In ‘Q & A’ Category
Q&A: Brick cavity insulation
I live in Sydney and my house has double-brick cavity walls which are painted on the outside. I’m renovating the attic and have access to the brick wall cavity from above. The cavity is about 5 cm wide and I was thinking of putting in blown-in insulation.READ MORE »
Is it okay to do this in Sydney? I’ve heard different opinions, with some saying that there’s a risk of moisture penetration. If it is okay to use blown-in insulation, what material would you recommend?
I had termites so I am not keen on cellulose, and it is also not hydrophobic, and foams are too chemical. The Your Home technical manual recommends Rockwool granulate, but the Rockwool company has advised that none of their granulated products is suitable for this purpose.
I’m thinking of using perlite. I had a look at the product description and can’t find any reason not to use it. It seems to be hydrophobic, light, non-combustible, safe for cables, and I can do it myself.
Any thoughts or recommendations would be much appreciated.
The problem with double brick cavities is that the surfaces inside the cavity are very rough, with lots of cement dags, brick ties, etc in the way, so anything fibrous is going to be difficult to install.
There are a few options, including envirofoam, which is supposed to be VOC and CFC free: www.envirofoaminsulation.com.
Another option is Insulbloc. This is recycled polystyrene, cut into small cubes, which is then blown into cavities; see www.insulbloc.com.au. My main issue with this material is during house deconstruction—it would be a very messy process, with a lot of the material escaping the work site, I would expect.
Perlite is also an option as it insulates well and is easily blown in and is a natural, if not renewable material (see en.wikipedia.org/wiki/Perlite). Given that, I would think that perlite is probably your best option.
Read more Q&A in ReNew 121
DC solar fans
I’m building my own house but am hitting a brick wall with searching for a couple of technical options as the house nears completion.READ MORE »
Specifically, I am searching for the existence of small, cheap solar-powered fans for use in 100mm diameter cooling tubes running up behind my fridge (to help air circulation across the heat-exchange coils), and where I could potentially put the PV cells to power them on top of my electricity meter box. I’ve heard of their existence but don’t know where to get them!
The best source of fans for this sort of work is computer fans: they can move a lot of air and there are low-noise models available. In most cases you can connect them directly to a small solar panel without any other circuitry, although some fans can be damaged if the panel voltage gets too high.
The 12-volt rating on a panel is the nominal system voltage it’s designed for. The maximum power voltage is usually closer to 17 volts, with an open circuit voltage closer to 21 volts. This voltage can be enough to damage some fans.
Fortunately there’s a simple solution—either a three terminal regulator IC (available in a kit with circuit board from places such as Jaycar Electronics) or even just a simple 5-watt Zener diode connected across the fan. Just select a 15V Zener and make sure the panel is rated at less than 5 watts (which it will be as a 120mm computer fan draws about 2 watts), and you’re fine.
Another option is a bilge blower, such as this unit from Whitworths Marine: bit.ly/KJlOrS.
I installed eight 180W solar panels (1.44kW) and a 1.5kW grid-tied inverter just over one year ago and I am very pleased with the result. I am a pensioner and this cost me $2800 after rebates.READ MORE »
I would like to increase the size of the system to 3kW and here is the problem. The people who sold me the system want to charge me $5400 to increase the number of panels to 12 and sell me a ‘bigger and better’ 3kW inverter. I thought that maybe it would be cheaper to buy a whole new system similar to what I already have and run it as a separate system in parallel to the first one.
Is this technically okay and would I get the same rebates as the first system—or am I only allowed one bite of the cherry? I had the electricity switchboard upgraded at the time and Ergon installed the appropriate meter.
Personally, I would go for a second parallel system. There are a few reasons for this.
Firstly, replacing the smaller inverter with a larger one leaves you with a used inverter that you then have to sell. I expect the resale value of them would not be high, as second-hand equipment is not eligible for a rebate.
Secondly, when you get a rebate there are restrictions regarding what you can do with the system. I seem to recall no changes can be made to the installed system for the first five years, but that may have changed; you would have to look at your documentation for details.
Thirdly, a single large inverter gives no redundancy. Should it fail, the whole system is down until it’s replaced. Two smaller inverters mean that if one fails, at least half the system is still operational.
There is a new player on the market fitting micro-inverters to 240-watt panels, with the equipment all made in Australia. They are called Tindo Solar (www.tindosolar.com.au), and to my mind this is a simple and easy way to expand any system without the extra cost of DC wiring. All you need is fixed AC wiring points for each panel, something a standard electrician can do.
I’ve come across ceiling heating with a client and am trying to quantify the efficiency of the system compared with both an electric in-slab system and a heat pump system.
Do you know the efficiency of these units, or an organisation that might?
All resistive-type heaters are 100% efficient in that all the energy going in turns into heat, but once you have that heat, how effective it is depends on the placement of the heat source. Placing heating elements in a ceiling is a problem, as heat rises so it will first heat the air near the ceiling and will take a long time to heat the room. Yes, there’s radiant heat from such systems but it’s low level. Frankly, a heated ceiling makes no sense.
A heat pump has an efficiency well over 100%, simply because it uses electricity to concentrate heat and move it from outside to inside, rather than actually generating heat. Most heap pumps have an efficiency (actually a co-efficient of performance, or COP) of at least 2 (200%) and some exceed 5 or more. So, with a COP of 3 for instance, 1kWh of electricity moves 3kWh of heat from outside into the home. For more information, see the heat pump buyers guide in this issue.
When it comes to electric heating, heat pumps (along with their more efficient, but more expensive cousins ground-source heat pumps) are by far the most effective system for the energy used, unless the home is extremely draughty. But in that case, you would fix the air leaks first anyway.
After reading Martin Chape’s article in ReNew 119, my appetite has been whetted to include a wind turbine like his.READ MORE »
We have a 2.1kW solar system on our roof and it has been highly successful in south Gippsland, Victoria. The inverter on my system is rated at 2kW, which is at the top of our system’s generating range.
I’ve always felt the loss of sunlight due to night time as a bit of a sore point. Would it be possible to fit a wind generator for night-time use of the type Martin has fitted, and still use my current inverter?
There would have to be some type of automatic shut-off device to stop power entering the inverter from the wind generator after the solar panels kick in.
The simple answer, I know, would be to fit a larger inverter. The cost is a bit prohibitive whereas the turbines (from bit.ly/JmonvO) seem extremely well priced.
They are a neat-looking little turbine but output is pretty low, just 10 watts at 4m/s and 80 watts at 7m/s, so whether it’s worth including will depend on whether you have a seriously good wind regime at your place.
To feed into the grid via your current inverter you would need the turbine to have an output compatible with your current inverter’s input range. It’s not clear from the product info on this turbine but many wind turbines require a diversion or shunt controller to maintain a load on the turbine, at least in high winds, so if you were disconnecting it from the grid during the day you might need to feed its output into a dump load. This can be in the form of a simple power resistor or a heating element in your water heater, which would make better use of the energy, albeit small.
Personally, I would look at using such a turbine only if I had excellent wind at the site (at least 5–6m/s average) and would use it to charge a standalone system for use in the home, say to provide backup power, or for lighting or similar. If you want to grid feed the turbine then I would recommend a small independent inverter designed for wind turbine inputs, such as the SWEA units from Ladder Technologies (www.laddertech.com.au).
Off-grid cable sizing
We have been living in a remote area in the south west of WA for over 20 years. We are not grid connected and rely on solar for all our power needs. Over the years, my biggest problem has been with the wiring. The cable has either melted the insulation or been so large that I get voltage drop. I have been buying your magazine since the days when it was Soft Technology but I can’t seem to find an article on how to work out the cable size needed, from both panel to regulator, and battery to individual loads. If it has been done, let me know and I will buy the back copy.READ MORE »
I also have some small solar panels (3.6 volts) from outdoor LED spot lights that I want to wire up to Cree LED star modules for use as lighting in areas that don’t need bright light, and so reduce the load on our house power. I had hoped to use the panels and their batteries to light these areas. Will it work? How do I work out what size resistor I need?
Cable sizing is seen as a bit of a black art by many, but it’s actually pretty simple. There was a sizing guide in ReNew 59 with some ideas on how to do it, but the important things are:
a) Make sure the cable is large enough to handle the maximum current. A good rule of thumb, up to 50 amps or so, is that you need 1mm2 of cable cross-sectional area per 10 amps of current. Above 50 amps or so, thermal issues come into play. Thicker cables have a lower surface-area-to-volume ratio than thinner cables, so there is more heat retention and you have to reduce the current per square millimetre.
b) Make sure the cable is large enough to prevent voltage drops over the required distance. You can work out the drop using Ohm’s law and the resistance of copper. There’s a table in the guide mentioned above and a number of resources online that give approximate resistances for larger cable sizes.
The trick is to make sure cable sizes are within both requirements. Generally, a 5% voltage loss at the maximum expected current is the most loss you should aim for.
Regarding using the LEDs, the battery voltage is almost the same as the Cree LEDs, so you will need a low-value resistor, something in the order of a 1-ohm, 0.5-watt resistor will do it. The LEDs will need some heatsinking, of course. There’s a useful LED resistor calculator at www.ledcalc.com.
Bear in mind that running the LEDs at 300–400mA will drain the batteries fairly quickly. Although you don’t say what capacity they are or the output of the panels, I’m assuming they are small units as used in solar garden lights. You might want to increase the resistor value to decrease the running current and extend the running time.
Low VOC materials
We are completely renovating a period home at Newstead near Castlemaine, Victoria. Our architect and cabinet maker haven’t been able to find a green product for use on the inside of kitchen cabinets that hasn’t been glued together with nasties. I want a low VOC product which isn’t solid wood if possible.READ MORE »
There’s a few options, such as E0 MDF, which is a virtually zero offgassing MDF. If you google ‘E0 MDF’ you will find suppliers. The other option is X-board, a building board made from recycled cardboard and other fibre. It is available as a plain board or as X-board plus, which has E0 MDF laminated onto it for strength. See www.xanita.com for the manufacturer and www.sharpplywood.com.au for an Australian supplier. There may be other suppliers carrying it too.
Wood heater emissions
I visited an eco-village where the burning of wood, such as in a pot-bellied stove for space heating, is not permitted.READ MORE »
The problem might be that fallen timber was scarce in the area that this village was situated. On the other hand it might be an emissions issue. But what if there is a forest nearby with a plentiful supply of fallen, and thus decomposing timber?
My understanding is that rotting timber generates CO2 in its decomposition process. If this is the case, doesn’t it make sense to generate roughly the same amount of CO2 by burning the timber to warm a house? Or does burning timber generate more CO2 than in its natural decomposition process?
There’s a number of issues here.
The first is that most people with wood heaters don’t know how to use them properly. They often overload the firebox, turn down the airflow and let it run at a slow burn. This produces not only CO2 but plenty of methane, soot and creosote, so wood heaters, the way most people use them, are shockingly polluting.
Another issue is that the collection of timber removes habitat from forests. There’s myriad tiny critters that rely on the cover it provides to survive, and some also eat the timber as it decomposes, so removing too much can stress an ecosystem to some degree.
Generally, due to the wood heater issues above, most environment centres have worked out that wood fires are not the eco-friendly heat source many used to think they were, and are now discouraging their use. Sure, most heaters are built to burn very cleanly when used properly, but very few are used properly, and that’s the problem.
There are better solutions, such as pellet heaters, which don’t control airflow, but rather fuel flow, so they always burn the fuel in plenty of air to ensure clean burning. The pellets are usually made from agricultural waste that would otherwise have been burned or landfilled anyway. The only issue is that the pellets are not sourced locally and so there’s transport emissions, which could be considerable.
If you want to go down the wood heating path, monitor your wood collection and also how you use it, making sure it is properly dried and burned with the air damper fully open.
Solar panel lifespans
I was hoping you might be able to help with a query I have received from one of our engineers about solar panels. What is the usage life of a solar panel, he understands it to be 15 years. And once they are retired are they recyclable, and do we have the infrastructure to recycle them or are we preparing for the boom in disposal?
The minimum life expectancy of a solar panel is around 20 years but most manufacturers give 25-years warranties now. Most rate their panels for at least a 25 year life and some rate them to 30 years. Uni-Solar rate theirs for a 40 year life.
As far as I know there’s no one recycling solar panels in Australia, although there are schemes elsewhere. There have been a few articles on these schemes, such as this Treehugger article http://bit.ly/solar-recycling and this on The Daily Green bit.ly/dg-solar
There’s even a company that’s collecting them in preparation for recycling schemes, see pvrecycling.com
Solar panels contain some valuable materials, including trace rare metals, silicon and aluminium. Therefore they do have recycling value and it’s only a matter of time before someone starts doing it here. However, as the PV industry has only geared up here in the last decade or so, it will probably be another 10 years at least before large quantities of panels become available for recycling.
A double duty fire pump
I am building a new house and will install a large water tank for combined domestic and fire fighting purposes. We will need an electric pump for the house water, and the Rural Fire Service require a minimum of 3kW (5hp) petrol or diesel powered pump and a 38mm or 65mm storz fitting for fire fighting. Is it feasible, technically and financially, to do away with the petrol pump and instead install just the one pump for domestic and fire, powered by mains electricity with a battery backup? I assume 30-60 minutes of pumping through the 38mm outlet would be needed in a fire.
While it is technically possible, it’s not something I would do as the two tasks are very different. A house pressure pump needs to flow a few tens of litres of water a minute at fairly high pressure, while a fire fighting pump needs to flow a great deal more. So, if you were to use a pump capable of being a fire fighting pump as a home pressure pump it would run inefficiently most of the time. The only way to avoid that would be to use a very large pressure tank for the home, at least 200 litres or more. Personally, I think all home mains pressure systems should have a tank this size anyway to greatly reduce pump stop/start cycles, but most homes don’t.
The other issue is that fire fighting pumps are often more useful if they are portable. Being able to move the pump if needed can reduce the length of hose required and the flow losses associated with it. Also, if a pump is fixed and tethered to a power system there’s always the chance that the system could fail at the most critical time. Fuses and circuit breakers can trip, or you could get caught when your batteries are at a particularly low level.
Personally, I would use a pump for the home that is optimised for that purpose and have a separate fire fighting pump. After all, they are only used very occasionally so there’s minimal running costs. If you did want to use an electric pump for fire fighting, you could put together a setup where there’s a separate battery bank for the pump which is kept on float charge by the main system via a DC-DC converter. If going down this path I would use a DC pump motor, not an AC one, which eliminates the need for an extra inverter and the associated cost and complexity. Really, anything is doable if you want to spend the money on it, but considering how often a fire fighting pump is used, you are better off keeping it a separate system rather than designing the main house system to include those capabilities.
Replacing air conditioner controls
Our Bonaire evaporative air conditioner is suffering from a deceased control circuit which is instructed via a remote hard-wired handpiece. According to the manufacturer, as my appliance is over 10 years old they no longer make a replacement board.READ MORE »
They claim that they can fit a more modern board, operated by radio, however, the quoted cost really cannot be justified.
In addition, a neighbour has replaced their old 2-speed motor air conditioner with the latest technology and seem to have swapped reliability for uncertainty as to whether the new machine is going to operate or not.
Technicians advise that problems are due to ‘local radio interference’ such as remote garage door openers and they are unable to rectify the faults.
It seems to me that these air conditioners are not really fit for purpose, hence my reluctance to venture down this path.
Looking further ahead, the time will come when our unit will be beyond economic help. With this in mind, I would appreciate your thoughts on the viability of using a modern industrial inverter speed control. The other functions performed by the current circuit board, i.e. water valve solenoid, water pump etc. can be easily bypassed and operated manually.
If this proposal is viable and in the interests of conservation, when the machine ultimately dies, I intend salvaging the motor/control unit for a new life in my workshop. In fact, I have two of these motors and sending them to a disposal site seems a real waste. The motors are made by Webster Manufacturing in South Australia, are rated at 800W and have four connection terminals on one end.
Without knowing what type of speed control the system uses I can’t really say, but many smaller devices use capacitive or inductive control, i.e. they just put a capacitor or inductor in series with the motor for the lower speed. You could do this just with a double throw switch if you were happy to do it manually. If it had variable control, you could use an off-the-shelf speed controller, some of those will handle up to 2000 watts. The rest of the functions, as you say, can be manually controlled. You could also remote control them using aftermarket remote units such as those sold on eBay. The store at stores.ebay.com/ColdfusionX-Electronics/ has a good range and I’ve used their remotes before and they work well.
The other option would be to use a small microcontroller board and program the operation into it. There’s a number of cheap options, the most popular now being the arduino boards as they are low cost, and the programming software is free and easy to use. There’s various interface boards available for them including relay and isolated triac control boards, so the interfacing shouldn’t be too hard.
It’s interesting that others are having problems with their air conditioner remotes; most modern remote controls are digitally encoded so that other radio sources don’t interfere, as the radio bands allocated for this sort of work have tended to become quite crowded with all the remotes out there now. It seems some companies are still not using properly encoded remotes—just cheaper to use the old technology I expect!
Panels not facing north
I live in a lifestyle retirement village at Seaford, South Australia, and we have recently been given permission to install a 1.5kW solar electricity system. I am looking at two options—monocrystalline and thin film.READ MORE »
What is the difference in efficiency between a six by 260 watt panel monocrystalline system and a 15 (or maybe 16) panel thin film system? I can only fit the thin film on the east-facing roof. The monocrystalline system will fit on either the east or west roof but installers prefer to put it on the west-facing roof. There is no possibility of installing on the north-facing roof—there’s no room for either system.
I am interested in which system will produce the most electricity and any other pros and cons there might be.
Panels really should face north, but if you can’t do this, try and get all panels facing the one direction. However, this depends on the array configuration and the type of inverter used.
For instance, you might have an array where all the panels are wired in one series string. If you face half east and half west, then the whole string will only perform as well as the side with the lowest insolation. In other words, in the morning you won’t get full power from the east facing panels as the west facing panels are getting almost no sun, so the whole array will put out very little. In the afternoon, the same thing happens.
If the east and west arrays are separate and are wired to separate inputs on the inverter (some inverters have multiple separate inputs), then each array half will perform as well as it can, so there’s no issue splitting it across roofs that face different directions.
Don’t worry about efficiency of the panels, this isn’t the issue really, all it determines is the physical size of a panel for its rated output—a 60 watt crystalline panel will have a smaller size than a 60 watt thin film because the thin film is less efficient, but they both are still rated at 60 watts. However, thin film panels are less prone to reduced power output as they heat up (known as the temperature coefficient) and so generally, given two equivalently rated arrays, the thin film array will produce more energy over the course of a year as it performs better when hot (the usual condition for panels in Australia). Some crystalline panels have improved considerably in this way in the last couple of years, but you need to look at the specs for each panel. The coefficient is given as a figure of percentage per °C above 25°C, the smaller this figure, the better. For instance, a panel with a temp coefficient of -0.5% per °C running at 60°C will actually put out 0.5 x (60-25) or 17.5% less power than its rating.
I am an ATA member in the process of building a new house and installing stand-alone solar power. We have been advised by one company to wait for the RedFlow batteries to appear on the market as they are better batteries. As we have never heard of them could you please provide us with the pros and cons of these batteries?
The standard workhorse in the stand-alone power system industry is still the lead-acid battery, but there are several newer technologies starting to make inroads. Flow batteries are one type and the RedFlow batteries are included in this category, as are Vanadium redox batteries.
The other technology that is now being used to replace lead-acid batteries is lithium iron phosphate and similar chemistries. A couple of examples of suppliers of these are ThunderSky (Winston battery, see http://en.winston-battery.com/) and Sky Energy (now China Aviation Lithium Battery Co (CALB), http://en.calb.cn/). Both of these batteries are available in Australia. While these are expensive initially, they have vastly longer lifespans than lead-acid and because they can be deep cycled with little effect on lifespan, you can often use a smaller battery capacity compared to a lead-acid battery bank.
LED lighting for the home
I have been an ATA member for about 12 years and we are currently preparing to build our new home in the Perth hills. I was hoping to use LED lighting when we build and have read most of the ReNew articles, particularly in issue 90. I am not up to date with the technology and was wondering if you may know of any products off-the-shelf and where I would find them, and if you had any system design advice for a novice. Internet searching has left me with more questions than answers.READ MORE »
We are also considering going stand alone with the power supply in the future, what impacts would this have on the light system?
My first suggestion would be to avoid downlights if at all possible. They cause all manner of problems, the main one being that they compromise ceiling insulation and the most common ones (narrow angle replacements for halogens) are not a suitable light design for general room lighting. There are LED downlights with wide beam angles designed for ambient lighting but they still require holes in the ceiling and insulation. There are some insulating covers designed to overcome this problem but they add to the cost and complexity of installation.
If you are looking at having the whole house running 240 volts (i.e. using an inverter for everything when you eventually go off-grid) then I would use light fittings designed to take standard GLS globes and fit them with LED bulbs—there’s quite a few good ones including those from EarthLED and Viribright, but there’s many others, some even have Australian approvals. Switch lighting (www.switchlightbulbs.com) is due to release a 240 volt version of their bulbs early next year and Philips is extending their LED bulb range in Australia later this year, so the options are growing.
Another option is LED strips and ribbons. The prices of these materials have dropped enormously of late. While most of it is Chinese sourced (the ‘brand name’ ribbon can cost up to $200 a metre), the quality is still not bad and you could expect up to a decade of use from it, depending on how long it’s used for each day. Most ribbon runs from 12 or 24 volts DC, so you power it from a suitable power supply, which are readily available and cheap. However, this also allows you to wire the fittings to a compatible battery bank at a later stage. Even if you have a 24 or 48 volt battery bank, you can simply use a DC-DC converter to supply 12 volts to the ribbon. The advantage of doing it this way is that you are not relying on your inverter for lighting, so should your inverter fail, you still have lights. Also, when running a house-sized inverter at low loads, the inverter runs very inefficiently. Indeed, at very low load levels an inverter can waste a great deal of energy, negating the use of efficient lighting altogether.
There are also rigid lightbars that are similar to the LED ribbons but are contained in aluminium casings. I have recently found one that comes in a 15mm x 10mm case with a clear cover and has an inbuilt switchmode driver and rectifier, so it runs from any voltage up to 30 volts, AC or DC. It doesn’t get much simpler to implement than that.
So, yes, LED lighting is complex, but that’s because there are so many options. And that’s a good thing, as you don’t have to stick with the same type of light in each room. You can mix and match and find the most suitable type for each room of the house. But, the simplest solution is standard GLS type light fittings and suitable LED bulbs. It’s a fast, simple and cheap option and gives you the opportunity to try all manner of LED bulbs.
Halogen transformer failure
Have you ever heard of plug-and-play MR16 LED downlights causing the failure of switchmode electronic transformers? I have been using some 6 watt LED downlights to replace 50 watt halogens and they seemed to work fine upon initial installation. In one recent instance, four lamps were installed and within a few days, three of the electronic transformers failed. If it was one, I would say the transformer was already on its way out, but a 75% failure rate seems to indicate that the LED lamps may have had something to do with it.
Standard transformers are designed to drive into a simple resistive load whereas the drivers inside the LED bulb would be drawing current in a non-linear fashion. This would affect some electronic transformers and not others, it just depends on the quality and/or design of the unit.
Generally, when doing LED upgrades, I try to encourage people to ditch the transformers altogether and fit GU10 fittings (the bulbs run directly from mains voltage), they look the same as an MR16 fitting just without the transformer hassles.
To solve your problem you should replace the transformers with proper LED transformers, which usually have a regulated 12 volt DC output. ATA has some in the ATA webshop and there are many other sources. If your transformers are plugged into power points up in the ceiling, then you could even replace them with standard 12 volt DC switchmode plugpacks of a suitable current rating.
Mini maximiser not a MPPT
Can you please tell me the input voltage rating of ATA’s mini-maximiser kit? I am thinking of driving 12 volt fans off a solar panel and I am wondering whether I could use amorphous silicon panels (which have an output voltage of around 40-60V and output power of 50W) as direct input or whether I’d have to level-shift the panel voltage first.
The kit is not a maximum power point tracking (MPPT) maximiser but rather just works off a fixed setpoint voltage. It allows the panel to charge the capacitors and when they reach that setpoint it connects them to the motor to dump a pulse of current into it. This causes the cap voltage to drop a bit and the motor is then disconnected from the caps and the cycle repeats. However, if the current from the panels is greater than the motor needs then the maximiser effectively leaves the caps and hence the panel connected directly to the motor. This causes two problems with such a large panel to motor mismatch.
The first is the motor is overdriven until it reaches a point where the voltage across it is high enough to cause it to draw the full current available from the panels. This means it could be running at a very high voltage and hence considerable overspeed.
The second problem is that the maximiser circuitry itself is not designed to handle such input voltages. For the 24 volt version it has a voltage regulator on board but not for the 12 volt version. You would have to adjust some component values in order to keep the regulator function but run it as a 12 volt output unit.
When running a 12 volt motor you should use a nominal 12 volt panel, and a 24 volt panel for a 24 volt motor.
Welders and gen-sets
I have a PV-run home and use a 6.25kVA gen-set for high demand work. I recently acquired a CIG 170 inverter welder and found that it wouldn’t run off the gen-set. I made enquiries and was told that I needed more than 6.25kVA to run it, and since the gen-set was about 16 years old and has done an enormous amount of work I decided to buy a Chinese made unit advertised as a 10kVA.READ MORE »
On checking the specifications on the internet it turned out to be 9kVA. I bought it and on reading the manual it is actually rated at 8kVA. Still, I thought it would run the welder, but it won’t on a regular basis. It did once and worked fine but it just switches itself off since then and prior to then. Could the problem be that the get-set is making dirty power? If so, can I buy any device to clean up the power. Any advice or suggestions appreciated, thanks. The welder works fine on mains power.
The problem is that welder has a kVA rating that’s exceeding the generator’s capacity. With AC, kVA is not the same as kW, you have to allow for power factor (which is a ratio of the real power to apparent power). What this means is that as the power factor of the load gets worse, the kVA capacity needed to run the load increases, even if the actual power in kW stays the same.
Your inverter welder uses a switchmode power supply and these can have poor power factors as they will usually draw their current in short, sharp spikes near the peak of the waveform. There’s a great example of this at http://bit.ly/gensetpf where you can see the current waveform distortion caused by a computer power supply. Even though the voltage and current are in phase, the waveform distortion reduces the power factor considerably.
To calculate the kVA capacity needed to run a particular load, you divide the rated power by the power factor. For instance, a 5kW load with a PF of 0.6 would need a gen-set rated at least 8.3kVA, but in practice it would need to be higher.
What you need to do is to find the power factor and kW rating of your welder. It should be listed on the specs plate somewhere, although power factor may not be listed. If not, then the only way to find out what it is (if the manufacturer can’t tell you) is to measure it with a suitably rated energy meter. Also, the power factor of a load can change depending on the power being drawn by that load. For example, when using the welder on a light setting it might have a PF of 0.8 but on a higher setting that might drop to 0.7.
If this is all too difficult then your only real option is to trade up to a heavier duty gen-set. I would buy something with a kVA rating of at least twice the kW rating of the welder.
I couldn’t find PF specs on the CIG 170 but the similar (in specs at least) BOC MMA 170 has a rated PF of 0.73. Judging by its output of 170 amps and voltage of 20 or so volts I would expect its input to be somewhere in the range of 4.5-5kW, meaning it could need at least 7kVA to run it. Assuming yours is similar then your gen-set is borderline as cheaper gen-sets rarely live up to their ratings. I would just upsize the generator or find one that can handle loads with poor power factors.
Tanks and solar hot water
We are in the final stages of having our farm resumed by the state government to build a cargo railway line. We have been thinking of going solar for a few years but the uncertainty of our situation has caused us to put it off. However, the new farm will give us the opportunity to set things up right from the start and we would like to generate enough electricity to meet our own needs whilst still being connected to the power grid.READ MORE »
We will not have town water and will be dependent on rainwater tanks. This means whether we get a passive or an active solar hot water system we will need to use electricity to pump the water to the roof or off the roof respectively. As much as we like the idea of solar hot water could there be disadvantages without mains water pressure?
Would it be easier, environmentally friendly and in the long run more economical for us to have an ordinary electric hot water system with a larger photovoltaic panel array rather than a solar hot water system with a smaller PV array? The house already has an ordinary electric hot water system in good condition.
There’s a few solutions, but generally people on tank water will usually have a pressure pump coupled with a large pressure cylinder to simulate mains pressure. This is the simplest solution and lets you run any mains pressure system you wish. Provided you go for a big pressure tank (at least 200 litres), the pump won’t have to run too often and you can use a smaller, lower powered pump. Many plumbers will specify a large, high powered pump and a small tank, but this is inefficient as it results in many stop-starts for the pump each day, which loads up the inverter and wastes energy.
If you are happy running everything on low pressure, then just pumping to a good-sized header tank will also work and it eliminates the need for a pressure-rated cylinder.
If you decide to go for an electric-only water heater, don’t get a purely electric unit as they waste a lot of energy; a heat pump system will produce the same amount of hot water for a third of the energy use (they work like a fridge in reverse, gathering heat from the air and concentrating it in the tank). This is especially the case if you want to power it from solar‑you need to make everything as efficient as possible.
12 volt washing machine
Some years ago I was given part of your book Build your own green technology. On page 89 there was an article by Chris Harkin on converting a Hoovermatic twin tub to 12 volt operation.READ MORE »
Unhappily I only have page 89 of this article and I am now in desperate need of the rest as I live on a farm without electricity so am totally dependent upon my wind/solar system.
Please would you be so kind as to send me the rest of this article so that I can get someone to convert my twin tub. I am based in South Africa.
Rev. Angora van Doorn
That’s an old article that first appeared in our magazine Soft Technology (now known as ReNew!) I’m not sure how relevant it will be for your machine.
I take it you don’t have an inverter, but instead everything runs from 12 or 24 volts DC? There are some very low powered washing machines around that can run on small inverters, but that depends on your budget of course and I’m not sure what sort of range of machines you have access to over there.
If you already have the machine and want to convert it, I don’t recommend rewinding the motor as they did in the article, it’s a great deal of work. 12 volt DC motors are readily available from car wrecking yards as they are used for fan motors, wiper motors, window winders etc. More powerful units can be found in trucks and buses. They are also used for electric wheelchairs and various other small electric vehicles and can often be found for low cost but it can take some searching. Ebay has a new global search site at global.ebay.com that can help you find suitable parts if you can’t find them locally.
A solar cellar
I’m interested in putting some solar heating into my cellar. What I was thinking of was building a greenhouse and then blowing warm air from the greenhouse into the cellar.READ MORE »
So what I need, ideally, is a solar powered fan that could blow warm air through a duct into the cellar. Some sort of thermostatic control would probably also be needed.
Can you suggest where I might get it?
Great idea. A solar greenhouse to heat the cellar…simple, cheap and you can do it yourself. For the fan(s) you could use a large 12 volt computer fan—Jaycar has a good range (have a look online and you may find a 12 volt fan and duct combination). Match the fan up with an appropriate solar panel. Choose one with a similar power rating to the fan.
You don’t really need a thermostat as the solar panel will only operate the fan when there is enough sun, and therefore heat, to make the greenhouse and hence the cellar warmer.
So there you are—a nice, simple, cheap cellar heating system. If you really want to use a thermostat there are some good ones available online such as the unit at http://bit.ly/pdnNAN.
However, you really don’t need a differential thermostat as the temperature in the cellar is likely to be constant and almost always cooler than the greenhouse. A simple temperature based thermostat would do. But I would try the simple way first and just use the solar panel to switch the fan on and off.
Ducting is available for central heating and airconditioning companies.