Posted by Jen Seder on Wed, Feb 15, 2012 @ 08:35 AM
Of all the ways solar electricity benefits the people on Earth, none makes as much difference in the daily lives as pumping water. By providing water for irrigation, or potable water has obvious benefits for people in rural areas and especially for those in develo ping nations.
There are 3 different ways that water pumps can be connected to PV (solar) modules.
DAY OR NIGHT SOLAR POWER WATER PUMPING
This method uses a battery for energy storage for easy pump starting and so water can be pumped at any time.
This method has some significant advantages. Water can be pumped during the day or night, in any weather. This can be critical for such applications as diverting flood waters, or providing potable water during emergencies.
The battery adds some cost, but since the PV array does not have to be large enough to start the pump, the system cost can actually be lower. An MPPT solar charge controller optimizes the energy harvest from the array and the inverter converts the DC to solid AC power for almost any pump. The pumps can be any size and single phase or 3 phase.
Designing this system starts with selecting the pump to meet the water needs. The inverter and battery are sized to provide enough power to drive the pump. The PV array must simply recharge the battery in the daytime.
AC MOTOR DRIVE AND AC PUMPS WITH SOLAR POWER
For pumping high amounts of water with solar power, a large AC pump is usually required. These pumps require well regulated 3 phase AC voltage and current.
By using an AC variable speed controller called a Variable Frequency Drive (VFD), the pump motor will have the proper voltage and current. The trick is to supply DC from the PV array directly into the DC bus inside the VFD. The normal AC input is not used. As the sun rises and PV voltage and current increase, some VFD products will accept the input and when the power is high enough, it will start the pump. The PV array must be large enough to provide enough power to start the pump with including the head of water. The size of the PV array required for this method can be very expensive.
This method will only pump when there is plenty of sunshine, but large pumps can be driven by large PV arrays. Selecting the right pump and the VFD are critical factors then they will dictate the size of the PV array.
DIRECT CONNECT PUMPING WITH SOLAR POWER
The most basic (and most elegant) system for water pumping with solar power is a Direct Connection from the PV Array to the DC Pump. As long as there is good sunshine, the pump will work. The water is either used as it is pumped from the ground, or it is stored in a pond or tank that is higher than the eventual need for the water. When the sun goes down, or during dark days, the stored water is available for use because gravity will deliver it.
The limitation is that the direct connect pumps are rather small. And since the pump must work over a wide range of voltage and current, they can be expensive.
The direct connect plan is difficult to beat for rural areas or developing nations where keeping things simple is the key to long life and easy support.
Designing the system is a matter of selecting the proper pump which will provide the amount of water required. Then the pump specs will dictate how many PV modules are required.
Posted by Jen Seder on Fri, Feb 03, 2012 @ 10:31 AM
This is our final post in this series on the topic of surge protection for solar installations. Here are 5 more basic tips!
6. THE EQUIPMENT -- The first piece of equipment that the home run sees is at the greatest risk. A second set of surge protection devices should be mounted directly on the incoming wires from the PV array or combiner boxes.
7. RISE TIME OF THE SURGE -- In the first Surge Protection blog, the website cited will show drawings of the 8/20uS spike. This is a typical, albeit small, surge that we are trying to keep out of the front ends of our charge controllers and inverters. It is defined as 8us rise time from 10% to 90% followed by 20uS fall time from that 90% peak down to 50% of the peak voltage. The tail can be very long after the 50% point and it not defined. The important issue is the rise time. Whatever components are used in the Surge Protection Devices, they must turn on fast enough to stay ahead and short that fast rising spike to ground. Remember that the components have no advanced warning. When the spike hits them, it says: “Jump”, and the components have to ask “how high and how fast” on the way up. Unless effectively shorted to ground, the spike will continue past your surge protection device at the speed of light.
8. CHOICE OF SURGE PROTECTION COMPONENTS -- This is where Apollo Solar has done our own research and experiments. The choices are MOVs (Metal Oxide Varistors), TVSs (Transient Voltage Suppressors), and GDTs (Gas Discharge Tubes). MOVs are the clear choice today because of their speed and ability to take multiple hits. Their weakness is that the clamping voltage is not accurate. TVSs will not take the amount of energy that the MOVs take, but their clamping voltage is more accurate. The down side is that they are not as fast as MOVs. GDTs can be accurate, but their parameters change with the number of hits and they are slightly slower than MOVs. The biggest drawback with GDTs is that once they start to conduct, their conduction voltage drops very low. That effectively rules them out from being used across the PV inputs.
9. HYBRID SURGE PROTECTION -- One solution which can work well for PV applications is a hybrid combination of the above devices. The key parameter is clamping speed. An old trick that we re-discovered is to slow down the incoming surge so the devices can deal with it. Specifically, good MOVs are used as the first component between both the + and the – PV inputs to ground. Then a small inductor in series with the input is used to slow down what is left of the spike so a pair of TVS with slightly lower clamping voltage can finish the job. We have also used GDTs effectively, but not on the PV input wires.
10. THE DEVIL IS IN THE DETAILS -- There is a long list of other issues which can circumvent the best grounding and surge protection devices. For example:
• A surge can easily be induced from the incoming wires into other wires in the system. Using a common wire raceway for PV input and other wires should be avoided.
• After all the effort to shunt the surge to ground, it must be clear that all that energy has to go someplace. It has a nasty habit of coming back elsewhere in the system because the ground has been elevated by the surge that you forced to go there.
• The surge is going to get in somehow. Not only the PV input wires, but all the AC lines, data lines and even occasionally the battery wires may need surge protection devices and they are all different because of the operating voltage.
Posted by Jen Seder on Thu, Feb 02, 2012 @ 11:05 AM
This blog is meant to be read in series with last week's blog titled Solar Installation Surge Protection Basics. Here are some general guidelines purposely oversimplified related to surge protection for solar:
1. GOOD GROUNDS 
-- The quality of the connection to earth ground is the single most important issue. The resistance from the ground system to the earth must be very low. At 10 ohms a medium size strike of 30kA will lift the wires that you thought were ground up to 300,000 volts. You will need many ground rods and if the soil is dry and/or sandy, extreme measures will be required to get a reasonably low resistance. Much is written on this subject.
2. EQUAL POTENTIAL GROUNDS -- Equal Potential Grounding is an important rule. Even if your equipment ground is elevated in voltage during a surge event, we want ALL our equipment grounds to be elevated the same amount. The differential is the killer. This means a single “star point” ground in your equipment with the best earth connection you have connected to that same star point.
3. GROUND WIRING -- All grounds must be short, thick and straight. Any coil in a ground wire makes an inductance which prohibits the fast surge from going to ground. All connections must be free of resistance. They are called “ground bonds” not ground connectors or ground tie points.
4. THE PV ARRAY WILL GET STRUCK -- Since a PV array makes a good target for lightning, it is important to add whatever surge protection you can afford to the wires coming from the array before the wires get to a building or equipment. This usually means putting devices in the combiner boxes and grounding those devices directly.
5. THE WIRING TO THE EQUIPMENT IS VULNERABLE -- Depending on the length of the home runs from the combiner boxes to the Charge Controllers or Inverters, various amounts of protection must be added. If the home runs are outside, bury them several feet down and bury a good ground wire 1 foot on top of the home runs.
Stay tuned for part 3!
Posted by Jen Seder on Thu, Jan 26, 2012 @ 08:42 AM
HISTORY:
There has been a great deal written about surge protection and lightning over many years. It is difficult to know what to believe or how to apply the advice in practical methods which make a meaningful difference for PV installations. We hope this post and our next post will provide some clarity to this complex subject for Solar Installers.
Apollo Solar had an opportunity to dig into this subject beyond where most companies will ever go. We were hired to redesign the front end of a PV powered system that lives on electric utility towers just below 360kV transmission lines. The systems take both direct and in-direct lightning strikes on a regular basis. The photo to the left shows a piece of our equipment undergoing man–made lightning strikes at a lab in Toronto. The results of the testing proved that we improved the survivability of the equipment by 1600%. Apollo developed circuits to protect the sensitive front ends of the equipment such that all of the 5 systems that were tested ran perfectly after taking over 100 strikes up to 25kA each with a 4uS rise time. The lab said that these were equivalent to real world strike of 35kW with the 8uS rise and 20uS fall time.
OVERVIEW:
From the work we did on that job and from research we have done before and since, we have come up with the following basic understandings:
1. There is no such thing as protection against lightning. The laws of physics can create more voltage and more current than any man can reasonably insulate against.
2. The proper term for the devices we deal with is “Surge Protection” and even that has to be tightly qualified.
3. There are no experts who know everything about this subject. (See point 1)
4. A good ground is hard to find and is essential for any surge protection.
5. The cost of really good surge protection including the design, multiple devices and the installation labor for a good ground system can easily cost more than the equipment it is supposed to protect. Of course when lives are at stake, the cost equation is irrelevant.
6. Reasonable surge protection is affordable, but knowing where to spend the money is not simple.
Apollo did the work of weeding through countless documents until we found some good ones written by honest researchers. The best overall set of documents were done by DEHN in Germany: http://www.dehn-usa.com/dehn-Lightning-Protection-Guide-pubcid4.html. It covers the grounding very well. The Littlefuse company addresses the circuit design and components used for surge protection better than most. See AN9769 - An Overview of Electromagnetic and Lightning Induced Voltage Transients.
Posted by Jen Seder on Thu, Sep 01, 2011 @ 09:18 AM
Commercial & Residential Battery Backup Power Using Inverter/Chargers
Utility companies are working around the clock to restore power to over 5 million homes on the east coast, but this could take over a week while homes and grocery stores throw out millions of dollars worth of refrigerated and frozen goods.
Commercial buildings and residential homes can benefit greatly by supporting critical loads such as refrigerators, computers, and business in general with battery backup systems.
There are several different choices for battery backup systems including:
• Battery backup charged from the grid
• Battery backup charged from a generator
• Battery backup charged from solar
From the grid – inverter/chargers that have an automatic transfer switch can sense when the grid power is available. The transfer switch closes when grid power is available to allow the AC power to flow out to the loads with seemingly zero interference from the inverter/charger. At the same time, the inverter/charger takes a small amount of the AC power to charge the battery bank or keep it topped off. Therefore, when the grid does go out the transfer switch opens turning the charger into an inverter to produce AC power from the DC battery bank. Depending on the brand of inverter, the power source switch occurs without a noticible drop in power.
From a generator – inverter/chargers can also keep batteries topped off, which can be especially important if you have to depend on your batteries longer than the system’s days of autonomy will allow. Some inverter/chargers will have automatic generator start modules built in. Preset automatic generator start and stopping capabilities are useful in protecting the batteries from being over or under charged. However, automatically starting a generator can be dangerous. The combination of fuel, heat, sparks and exhaust fumes unsupervised can be a hazard should anything go wrong. If using a generator manually, it also requires supervision. It is best to turn it off when the inverter/charger goes from the Bulk stage to the Absorb stage. At this point, the batteries will be about 80% full.
From solar power – inverter/chargers keep batteries continuously charging while the sun is shining. Charge controllers take care of the battery bank and keep it from over or under charging. Often off-grid solar systems are specified to 3 days of autonomy. If more than 3 days (or how ever many days the system is specified to support) is exceeded without sunlight a backup generator can be used to charge the batteries. In addition to the auto gen start capability of some inverter/chargers, various charge controllers can be used to automatically turn the generator on and off to protect the batteries from over charging. Many commercial and residential systems supplement their power needs by connecting loads to a battery based solar system. This way one does not have to worry about critical loads that are hooked up to the system when the grid goes down because these loads are always independent.
photo credit: wantadog
Posted by Jen Seder on Fri, Jul 08, 2011 @ 10:08 AM
DEFINING THE PROPER SIZE BBU/UPS FOR THE JOB:
The amount of load a BBU (battery backup unit) can support and the length of time it can do so are the 2 important factors that define the BBU. The amount of power your load requires defines the size of the inverter in kW. One can measure the load in terms of AC Amps and multiply by either 120 or 240 volts AC to get the power required in watts or kW. If an entire home full of appliances is run from the BBU, then a full energy audit is required. Simply list every load, write down the number of watts from the nameplate. Remember that your purpose is to have enough power for essential loads, and making the decision of what is really essential, will bring you to a new level of appreciation for the electricity that we do have.
The run-time defines the size of the battery bank required and can be stated simply in hours. The amount of power in kW times the number of hours will give you the amount of energy which must be stored in the battery in terms of kWh (kilowatt hours). If you did an energy audit to determine the amount of power required from the inverters you now want to multiply each load by the number of hours it will be used during the average day. The product will be a list of your energy requirements in kWh.
A safety factor has to be added so the batteries do not become damaged. Deeply discharging a battery will shorten its life severely. The batteries for a BBU system should be designed such that they are almost never discharged below 50% of the total capacity. So if you think you need 1000kWh when the grid goes down, you must buy a battery which is at least 2000kWh. If the battery will be discharged often, then 30% is recommended for
maximum depth of discharge.
Other safety factors must be considered such as the lowest temperature the batteries will be living at when you need them. You will want to add 1% to the size of the battery for every degree C that the battery is below 25 degrees C. This is apparent to anyone who has had trouble starting a car in the winter. A second factor is for aging and stagnation in the batteries. Those factors can add between 5% to 20% to the battery size requirement depending on the critical level of your mission. If the BBU is just to keep the TV going during the big game next month you may not need to spend the extra money on a larger battery bank. However, if the BBU is meant to run a piece of life support equipment for a number of years, then you will want those batteries to be plenty large so they last a long time and still have all the energy you need even if the batteries are cold, old and stagnant.
The bottom line with the size of both the inverters and the batteries is that more is always better. If the inverters are too small for the loads, they will simply shut off to protect themselves. If the batteries are too small they will become drained prematurely and again, the inverter will shut off to protect themselves and what is left of the batteries. It is relatively easy to add more inverters in parallel if you didn’t have enough power at first. People always find ways to use more power, never less. But, if the batteries are not large enough, it is not a good idea to add new batteries to an older string. The new ones will get pulled down by the weakest battery in the bank.
Posted by Jen Seder on Thu, May 26, 2011 @ 08:50 AM
What is your motivation for going Off -Grid?
Off-grid solar installations can be much more expensive than grid-tie systems due to greater equipment, installation, and design costs, however they can also be much more liberating. It is important to determine why one is choosing to invest in an off-grid system including, but not limited to:
- Energy independence
- Critical load backup
- Environmental sustainability
- Remote location energy generation
What is your lifestyle?
The way one lives and the appliances or loads the customer wants to support with an off-grid system will determine the overall system size and cost. It is important to reevaluate energy usage, and determine which appliances need an upgrade to energy efficient models, and which appliances one can use less of or eliminate.
With every off-grid system it is crucial to reflect upon one’s current lifestyle and knowledgeable about how becoming energy conscious will change the way of life. After reflection, and most times compromise the customer will have to accept a new lifestyle . At this point, customers are closer to knowing whether they want to completely cover their energy needs with solar, or just off set their energy needs with a smaller system.
Credit: eyeweed
What is your budget?
Now, the customer knows what they want, but what will their budget allow? It is important to look at all costs associated with system installation including:
- New appliances
- Structural changes / carpentry work
- Maintenance / support
- Backup generator
Ultimately, one needs to determine how much the first question, “what is your motivation for going off-grid,” is worth in terms of monetary means and lifestyle changes. System costs should also include state and federal incentives, which can be found at www.DSIRE.org.
The best way to answer these questions is to talk to those who already live off-grid. This way, one can find out first hand what challenges and benefits those with off-grid installations have experienced.
Posted by Jen Seder on Fri, May 06, 2011 @ 08:42 AM
Reliable Power in Remote Areas
5% of the people of Uganda have electricity. However, more than 1/3 of the population owns a cell phone. The homes and businesses that do use electrical power from Uganda’s grid can experience power outages multiple times per day. Solar power for telecom systems can provide the reliability needed for uninterrupted communication.
Telecom systems facilitate the ability to conduct business, spread news, and share knowledge, as well as many other life-changing benefits. Solar gives less developed countries and remote areas the resources to support a higher quality of life.
Reduction in Diesel Fuel
The most cogent reason to use PV for remote Telecom applications is the reduction in diesel generator fuel use together with the added benefit of the reduction in generator run time/product life/O&M costs. Diesel fuel costs continue to rise and when powering remote applications the cost of transporting the diesel fuel can many times be 3 to 4 times the cost of the diesel itself. Diesel generator emissions also add a good deal of polluting particles to what is in many instances otherwise clean air. PV can pay for its capital and installation costs in remote currently diesel-powered applications in a very short payback period, after which the energy becomes cost-free. With the quality and reliability of PV Power for Telecom currently available, it is a direct and effective method to reduce costs and the externalities of diesel emissions.
Read about our mission to Uganda
Posted by Jen Seder on Tue, Apr 19, 2011 @ 09:37 AM
The NEMA ratings for typical enclosures used in the PV industry are described in simple terms as follows in order from least to the most protection:
A NEMA 3R enclosure can be used outdoors for equipment, which needs to have some outside air for cooling. It means that the enclosure is going to have louvers to prevent falling water or snow from getting inside. A jet of water however, from a pressure washer or just a hose will get in through the louvers. A NEMA 3R enclosure can have knock-outs on vertical surfaces as long as water can not run in.
NEMA 3 is a small step up since filters are added behind the louvers to stop wind blown dust. The “wind” can be the internal fans that are bring in air to cool the equipment inside. Of course, the filters have to be cleaned or changed periodically.
NEMA 3X adds corrosion resistance. This means that the NEMA 3 enclosure is made from Stainless Steel or Powder Coated Aluminum. This is a good idea for salt sea air environments, but if the air is corrosive, the enclosure should be sealed in which case NEMA 4X is recommended. Sometimes aluminum is preferred simply because it is lighter and easier to work with. This makes NEMA 3X worth considering.
NEMA 4 is totally sealed. The doors have gaskets and there are no knockouts which could leak. Any wiring to a NEMA 4 enclosure will require that holes need to be drilled by the installer. If cooling is required, we add an external air conditioner which is also NEMA 4 rated.
NEMA 4X adds corrosion resistance. This usually means that the NEMA 4 enclosure is made from Stainless Steel or Powder Coated Aluminum. This is a best possible enclosure for outdoor PV installations. If cooling is required, we add an external air conditioner which is also NEMA 4X rated.
Ratings below 3 are for indoor use. Ratings above 4 are for total submersion in water and you had better not need that in the PV business.
Click here to link to the NEMA Enclosure Ratings whitepaper and for much more detail on solar application NEMA enclosures.
Posted by Jen Seder on Thu, Apr 07, 2011 @ 09:55 AM
Auto Generator Start Concerns:
A generator is often viewed as a necessary back up source of electricity for renewable energy systems. Many see generators as a necessary evil. Without taking sides in that discussion, we do warn that providing automatic starting of a generator can be dangerous. There are those who believe that a generator is hazardous enough just when running since the combination of fuel, heat, sparks and exhaust fumes are not friendly to life. So, to have a set of preprogrammed electronic parameters that start the generator without requiring a person to be present to make sure it is running safely, is a fire waiting to happen. Therefore, use caution if you need to install automatic generator starting at your home. And please make sure your customer understands the risks if you are asked to install one for someone else. It will probably be at a remote location which brings some interesting responsibilities with it.
Not all generators can be started automatically:
The smallest size generators (about 2kW or less) don’t have a starter motor. They require that a person pulls a cord. Obviously we can not discuss remote starting of that class of generators.
Moving up to the 5kW or 6kW generators, include starter motors and a small battery. Some of them have manual chokes which require a person to monitor the engine after he pushes the start button. These generators are not good candidates for automatic starting either.
When you get up to the 8kW to 10kW generators, there is enough money in the genset that wiring is usually provided by the generator manufacturer for a start switch, thus the ability for remote starting and stopping. If these serious machines are of good quality, they have enough smarts so that a simple remote ON and OFF switch will allow it to be started and stopped. Importantly, these gensets also monitor a few critical parameters like oil pressure and some temperatures so they can turn themselves off before self-destructing.
Small systems with pull start gensets:
For small (<3kW) systems, if the PV is not sufficient to keep the batteries charged, then the choice is simple: Periodically pull out a small generator, hook it up to the AC Input of the Inverter/Charger and pull the cord to start it. Keep an eye on it and turn it off when the batteries go from Bulk into Absorb. They will then be about 90% full.
Large systems with smart gensets:
From both the business and system design perspectives, we believe that if an installation requires a large (>10kW) automatic starting genset, it should be a self contained module which takes care of all its own issues internally. In other words, the external system should tell the generator when to turn on and when to turn off, but it is up to the generator to do everything it has to do so it doesn’t burden the renewable energy system.
To download the extended Automatic Generator Start Application Note Click Here