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Details about  Practical off-grid system - 4kW PV & 40kW battery bank w/ gen

Practical off-grid system - 4kW PV & 40kW battery bank w/ gen

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New other (see details)

This system is a combination of manufactured goods with full product warrenty. Please contact us for

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GBP 17,289.51
Approximately C $31,451.25(including shipping)
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Item location:
Heiligenberg, Germany
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Last updated on  Oct 14, 2014 07:25:16 EDT  View all revisions

Item specifics

Condition: New other (see details) : Split the cost with friends
A new, unused item with absolutely no signs of wear. The item may be missing the original packaging, or in the original packaging but not sealed. The item may be a factory second or a new, unused item with defects. See the seller’s listing for full details and description of any imperfections. See all condition definitions- opens in a new window or tab
Seller Notes: This system is a combination of manufactured goods with full product warrenty. Please contact us for full details.

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Fully specified solar PV off-grid system with battery bank, panels, generator and a pre-wired mounted control unit including the inverter, charge controller, safety features and monitoring hardware. The FLEXpower ONE unit is highly practical and easy to install. Ideal for locations where grid connection is unfeasible due to expense, location or logistical reasons, this system allows for uninterrupted AC power supply even in the most wild or isolated areas. Wired to 48V on the DC side for maximum efficiency, and featuring a 40kW battery bank, a 4kW solar array and capable of delivering a continuous output of 3kW (or a peak output of 5.7kW); this system is well suited to powering a house or business with modest power requirements.

Please note that the picture supplied above is of the central FLEXpower One control unit, the full kit contains many other components including solar PV panels, a battery bank, a generator and additional cabling and accessories.

Location-based output projections
Southern UK
Central Europe
Southern Europe
Central Africa

The difficulty with off-grid systems is that they can be complicated to design. In order to alleviate this challenge we've done all of the work for you. Not only have all the major components been specifically chosen for the compatibility with one another, but all of the more minor elements have been carefully selected according to their specifications.

This means that the panels are of the highest quality, and configured to utilise the charge controller as fully as possible. The charge controller itself is chosen to draw every last ounce of power from the panels, and also dovetails perfectly with the inverter/charger in order to give the best treatment to the all important battery bank. All of the cables have been selected so that they can safely handle the maximum current running through them with minimal losses, whilst remaining as cost effective and flexible as possible. The system also comes complete with all the breakers, switches and monitoring devices you need to run it without any hassle. In short, all an installer need do is connect the components and the system is ready to go.

In order to fully replicate the convenience of being on the grid, the power supply from an off-grid energy system needs to be completely uninterrupted. The solar array keeps the battery bank charged and this charge is then drawn by the inverter/charger when power is required. Sometimes though – particularly in winter – the sun's energy is insufficient to keep this process going. This is why we include an efficient backup generator with our off-grid systems, to ensure there is no reason for the power to ever go out. This switch-over needn't be a concern though, as the inverter/charger can be programmed to automatically start the generator if the battery drops below a certain state of charge, allowing for a seamless transition and constant power delivery.

The inverter, charge controller and safety features come pre-mounted and pre-wired on a sturdy casing, which can be wall mounted for convenience. This control casing should be housed in the same room as the battery bank, with the system optimised for the generator being nearby (under 10 metres away) and the PV array no more than 15 metres distant. All homes and sites are unique however, so if your requirements differ from these please do get in touch and we can redesign the system to better suit your needs. For the same reason we do not provide a generic mounting solution for the solar panels as all sites present unique challenges, if you would like a mounting system please contact us directly.

Before going any further, we urge you to read this section on planning your system and our full tutorial section in the top left.

Predicting solar array output depends on a few variables, please contact us with your location so that we can provide you with estimates. For this system, this medium-sized array is suited to places with an average amount of sunlight: Central & Southern Europe. Low winter sunlight limits the system. If it is unable to recharge the battery bank sufficiently, then reliance on the generator will increase and repeated diesel refueling will be required. If the system is to be used mainly during the summer then it is suitable for places with worse sunlight such as the UK.

Battery bank capacity depends on the amount of current you draw. The faster you discharge a battery bank, the lower the overall capacity for that cycle. If you use the Outback VFX3048E inverter at its maximum continuous output (3000w), you will discharge the battery bank to 50% (not recommended to go lower) in 4.5 hours and receive 13.5kWh. Usage in this way would make sense in places with much sunlight, or as an emergency power source. Otherwise you could go easier on the bank. The total amount of power in this case would depend on your consumption profile. Below are some examples based on C (discharge) rates. 

If you draw 555 watts per hour, you will have 50 hours of power at this rate (C100) and your total power will be 27.7kWh. If you consume at this rate for 10 hours a day, you will have 5 days of battery power. 
If you draw 969 watts per hour, you will have 25 hours of power at this rate (C50) and your total power will be 24.2kWh. If you consume at this rate for 10 hours a day, you will have 2.5 days of battery power. 
If you draw 1968 watts per hour, you will have 10 hours of power at this rate (C20) and your total power will be 19.7kWh. If you consume at this rate for 10 hours a day, you will have 1 day of battery power. 

Knowing how you will consume energy is an important calculation in sizing the system to your needs. It is unlikely that your consumption will be as straightforward as above. You will have surges and lows so it is never an exact science. Having an inverter with a 3000w continuous rating will allow you to run heavy appliances if necessary. 

Having discharged your battery bank completely, and if the sky is still overcast, the generator acts as a standy reserve of emergency power. The VFX3048E will start it automatically, and use it to recharge the battery bank to 100%. It is limited by the the amount of DC charge this unit can put out which is 45A. You will have one full recharge per fuel tank. You will also have to perform an equalisation (maintenance) charge every few months to make sure you are fully recharging the cells and keeping them in line. 

Finally, off-grid systems are inefficient. As a rule of thumb, you will lose several % at each component and 10% putting electricity in and out of your battery bank. This has implications for the figures presented above.

The most important part of an off-grid PV storage system is the battery bank. Treating it correctly will prevent you from needing to replace the most important component prematurely. Batteries have cycle ratings based on the typical depth of discharge. If you only consume 20% of the battery banks power before recharging it daily, your battery bank will last much longer than if you discharge it to 50% daily. You are most likely to go down to the 50% rating during overcast conditions (winter) so this is where you reduce the lifetime.

Rolls 5000 series batteries are amongst the best you can buy for this application, their 10 year warranty backs that up. At 20% DoD you will have 5000 cycles, at 50% you will have 3200 cycles. Therefore if you discharged it to 50% every day, 365 days a year you will still have 8.7 years of estimated use. Since this is an extremely unlikely consumption pattern (due to summer), average life expectancy for Rolls batteries is 15 years. Do not take this figure for granted as there are things that could go wrong. Battery maintenance is an essential consideration. Will someone be able to monitor and react to your battery bank's condition? Heat is a killer, so make sure you have thought about where you will put your batteries.

Main Components

15x Sharp 250W ND-R250A5 panels (arranged in 5x strings of 3 modules each)
These highly durable Sharp panels represent the pinnacle of Sharp's many years as a leader in the solar panel manufacturing business.
Full information

Stephill SE4000DLES Generator
This Stephill diesel generator is an ideal backup to the solar array. Its sturdy outer casing hides a well crafted interior, complete with advanced silencing technology and overload protection features – which enable it to work quietly and safely whilst generating economical backup power. Comes with an electric start to allow the inverter/charger to use it when needed without human interaction.

40kW Rolls 6CS25P battery bank - 8x 6v batteries
Rolls deep-cycle batteries are known for their durability. Widely considered to be one of the best deep-cycle battery manufacturers, they come with a 15 year life expectancy. Recombiner caps prevent gases escaping, reducing the amount of maintenance necessary to once a year. This 40kW battery bank has been sized to allow for 4 days of backup power - assuming a daily usage of 5kWh.

FLEXpower ONE: (45kg)

Outback VFX3048E Inverter / Charger*
This hugely reliable Outback VFX is the heart of your off-grid system. Not only does it take the DC current from your battery bank and convert it to the silky smooth AC that your applications require, but it also manages the re-charging of your battery bank by rousing the generator when needed.

Outback Flexmax FM80 Charge controller*
Like all Outback components, the FM80 is an exceptionally well made piece of technology. It ensures that the charge being delivered to the battery bank is as even and efficient as possible. This not only makes the very most of the output that your panels are generating, but it also protects the battery bank and improves its longevity.

*Both the inverter/charger and charge controller are housed in the integrated pre-wired FLEXpower ONE control system, which also features a MATE monitoring unit, a HUB networking device, battery temperature sensor (RTS), and numerous breakers and protection features.

Additional Components

There are many small components in off-grid systems. The pre-wired FLEXpower ONE unit removes the need for many of these, however there are a few that remain. We supply the entire package except a few items which are easily obtainable. We take care of everything on the DC side. Please phone on the number below for more information.

Technical specifications

Sharp Solar array (5x3) 
Maximum power: 3750W
Voltage at Pmax: 92.7V
Current at Pmax: 40.5A
Open circuit voltage: 112.5V
Short-circuit current: 43.4A

Rolls 6CS25P battery (individual)
C20 capacity: 820Ah
Cycle life at 50%: 3200 cycles
Dimensions (LxWxH mm): 559 x 286 x 464
Weight wet: 144 KG

Outback VFX3048E Inverter/Charger 
Continuous power rating: 3000W
Surge overload power rating: 5750W
Generator to battery charge current: 45A

Outback FM80 Charge Controller 
Maximum Output Current: 80 amps @ 104° F (40°C) with adjustable current limit 
PV Open Circuit Voltage (VOC): 150 VDC absolute maximum coldest conditions / 145 VDC start-up and operating maximum 
Power Conversion Efficency: 97.5% @ 80 Amps in at 48 VDC System voltage - Typical
Charging Regulation: Five Stages: Bulk, Absorption, Float, Silent and Equalization
Equalization Charging: Programmable Voltage Setpoint and Duration - Automatic Termination when completed
Battery Temperature Compensation: Automatic with optional RTS installed

Stephill SE 4000DLES Diesel Generator 
Rated Watts: 3200 (100%)
Output: 2.4kw (75% load)
Fuel tank: 13 litres
Run time: 13 hrs (75%)
Noise level @ 7m: 71 dBA

We also supply a full wiring diagram with each kit, along with technical advice to the installer.

Off-Grid Europe

Business seller information

Off-Grid Europe
Christiane Waltl
11a Alston Works Alston Road
United Kingdom

Value Added Tax Number: UK 288214465
I provide invoices with VAT separately displayed.

Return policy

Item must be returned within
30 days after the buyer receives it
The buyer is responsible for return shipping costs.
Return policy details
OFF-GRID EUROPE Return and Refund Policy. If unhappy, all items must be safely and undamaged returned within 30 working days. Any refund will be made through the original method of payment. The buyer will be responsible for costs of recorded postage and secure packing for the item to be returned. If item is damaged upon arrival at the location you have designated, we will offer replacement of cells after receiving a picture /pictures illustrating the damage. We are operating on a 100% Satisfaction Guarantee - if you have any queries or complaints please do not hesitate to contact us via the eBay messaging system.

Questions and answers about this item

No questions or answers have been posted about this item.

Seller assumes all responsibility for this listing.

Shipping and handling

Item location: Heiligenberg, Germany
Shipping to: Worldwide
Excludes: Russian Federation
Domestic handling time
Will usually ship within 1 business day of receiving cleared payment - opens in a new window or tab.
VAT price: 19.0% (included in the listed price).
If you have questions about this VAT tax, please contact the seller. The actual VAT requirements and rates may vary depending on the final sale.

Payment details

Payment method Preferred/Accepted  
Credit card or Pre-authorized Debit through PayPal
PayPal Preferred
Other - See seller's payment instructions

Seller's payment instructions

For bank transfers for GBP payments to UK bank account or EURO payments to German bank account, please contact us.
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