Part two. Forgive me if I skirt over the issues faster than you can really assimilate them. You can always ask me for an explanation and I will always answer an email. You can read part 1 here http://courier-spain.co.uk/blog/photovoltaic-pv-installation-spain-courier-uk/
Batteries. Assuming you have a largeish installation you will either be running a 24v or 48v system. Which to choose? We have 48v which means 24 x 2v batteries. A 24v system which had the same battery capacity would have 12 batteries of 2v but each battery double the size. Why would you choose one over the other? Well, my opinion is that 48v is more elegant but there again there is more kit available for 24v. How on Earth can you understand this? A four cylinder car engine is perfectly good but an eight cylinder is better, although more expensive. I don´t think it matters massively which you choose, 48v will cost you a little more so if you´re on a budget go 24v but the difference isn´t huge.
What is the difference between 24v and 48v? The higher the voltage, the less the loss in the wiring connections between the panels and the charge controller and the charge controller and the batteries. So, if 24v needs a cable of 25 mm square in diameter to deliver the power from your panels then 48v needs half the size of cable.
Batteries. What is the only important thing about batteries? That they are NEVER discharged beyond their nominal value. So, we have 24 x 2 volt batteries making a nominal 48 volts. These batteries will actually charge up to around 60 volts, depending on temperature. This “overcharging” cleans the lead plates and after a couple of hours the charge controller will drop the voltage to around 54 volts. If your batteries discharge lower than their nominal value, 48 volts in our case, they will be ruined, meaning that they will never be able to store a full charge again. Please understand this it is the most important fact in all your solar power installation, if you learn nothing else from this, please remember to NEVER let your batteries discharge below thier nominal voltage.
Ruin your batteries and you can NEVER recover them. From here, you can progress but ONLY if your batteries are sound.
Batteries need to be topped up with distilled water, nothing else. So, as long as you never let them fall below their nominal voltage, don´t worry about anything other than keeping them topped up and keeping the connections well greased to keep out the oxygen which might corrode them. When there is no sun and no wind and you need to top them up, you will have to use a generator. Normally, you would have a large enough battery bank to survive three days without sun but during those three days you do not use the swimming pool pump, the washing machine, your hairdryer etc. You can still use the lighting and a few luxuries like the TV but common sense tells you that the more you take out of your batteries the sooner they get close to 48 volts and then you have to act.
Generators are dirty and noisy and consume expensive petrol or diesel so the less you use them the better. However, the biggest cost of a generator is the machine itself. A proper generator is powered by a multi-cylinder water cooled engine and will cost you around €5,000 new. Correctly serviced, this should last you a lifetime. At the other end of the scale are little, Chinese made, single cylinder, air cooled engines. We paid €2,000 for our first diesel one with electric start and sound-proofed box and we are on our third which cost less than €200 and is the most basic I could find. However much you pay for these “cheap” generators, do not expect them to last 500 hours, even if you change the oil every 100 hours and clean the air filter every 50 hours. That is why we buy the cheapest possible.
NEVER lend your generator to anyone else. The reason that they want to borrow yours is that they have broken theirs and they will return yours in the same state. When they return it, it might appear to work but they will have altered the speed at which the engine runs and this alters the output voltage of the generator. The generator is often wired into your inverter (see below) which is the single most expensive piece of kit in your whole system.
If the voltage coming out of your generator is too high it will blow up your inverter, which cost us €5,000, and the guarantee will not be valid unless you are really lucky, as we were, twice! So, my recommendation to you is not to wire the generator into your inverter but to use a stand-alone battery charger. Ours was designed to recharge a fork-lift truck so it knows to turn itself off when the batteries are full, although I can’t imagine anyone using a generator for that long.
The inverter turns your DC battery-stored electricity into AC voltage at 230v (or 120v in the USA) which means that ordinary machines that you buy in the high-street shops will work. If your generator is wired into your inverter the mains type power produced by the generator can be diverted into the house when not powering the batteries and, in our instance, this caused endless small power surges as the inverter switched our electric supply between generator and battery, another reason to use a stand-alone battery charger. The inverter is a large and very heavy box because, other than some delicate and complicated electronics, it contains a coil that actually converts your battery power to mains-type electricity. As stated above, it can be really expensive and for this reason some people use more than one. Two small ones are far cheaper than one large one but we opted for a single one that produces 5kw continuous (with a maximum load of 10kw) on the basis that 5kw is represented by the diswasher, washing machine and swimming pool pump running together so you don’t want the whole system to overload when the fridge cuts in. Ours is produced by Mastervolt in Holland and they are such a joy to deal with, thank you Mastervolt. However, many people have a small inverter for the lighting circuit and a larger one for the ring-main.
When our inverter went wrong last time, I installed a 48v computer UPS (uninterruptable power suppy) in its place until it returned. This cost me (second hand and without the battery, I’ve got batteries) less than €100 and produced around 2.5kw of perfect power. Luckily, I don’t really have to think about it but if I was starting over I might well have a bank of UPSs rather than a single inverter, however you would need to wire the house differently as you cannot mix the AC current from different sources.
The next most important piece of kit (other than the panels) is your charge controller. Here, I can recommend the Outback MX60 (one of only three names that I will recommend to you in this article). The Outback takes the power from the solar panels and uses it to charge the batteries. The MX60 is limited to 60 Amps output power (unless you read the manual and work out how to get it up to 70) and volts x amps = watts (power). Therefore in a 48v system power output from the MX60 is twice what it is in a 24v system, this could be another deciding factor. There are three really clever features on the MX60, which is configurable for 12, 24 or 48v output. Firstly, it will take a much higher input voltage than its output voltage (but only up to 130v maximum). This means that we have linked three 24v solar panels in series to produce a nominal 72v output and an effective output much higher, ours has peaked at 118v. The higher the voltage, the less power is lost in the wires beween the panels and the batteries. As we have 12 panels, there are four sets of three with the four sets linked in paralel. Then the MX60 benefits from MPPT, maximum power point tracking, which wrings a little more power from those expensive solar panels. Lastly, the MX60 comes with an optional external thermometer which attaches to a battery and it therefore alters the charging of your battery bank to optimise it for temperature, thus extending the life of your batteries.
Solar panels are a commodity and they are the only things backed by a long guarantee. The Spanish government insists that they should be guaranteed to produce 80% of their rated output after 25 years. The first set that we got were branded Suntaics, a German company who are among the least helpful people you could ever come across. These panels went wrong within six months as connecting wires within them melted. My recommendation is to pay a little more and get a really well known brand from a company that will be around in 25 years to honour their guarantee. Since installing ours into a frame that hinges at the bottom to allow us to change the angle at different times of the year, I need at least one other strong man to help me raise or lower them. My recommendation would be to mount the frame on a central pipe, like a scaffold tube, which could be rotated to change the angle and would require very little effort compared to physically lifting the set of six panels which are fitted in a single frame.
Solar panels give off electricity, called photovoltaic or PV, when they receive light and they can be wired together in series, as seen above, to produce higher voltage. I know this may sound a little simple, but you can only charge your 48 volt battery if you are inputting more than 48 volts. And remember that in its “absorbing” stage, your battery might get up to 60 volts before settling down and “floating” at 54 volts or so (this changes with the temperature and with the type of battery). Therefore, you can’t charge a 48 volt battery from a single 24 volt solar panel, you need at least two wired together. This concept is vital when we consider the windmill.
We only have a windmill to qualify for the grant. Having said that, we wouldn’t be without it now. It was cheap and manufactured by FuturEnergy from the UK who are extremely helpful. You can get the whole thing from eBay for less than £1,000, windmill, charge controller, stop switch and dump loads for something that outputs a nominal 1kw (our solar panels are rated at 2kw but rarely produce more than 1750w because they produce less as they heat up).
So when it blows a gale, normally when the sun is not shining, we don’t have to use the generator to charge the batteries. However, most of the time, the windmill is useless because the voltage it produces depends on the speed at which it is turning (I only found this out by disconnecting it from the batteries which you are not meant to do). If the batteries are normally at around 49 volts at night or when there is no sun, which is a “comfortable” level, then the windmill cannot charge them unless it is producing more than 49 volts. I haven’t measured the wind speed at which this happens but it is only when there is so much wind that it is uncomfortable being outside – I know that that is subjective but is important that you don’t think you’re going to get a constant source of electricity unless you live in a very windy place. Comparing the windmill’s input with other people’s experiences, I would say that it is very useful but you would never get to float the batteries from it, even if you had 48 hours of constant 25mph wind, whereas a couple of sunny days will easily float the batteries. Better to rely on the windmill as something that might avoid you having to use the generator on a day without sun.
I had the tower for the windmill made at the local blacksmith’s of which there are plenty in Spain. It consists of one and a bit scaffold tubes welded together on a hinged base and supported by 5mm steel wires from four steel plates bolted to a concrete base. At first, there was only one wire from each plate to the top of the scaffold tube but the pipe would definitely have buckled without a second wire to support it half way up and keep it rigid.
How to give a summary of our three year adventure in alternative energy in Spain? The first piece of advice is to trust no one, our original installer has gone out of business and didn’t know what they were doing anyway. The more you learn yourself, the less likely you are to make a costly mistake. Now that it is all over, I would not choose the option of installing a serious on-demand diesel generator which seemed the better way for a long time. However, I would do without the government grant and would buy all the items that I need (other than the batteries which really need to be delivered to you from the factory) from eBay and fit them myself. This would save more money than the grant provided and, although electricity is very dangerous and I recommend you use a qualified electrician to connect up your system, the whole concept is very easy and just takes a little common sense. Fear of the unknown leads us to consult an ‘expert’ and, while undoubtably there are well qualified off-grid engineers out there somewhere, neither we nor our neighbours have found one yet and we have consulted many ‘experts’.