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Solar PV System guide: Off-Grid systems

In the first part of this Solar PV systems guide, we covered . In this part, we will discuss solar installations that are not connected to electrical grid – Off Grid solar systems, which use battery backup system sto store electricity generated by your solar panels.

Off-the – Battery stored solar energy

A solar system that is not connected to the grid and relies only on the power it generates and stores in a battery is an off – the – grid system. Purchasing this type of a system is not common and there are two main reasons why some people may choose to go for an off -the – grid solar system. First, this is a viable option for people that live in remote areas where there is either no access to grid electricity or it is extremely costly to be tied to the grid. Second, as mentioned before, some people choose this system for ideological reasons of wanting to rely solely on a clean source of energy from the sun.



An off-the-grid solar system has a number of serious disadvantages. The main disadvantage is that you end up paying alot more for an off -the – grid solar system both for the system’s components and for the electricity itself. You also do not have the advantage of further lowering your utility bill by selling excess electricity back to the grid. Another disadvantage is that in cases when there are poor weather conditions and your solar system is not producing enough power and you are running low on power stored in your battery, or if your battery is broken and needs to be replaced, you are likely to have a power outage and no back – up source of electricity.



Equipment

In addition to solar panels and all the components present in a grid-tied system, an off-the-grid solar system has a number of additional essential parts:

1. Charge Controller.
2. Battery Bank.
3. Additional DC Disconnect.
4. Off-Grid Inverter.
5. Back-up Generator.

A charge controller is also known as a battery regulator and serves the purpose of limiting the rate of current that is drawn and delivered to the battery. This protects the battery from overcharging and maximizes its lifetime. You can expect to pay between $750-$900 for a charge controller.

A backup battery bank allows you to have access to electricity in times when there is no sunlight such as during cloudy weather conditions outside or during night hours. A battery bank will ensure that you have electricity until its supply of power runs out. Battery banks have different capacities and therefore vary greatly in price. Buying a battery bank that will supply your home with power during prolonged periods of adverse weather conditions can be very costly.

You need an additional DC disconnect that will be placed between the batteries and the inverter, and is needed to switch off the current flowing between the two parts. This is an important piece of equipment to have for troubleshooting, as well as to protect from electrical fires.

An off-grid inverter converts the DC current from the solar panels into the AC current, but it is not built the same way as a grid-tied inverter. Thus, it is important for you to get specifically an off-grid inverter so that it is most compatible with your off – the – grid solar system. An off grid inverter can cost you anywhere from $700-$1200.

With an off – the – grid system, you have the option of purchasing a back-up generator, and it is typically strongly recommended to do so. This is because it is cheaper to get a back-up generator than spend a whole lot of money on getting a large enough battery bank to ensure that you always have electricity. This generator usually generated an AC current, which is sent through to a standalone battery charger or an inverter/battery charger combo, and is then delivered as a DC current to your battery bank.

Hybrid

A hybrid solar system is a combination of both grid-tied and off -the – grid solar systems, offering extra security for homeowners that want to be sure that they have solar power in rare cases when the grid goes down. A hybrid solar system is the most expensive of the three, and is typically not recommended unless there are known issues with the grid or other reasons specific to a particular home and location.

Equipment

A standard hybrid solar systems has the following components: 1. PV Array Disconnect. 2. Charge Controller. 3. Battery Bank. 4. Power Meter. 5. Main DC Disconnect. 6. Breaker Box (AC). 7. Battery-based Grid-tied Inverter.

In addition to all the components summarized for grid – tied and off – the – grid systems, a hybrid system needs a special battery-based grid-tied inverter. It is used to harness the energy stored in batteries during the times of utility blackouts. This inverter comes together with a charge controller, either as two separate components, or integrated into one device.

Levchik (Leo) is a renewable energy activist from Boston, MA, and has been involved with alternative energy and green construction since 2004.

In 2009, Leo and his green roofing company (CoolFlatRoof.com) sponsored Boston’s Solar Decathlon Team, providing materials and installation labor to install a cool white roof on the top of Curio home (Joint effort by Tufts University and Boston Architecture College) – more info about the project here.

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with one comment

Written by Levchik B

Posted on July 3rd, 2012 at 8:47 pm

Posted in Solar Installation

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One Response to 'Solar PV System guide: Off-Grid systems'

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  1. You do not know what you are talking about. I have lived off grid on solar with batteries for the better part of three decades and I have never had a power outage. If an off grid system is set up by people who do not know what they are doing then it will be a failure. Articles like this one do a real dis-service to the world by presenting false, unsubstantiated information. The fact is that grid-tied systems fail every time the grid fails. The fact is that grid-tied systems still provide the user with very dirty power, by that I mean high voltage transients and brownouts which damage your electrical equipment. In 30 years off the grid I have never even burnt out one light bulb. If people want factual information about solar energy, please visit (url removed) where the information is FACTUAL.

    Jonathan Cole

    9 Jul 12 at 3:06 am

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