Archive for June, 2012
My solar panels have been sitting on old tires, just off the ground to keep the moisture from the ground off them. They have been putting out about 30% of their rated capacity all this time. I noticed a few days ago that they were incredibly hot on the bottom side. Solar panels heat up when the sun is shining on them. This reduces their output capacity. The hotter they get, the less power you get out.
So I got thinking about some way to cool off the solar panels and get more power out of them. I was thinking about how passive solar heating works. The sun heats up a dark colored surface, heating up the air inside the heater. Hot air rises and flows out the top of the solar heater. Then holes on the bottom allow cooler, fresh air to flow into the solar heater. I figured this could work for cooling solar panels as well. The sun heats up the solar panels. If I allow air to flow underneath the solar panels, in the bottom and out the top, I can get them cooled off a bit.
I had no idea how much difference in power I would see, if any, but figured it was worth a try.
So I started to make a frame to hold the solar panels.
I got some 2x4s and 2x3s by 8 feet long. All of my solar panels are 2 feet by 4 feet in size. I planned to make a frame that will be 4 foot by 8 foot and allow me to mount 4 of my homemade solar panels on it. The biggest point though, is to allow air to flow underneath the solar panels. So I made the frame in such a way as to allow free air flow from bottom to the top under the solar panels.
I cut three boards at 38 inches long for the front legs. Then I cut three more boards at 48 inches long. The pros recommend placing your solar panels at about a 30 degree angle, facing south. This is supposed to bring you the best charging rate. So I guessed that with my setup, I should get enough air flow underneath the panels and also be angled into the sun slightly.
Then I placed the solar panels on the new solar panel cooling rack. They immediately started to show an increase in charging current in full sunlight.
Since I got one board too little, I did not get to put the last piece in the middle for the solar panel on the right side as you can see in the photo. But this new solar panel cooling rack is actually working better than I had expected. Before, the three 65 watt solar panels were putting out 2.5 Amps total in the heat of the day. That is not much power at all. The solar cells I used are rated at 3.75 Amps each. That means I should see about 11.25 Amps of power, in theory. The reality though is that the solar cells were chipped and broken, reducing the output power a little bit. And I used plexiglas instead of solar glass, further reducing output a bit. Then there is heat loss. And then there is a mismatch between the solar panel output voltage and the battery voltage, further reducing charging current.
So I had about 2.5 Amps in full sunlight before. Now I am reaching as much as 4.25 Amps in full sunlight with the new passive solar panel cooling rack. This cooling rack works passively by allowing air to flow in, underneath the solar panels and out the top. This cools the panels greatly and increases power output a lot. That is nearly double my original power output with the cooling rack in place.
The next step is to make some sort of dynamic voltage booster and voltage reducer to match the battery voltage to the solar panel output voltage. If the solar panels are each putting out 19 volts at 3 Amps and the batteries are sitting at 12.5 volts, then I want to reduce the solar panel voltage to match the battery voltage while increasing the output current. 19 volts x 3 Amps = 57 Watts.
57 Watts / 12.5 volts = 4.56 Amps going into the batteries (per panel).
If the panels are putting out less than the battery voltage (cloudy or indirect sun), then I want to increase the voltage while reducing the current. With this method, I should start to see solar panel charging output closer to the manufacturer’s rating. Take an example of 3 Amps and 12 volts at the solar panels with the same 12.5 volts at the battery. With no special system in place, you would not see any charging at all on the batteries due to the lower voltage. 12 volts x 3 Amps = 36 Watts out of the panels. 36 Watts / 12.5 volts = 2.88 Amps going into the batteries.
Of course this is all theoretical and the actual numbers will vary a bit from my example, but hopefully you get the point.
The problems you see here are nothing new to my own homemade system. Every solar panel setup has the same problems (except for losses due to poor construction).
Another later project will be to set up a solar tracker to have the panels facing into the sun at all times.
See the passive solar panel cooler video here:
I hate to be all gloom and doom, but preparing for a disaster or an emergency is a good idea. After living through a hurricane in Upstate New York, in the mountains and seeing the destruction far from the coast, I am a believer of prepping. You may suddenly find yourself living with no electricity and just the skills God gave you.
Salvaging electronics to cannibalize for other uses is nothing new to me. Growing up with a love of electronics but little money teaches one how to find what you need from used electronics. Even old, discarded stereo equipment laying out in a field may yield up some very useful electronics parts.
Take, for example, the old stereo below:
And the bottom side:
I found this old stereo out in a forest, laying exposed to the elements. Most people would think this was total junk and had nothing useful left in it. Not so. This old piece of electronics junk still has rugged old power transistors, high power resistors, variable resistors, heat sinks, capacitors, switches and wire in the transformers. Some of these parts are now being used in my homemade solar charge controller in the off grid trailer.
Most electronic parts from the older days are very rugged and can withstand a lot of abuse from nature. The power transistors in an old stereo still work well and can be used for a variety of projects. They make good high power electronic switches, for example.
Post nuke electronics should still function just fine. Maybe some things will get destroyed, but some parts will be salvageable. You can keep your old radio or basic electronics going with a little skill and searching.
After disaster strikes and the economy collapses, junk piles and back yards will become your shopping mall.
After living off the grid now for the last 4 weeks full time, I am getting a better idea of the true solar panel output during any given time of the day. I can also see how rain or cloudy weather affects the solar panel output. When you buy a solar panel, you see a wattage rating on it. But the real solar panel output is a totally different story.
I have two homemade solar panels, each rated at 65 Watts. That means I should have about 130 Watts total energy output during every hour of the day. At 12 Volts DC, that means about 10.8 Amps of power being put into the batteries every sunny hour. But the reality is much different.
First of all, your solar panels (or cells) were tested at the factory under a bright light simulating full direct sunlight with no clouds. This would be the optimum condition for maximum output. Of course, we rarely have that condition except for a couple hours each day when the sun is directly overhead and there are no clouds.
I just installed a high precision Amp meter in my charging system and was totally shocked to find that I am only getting about 3 Amps output with the sun directly overhead and no clouds. At any other time of day there are about 1 to 2.5 Amps output. If it is raining or cloudy, I get about 1 to 1.5 Amps. That means I get between 10% to 30% of my solar panels rated energy output at any given time!
I have checked and re-checked all of the wires and connections. There is nothing wrong. And I am not alone in this. Most off grid power systems do not produce anywhere near their rated energy output.
But why then do we not get the full power output to the batteries?
There are a few different factors that influence total solar panel output.
First of all, the sun is moving (well, we are). The solar panels are only getting direct full sunlight for a couple hours each day. That is the easy one to figure out. To remedy this you need a solar tracking controller which moves the complete solar panel array so that it is always facing directly into the sun at any given time of the day. But these cost money or are complicated to make yourself. They need to be rugged in order to survive extreme winds and storms.
The next problem is that solar panels are made to produce about 18 Volts. This is so that when the sun is not directly overhead, the panels are producing at least enough voltage to charge your batteries a bit. Lead acid 12 Volt batteries need about 14 Volts to charge them. If your panels are producing 18 Volts, but your batteries require 14 Volts, then you are just dumping all the excess energy. It is wasted. Your solar panels are forced down to 14 Volts. It is even worse when your batteries are lower. At 12 Volts you loose even more potential energy because you force the solar panels down to the battery voltage of 12 Volts. Anything above 12 Volts is lost. Of course, any voltage below your battery voltage is lost as well. This means on cloudy or rainy days, mornings and evenings, you may get nothing.
The solution is a MPPT solar charge controller. This is a Maximum Power Point Tracking charge controller. This device monitors your solar panel output voltage and the battery voltage. When the solar panels are producing less than the battery voltage, they boost the voltage, while reducing the current and charge the batteries. When the solar panel output is higher than your battery voltage, the MPPT controller reduces the solar panel output voltage while increasing the current into your batteries. What is does in essence is matches the solar panel output voltage to your battery output voltage to get maximum charging current at any given solar panel voltage. These are also very expensive.
Due to the costs many solar energy systems do not include either solar tracking controllers or MPPT controllers. But at $5 to $10 per Watt, that is a lot of wasted energy. Take my example numbers and extend them out to a 1,000 Watt solar array. That means that for an initial investment of as much as $10,000 I may only get about 100 Watts to 300 Watts of total solar energy output at any given time. These numbers are averaged for a northern climate and throughout a variety of weather conditions. Sunny states will get much better output.
Now the cost of a solar tracking controller and a MPPT controller seem more reasonable.
I will be building both of these in the coming months. Living off the grid on 1 – 3 Amps of power is a joke. Ask any auto mechanic and he will confirm that this in nothing for a battery. I get about 300 Watts of total usable energy a day. A common desktop computer uses 300 Watts (per hour minimum). Your light bulb uses 100 Watts. Run a light for three hours and that is all I have.
Well, anyway, this blog post is being typed on a laptop that is charged by off grid power. It is a clean, challenging and fun way of life to say the least.