Zone5

I just wired up a new photovoltaic array- an auspicious time to do it on the longest- and so far the sunniest- day of the year.

Delivering a cool 600 watts of raw solar power at 24volts, the impressive bank of solar electric panels represents a true powering up here at Derryduff.

The panels cost me about 2000 euros on ebay- about 2/3 of the new price; they were originally from Surface Power.

I also have a bank of 4 Rolls batteries (244Ah each) bought from Wind and Sun. Cost: 1300 euros.

The 2.5Kw inverter is from Victron; I bought it a few years ago for around 1500 euros.

The controller is a  ProStar -30 from Morningstar, supplied by the Sustainability Institute for 85 euros.

Add in 24v compact fluorescent lights, cables and connectors and you are looking at over 5000 euros for this system.

(I also have another two pv panels I have had for some time which would add an extra 150watts, giving a total of 750 watts).

People often ask: does that give you enough power? but when living off the grid, this is really the wrong question- you have to cut your cloth according to your measure, and a battery system involves juggling energy supply- the amount of sunlight- with storage capacity, which determines how much power you can actually use.

In an often cloudy northern latitude country like Ireland living with just solar  means that there is a huge variation in supply, from a massive surplus in the summer- the batteries are full but the power just keeps coming in when the sun is out.

(The panels will still charge when it is overcast, but only at a small fraction of their capacity.)

The 100 shortest days of the year here generate only about 10% of the annual sunlight, giving an indication of the issue here- which is also an issue for bigger scale national solar systems.

On the other hand in the winter, when demand for lighting is highest and sunlight is lowest, I may be struggling to run my basic needs for a light, radio and laptop.

(Energy saving tip for laptop users: my Lenovo laptop uses about 50 watts, but this can be reduced by half if you take the battery out while using it, even if the battery is full.)

You can’t just keep buying more batteries or more solar panels because of the cost, so it is a completely different philosophy from living on the grid where you can just plug anything you want in any time. I will need to try to time my maximum power use- such as building work with power tools- to coincide with the longest days of sunshine.

The cheapest way of improving the system then would be to install a small wind turbine,which would make a huge difference and probably tide me over quite well through the shortest days.

Solar costs something like twice as much per kilowatt hour as wind in Ireland, but only in optimum sites; I am in a not particularly suitable site for wind, and a substantial amount of cost of wind would be in the tower, with costs increasing according to the height of the tower. The height of the tower is critical, you need it as high as possible to catch the faster wind speeds and avoid turbulence from obstacles.

It was technically much simpler to set up a solar array, and since there are no moving parts this system also has the advantage over wind of minimal maintenance.

So what can I actually run from my system? Since I am coming from a very low base of consumption with hardly any electrical appliances, for the summer at least I am in the luxurious position of being able to dream about how i would like to use my surplus power. I have already bought a small 1L electric kettle which uses 1Kw, and this I consider a very useful addition because it will save a significant amount of gas (my ususal form of cooking) during the summer.

Power tool use will be very important for building work over the summer, but the next major step will be to get… a washing machine!! in terms of labour saving devices, this has got to be tops, and only then will I be able to feel that I have left the domain of the beasts and joined the rest of the human race.

(Currently I cheat: the launderette or relying on my girlfriends; goodwill, which is probably running short by now in any case.)

Make no mistake: living off grid is hugely expensive, and requires some knowledge and skills which I only have in rudimentary fashion. It requires a quite different relationship to energy use than that which most are accustomed to as you can’t assume you can just turn on what you want when you want.Overall, it would be prohibitive in cost to have a system that approaches the profligate domestic energy consumption of the average household- I rarely have more than one light on for example!

One result of this is that you become much more aware of your energy consumption and much more cautious about increasing it and thereby increasing demand.

Maybe one day the grid will start to fail and all my investement will seem worthwhile as I am the only one in the valley still with the lights on.

Until, that is, the batteries start to fail- as the Achilles heel of an off-grid system, their life expectancy is unlikely to exceed 10 years by much, by which time who knows if society will be able to supply replacements?

In the meantime, I’m going to put the kettle on again and then go and soak up some of this glorious weather.