I just read an article on yahoo about the effectiveness of solar panels on the home. Here it is if you want to read it. Don’t worry too much if you don’t because it’s not that great. While not untrue it is poorly researched and misleading. Lots of people, particularly kayakers in the klan and NSW Seakayak Club frequently drill me on all things solar so I thought it was time for a bit of a lengthy blog article to clear things up. Please bear in mind that the figures I use are for NSW and while the principles are all the same, each state has different government incentives so there may be some variances. There are two main areas of solar: grid-connect and off-grid. Off-grid can be a house or facility running entirely on solar/battery combinations or it can be a recreational setup like a 4wd, caravan or campsite, the principles are the same. Grid-connect is where you are connected to the electricity grid but have a percentage of your power sourced via the sun. Let’s look at each.
There are two types of system depending on the metering: Gross and Nett metering.
Gross metered solar generates power all through the day and exports every watt back to the energy retailer who then pay you per kilowatt/hour. Think of it like a farmer who harvests a crop and sells all of it at market. This means you still have to pay your electricity bill but hopefully the money you earn from the sale of your power will cover it. The success of this depends on the feed-in tariff per kilowatt/hour and up till October 2010, the NSW government had set a price of 60c/kilowatt hour. This was called the solar bonus scheme and was like having a money tree. Of course, this price was insane and the government quickly ran out of money so the tariff dropped to 20c. Still good but people panicked and the industry nose-dived. With the new Liberal government in March 2011, the scheme was abolished and the price per kilowatt was set at what the market could afford which is presently around 8c/kilowatt hour. At this rate, Gross metered systems were producing very little money so the industry reverted to Nett metering, the traditional method of connecting solar to the grid.
Nett metered systems are physically the same as gross metered except the meter measures both imported and exported power. So the solar you generate, you use. It’s like a farmer harvesting a crop, taking what he needs for himself and selling the rest at market. Now, 8c/kilowatt hour is not a lot but if you are being billed at 25c or 57c/kilowatt hour and you are generating free power at the time then you are saving 25c or 57c from your bill. Saving 57c and earning 60c are nearly the same thing. So Nett metered systems increase in value to you as energy prices rise.
Solar only works through the day.
This means that solar systems on Nett metering require a lot more thought to get the best from them. Most houses use more power in the afternoon than morning as most people are at work and kids are at school. In the afternoon the sun is heading West so it makes sense to aim your panels West or North-West to offset your peak usage whereas Gross metered systems are better placed North to generate maximum power as your consumption is not a factor. You will lose a little performance on the West but you will have a bigger impact on your bill. When you have a Nett metered system, it is important to understand your load pattern for the house. Understand that at certain times you have free power and set things to run then. Swimming Pools, washing machines, dishwashers etc can all be controlled this way. Obviously not everything can. You want dinner in the evening and in Winter in NSW it gets dark around 4:30pm but your system will still offset a big chunk of your bill if you manage it properly.
Everyone is obsessed with rebate. People always want to know what the government rebate is to buy solar. I tell them to forget it. In Australia the rebates have ended except for the generation of STCs. (Look these up). The rebate was there to help the industry grow. As the price of solar systems fell, the rebate reduced annually and now is gone but systems have never been cheaper and even without rebate people are constantly surprised at how affordable systems are. In Australia, you can buy a 3kw system (the average) for around $5000 using quality gear and 10kw systems for around $15,000. That is damn cheap. If you have a business and you don’t have solar on the roof then you are poorly managing your business. It is an easy way to hammer fixed costs with only a 2 year ROI.
How about we stop obsessing about the Germans. Their stuff is NOT better than the Chinese. It just isn’t. This idea is a legacy from the Second World War, particularly in Australia. German gear is not hand tooled by wizened German machinists it is put together by Turks and Bulgarians in EU controlled factories somewhere in Europe or even South America. Many German brands operate out of China anyhow. If you believe Chinese gear is made by slaves in a corrugated iron lean-to on a dirt floor then you are WRONG. Chinese solar factories are state-of-the-art and are often generations ahead of the rest of the world. If you look at the top 50 panel makers world-wide, and these lists are published on the net, almost all of them are Asian and the majority are Chinese. Here’s some brands for you:
Suntech, JA Solar, Trina, Yingli, Renesola, Hanwha, Samil, Aurora, Optik.
The list is endless. Systems don’t get defected because of panels or inverter. They get defected because of dodgy installation. Make sure you have the best isolators, the best cable and the best conduit. Make sure everything is UV rated or you will be changing it every few years. The installers make or break your job not the country of origin of the stuff. Make sure the placement of panels is sound. Some companies slavishly insist on North facing systems even though for most people this will have a poor outcome as the peak generation will be around noon when nobody is home. Shade is vital to avoid. What you thinks is only a little shade can have a big impact on performance.
The next big thing in the industry is battery backup systems. These retro-fit to Nett systems to capture excess solar generated but not consumed and then fed back to you at night. So instead of your exported kilowatt-hours being worth 8c they are work 57c on Time-of-Use billing systems. I was working with these just prior to leaving the industry. This is getting close to off-grid so I’ll cover some considerations there.
String versus Micro Inverters
Here’s another thing you might have to navigate. The industry is moving from string to micro inverters. There are pros and cons for each.
With a string inverter, you have one central inverter with either one or two channels generally. Each channel can take a certain number of panels connected in series. This number depends on inverter voltage input and panel voltage output. The number of panels is critical. String inverters are pretty universal but have some problems. First, if you shade panels in a string it can reduce the total voltage to the inverter and make the inverter switch off. Second, all the panels in the string have to face the same way or you get big losses. This limits your options when measuring roofs. Third, if a string inverter fails the whole system fails.
With micro-inverters, each panel has its own inverter bolted to it. This means you get 240v out of the panel/inverter combo. You don’t have to worry about stringing panels so this means you can place panels anywhere you please without compromising the whole system. Because you have 240v ac output, you don’t have as much conduit to run, the system is much safer and more easily compliant. Furthermore, if you shade out some panels the whole system is not compromised. In theory, because you have more inverters you have many more points of failure. True but a failure won’t bring the whole thing down and micro inverters from top brands tend to have 25 year warranties so failure isn’t your problem. Generally, micro inverters are used on complex roofs where you can’t get string lengths right or you have shade afflicted areas.
Poly versus Mono versus Thin Film
Solar geeks will fight to the death over this but at the end of the day the difference between Poly and mono crystal panels is negligible to zero. Mono had an historical advantage that is now long gone and all development seems to be going into hybrid poly crystal. I have used both extensively and generally only deployed mono where colour was an issue.
Thin Film panels had huge advantages and huge disadvantages. They are non-crystalline so angle-of-incidence of sunlight is not as important to them. This means they operated longer in the day capturing more light and generating more power. They were also shade tolerant. However, they are not as energy dense as a crystal panel so a 100w Thin Film is roughly the same size as a 250W crystal panel. This means you need more than double the roof space. Thin Film do not have the advantage of economy of scale so prices haven’t come down much compared to crystal so they are expensive. These days you need a strong case to use them.
Lots of people want to get off the grid. I do too and will eventually but it’s not that easy. For a start. you are essentially having a battery operated house and batteries run flat and eventually die. This is the core issue with off-grid. You have to be constantly energy conscious and everything you buy and use has to be counted or your house will run out of power till the next day or worse you start to reduce the life of your batteries.
When people ask me about off-grid, the first thing I ask for is a list of every single item they plan to use and what the current draw is. Often this alone puts people off but without it, you can’t calculate how much battery power you need and without that you can’t work out how much solar you need to charge it. Everything starts with the load. Off-grid systems are more complicated and a lot more expensive. Generally, it is much better value to stay on the grid but have a decent grid-connect system to reduce costs. However, if you cannot be connected to the grid and have no choice then energy will be something you have to deal with daily.
Much more common is recreational or mobile solar and battery systems for your 4wd or camper. These are much simpler and obviously less expensive but the load principles are the same. If you are looking to set up your trailer or truck here’s the process:
OK. So a car fridge is anywhere from 1.5A to 3A at full compression. Engel fridges use a Sawafuji compressor which has low draw but makes the fridge expensive. Fridges like Waeco and Evakool use Danfoss compressors which are tried and true, cheaper but have higher draw. Typically around 2.5A.
What else are you going to do?
LED lighting. Very low draw for camp lighting. Not even an amp. Charging computers/phones etc. Very low draw.
So let’s say we have a total peak draw of 5A and that is pretty generous for a camp. What battery to use?
Currently the leading deep cycle battery type is the Gel or Absorbed Glass Mat. Both are lead-acid and have the advantage over wet lead acid that they won’t leak and can be tipped over. Handy in a 4wd or boat. They still have the normal lead-acid problem of poor depth-of-discharge (DOD). This means they can only be discharged to a 50% of their rating before they start to fail. So a 100Ah battery in lead acid is really only 50Ah. This means a 100Ah battery will deliver 5A of load for 10 hours depending on battery condition. This is called “autonomy time”. Now, a car fridge doesn’t draw peak load all day long, only under compression, so you probably won’t be pulling 5A all day so a 100Ah battery will give you about a full day’s delivery and this is why the 100Ah is the leading battery size for 4wd and trailers.
There are new batteries coming out right now that are lithium based such as Lithium-ion and Lithium-Iron (LiFePo) or Lithium Ferro Phosphates. Lithium-ion is actually old hat now but LiFePo are the battery to have. While dearer than AGM, they have a theoretical 100% DOD and rapid recharge time making them far superior for 4WDs. A 100Ah of this type will draw 5A for 20 hours in theory but in practice around 18 or so.
To recharge any of these batteries in a 4wd most people isolate them from the cranking battery but charge them off the alternator. That’s OK but really doesn’t do much for the battery. An alternator doesn’t maintain sufficient charging control to keep deep cycle batteries full charged and can reduce life in them. It is far better to have a DC-DC smart-charger installed which will keep the battery at optimum condition. If you are charging with solar, then you need to know the current output of the panel. A 100W -120W panel will typically produce around 10A. So 10A going into a 100A deep cycle battery at 50% discharge will take 5 hours to recharge. That coincides with the average solar day of 6.5 hours. This assumes a sunny day so you need to have a non-solar backup because everyone knows that when you go camping it almost always rains. Here’s my system. I have yet to install a DC-DC controller but so fay this system has let me run an Evakool car fridge for days on end as well as charge my electronics and proved LED lighting. The batteries for a Defender are under the passenger seat so I have connected as nice fat cable with Anderson plug so I can keep it out of the battery compartment for convenience. Works very well.
This is very basic for an overview and there are numerous variables when calculating for accuracy and mission-critical applications but the principles apply across the board for things such as a kayak bilge pump. Pretty simple. Get your pump. Find the load current when pumping (should be on it’s label). Find your battery. For a kayak it’s generally around 3Ah. Halve it because it’s lead-acid and divide this number by the load current. This will give you the autonomy time in total hours of constant pumping. Now a bilge pump works under load for about 30 seconds at a time so you can calculate the number of full cockpits your battery can run the pump. Pretty easy stuff.