It’s been a long and mainly uphill struggle over the last twelve months or so and it’s not over yet, but the Powerspout http://www.powerspout.com/ hydro turbine is at last commissioned and working. Or at least it was working albeit briefly yesterday just to test that the theory works. I’m awaiting word from SEPA http://www.sepa.org.uk/ to see how much and when I can use it.
From the epic laying of 800m of pipe and dragging almost as much armoured cable over the hill I never doubted that it would (eventually). What I was not so sure about was how to integrate into my existing system to best effect over that huge distance from the turbine to battery bank, almost a kilometre 😦
A straight 48v turbine http://www.powerspout.com/powerspout-be/ feeding the batteries would be the simplest answer but cable costs ruled that out. A 250Vdc version using an MPPT controller http://www.powerspout.com/powerspout-me/ would have brought cable costs down but still expensive over the 800m route and I’m not a fan of MPPT http://en.wikipedia.org/wiki/Maximum_power_point_tracking controllers. This may well be just ill founded prejudice on my behalf but I’ve heard of quite a few going up in smoke, and whilst there’s no doubt that they do produce more more power they actually use some as well. This is something that the manufacturers seldom bother to mention, quoting only the 20% increase in performance (under certain conditions) and not mentioning the 5% required to power it 😦 Those figures are off the top of my head so don’t quote me, but I’m still to be convinced that current models of Outback, Morningstar and Midnite Solar are reliable enough for LATETOR 🙂
The best option to my way of thinking was the HV version of the Powerspout http://www.powerspout.com/powerspout-he/ that produces up to 600Vac three phase and is transformed down to 48Vdc at the batteries for charging. There are losses associated with the transformer but cable could be cut down to a mere 1.5mm square. However this Unit is not sold outside New Zealand, and whilst I’m pretty sure I could have overcome that hurdle I decided to opt for the GE version (grid enabled) http://www.powerspout.com/powerspout-ge40/ . This model works at voltages of up to 400Vdc and is designed for those who wish to feed into the grid via a standard ‘grid tie inverter’ but of course I’m not actually on the grid 😦 Fortunately the ‘off grid’ inverter that currently supplies our house, a Trace SW4548e is capable of ‘back feeding’ any surplus power into the battery bank. Trace don’t tell you this and if you have no means of regulating your batteries state of charge they will cook, but it is, in theory at least possible to connect a standard GTI (grid tie inverter) into your ‘AC bus’, use the power produced and then charge you batteries http://currentgeneration.co.nz/site/current/files/Partial%20AC-coupling%20in%20Minigrids.pdf .
This is exactly what SMA do with there ‘Sunny Island’ system using a slight shift in grid frequency to allow the various inverters to ‘talk to each other’ and control battery SOC.
Designing off-grid wind and solar installations differs from grid tied installations in a number of important ways such as:
- The solar array must be in a certain restricted voltage range
- The solar and/or wind generator must be kept very close to the battery bank
- Expanding the system in the future can involve complex wiring
SMA has addressed many of these issues in their Sunny Island product range by offering a unique system configuration where all power generation sources can be connected directly to the AC bus as illustrated below:
The system certainly is innovative and offers a number of advantages over traditional DC coupled systems, but there are potential downsides too.
In this article, I’ll explore the advantages and disadvantages of AC side coupling using the Sunny Island and Sunny Boy with more traditional DC side coupling using the Outback MPPT charge controller.
And I’ve just lifted the above from StephenDV’s excellent blog http://www.casanogaldelasbrujas.com/blog/2009/05/13/sma-sunny-island-ac-coupling/ to save me waffling 🙂
Anyway, after doing all the feeding yesterday and finally finishing installing all the hardware
I tested the connection to the current system 140m away at number 3 http://www.iosea.co.uk/3sarnish.shtml , firstly with a bulb, then a circular saw and finally a 2Kw heater. All worked perfectly without tripping the RCD so I was pretty chuffed. Next, and the most hair raising step was to try out the turbine around 800m away as the crow flies. A hasty phone call to Hugh at http://scoraigwind.com/ the supplier of all my kit and repository of all knowledge ‘renewable’ followed and on his advice I started up the Powerspout first on account of my ‘DC disconnect’ which was just a double fuse holder and would probably give a large flash when connected under load 😦
The next twenty minutes or so as I raced back from the turbine to the shed were ‘hair raising’ to say the least but eventually the GTI connected and produced a good 750w for the next few hours until I switched it off 🙂 There is room for improvement by altering the settings via a communication cable to my laptop but that will have to wait until another day.