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Very Pleased
I have received your Fronius 3.0-1 inverter and am very pleased with the the prompt shipping and the ...
(read more)
By Ron
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| Frequently Asked Questions |
| Click on question to reveal the answer. |
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| 1. Charge Controllers: What is the difference between MPPT or PWM? |
Currently the most common charge controllers are Pulse width Modulation(PWM) charge controllers which simulates a variable current by switching a full current On and OFF at high speed for varying lengths of time. A Maximum Power Point tracking (MPPT) charge controller is a charge controller that operates the solar array at its maximum power point under a range of operating conditions as well as regulating battery charging.
The interesting features of the MPPT technology is that it usually allows you to
have a solar panel array with a much higher voltage than your battery bank's voltage.
The MPPT charge controller will automatically and efficiently convert the higher voltage
down to the lower voltage.
A big advantage to having a higher voltage solar panel array is that you can use smaller
gauge wiring to the charge controller. And since a solar panel array can sometimes be
over a 100 feet away from the charge controller, keeping the cost of the wiring down to
a minimum is usually an important financial goal for the whole project. When you double
the voltage (e.g. from 12 to 24 volts), you will decrease the current going through the
wires by half which means you use a quarter as much copper (or cable with half of the
diameter). |
| last updated - 2011-02-03 14:28:27 |
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| 2. Predesigned Systems; Whats the difference between a Grid Tied System and an Off-Grid System? |
Grid-Tie Systems
Grid-tie home solar systems are much more prevalent for several reasons:
- Cheaper up front to install – It is easier to tie-in to the grid than pay for and install a safe battery bank.
- Net metering laws or, in some cases, feed-in tariffs are powerful incentives for homeowners to connect to the local grid. Net metering allows homeowners to trade with their utility. Excess solar energy produced during the day is used elsewhere and credited to the solar homeowner to offset the costs of using grid electricity at night. Feed-in tariff laws require the utility to buy that excess daily power at an inflated price, which can turn home solar power into a profit deal.
- Grid-tie systems require less maintenance – Batteries need some occasional TLC and must be replaced every few years (at present technology levels). They can also be hazardous if not handled correctly.
- Benefit the community electric grid – Feeding that clean, green solar energy into the grid during the day, when power demand is at its peak, eases the burden on an already overstressed electric infrastructure. It also helps cities and states reach their renewable energy goals. Furthermore, distributed generation (the collective term for home solar power systems) may play a key role in the Smart Grid of the future.
- More flexibility – Being tied to the grid provides security in knowing that if you have a spike in energy usage (i.e. visit from family, in-home wedding, etc.), back-up is ready and waiting.
Off-Grid Systems
Getting off the grid has its definite advantages as well. Particularly for homeowners in remote areas, not to mention those in the developing world without any electric infrastructure, off-grid systems offer:
- Total freedom – Off-grid home solar power means that when the grid goes down, you don’t. There is safety and security in knowing that your home is energy-independent as well. A downed power line 20 miles away and rolling blackouts don’t affect the off-grid homeowner.
- Totally clean, totally green – Bye, bye transmission cables. When you’re off-grid, you are totally free of coal-fired and other fossil-fueled electricity. Your energy is clean and your home’s carbon footprint greatly reduced.
- Off-grid systems also benefit the local community – They make life easier for the local energy grid by providing one less house in need of outside power sources.
- Powering the outer limits – Off-grid systems are essential for folks who want to live “outside the box,” but don’t necessarily want to rough it for the rest of their lives. In comes off-grid home solar power to provide that comfortable, country home of your dreams.
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| last updated - 2011-02-03 16:37:16 |
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| 3. Charge Controllers: How do you calculate size of charge controller required? |
Example of Sizing an MPPT Charge Contoller
So, for instance, you could have a 1000 watt solar panel array that operates at 48 volts
DC and your battery bank is 24 volts DC. MPPT charge controller are rated by the output
amperage that they can handle, not the input current from the solar panel array. To
determine the output current that the charge controller will have to handle we use the
very basic formula for power (watts), which is:
Power = Volts x Amps
Here we know the power is 1000 watts, the battery bank is 24 volts, so:
1000 watts = 24 volts x Amps
which gives us:
Amps = 1000 watts/ 24 volts
Amps = 41.7A
We still want to boost this value by 25% to take into account special conditions that
could occur causing the solar panel array to produce more power than it is normally
rated for (e.g. due to sunlight's reflection off of snow, water, extraordinarily bright
conditions, etc). So, 41.7A increased by 25% is 52.1A. In this case we'd probably choose
a 60 Amp MPPT Charge Controller, like Outback Power's FM60 or Xantrex XW MPPT60
Be aware that MPPT charge controllers have an upper voltage limit that they can handle
from the solar panel array. It's important that you make sure than there is no condition
that the solar panel array voltage will go above this limit or you will like burn out the
controller. You want to make sure that the open circuit voltage of the solar panel array
does not go above this limit. You should also give yourself a little bit of a margin for an
error to take in account the possibility that a solar panel array's voltage will actually
increase the colder it gets. The voltage multiplier is based on the lowest expected ambient temperature where the system is to be installed. The NEC gives Table 690.7 for ambient temperatures below 25 degrees celcius. Most of the higher end charge controllers from Outback and Xantrex have an maximum Open Circuit Voltage (VOC) of 150VDC, the exception is the Apollo T80HV which has a VOC of 200 VDC. You want to make sure that the open circuit voltage of the solar panel array
does not go above this limit.
Here's an example:
We'll use four 12 volt Evergreen 102 Watt solar panels all run in series for a nominal
voltage of 48 volts and our battery bank is at 12 volts. We'd like to use BZ Product's
MPPT500 charge controller because of its price. If we look at the panel's specification page we see that each
panel has an open circuit voltage of 21.3V. That means the array has four times that
(because there are 4 panels in series). So the array open circuit voltage is 21.3V x 4 =
85.2V. In central Oregon our lowest min recorder temperature is -26 dgreeF so we would multiply the 85.2V by our multiplier which is 1.25 and we get 106.5V. Now we'll look at the
MPPT500's specifications and we see that it can only take a maximum of 100 volts. So we can't use that product in this instance and would need to use a product with a higher VOC such as the Outback FM60 or Xantrex XW MPPT60. However we could arrange the panels in two series string of two panels which would reduce our VOC to 53.25V |
| last updated - 2011-02-03 14:30:12 |
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| 4. Pre-Wired Power Centers: Why choose a prewired power center? |
The inverter system, sometimes called the "power center", is the most important part of your solar power system. This combo of inverter(s), charge controller(s) and safety components is responsible for running your off-grid power system.
Pre-wired Power Centers are pre-assembled on metal mounting plates. This is all the gear that converts DC electricity produced by your solar panels, wind turbines or gas generator into useable 120 or 240 volt AC power and directs it into your home (or business or workshop or cabin!).
Pre-wired, pre-tested power centers save you time and money. Of course, you may buy all the components separately and assemble them yourself or you can pay your installer or electrician to do so.
Paying a contractor to wire the essential electronics is costly, particularly if that professional has not done lots of them. |
| last updated - 2011-02-03 16:45:43 |
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| 5. Inverters: How do they work? |
| An inverter takes the DC input and runs it into a pair (or more) of power switching transistors. By rapidly turning these transistors on and off, and feeding opposite sides of a transformer, it makes the transformer think it is getting AC. The transformer changes this "alternating DC" into AC at the output. Depending on the quality and complexity of the inverter, it may put out a square wave, a "quasi-sine" (sometimes called modified sine) wave, or a true sine wave. |
| last updated - 2011-02-03 14:14:30 |
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| 6. Inverters: Which is the best inverter? |
| Although the Outback Power & Xantrex are considered by many to be the top of the line, it does not make sense to spend $500 to $3000 when all you need is a little Statpower Prowatt or Exeltech 125 watt sine wave to power up a laptop. The best way to decide on what inverter is best is to work backwards - figure out what you are going to use it for and the continuous power wattage required. i.e what appliances will you be running all at once), and then find one that fits those requirements. Also, some inverters have built in chargers, which may be needed in some systems. The Outback, Apollo Magnum & Xantrex sine wave units include software and hardware for remote generator start, alarms, remote control and monitoring, computer data, and other functions - in many applications this is very important. If you are running pumps or other large motors, Xantrex, Magnum, Apollo or Outback are the only ones we will recommend, even though some others might work. |
| last updated - 2011-02-03 14:20:22 |
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| 7. Inverters: Whats the difference between an off-grid inverter and a grid tied inverter? |
| The difference between a off grid inverter and a grid tie inverter is an off grid inverter converts stored energy from a solar battery bank and converts or inverts the stored electrical energy in to AC household current. A grid tie inverter on the other hand takes solar or wind energy as it is produced and stores it in an electrical grid.
Inverters from Outback (GVFX and GFX) and Xantrex (XW) can be used as grid tied inverters with battery backup. We do not recommend using the Outback inverters in off grid applications as it will have trouble excepting the rough AC power from a back up gas or propane gen set. |
| last updated - 2011-02-03 16:32:24 |
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| 8. Water Pumping: What are the main differences between the different SQflex pumps? |
Grundfos SQ-Flex solar pumps will pump water up to 820 foot total head, and can pump up to 85 gallons per minute for shallow wells, depending on model of pump. The helical rotor pumps are recommended if you have any dirt, sand, sediment, or high mineral water from your well. The pump can tolerate up to 50 PPM of sand contant. The 3 SQF, 6 SQF, and the 11SQF are helical rotor type pumps. All others are centrifugal. All SQF pumps are 17 to 23 pounds in actual weight.
| Model Number |
Type |
Max Head |
Max Flow |
PV Watts (Min-Max) ** |
Pump Diameter (Pipe Size) |
| 3 SQF-2 |
Helical Rotor |
360 Feet |
3 GPM |
100-900 |
3" (1" NPT) |
| 3 SQF-3 |
Helical Rotor |
600 Feet |
2 GPM |
130-900 |
3" (1" NPT) |
| 6 SQF-2 |
Helical Rotor |
360 Feet |
6 GPM |
100-900 |
3" (1" NPT) |
| 6 SQF-3 |
Helical Rotor |
820 feet |
6 GPM |
100-1400 |
3" (1" NPT) |
| 11 SQF-2 |
Helical Rotor |
300 Feet |
11 GPM |
50-1400 |
3" (1-1/4" NPT) |
| 16 SQF-10 |
Centrifugal |
210 Feet |
20 GPM |
400-1400 |
4" (1-1/4" NPT) |
| 25 SQF-3 |
Centrifugal |
45 Feet |
40 GPM |
120-1400 |
4" (1-1/2" NPT) |
| 25 SQF-7 |
Centrifugal |
185 Feet |
39 GPM |
130-1400 |
4" (1-1/2" NPT) |
| 40 SQF-3 |
Centrifugal |
45 Feet |
38 GPM |
200-1400 |
4" (2" NPT) |
| 40 SQF-5 |
Centrifugal |
90 Feet |
70 GPM |
300-1400 |
4" (2" NPT) |
| 60 SQF-3 |
Centrifugal |
45 Feet |
85 GPM |
20-1400 |
4" (2" NPT) |
** The watts shown for the PV panels or array are absolute minimum that the pumps needs at the shallowest depth. See the pump curves for more information. To account for wire and other system losses we recommend 15% to 25% more.
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| last updated - 2011-02-04 10:53:15 |
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| 9. Batteries: What is the difference between AGM and Gel and Flooded? |
| AGM batteries have several advantages over both gelled and flooded, at about the same cost as gelled:
Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage.
Nearly all AGM batteries are "recombinant" - what that means is that the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.
The charging voltages are the same as for any standard battery - no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. The Concorde (and most AGM) batteries have no charge or discharge current limits.
AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. The Concorde batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged.
AGM's do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.
Even with all the advantages listed above, there is still a place for the standard flooded deep cycle battery. AGM's will cost 2 to 3 times as much as flooded batteries of the same capacity. In many installations, where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice. |
| last updated - 2011-02-03 14:28:04 |
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