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Help: I'm getting conflicting advice about split aspect solar PV and inverters

Posted by Cathy Debenham on 10 April 2012 at 9:01 am

Q: I have had 3 consultants for solar PV and now I am confused. I already have a 2kW system, and wanted to get another 3kW installed. One company said they could not do it, the next said I would get rid of my bill and was going to do split aspects on one inverter. The third one said that I couldn't do split aspect with out having 2 different inverters, and that it would still have a power bill.

A: First, you won't get rid of your power bill unless you invest in a bank of batteries to store the power you generate for use when the sun is not shining and at night. Unless you live somewhere really remote and off grid, this does not make sense for most people. I'd be quite suspicious of anyone who told you that you would.

The system works so that when the sun is shining, you use the electricity generated by your panels, and any excess is exported to the grid and used by your neighbours. At night (and on cloudy days) you will continue to buy electricity from the grid.

The trick to getting the best out of your solar panels (or any other form of microgeneration) is to use as much of the solar electricity that you generate as possible, so that you don't have to buy as much from the grid. To do this, make sure that you do discretionary things like run the washing machine or Hoovering when the sun is out and the panels are generating.

As far as the inverters are concerned, there are three options for a split aspect system: A single inverter with two separate maximum power point tracking inputs; two separate inverters or micro inverters fitted on each solar panel. Click the links above to read more about each of them.

The third thing you need to consider is that by adding a 3kW system you will put yourself in the next bracket for the feed-in tariff, and will get a lower rate of feed-in tariff as a result. New installations of solar of 4kW or less will get 21p per kW, but because yours will be calculated to be 5kW in total, you will get 16.8p per kW on the new 3KW system. The export rate will be 3.1p per kW on both.

With a bit more knowledge under your belt, you may want to get a couple more installers round to quote. You can find local solar installers in our directory, and read what their existing customers have to say about their professionalism and customer service.


If you have a question about anything in the above blog, please ask it in the comments section below.

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6 comments - read them below or add one


andrewmcgComment left on: 7 July 2012 at 8:54 am

More importantly, you wont be able to add 3kW with an already existing 2kW system unless you have more than single phase supply. You can't have more than 16Amps per phase. 

The Gov also changed the rules on increased capacity. The new system will count as a different one from your previous, and be on the FIT rates at the time. 

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Cathy Debenham

Cathy DebenhamComment left on: 11 June 2012 at 9:07 am

Good point St3ve. Thank you for highlighting that.

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st3veComment left on: 8 June 2012 at 8:21 pm

Cathy, think carefully about this expansion. As mentioned, if you add 3kw to a 2kw system, not only will you only get the 4 to 10 kW rate on the new part (assuming 12 months have elapsed since first system installed), but you will need to consider how your expansion is achieved.

If you add a new system with a new inverter that would be straigtforward, but if you replace the existing inverter with a new one capable of combining the 2 systems,say, then the FIT scheme for the first system will cease and re-start at the new (ie lower) rate for the combined 2+3kWs. This could result in you actually losing income on the combined system compared to the original only!!! 

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SteveZComment left on: 12 April 2012 at 10:47 am

I almost went for the Enecsys, but the delivery times and the prices were a problem. The Enecsys micro inverter (available as a dual panel item too) has all the circuitry required to carry out MPPT, convert the DC to AC and report its performance, contained in a small box mounted on, or built into, the Solar Panel. The output is brought from the roof using normal 13A household cabling. The Enecsys has a 25 year warranty, but I don't know if it is insurance-backed.

The SE PowerBox has just the MPPT and reporting functions on the roof, the rest is in the simplified design inverter in the house or garage. The PowerBox has a 25 year warranty and the Inverter has a 12 year warranty, which is longer than the usual 5 years. Again, not sure if insurance-backed. The SE system has a safety feature i haven't noticed on any others. When the system is isolated from the mains, the maximum DC voltage produced by any panel is limited to one volt, making working around the panels much safer than a conventional set-up.

Both systems report the status of every panel and report any faults, which a single or two string inverter cannot, as far as I am aware.

 I hope this helps

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pigasusComment left on: 11 April 2012 at 10:32 am

I have been reading about micro-inverters  and optimisers.  Can someone explain to me what the differences are between the Enecsys micro-inverters and the SolarEdge and Tigo optimers?

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SteveZComment left on: 10 April 2012 at 4:52 pm

There is another option available for your split aspect system (and single aspect. too) . I have an East/South 4kW SolarEdge system which has the Maximum Power Point Tracking function on each panel, but still uses a single inverter. This means that each panel runs at the best voltage for the inverter and does not interfere with the output of any other panel. If you have any shading, this can be very important. I have noticed that even a cloud passing will show up as very different panel outputs, which will reduce the power output on a normal single or two string arrangement. It did cost a little more than a normal two string inverter system, but I believe it will pay off in increased output in my particular case - I'll know more next year!

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