Special Offer of the Day – 20W PV Solar Panel £25.99

While the price per Watt of PV solar panels has been tumbling, the cost of smaller solar panels (<30 Watt) have remained relatively high in most cases because of the fixed costs of postage, and manufacturing without the benefit of scale.

Smaller panels are particularly useful for battery powered outdoor projects such as shed lighting, electric fencing, irrigation systems, and much more.

20 watt PV solar panel special offerPictured above is our special offer recommendation of the day – a high quality 20 Watt monocrystalline PV solar panel for just £25.99 plus £2.99 postage (and no extra postage if you purchase 2 or more of these panels).

This panel is 363mm x 529mm x 25mm in size and 2.5Kg in weight, and is fitted with 1.5 metres of cable and a bypass diode to prevent reverse discharge at night.

Click here for more information or to snap up one of these panels now: 20 Watt PV Solar Panel Offer.

Reducing Reflectivity of PV Solar Panels to Increase Efficiency

The US Department of Energy’s National Renewable Energy Laboratory (NREL) is carrying out research on reducing the reflectivity of PV solar panels to increase their efficiency.

Standard silicon solar cells (out of which solar panels are built) reflect around 35% of all the light which hits them – therefore one third of the solar energy hitting them is immediately lost. To reduce these losses, commercial solar cells receive an anti-reflective coating (gas molecule deposition) which brings down reflectivity to 7-10% typically. (It is this coating which makes solar cells appear blue). This process is toxic and the equipment used to achieve it is very expensive. Therefore NREL are looking at ways to reduces reflectivity of solar cells while at the same time reducing costs of manufacture.

NREL Natcore technology black silicon solar cellNREL’s solution called black silicon uses an acid bath with a silver nitrate catalyst to put trillions of tiny holes into the surface of each 6×6 inch solar cell. These holes trap the photons of sunlight increasing the chance they will be absorbed by the solar cell and converted into electricity. With this technique reflectivity is reduced to less than 1.5% (which results in solar cells which appear black).

An added benefit is that solar cells treated in this way perform better in the morning and afternoon when the angle of the sun is further from the optimum (perpendicular), and they also perform well in overcast conditions.

NREL black silicon under microscopeNREL have exclusively licensed this black silicon technology to Natcore Technology  specialists in thin film solar panel manufacturing. With further development they hope to make more efficient and cheaper solar panels than anything on the market today.

Low Voltage Disconnect with Display and Datalogger

Our user-programmable low voltage disconnect (LVD) circuit remains one of our most popular products – very useful to protect batteries from deep discharge damage.

One request we have received many times is for an LCD (liquid crystal display) to be added to our low voltage disconnect circuits so that the actual voltage of the battery being monitored is shown together with other useful information such as the low voltage disconnect set point, state of the system, and so on.

A second request is for some datalogging of the voltages measured – ideally to be displayed on an LCD. Therefore we have developed a new REUK low voltage disconnect circuit with LCD and data logger to meet both of those requirements.

low voltage disconnect with LCD and data logger

We have attempted to make this device as useful as possible while being as simple as possible to use. The LCD pictured above from our prototype shows (from top left to top right) the current voltage measurement (updated every 0.1 seconds), the target voltage for change of state (in this example 12.5V is the voltage below which the low voltage disconnect will engage), and the state (in this case, output ON).

The bottom row shows the data from the data logger, from left to right, minimum voltage logged, average (arithmetic mean) voltage logged, and maximum voltage logged.

The voltage measured is logged once every just over 7 minutes, with the most recent 200 measurements logged. That gives a 24 hour record of the battery voltage which is very useful for identifying problems and understanding battery usage.

reuk LVD with LCD and data logger

In the screenshot above, the state is now ‘LO’ since the measured voltage (11.9V) is below the LVD voltage (12.5V). After 10 seconds of this state being maintained, the output would be turned off automatically and only turn back on after 10 seconds of the measured voltage exceeding the LVD cancellation voltage.

The user can easily set the disconnect voltage and cancellation voltage using the display and a button on the LVD circuit, and the datalog can also be cleared by the user. All data is retained by this LVD circuit even when it is disconnected from the battery.

If you are interested in purchasing a low voltage disconnect circuit with display and datalogger, email neil@reuk.co.uk with details of your exact requirements.

Saudi Solar Power Boom About to Begin

Reuters yesterday published a very interesting analysis article on the future of solar power in Saudi Arabia. Perfectly located for solar power generation, Saudi Arabia currently has just 12MW of installed solar capacity – less than was installed in the UK in the first half of May, and a long long way behind the 5,000MW of capacity installed in China during 2012.

solar power boom in saudi arabia

Saudi Arabia is has relatively low natural gas reserves, but vast oil reserves, so Saudi power stations are oil fired power plants which give an efficiency of just 30%. Since oil used in domestic power generation is oil which cannot then be sold on the international market, there are billions of dollars per month of opportunity cost, effectively pricing Saudi electricity generation at a huge 26 cents/KWh.

With the price of solar panels falling to US$0.80 per Watt, and assuming installed costs of US$1.50 per Watt for utility-sized solar power plants, solar generation costs would be just 9.6 cents/KWh – less than half the cost of using domestic oil.

For these simple economic reasons, the Saudis plan to install 5,000MW of solar over the next 5 years, and 41,000MW over the next 20 years which will give them billions of additional barrels of oil to sell on the international market.

Click here to read the full Reuters article.

Compressed Air for Storage of Renewable Energy

The wind tends to blow more strongly at night when demand for the electricity wind turbine generators can make is at its lowest. Therefore, finding ways to store energy so that it can be used at times of high demand is essential.

The Pacific Northwest National Laboratory has been studying how compressed air could be the solution to this energy storage problem.

compressed air energy storage facility

When electricity generation exceeds demand, a large air compressor (powered by the generated electricity) forces air underground into natural porous rock reservoirs. When demand increases, this high pressure air is release back up the surface where it is heated and turns turbines to generate electricity. The overall cycle is up to 80% efficient.

The research looked into suitable locations for this type of compressed air energy storage – not easy since the location must be near to high voltage power lines, have very specific geology, and be near to either natural gas lines or a geothermal heat source for heating the compressed air.

One of the locations they studied had an air reservoir large enough that the energy stored could be used to generate electricity for 40 days – perfect for storing the surplus hydro electricity generated in the spring for example.

For more information see this press release.

Offer of the Day – 80W Monocrystalline Solar Panel £71.98

With the EU about to impose high tariffs on imported PV Solar Panels, and prices of solar panels likely to increase soon for other reasons, now is definitely the time to get your hands on some competitively priced panels.

80w monocrystalline solar PV panel - 12VDC

Our recommended offer of the day is this 80W 12V monocrystalline PV solar panel best priced at just £71.98 while stocks last. It weighs in at around 8kg and has 1205mm x 545mm x 35mm dimensions.

The panel is fitted with a sturdy aluminium frame, a waterproof wiring box, and is supplied with solar cable, plugs, and bypass diodes fitted.

Click here to purchase one or more of these panels or for more information: 80W PV Solar Panel. The panels are despatched from Germany quickly and well packaged in our experience.

Project of the Day – Wind Turbine Dynamic Blade Pitch Controller

Today we have been working on a dynamic pitch control system for a wind turbine generator. Dynamic pitch enables the blades of a wind turbine to be rotated into or out of the wind to increase or decrease the amount of wind energy they can exploit. It is used for power control in some of the largest commercial wind turbines, but the controller pictured below is to be used on an off grid DIY 3kW wind turbine generator charging an 800Ah 48V battery bank in Murcia, Spain.

wind turbine dynamic blade pitch controllerThe designer, owner, and builder of this wind turbine has housed a 24VDC epicyclic motor inside the main shaft with slip rings to connect cables from the bottom of the mast to the turbine. This motor can turn the individual wind turbine blades clockwise or anti-clockwise, and he fitted limit switches at the position of maximum rotation in either direction to limit their motion.

At the top of the mast by the turbine generator is a 12V DPCO relay which is used to switch the +24V and 0V connections to enable the direction of the motor to be changed. When that relay is energised the motor turns one way, and when the relay is not energised the motor turns the opposite way.

He also has an anemometer (wind speed measuring device) which closes a relay when the wind speed exceeds 5 mph.

Schematic for wind turbine dynamic pitch control systemThe schematic above shows how our controller fits into the system. 12V (nominally) is tapped from the 48V battery bank, and the exact voltage measured. If the voltage exceeds a user programmed set point (13.5V) then we want the turbine blades to turn out of wind to reduce the power going into the battery. If the voltage is less than the set point then we want the turbine blades to be turned into the wind to try to increase the power going into the battery.

There are two relays on our controller: one switches +12V to the DPCO relay to dictate the direction the motor will turn, and the other switches the +24V (tapped from the 48V battery bank) which will power the motor.

If the wind speed is low (as measured by the anemometer) then the motor is not turned. If the wind speed is good then if the battery voltage is high the motor is powered for 1/4 of a second to turn the blades a little out of the wind, and if the battery voltage is low the motor is powered for 1/4 of a second to turn the blades a little into the wind. The limit switches override this setup so if the blades are already at their limit, the motor will not try to turn them past the limit.

This process is repeated every couple of seconds to keep everything as efficient as possible while protecting the batteries from overcharging.

Morocco Starts Vast Solar Energy Project

Unlike most of its North African neighbours Morocco has negligible gas and oil reserves to exploit. It does however have a near perfect geographical location and climate for solar power.

This month work started on the first of a series of huge solar power plant construction projects which by 2020 will have a generation capacity of 500 Megawatts and cover 3000 hectares. Located by the desert city of Ouarzazate 200km drive from Marrakesh, this concentrated solar power (CSP) plant will eventually meet the electricity needs of the city’s 1.5 million residents.

Ouarzazate morocco CSP solar power plant

Phase one is a 160 MW solar power plant to be built by a consortium led by Saudi company ACWA Power. The contract for the second phase will be awarded later this year which will raise total capacity up to the targetted 500 MW.

Morocco are planning to construct five such solar power plants over the next 10 years giving it a generation capacity of 2000 MW at a cost of around US$9 billion. Funding will come from The World Bank, the African Development Bank and the European Investment Bank.

Morocco are aiming to generate over 40% of the country’s total power needs from renewable energy sources by 2020, with additional plans for huge investment in wind farms along their windy Atlantic coastline to mix with the solar to give it renewable electricity generation night and day.

If these projects are all completed and others are developed, it is likely that Morocco will look to export clean electricity to their European neighbours, a model likely to be repeated across North Africa and something we looked at back in 2008 in our article Solar Power for Europe from the Sahara.

Follow Up to RC Helicopter Lighting Controller

A few weeks ago we put together an automatic lighting controller for a radio controlled helicopter – see here for details on that project: RC Helicopter Lighting Controller.

That controller has now been successfully installed on the RC helicopter. Here are a couple of photographs – first the helicopter and secondly a view of the light detector mounted to it. We also have a video of the navigation lights coming on and turning off automatically according to ambient lighting conditions. Thanks to Troy for those.

rc helicopter automatic navigation lights rc-helicopter-light-detector

Low Voltage Disconnect – User Programmable Set Points in Binary

Our REUK Programmable Low Voltage Disconnect (LVD) is a product which is used to protect batteries from being excessively discharged and therefore permanently damaged. The user of this device can set the voltage at which the low voltage disconnect is activated, and a second higher voltage at which it is cancelled.

In programming mode, each button press reduces the low voltage by 0.1V from a default value of 12.5V, or increases the cancellation voltage by 0.1V from a default value of 12.0V. For example, they would press the button 7 times to set the low voltage to 11.8V (12.5-0.7V) or 9 times to set the cancellation voltage at 12.9V (12.0+0.9V).

This method of user data entry works very well as it is simple and much cheaper than using a digital display or digital keypad BUT where it does not work so well is in situations where the low voltage is to be set very low, or the cancellation voltage very high – for example, to set a low voltage of 10.0V would require 25 button presses. That is not convenient, and so many button presses increases the likelihood of the user making a mistake.

low voltage disconnect with binary entry of cut out and cut in voltages

To get around this occasional issue we have come up with an alternative design (prototype pictured above) which enables the user to enter the voltage set points using binary via a couple of buttons with corresponding red and green LEDs.

Let’s say someone wants to set the low voltage set point to be 12.4V. Removing the decimal point gives us 124 which is 1111100 in binary (just type a number followed by ‘in binary‘ in google to find out its binary value). The user enters this binary value pressing the red button for a ‘0’ and the green button for a ‘1’. The LEDs then replay the sequence of 1’s and 0’s for visual confirmation of correct data entry, and that’s it – the unit is programmed.

More Technical Detail

We were going to use an 8-bit value for the voltage entry, but that gives a maximum value of binary 11111111 which is 255 in decimal. Since we want our LVD’s to be suitable for 24V battery systems without software modification, 25.5V is almost always going to be too low and so 8 bits is simply not enough. Therefore we changed the design to 16-bit (maximum decimal value 65535) but this means that for the expected maximum voltage of 30.0V we have for the decimal value of 300 a 16-bit binary value of 0000000100101100. This has a lot of leading zeroes which again increases the chance of the user making a mistake – therefore in the final design the user enters the binary value starting with the least significant bit (i.e. going from right to left) and any leading zeroes (which are now following zeroes) are added automatically by the microcontroller.

For example, if a user with a 24V battery system wanted a cancellation voltage of 27.4V, they would type in the Google search box convert 274 to binary and get the following result:

convert decimal value to binary

The leading 0b just tells you that what follows is in binary – 100010010. The user then uses the red and green buttons to enter this binary value starting from right to left 0-1-0-0-1-0-0-0-1, and that is it – 27.4V has been successfully saved in the device.