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35% of domestic solar systems may be underperforming

Posted by Cathy Debenham on 28 January 2014 at 11:23 am

Some homeowners are getting a significantly lower return on investment from their solar panels than expected according to PassivSystems. The company found that a third of residential solar panels monitored by its home energy management systems are not generating as much electricity as promised. It also found that when owners manage their PV installations well they can perform up to 17% above the expected benchmark.

PassivSystems carried out a study on solar PV returns using its portfolio of 16,000 monitored PV systems on homes across the UK between 2010-2013. It used the data to analyse the performance of the solar panels against a range of different criteria, looking at how the installation, maintenance and monitoring activities influenced the return.

"If this under-performance is measured and well understood, it is possible to take steps to counter it," says PassivSystems professional services director Ian Rose. "This may be through improved installation practices, altered maintenance regimes, or through better education and support of the householder.

"The causes of system losses are commonly down to shading and technical faults with the inverter. However, our research identified a number of additional reasons. These include poor or incorrect wiring during installation, residual current devices (RCD) tripping (which in many cases can go unnoticed for many days or weeks), tenants inadvertently disconnecting the system and pay-as-you-go meters cutting out generation.

"This highlights that human interaction with the system, whether from interference or failure to monitor the system status, can result in significant impacts on the levels of generation achieved."

The study found that solar PV is energy efficient. However, in order for it to be financially efficient Ian Rose recommends that the system is properly monitored and managed. If not, system owners may lose hundreds if not thousands of pounds over the life of the PV system.

There are a number of monitoring systems available to help people get the best returns from their solar panels. The PassivLiving system (and others, see links below) show you how much electricity your solar system is generating versus how much your home is using. This makes it easy to choose when to turn appliances on or off so that you can use as much of your free solar electricity as possible. The more sophisticated monitoring systems let you compare your current PV generation against your anticipated generation, track the performance, view your latest meter reading online and easily download and review the data for your quarterly feed-in-tariff submission.

The implications for owners and funders of residential PV systems are clear says Ian Rose. "These are not 'fit and forget' assets, but are prone to a range of technical, human and environmental factors that can influence performance and the rate of return. To fully optimise your solar PV system, both from an environmental and a financial point of view, domestic installations need to be well managed and maintained. The right type of energy management system can pay for itself very rapidly."

More information about solar PV on YouGen

The YouGen guide to solar PV

From the blog

Making the most of your solar PV system

Review of Elios4you energy management system

Wattson Solar Plus helps me to get the most out of my solar PV

Wattson Solar Plus brings electricty use and generation to life

Photos: PassivSystems By

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

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Comments

7 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 25 February 2014 at 11:39 am

Hi Tim - am I right in assuming that you've got a combi boiler? If so, you can still use solar thermal panels as long as the boiler you have accepts pre-heated water. There's more information about it here.

I can't answer for the suit, but there are a lot of solar switches on the market which divert excess electricity to the immersion heater.  Read more here and here.

The problem with solar PV and storage heater is that when you most want the heat, you generate the least solar electricity, so if he wants them to get hot every day he's best sticking to Economy 7.

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Tim Weller

Tim WellerComment left on: 22 February 2014 at 5:58 pm

Can I use my excess solar elecy to heat water in a super insulated hot water tank, when I have instant gas water heating? To put it another way: Can the solar hot water work in conjunction with gas water heating by heating the water that goes into the gas water heater for further heating by gas?   Could 'The Suit' tell me, please how he/she is using the solar elecy to get his/her hot water.  What size hot water tank and manufacturer?  And, what storage heater do you use?  What a great return on a 4kWp system!     Cathy, my friend has just had a 4 kWp system commissioned.  Should he use his storage heaters on Economy 7 or, should he rely on solar elecy to power up the storage heaters?  Excess solar elecy goes into his hot water tank that has, of course, an electric immersion heater.   Thanks.

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Tim Weller

Tim WellerComment left on: 22 February 2014 at 3:38 pm

Can I use my excess solar elecy to heat water in a super insulated hot water tank, when I have instant gas water heating? To put it another way: Can the solar hot water work in conjunction with gas water heating by heating the water that goes into the gas water heater for further heating by gas?   Could 'The Suit' tell me, please how he/she is using the solar elecy to get his/her hot water.  What size hot water tank and manufacturer?  And, what storage heater do you use?  What a great return on a 4kWp system!  Thanks.

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Cathy Debenham

Cathy DebenhamComment left on: 11 February 2014 at 9:37 am

@SimsSolar Hi Paul - it's a mixture of social housing and independently owned systems.

@The Suit - that sounds like a pretty good return. The easiest and cheapest way to know whether you're getting the right return is to check the generation figures against the predicted generation. Figures from the MCS guide state that a good south facing site in Kent or Sussex would generate 1,132kWh/kWp. In Shetland it would be 714kWh per kWp. Everywhere else would be somewhere in between.

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The Suit

The SuitComment left on: 31 January 2014 at 3:01 pm

I've run a 4kW PV for three years which  has given me a 16% tax free return on capital and I am woundering if this is about right. I also use it to supply hot water and a 1.7kW storage heater.

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mdj

mdjComment left on: 30 January 2014 at 4:32 pm

Seems like the main problem is if people don't notice that the system isn't working, due to RCDs tripping or similar.

Simply having a display where the occupants will notice it can reduce the problems a lot.

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Sims Solar Ltd

Sims Solar LtdComment left on: 28 January 2014 at 3:55 pm

Interesting article. What is the nature of the portfolio? Is it of the rent a roof type schemes?

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