Permaculturing in Portugal

One family's attempts to live in a more planet-friendly way


I’ve been mulling over this dilemma.

Is our energy budget better balanced by being independent from the grid, so we’re not adding to demand or drawing power from any non-renewable generating capacity?

Or, taking a bigger view, is it better to hook up to the grid as a micro-generator and contribute renewable energy to a communal resource?

Using the grid instead of battery storage makes a lot of sense. Electricity doesn’t store very well and batteries are not hugely efficient, have limited lifespan, and are expensive. But it also seems slightly daft to be exporting all our capacity to the grid only to take it back again, since a lot of energy is lost in transmission.

It’s kind of like our situation in Scotland where water from the local reservoir now travels all the way to the outskirts of Edinburgh (where it’s subjected to all kinds of abuse) before being piped all the way back out to us again, a round trip of about 60 miles, a fair bit of energy used in construction and operation, and water that doesn’t taste anything like as good as it used to.

Maybe some sort of hybrid is the thing? A relatively self-contained system that only exports surplus power to the grid (instead of dumping it, which the hydro generator I’m looking at is designed to do) and draws power down only when demand temporarily exceeds generation and storage capacity? This might give us the best of both worlds. On the one hand, enough oomph for wielding the odd power tool plus power to keep us going when the water’s low and the sun’s hiding. On the other, minimal transmission losses, power during power cuts, and contributing our surplus to the community instead of wasting it.

I’m not sure I have the definitive answer to this yet. For one thing I have to find out how much it would cost to connect us to the grid, and cost that out in various permutations with batteries. And I think somewhere at the back of my mind I don’t quite trust myself not to get more careless with power usage if I’ve always got unlimited supplies on tap …

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  1. sophie February 11, 2009

    we’re mulling over the very same thing, since the solar guys were round today and told us the batteries alone will cost 6,000 euros! eek!!
    but … i don’t think with edp you have the option of selling only your surplus :(

  2. Quinta do Vale February 17, 2009

    Hmmm … that changes the thinking a bit, doesn’t it?

    €6,000 sounds a lot. What sort of capacity are you getting for that? Regardless, what gets me is the thought that in 10-15 years time you’ll need to start shelling out major money again, even allowing for improvements in technology and pricing, so the grid looks attractive over the longer term.

    However, supplying all your power to the grid leaves you wide open to the uncertainties of utility pricing policies (€/kwh supplied vs €/kwh consumed), and offers no protection against power supply failures. And while I like the idea of adding to the total of renewable generating capacity, I don’t so much like the idea that by doing so I’m helping to power unsustainable and polluting industries.

    It’s a difficult one. Instinctively I’m more drawn to the self-contained option, but philosophically feel quite strongly about the community thing. Perhaps the former is more appropriate for now and the latter will evolve over time?

  3. Christopher February 19, 2009

    Interesting discussion. I too am looking to investing in an upgrade in my solar system. A decent solar system you can get for €5000. Ihave a 125W Kyocera Panel, 225Ah 12V battery and small inverter and controller. I am looking to get another panel and a big 2KW inverter (for power tools) controller and batteries (haven´t decided the capacity yet). You must have quoted for the biggest batteries!

    Baterias Estacionárias Classic Solar – 2 V
    Descrição PVP €
    190 Ah / 120 h 92,00 €
    245 Ah / 120 h 105,00 €
    305 Ah / 120 h 119,00 €
    380 Ah / 120 h 136,00 €
    450 Ah / 120 h 166,00 €
    550 Ah / 120 h 172,00 €
    660 Ah / 120 h 180,00 €
    765 Ah / 120 h 197,00 €
    985 Ah / 120 h 229,00 €
    1080 Ah / 120 h 274,00 €
    1320 Ah / 120 h 313,00 €
    1410 Ah / 120 h 334,00 €
    1650 Ah / 120 h 364,00 €
    1990 Ah / 120 h 416,00 €
    2350 Ah / 120 h 502,00 €
    2500 Ah / 120 h 550,00 €
    3100 Ah / 120 h 742,00 €

    So looks like the batteries you wold be getting are 2500Ah. That is a large capacity and so quite expensive. Don´t forget when you calculate how much energy you think you will use the solar dealer will try to sell you a bigger battery capacity than what you need. What will you run off your system?

    I would run sound equipment for my music studio, a fridge in the summer, possible washing machine ( really important to heat the water by other means when running a washing machine than electricity as this uses a lot of power). computer, maybe a kettle in the summer ;-)

    It is true that the batteries do not last forever and so are inefficient. And this is a good reason to connect to the grid. But I think it better to be off grid…I´ll let you know if I change my mind if we get some 60Kv Pillons lines passing close by (how close still don´t know).

    In essence I think smaller systems are better…the grid is a big centralised inefficient system. Bad weather can cause a lot of disruption with all those cables. And transporting electricity is hugely inefficient in these cables.

    If more of us invest in off grid maybe it should bring down the costs for others.

    We should certainly look into mini hydro systems as power generation for lights say. Right now there is plenty of water in the stream at Quinta dos Melros. Magnus Wolfe in Nothern Portugal is writing a thesis on this topic.


    I understand you can be supported by the state to produce solar electric, a bit crazy that you can´t use it yourself!

  4. Quinta do Vale February 19, 2009

    Thanks for the battery prices Christopher. Where did you get that list from? It would be a good exercise to compare UK and PT prices.

    Apparently the PT government has just (as in last week) made an announcement about paying 50% of renewable energy installations. More details are awaited.

    More here.

  5. Prajna September 7, 2015

    This is a big subject. I’m not surprised someone is writing a thesis on it, it warrants a book-length thesis.

    However we choose to generate, store and transmit our energy one thing is certain: we need to focus on more efficient use of energy. There are many people working on developing ‘free’ energy/zero-point energy, micro solar/wind/hydro systems; indeed all kinds of energy generation systems. But even with unlimited free energy we have the problem that all of our electric and electronic devices are, in most cases, hugely inefficient, and that inefficiency translates to generation of heat or, even worse, to wear. So really our first priority should be to cut down on our energy use and to make our equipment more efficient.

    The next part of the problem is that storage is difficult, expensive and inefficient. Lead-acid batteries are heavy, high maintenance, require careful use (they can be over or under charged, overheat or freeze, etc), are bulky, have limited lifespans and can be difficult to dispose of, amongst other things, particularly that they are expensive.

    We have ambitions of building reservoirs on our mountain that we can fill with excess wind and solar, to then run micro-hydro, since that is a very efficient storage system that is low maintenance, ecological, long lasting and offers the added advantage that we have another reserve of water as a buffer if our spring fall short.

    Designing a solar system is a science in itself. There are many factors to consider and any system will require comprises between the various factors. You’ll have to understand volts, amps and watts, amp hours and watt hours, parallel and serial, that a 12 volt panel likely puts out around 20 volts and a 12 volt battery seldom measures at 12 volts. You’ll need to be able to calculate peak usage and assess reserve requirements. As I say, it requires a great deal of study and thought. Having said that, a basic system is not so hard to put together and many find that developing their energy system is an iterative process.

  6. Quinta do Vale September 7, 2015

    Thanks for the comments, though this post is now over 6 years old so I’ve long since made my decisions about power here and climbed a good way up the renewable energy learning curve!

    With that experience in mind, it’s interesting to revisit how I was thinking back then. The sense that neither solo generation nor national grid-scale generation was quite ‘right’ is still there. I think the answer lies in local grids. There are efficiencies to be gained – both cost and operating – from scaling up to a certain level, and it allows use to be made of optimum sites and resources for generation at a community level. For instance, in these valleys we have year-round running water and abandoned and ruined mills every 100m or so along the rivers. If these were restored to generate hydroelectricity, there would be enough for everyone within the community without the need for battery storage. We could possibly even sell electricity to the national grid, generating an income for the community which could be used to develop other sustainable initiatives at community level.

    There are other types of storage though. You mentioned pumping water into an uphill reservoir for hydroelectric generation. There’s also a fair amount of flexibility in terms of power source – in other words, we don’t necessarily have to use electricity for everything in the way we’re currently used to doing.

    I particularly like Jürgen Kleinwächter’s designs for Tamera’s Solar Village in the Alentejo which involve using Fresnel lenses to heat oil which is then used for cooking both directly (pots suspended in an oil bath) and indirectly (heat exchanger provides steam), or to generate electricity or mechanical energy (via Stirling engines). I’d like to start experimenting with this for summer cooking at some point, and take it from there.

    Another option would be to use compressed air. We have a local fault-line (with waterfall) that offers a 40m vertical drop. Installing a trompe compressor here (discreetly, since it’s a tourist destination) and storing the compressed air in a large tank in another nearby ruined mill building would offer the potential for running eg. power tools, fridges/freezers, even cars. Distribution would likely have to be via tanks rather than pipes because of the distances and terrain involved, but with a free, sustainable, environmentally-benign, permanent power source like this, efficiency is much less of a concern.

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