Our power project

From Organic Design
Revision as of 13:07, 3 February 2015 by Nad (talk | contribs) (Solar panels (v3))
Petrycoski land cover image.jpg
At the end of 2011 on the 11th of November we moved to Brazil and bought some land to set up a more independent and meditative lifestyle. We started in a flat in Curitiba, then about a year later moved to Canela which is the closest town to the land.
1. Moving from Curitiba to Canela          Our power project
2. Moving on to our land          Our rural net connection
Year on the land: 1 | 2 | 3 | 4 | 5 | 6          Our first house
           Our second house
           Lada Niva

New SureSine inverter installed.jpg

In our area the council will actually bring the grid power to our land for free and then charge only a small monthly fee to access it, but we decided that we prefer to have things set up independently for ourselves anyway so we can gain valuable experience in independent power solutions of many different kinds.

We don't need much power as our main requirements are just for lighting, internet and laptops which is around 50W of power when all in use. I initially estimated that we'd be able to get by on about 600W hours of power per day, but after living here for a few months and doing the numbers it turned out that our average usage is actually a lot lower at around only 200 watt-hours per day!

We'll be using solar for water heating, gas or fire for cooking, a water-wheel for pumping water to four or five meters height for some pressure, and we won't be using a fridge because we have no dairy products and all our vegetables stay fresh by only picking them as we need them.

Our power consumption

Measuring power consumption.jpg

I've done some current measurements on our inverter while using different items to map how much power each thing uses. I attached the multimeter before the inverter so that the power the inverter consumes is also included in the results. Here's a table of the items measured.

Item Current Power
Nothing 160mA 1.92W
LED Light 380mA 4.56W
Net (Hub & 3G router) 700mA 8.4W
Dell adapter 310mA 3.72W
Dell (on, not charging) 1.45A 17.4W
Dell (on, charging) 2.45A 29.4W
Dell (off, charging) 1.13A 13.56W
Dell (standby, not charging) ? ?
Lenovo adapter 210mA 2.52W
Lenovo (on, not charging) 1.13A 13.56W
Lenovo (on, charging) 2.82A 33.84W
Lenovo (off, charging) 2.92A 35.04W

A couple of interesting things show up here, firstly, the inverter actually uses about 2W of power when nothing is being used, so it would be best to include a switch for that in a handy location so that we can turn it off throughout the night to save around 20 Watt-hours. It wastes less power when it's being used as can be seen by the fact that our 4.2W light shows 4.56W being used which means the inverter is then only using 0.36W.

The next surprising thing is that the computer power adapters also use a lot of power when not in use and so should not be plugged in if the computer batteries don't need to be charged. My adapter consumes over 3.7W and Beth's over 2.5W when not powering anything.

The charging of the computer batteries consumes a lot of power, but does so for less time than what it took the computer to use that power from its battery - how efficient this is we don't know yet, but in general it's best to avoid wasting the computer battery.

The power consumed by the computer in normal operation is actually quite a bit less than I was expecting, I thought it would be around 30-40W but is actually only 17.4W. The net hub and router are about what I was expecting at 8.4W, I estimated it should be under 10W.

On a typical day at the land we'd have the computer and net running for about six hours and the light running for around four hours, plus a few extra items such as charging and inverter power brings us to about 200 watt-hours per day for our current consumption.

Our power generation

On overcast days we're only bringing in about 15W of power from the panels, but this is quite consistent for the full time of daylight since its mainly ambient light and not limited to the direction of the sun so much, so this equates to around 150 watt-hours in a day. This is a little less than we consume though so after a number of overcast days, which is quite common during winter, we get down to a critical level of power and have to go into power-rationing.

We're going to have two more 150W panels soon which means we'll have a total power input that's triple what we currently have as of October 2013. This will mean that we'll be brining in over 400 watt-hours on overcast days which is double what we consume, so even if we have weeks of very bad weather we should still be able to use our power normally.

Petrol generator

Petrol's not exactly a sustainable independent solution! but having a few kilowatts available in a portable format can sometimes be invaluable especially in the early stages when other more independent solutions are not yet ready. Also a high power inverter is very expensive and we're unlikely to be purchasing one for quite some time, if at all. So for when we need to use power tools, we use our GeraMac 3100M 3KW petrol generator which has a Mitsubishi engine made in Japan and cost about R$1000. It's been really reliable and starts easily every time, even in very cold weather. It has output connections for 115vac, 230vac and 12vdc.


Solar panels (v1)

If we consider a worst-case of about four hours of sun per day (which is about right for winter in Rio Grande do Sul) and we want at least 600W hours of power per day then we need at least 150W of panels initially. I'd like to double this reasonably soon and eventually have 1KW of panels so that we can afford to be less frugal with our power, for example by beaing able to keep the computers running when we're not using them so that we can receive incoming calls etc.

We're going to start with a basic 152W kit like this (I also found this one which is a bit cheaper). Building our own panels from the a kit of individual cells gets the price down to around R$2.40 per Watt which is about half of the best prices available in Brazil for ready-made solar panels.

Solar cells.jpg

Having our panel mounted on or near the house isn't really very practical in our situation because we're in a bit of a valley and also have many tall trees near by on all sides. Since we have installed a long power cable up to the top of a near by hill for our rural net connection it seems a practical choice to also use that location for our solar panel.

The only problem with this is that we don't want the net hub and router to be constantly on, we want to be able to turn it on and off from the house, but if the panel, battery, charge-controller and inverter are all situated at the remote end of the power cable we can't simply connect or disconnect the power from the net circuit like we could if it were located at the house end.

A reasonably simple solution could be to put a switch at the house-end of one of the spare pairs in the LAN cable. The switch would be used to control a Solid-state relay in the middle pole that activates the hub, and another at the end that activates the router. Only a very low voltage and current then needs to be running through the LAN pair with the switch on it.

Soldering the cells together

I watched this video to learn how to assemble the cells into a functional panel. The first step is to solder the tabbing wire onto the backs of all the cells; each cell is 0.5 volts with the backs positive and the fronts negative, so the idea is to wire all forty cells in series which makes a panel with a maximum output of 20 volts and a nominal output of around 16 volts. This output is then feed into the charge controller which adjusts it to suit the battery and load state.

Soldering cell back.jpg First cell back done.jpg All cell backs done.jpg

Next I started soldering the cells together into groups of five in series by attaching the tabbing wire that had previously been soldered to the backs to the fronts. One problem that came up with this procedure was that I discovered that I actually have three different types of panels! they're all the same size, but there's two slightly different widths between the connection strips, which meant I had to do some dodgy connecting of some of the cells as shown in the second picture below. The final pictures show a voltage measurement on a series of ten cells which is reading correctly at just over 5 volts.

Soldering cell fronts.jpg Unmatching cells.jpg Measuring voltage of ten cells.jpg Cell measurement close.jpg

I've now got all four rows of five cells soldered together to make the first panel. I temporarily joined them to test the voltage and it's looking good at 10.59 volts :-) The cells are incredibly fragile and I've broken some small bits of some and have some cracks in others, it's like trying to solder together slim potato chips! Not all cells are quite as fragile as this though, one of the three types I've got feels a lot sturdier, so I hope that the next set of forty I purchase will all be the same and of the more sturdy type.

First 20-cell panel voltage test.jpg

Assembling the frames

First I got a large sheet of weather-proof ply wood and got it chopped into four equal pieces of 80cm by 120cm which is enough for three panels (I only have enough cells for two panels so far though). Each cell actually only needed to be 80x94 though so these were then cut a bit more.

I then cut four long pieces of the ply 6cm wide and another four 5cm wide pieces to form a frame for the glass to sit in. I used a G-clamp to hold the frame pieces in position while drilling the screw holes, and to hold it together tightly while putting each screw in to help ensure that its water-tight, and then Beth put silicone sealant into the remaining cracks before painting it.

Solar panel - screwing frame together.jpg Solar panel - sealing cracks.jpg Solar panel - painting frame.jpg

Now that the first frame is painted and dried, we can put some bolts in for mounting the panel securely, put some plastic on to hold the panels away from the bolts and from the wood which can expand and contract a bit with changes in the temperature, and put the power cable through in a secure and water-tight way. I decided to do the first panel completely before doing anything more on the second panel in case I come across problems or find better ways of doing it along the way. For example, I've discovered that sealing the cracks with putty would be better than silicone because the silicone won't allow the paint to stick to it. Also, on the next one I would make the counter-sink holes slightly deeper so that I could putty over all the screws to make them more water-tight and invisible too.

Solar panel - first frame done.jpg

The second frame is now ready for putty and paint. You can see here that I've made the counter-sinking a bit deeper. I then drilled four holes into each panel and put sturdy bolts through the so we have a good strong means of mounting them later.

Solar panels - second panel frame ready for painting.jpg Solar panels - second panel frame deeper counter-sinking.jpg Solar panels - support bolts.jpg

The first panel being all painted and dried was then ready to have some cells put into it :-) First I screwed a plastic base onto the frame with holes drilled into it to make way for the bolts. The plastic is to avoid the cells being directly on the wood which may get moisture on it and can bend or expand and contract in differing weather conditions. The plastic was also useful for raising the surface so the cells aren't in contact with the bolts. Before actually bonding the cells to the plastic, I thought it would be best to test that the silicone we're using would bind well to them both, so I took a small piece of cell that had broken off one of the corners when I was soldering them together and did a test which showed that the silicone is indeed a good choice :-)

Solar panels - plastic base for cells.jpg Solar panels - plastic base hole for bolt.jpg Solar panels - testing cell bonding.jpg

Installing and wiring the cells

And finally, the process of actually getting the cells into the frame. I first marked with pencil on the plastic a grid so I could position each row of cells accurately, and then put a couple of lines of silicone on the plastic for each of the five cells in a row. I then picked up a row of five that had been soldered together a few weeks ago and carefully placed it in position and slowly moved it in a small circular motion pressing very gently on each cell to get the silicone bonding nicely with both the plastic surface and the cells.

Solar panels - first row of cells in place.jpg Solar panels - silicone for second row.jpg Solar panels - first panel cells done.jpg

Here's the first panel all wired up and the voltage tested and showing at a little under 10 volts - which is right for a fairly overcast grey day :-)

Solar panels - first panel wired up.jpg Solar panels - first panel voltage test.jpg

And now the same process for the second panel...

Solar panels - second panel ready for cells.jpg Solar panels - second cells soldered.jpg
Solar panels - putting in a row of cells.jpg Solar panels - positioning a new row of cells.jpg Solar panels - pressing a new row of cells.jpg

And then we do some final tests to ensure they're both working correctly before calling the glass guy :-) here's both panels wired together in series with the voltage showing as 17.88 which is very good since they're in the shade with no direct sun light on them anywhere.

Solar panels - testing both joined.jpg Solar panels - testing both joined (close).jpg

Installing the glass

And finally putting the glass in! it only cost an extra R$5 for the glass guys to come over and measure everything and then bring the glass here to us, and then they install it for free so we decided we may as well let them do it :-)

Solar panels - glass positioning.jpg Solar panels - glass silicone.jpg Solar panels - ready to go.jpg

Solar panels (v2)

The first panel design has some problems which allowed moisture to accumulate on the inside and also has allowed the cells to bend and crack. They seem to have settled to a final position where no more damage is occurring, but some of them have cracked all the way across, others have just small bits broken off. Amazingly all of this damage has only resulted in about 5% or less reduction in output as we're getting about 140W from them in full sun.

Broken cell 1.jpg Broken cell 2.jpg

I ordered another eighty cells from this place which is doing packs of forty for R$289. We actually ordered a pre-built panel for about 2.5 times the cost but it arrived smashed, the guy then sent a replacement panel which also arrived smashed!! so we got him to send two kits of forty cells each instead.

This time I've made a slightly different design whereby the tabbing wire is first soldered to the front side of the cells and then the cells are placed face down onto the glass and then glued in place with silicone around the edges of the cells (the pictures show only blobs of silicone in the corners and centres of the sides, but after they were soldered together I put silicone all around the edges).

Solar panels v2-1.jpg Solar panels v2-2.jpg
Solar panels v2-5.jpg Solar panels v2-6.jpg

The frame is simpler for this version as there's no "shelf" that the glass sits upon, instead a soft underlay was placed on the ply panel (a thin sheet of polystyrene or similar could be used, we used a thick compressed-wool blanket) and the glass then sits directly onto this. The soft underlay is so that the glass isn't directly exposed to vibrations received through the hard wood, and also to distribute uneven pressure caused by the uneven height of the silicone holding the cells to the glass. The glass is then held in place with silicone around the edges, and the power cable goes through a 6mm hole in the ply panel at one end as usual.

In order to ensure that the glass fits very tightly I screwed two adjacent side pieces on first, then positioned the glass (on it's soft underlay) tight up against those two sides, and then positioned the remaining two sides tightly up against the glass.

Solar panels v2-3.jpg Solar panels v2-4.jpg
Solar panels v2-7.jpg Solar panels v2-8.jpg

Another simplification is that I've dropped the installation bolts from this design, instead I've just drilled four holes through the frame and bolted right through rather than having bolts built into the panel structure. Now that we have another panel which is as big as the current two combined and another big one waiting to be assembled, we need to install them in their permanent position on the new north extension roofing panels. I've put silicone on the tops of the bolts so that rain can't enter into the frame and I've put a rubber grommet in between the roofing material and the panels to prevent the tightening of the bolts cracking the fragile roofing material.

Solar panels v2 installed 1.jpg Solar panels v2 installed 2.jpg
Solar panels v2 installed 3.jpg Solar panels v2 installed 4.jpg

Another good aspect of version 2 is that it can be disassembled without damaging the cells, which is really important because a few days ago it started having problems with the current not adding to the output of the other panels properly. I could see that there was some moisture between the glass and some of the cells so the panel wasn't water-tight, and after I took it down and disassembled it I found that the blanket that the glass lays on to distribute the pressure of the uneven surface on the back of the cells was completely soaked and had caused the tabbing wire to disconnect from the back of many cells, and was also causing a partial short-circuit.

Solar panel v2 disassembled.jpg Solar panel v2 wet blanket.jpg

Solar panels (v3)

The version 2 panel has been running for a few months now and a few problems have begun to show up. Firstly the wood sides are a problem, they bend and the paint comes off allowing water to enter. Secondly I should have used something for the soft underlay that the glass sits on that's doesn't absorb water like polystyrene or a form mat, because the water that has entered won't exit, it just sits in the blanket probably draining a portion of the energy from the cells since it's in contact with the tabbing wire on the back of them.

One aspect of the version 2 design are successful though, which is the method of attaching the cells directly to the back of the glass with silicone and support it with a soft underlay. There's not the slightest hint of change in the cells themselves - although they haven't been through the test of snow yet, but it's certainly a much better method than version 1.

Version 3 is new design which is similar to version 2 but using a bubble-wrap backing to support the glass and using L-section aluminium for the sides. I can't do a design like the professional ones that smashed because they require specialised aluminium framing, rubber sealing to match and some specialised adhesive to attach the cells with. I want to come up with a design that's durable but also made with minimal work and completely with materials that are readily available at any small town hardware store.

After the version 2 panel started having problems due to moisture, I took it down and upgraded it to our first version 3 design. There's a couple of slight problems with this design that I'll need to iron out when I assemble the next one which is almost ready. The first issue is that either we need to get slightly thinner ply for the backing, or find some different L-aluminium that has at least one of the sides a little longer. But I've assembled it anyway and just used more silicon to ensure it's sealed ok.

Solar panel v3 1.jpg Solar panel v3 2.jpg

I've also improved the way the v3 panel is installed so that we can adjust the angle for summer or winter - mainly winter as we need to have optimal sun on the overcast winter days when the sun is low in the sky.

Solar panel v3 support.jpg Solar panel v3 support close.jpg
Solar panel v3 installation.jpg Solar panel v3 installed.jpg

Finally months later the second v3 panel was completed and installed.

Panel v3 installed 1.jpg Panel v3 installed 2.jpg Panel v3 installed 3.jpg

Charge controller

The sources of power such as the solar panels don't connect straight to the battery because this can damage the battery if it's already fully charged, or if the voltage coming from the panels is too high or too low. So instead the power sources must first connect to a charge controller which assesses both the source power and the battery state and conditions the power to the battery's requirements. Charge controllers have two terminals to connect to the power source, two for the battery and most have another two for the load (i.e. the equipment you want to run). The reason for the separate load connections is so that the charge controller can completely disconnect the battery from the circuit if it's fully charged, but still supply a high current to the load.

Our charge controller is the SML-60 from MovTec here in Curitiba (Rua Carmem Maito Stinglin, 80, ph. 30145114). We decided on the SML-60 because we'll be running a 12V system which means that the SML-25 would only be able to handle 300W which is less than another one of our current 152W sets of cells. The SML-60 can handle 720W which means four of or 152W modules will be no problem at all for the unit to handle.

60A charge controller.jpg

I think that sometime in the near future it would be worth investing in the more expensive MPPT type of charge controller because then we can efficiently utilise power from any source regardless of the voltage (as well as getting the most out of our solar cell's output as well). Not only does an MPPT charge controller ensure that no portion of the input power is wasted, it also dynamically tests the characteristics of the panel which changes as the light conditions change to ensure that the current and voltage being drawn from the panel are at the most optimal efficiency - i.e. the Maximum Power Point.

Our charge controller is giving incorrect results for the battery state, it seems to be showing the input state instead and is also affected by the amount of output being drawn. The manual is not very helpful and seems to have a section missing which is supposed to describe how to configure it by setting the jumpers inside. I found this manual which has a similar circuit board with the same jumpers, so I'll try basing the configuration on that one - if it's correct then it shows that two of our jumpers need to be changed, the first was set to gel battery type instead of fluid, and the second to voltage-controlled disconnect instead of state-of-charge controlled.

I was going to build a build my own MPPT charge controller using a Raspberry Pi based on this DIY Arduino-based MPPT charge controller project, but first the Pi got lost in the post, and secondly there is a huge amount of discussion on the charge controller mailing list suggesting that the design is not completely functional. So for now we've bought a new PWM controller so at least we have a backup if one should fail.


We've been looking for a battery suitable for using with our solar panel and whatever other sources of pwer we end up using and the charge controller, but we've had a lot of trouble finding anything for a practical price. Then when we were going to a cafe to meet one of Beth's friends we saw a small battery shop on the other side of the road, so we decided to pop in and ask if they had anything, or if not, if they knew of anywhere we could go. Well it turned out that the place was actually very large inside and had a huge range of batteries including the exact kind we were looking for at a good price :-) and better still it turns out that the owner travels to Canela each weekend and said he can drop it off at the Pensão for us! This was really good luck because it weights over 27Kg and batteries require a special expensive courier service to transport. We got a 115Ah Freedom DF2000 battery for R$440. The DF2000 is a fluid electrolyte battery which allows for better thermal dissipation and are less sensitive to temperature variation than gel (VRLA) batteries.

Freedom Battery.jpg

Power inverter

Since most normal lighting and appliances such as laptops, phone chargers and routers all run off 110 or 220 volts AC, we need an "inverter" to convert to this high AC voltage from the 12 volts DC coming from the battery. There's quite a range of inverters available from very cheap to very expensive. Th most expensive ones are required if you need very high power and/or very perfect "pure sine" wave-form in your output. We don't need either of these things because all our appliances use their own power adapters to provide them with the exact specifications of power they require, and our LED lights aren't fussy either, so for us the very cheap options are available :-)

We got a cheap 200W inverter from dx.com for only US$20 and free delivery to Brazil. This will be fine for our requirements, and for the rare times that we need to use power tools, we can use the generator. Most of these cheap ones come with a car cigarette-lighter plug for input because they're designed to be used in the car so you can charge your laptop or phone when you're on the road. We have a cigarette-lighter socket which we'll attach to our battery so that we can easily unplug the inverter and take it with us in the car if we ever need to.

200W inverter.jpg          SureSine 300W.jpg

In August 2013 we decided to get an 800W inverter as well firstly as a backup in case our current one blows up (we also got a second charge controller). But also we've found that we use the drill very often and the jigsaw quite often too, and small tasks become a major hassle when you have to lift the generator out of the packed trailer and stretch long extension cables into the house from it etc. The problem with a higher power inverter though is that they use more standby power. Our 200W inverter uses less than 2W for itself (and less if you're using some load), whereas the new 800W inverter uses 12W, so we use the 200W for most purposes, but have the 800W permanently connected with it's own extension cord so it's easy to switch on whenever we need it. There are very efficient high-power inverters available, but they're extremely expensive.

In February 2014 our 800W inverter blew up and I had to replace some of the capacitors in it. That got it working again, but I decided that we really needed a professional quality inverter designed for solar purposes rather than a cheap one made for using in the car when travelling. Since Mum & Dad were visiting at the end of the month I decided to buy a decent one in NZ which is a lot cheaper than here in Brazil. I got a SureSine 300W (600W for ten minutes) made by Morning Star which is the best company in the business :-) The right-hand picture above shows this new one.

Wind & Water

We'll eventually get a small wind turbine and water wheel set up, but we'll start with the solar and work on these later. The common factor in both of these is the generator. I want to get in to building my own after I downloaded Energy Creator's DVD and found that building really efficient generators of a few hundred watts of power is totally doable and quite cheap.

Tesla coils

After reading some of the 2600 page Practical Guide to Free-Energy Devices eBook, I really want to try some of the simpler designs out for myself.

The first being one of Don Smith's designs on page 236:

Don Smith 1.jpg

The second is another of Don Smith's designs on page 248:

Don Smith 2.jpg

Tesla aerials

And I've always found the Tesla Aerials pretty interesting which are discussed starting on page 586.

Tesla Aerial.jpg MiniTeslaCircuit.jpg
Whiteboard notes
from 2011

Lessons learned

  • You need a really good inverter like a Morning Star SureSine, not just a cheap car inverter as these will shorten the life of your equipment and reduce their operating efficiency.
  • If you use anything that has a motor in it (fridges, power tools, blenders, coffee grinders, hair dryers etc etc), then you need to multiply the power rating of the item by three to determine how much power your inverter will need to supply, because when motors start up they consume three times their rated power for a fraction of a second. This will cause a cheap inverters parts to sustain damage, and a good inverter to temporarily disconnect the power.
  • A normal AGM battery will last about four or five years, and this is a gradual degradation process, so if you have a 100Ah battery, you'll have something like half that after a two or three years of use. Furthermore the charge controller won't let the battery discharge to less than about half capacity, so in practice your 100Ah battery may only be giving you around 25Ah after a couple of years.

See also