then allowed to connect to the grid via its inverter and a test was performed to simulate a 'loss of grid' event to check the circuit board instantaneously diverted power to the dump load; all tests were satisfactory and I felt confident the board could be epoxied.
The secret to constructing a mould which can be used more than once is to use material for the mould to which epoxy does NOT bond, and that means polypropylene; a convenient source is a kitchen cutting board and such is what I used, price £7; for the curved bottom, on my first effort, I used a strip of flat rubber sprayed with silicon lubricant to act as a releasing agent; but the epoxy bonded to it and when the mould was disassembled, the rubber had to be carved off the cured epoxy block; on my second effort I used a non-stick sheet, PTFE coated, marketed as oven shelf  liner; it worked fine but needed to be supported by a backing for which lead sheet, as used in roofing, proved OK. Where pp or PTFE is used, no release agent is necessary, - the cured epoxy separates from the mould very easily.
The epoxy I chose to use was "Water clear" Transparent Epoxy Potting Compound from MG Chemicals; I bought it through RadioSpares; for the size of mould I had made each board needed 1.125 litres of epoxy; conveniently for two boards this meant buying one kit of 1.5 litres (RS no: 181-0370) and two kits, each of 375 mls (RS no: 181-0369); each kit comprises resin and hardener in a ratio of 2:1. It is not wise to attempt a mix of 1.125 litres to fill the mould in one go because this will lead to unmanageable thermal runaway; it could get hot enough to damage components on the board; I mixed 300 mls at a time (200 resin + 100 hardener) at half hourly intervals to stagger the curing time and reduce the temperature rise; it therefore took about 2 hrs to fill the mould; even doing it this way, the temperature still reached about 80 deg C and the 300 ml mixes added last cured more quickly than the earlier mixes because the mould had by then begun to get hot.
You are helped to a good outcome in epoxy potting by being well prepared: graduated beakers for mixing resin and hardener, stirring sticks, cleanliness in the work area, a means of de-aerating the mix before pouring it into the mould, a kitchen timer or clock, warming the resin and hardener in the oven to 45 deg C before you start so their viscosity is as low as possible to facilitate mixing and de-aeration. Thorough mixing is particularly important because any resin not mixed with hardener will not cure; it will lead to a sticky patch in the finished block; I stirred for 5 mins timed on a timer; the type of epoxy I was using will remain workable for up to 1 hour at 20 deg C but for less time if it is warmer; each successive mix of 300 mls will bond to the previously poured batch as long as the cure has not reached the stage of being hard, as estimated by whether a finger nail can indent the surface.
Getting the bubbles out after mixing the resin and hardener is important; it can be done by waiting if the mix is not too stiff, or it can be done by placing the mix in a chamber and reducing the pressure; I chose the latter method and used a vacuum cleaner to suck out from a closed container; it seemed to work and I supposed it worked by making the air bubbles in the mix expand and so rise to the surface more quickly.
There are two stages to the curing process, soft cure and hard cure; you don't want to remove the block from its mould until hard cure has reliably been achieved throughout its mass; this can be ensured by 'post-curing' in an oven at 80 deg C for 4 hours, and this is what I did, waiting until the next day when it had cooled down to disassemble the mould.
The result was better than I had expected: the epoxy had filled all crevices and the mould left clean edges; the original V-Clamp board attached to the Powerspout bulkhead with self tapping screws driven in through the bulkhead from the pelton side but a modification in this epoxied board was to incorporate M5 machine screws into the epoxy, onto which Nyloc nuts fasten to draw the heatsinks tight against the bulkhead. I had expected to have to reduce the bulk of the finished block with a disc sander in order to get it to fit in the confined space it occupies above the Powerspout's bearing housing, but in the event it fitted perfectly by entering it from the bottom right side and then rotating it anticlockwise into its final position. 

The board depicted was installed in the turbine on 7th October 2020 and has so far worked perfectly; it should, I hope, go on working for years to come.
Repairing and epoxying these two boards has not been without expense: the more severely damaged one was beyond my repair abilities and cost £320 to have done professionally. The other board only cost the price of replacing one MOSFET, - a few pence.
Clear epoxy of the type I used is not the cheapest available but I wanted to be able to inspect the encapsulated components should failure occur, - not that repair would be possible once potted.
For each board the epoxy cost worked out at £232.
I did have the option of ditching the present system in which a V-Clamp board is necessary, either by changing to using a Klampit device and continuing with the SMA inverter I use, or by discarding the SMA inverter and changing to one which can accept 600v dc rather than the 400v dc the SMA is designed for.
Either alternative would have meant disrupting a system which has proved bomb-proof for 7 years, and having several spare SMA inverters and V-Clamp boards, I decided to stick with that way of dealing with voltage capping.
Getting to the point of having these two boards repaired and ready for use has been a long journey; for several years I didn't think it was going to be possible; but having done them, and having learned a good deal in the process, I'm glad of having pursued it.

An alternative method to cooling to remove hot melt glue is to use heat; at 120 deg C the glue becomes liquid and drips off; the circuit board is hung in an oven;