2.4kW – PV – Makes It To Our Roof!

Welcome again to another interesting post? Well, I hope so.

PV what is it?

Well, you have probably seen a few street signs on the UK road with either a small wind turbine and a flat panel normally facing South in direction. These are a smaller version of the Domestic installations that allow the street sign to work without the requirement of electrical cabling having to deliver electricity to the sign.


PV panels allow daylight to be converted into Electricity. The physical process of how it happens is not really the topic for this post. So, here is the link to Wikipedia for those that wish to understand the actual process of how it actually happens.

Yes, you did read correctly. PV panels produce electricity when it rains, snows and an overcast day. Yes, it doesn’t set the world on fire with the amounts. But, it is enough to generally cover the tick over of the home during the day time.

The UK, the Government is providing a fixed tariff for those owners occupiers that wish to generate their own electricity using the everyday daylight. It has to be installed by an MCS installer. They will pay £0.41 p per unit of electricity generated to a 4 kW system. So, our system can produce 2.4 units per hour on a good day.

So, if we have a very dry hot summer and produce more units than expected (1,900 for us) you still will get paid. Also, the HM Government estimations tend to be on the low side as they take the whole of the UK rather than regions. Most PV installations are seeing anything from 15-35% more units than expected. However, as there is no cap to the 0.41p units, all the units produced are paid for. The Generation Meter keeps track of the number of units achieved. Larger systems are allowable but they have a lower tariff.

You also get to use this energy that you have been paid 0.41 pence to power the household. So, you in effect save another 12.5p as you don’t have to pay for the electricity board to provide the power.

So, typically we use around 300 watts when we are not cooking or mowing the lawn. On a cloudy day, the PV produced around 225Watts. So, we only pay for the additional 75w coming from the electricity board. When we have a brighter day this turns into 1,000-1750w (1-1.75Kw), on a nice sunny day this wander up to 2Kw. We are then in effect pushing the additional amount power back on to the Grid for another household to use. So, by now, some of you would have spotted that it make more commercial sense to turn on Washing Machines, Dishwashers during the day. Even part cooking the evening meal to warm up later on!

For those that wish to find out how much electricity they are using. May wish to look at our post on Linking GOOGLE Power Meter with monitoring devices here.

The good news is that under the scheme they assume that 50% (1,900 units)  is put back onto the grid again. It is worked out on the basis that we have normal weather conditions. As everyone in the UK is aware. This hasn’t happened this year with the SNOW and Rain. However, 50% of this expected number of units is again paid for. £0.03p x 950 in our case. So, it will not pay for too many shoes. However, is very generous. So, don’t put in an export meter!

If you have a system more than 4kW, then you have to have an export meter fitted. Well, you are now talking in Corporate range!

So, what does that mean?

Ok, if you went out to the kitchen and boiled a kettle of water. You would be using about 3kW of electricity. Now, if you kept it going for an hour, which obviously you don’t, then you would have used 3 units of electricity. 3 x 0.12p = £0.36.

So, as you can see to cover the whole electrical needs of the house would require a large array. So, how do you size a PV installation? Well, there are a couple of ways of thinking about this.

First, how large is the space that you have that is facing in the right direction – South, South West or South East.

Use Google Maps to find your address and then zoom into your street. Google Maps usefully puts the South compass point on the bottom of the browser. If you want to be a little more accurate, you can use this link here to place the Compass Position over the Google Map. With this in place, you have to know where you live! Zoom in using the bar on the left-hand side.

When you have decided on the right part of the roof to place the PV panels. You will then have to take account of ANY shadowing that occurs. Chimney, Trees other roof shadows.

The PV panels are normally daisy-chained together. So, if one panel is in shadow, it affects the total system!

If this happening early in the morning or late at night that is fine. But, if it occurs between 8 am and 6 pm during the day, it will have a significant impact on the production of power.

Like, every appliance in your home. The efficiency of a device to convert the electricity from that form to motion in terms of the Washing machine/Dishwasher/Fridge or pump on the heating system has become a lot better recently. So, if you have a device that is in used a lot and is over 15 years old. It could actually be cost effective to change it, even, if it isn’t broken. As the energy savings alone would justify the purchase. Most now are in the region of 75-95%.

However, the PV panels have a long way to go on this score. Typically, they provide 13-14.5%. This means for every 1,000 W that the sunlight provides. Only 13-14% is converted to electrical energy.

The second option is to cover what it used 24/7. Now, just having an average of 300 watts load on all day. Every day will use 7.2 units in 24 hours. In a year that’s 2,628. The average use in a UK home is 3,600 units a year. So, that 300 watts is going to cost  2,628 * 0.125p = £328.50!

For those of you that use more than 10 units of electricity a day. Then, the size would have to be even larger! Most, houses that I visit use more. :o)

Even, though we have changed all of our lights to using LED lighting, ECO fridge and a V-Phase unit in. We are being serious! We still tick over between 8-10 units a day. Although, I do work from home. I’ll have to put my Laptop on a diet!

So, you would need a Southerly facing space of 26.4Sq Meter. Which, would then contain two strings of 8 x 240w panels to an SMA 4000S inverter provides a generation capacity of 3,992kWhrs a year. Which, would cover the average usage in a home based on Government estimates. Now, remember the comment above?

So, how much is that going to cost? I hear you say. Well assuming that the roof is large enough, then you are currently looking at around £16,000. (2014 now £4 to 5,000) However, the payment rate has changed from 0.41p to 0.13p per unit)

Quotation Process – Remember Double Glazing salesman?

So, how do you go about it and what pitfalls?

Well, we asked over 20 companies to provide a quotation for the Southwesterly roof space that we had. I knew, most of what was involved, as we had installed large systems before.

However, there was a great debate, on, if the roof was facing the right way. Why were we not using the Southerly facing roof? etc.

The main reason we were not using the southern facing roof was to shadow issues. Where the Southwesterly did have any shadow issues. However, this does have a knock-on effect, the Sunlight would not hit the roof to produce full power until 10 am.  Using my local weather knowledge. Most of the time the skies are cloudy occurs in the early morning. So, we generally get better afternoons than mornings here. However, the panel starts producing energy at 8 am in the morning. Ok, it doesn’t go up to 2kW until later morning, but, then, the sunlight is stronger anyway.

So, using your local knowledge will become invaluable. However, each site will be different! There are options to split the panels between each roof plane. Most Inverters allow this to happen. However, this tends not to be economic. Very large systems may have an edge to do this. But small sized, I don’t think stack up in my view.

So, you don’t have large enough roof space or it’s facing the wrong direction? Not all is lost. You could, if, you have a large enough garden or backyard position the PV systems on the floor or on a gallery system. The gallery systems come in a couple of flavors. Single axis and Dual axis. These can track the sun during the day. So, you tend to increase the number of units generated by 30-45%.

This is a small one. However, the normal size version will allow 10-16 panels. That’s 2.4 to 3.84 kW systems using 240W Panels.

But the tracker themselves cost £3,500-4,500. But, then you don’t have anyone on your roof and you will probably produce 30-45% more power. Swings and roundabout come to mind.

Also, you don’t have to get for the 4kW systems. Typically, most installs are 2,2.4, 3.6 or 4kW in size.

So, out of these 20 companies.

We had firms that turned up looked at the roof and-and gave a price without actually measuring the roof! We had those that wanted to price the system by capacity, again stating that the installers would size the system on the survey. So, what are you doing here?

We had those that provide the best deal in terms of cost but were a little light in the way that the system was to be installed. Until I mentioned that they would need scaffolding. This tended to be added on to the price, rather than be there in the first place.

We had some that used actual roofers to install the frames onto the roof then a PV team to install. Which, always leaves me with who do I complain to if the roof leaks afterward? I can see a case of ping pong between suppliers.

OK, So how do you tell?

This is what I did.

  1. Looked up Companies House to see when the company came into existence.
  2. Looked up the Domain Name Registration to find out when that was registered.
  3. What was the Payment schedule? The deposit was for some 50%, others 75%. The one I choose was 15% up front, which was insurance backed.
  4. Were they registered on the MCS scheme? Silly, but if they are not then the electricity board will tell you to go away!
  5. Did they have reference sites? Call them!
  6. The one I picked had a 15% Deposit, 50% on installation and the 35% balance once the paperwork had been sent.

In the end, it was down to three suppliers. I eventually choose Konnect Services who were already an electrical contractor in their own right and they had been installing PV systems for 4 years. This and the payment terms generally shows the companies that are set up and funded correctly. They provide 3 options to choose from and provided the costs for all and relative outputs. They showed their experience with me asking a few technical questions that were answered perfectly. As, I was talking to James, the man who was going to install the system!

Second were Solar Advance Systems contact John Dense who gave a 2.1kW system rather than a 2.4kW. They did provide an Insurance backed Guarantee. The third was John Sandison from 1stSolarPV Ltd and again they provided a 2.1kW system with a higher price. I have no hesitation to recommend all 3 for a quotation. As they all knew what they were doing. So, if you do call them, let them know it was me that put them in the frame!

So, here are some pictures over the three days they installed the system. To their credit, they turned up on 23rd December and as you can see it had snowed a little!

This is when the scaffold went up and was the Friday before they started.

As you can see. There was plenty of sunshine on that day. But, your tea was ice cold in minutes!

This is our crew setting out the rails to which the PV panels are later attached to. As you can see, they had a few environmental issues to resolve. i.e Sweeping the snow off the roof!

All credit to the crew. They, took off their boots when they had to go up into the roof space and left the place tidy each evening.

All I had to do was to make tea. But, I couldn’t help getting involved when we had to run the 240 AC cabling down from the roof via the bathroom into the kitchen then into the meter cupboard space. But, that was totally my choice!

The Sparky and I had great fun running the cable down the non-existent trunking!  I could have sworn I put in trunking?

However, we found a suitable route eventually!  After that. It was pretty straight forward.

This is the view when all of the panels had been fitted and they switch to working inside on the actual inverter and wiring.

This is the SMA SB-2500HF-30 Inverter. This is the newer type without the heavy transformer. It also has BlueTooth embedded transmitter. So, you can monitor its performance during daylight hours. Using the SMA Sunny Explore software. (You select software tab, then should see listing including Sunny Explorer. Then select PC software). You need to have Bluetooth enabled PC/Laptop. But you can buy one of these from here.

You can also find “Sunny Designer”.  Which, then allows you to design your own PV system from scratch.

The PV panels are linked in a daisy chain fashion, which, then via the white box in the picture is fed to the Inverter in DC form and this is output to the Yellow box in AC form which is used by the household.

This picture shows where that cable turns up. The cable from the roof goes into the yellow box with the red switch. This is then fed into the Generation Meter. This is what actually counts the number of units generated. This then feeds to the single way Consumer unit and fuse.

The grey cables from there are wired to the electrical Block. Which, is where the normal household supply is taken. By doing it this way you can sidestep updating the rest of the households electrics to the current Regs. As this is considered a separate system. As the consumer unit is separate to the main one.

If, your household electric do comply. Then, the feed would go to the normal consumer unit via a 10 Amp MCB.

We are just below 100 units to now. But, Spring and Summer are the main seasons that PV creates most electricity.

So, Why do it?  – Financials.

Well, the £0.41 will be indexed to the RPI. So, with inflation taking off, the rate paid will not be left behind. Also, when you consider that the electricity companies have not been slow in increasing their prices recently, the savings can only grow. Now for most UK citizens, the inflation rate is 4-5% by 2011 and the way things are in the world. We will probably not see the Savings rate increase for a considerable time. As, if it did, the banks, will be back to square one again!

So, the current rate on savings is 1.5% at best before Tax. So, that money that you might have sitting in a savings account is unlikely to see 5% interest for at least 5-10 years! So, this is the reason why I jumped. Obviously, you should ensure that you have enough held me backs. But, if you have money in long term funds. Then, this is probably the best deal in town.

It also, helps that the Taxman is not going to Tax Domestic installations income. (up to 4kW). So, this £1,000 of income. Would have required £1,500 worth of salary.

Well, it’s your call. But, it does seem to be a no-brainer to me.

Well, here is the picture when its all done!


Number of Units Generated in 2011

1,989 kW

Number of Units Generated in 2012

1,933 kW

The number of units Generated despite all this rain!

2013  – 1,923 kW.

2014 – 2,050 kW.

2015 – 1,998 kW.

2016 – 1,994 kW

This now totals 12.052  MWh over the 2010- 2016. Not bad for our little setup.

Well, if you have any comment then just fill in the box below. Questions? bounce a comment and I will try to answer them.

In the meantime. That all Folks.

About tagware

I've worked in IT for over 30 years. As the owner of one of the earlier AutoDesk Dealerships, when Richard Handyside was the main UK guy in The Cut! We supplied complete CAD, Networks and visualisation systems to Corporate clients such as RIBAS, Channel 4, NHS, BBC, Merrill Lynch, COMET Plc, Morgan Stanley too mention a few. We also developed the graphical ADB system for the Department of Health and a graphically lead Asset system for Merrill Lynch. Subsequently became a contract IT Consultant in both Developement and Production area's for both Large and small businesses. Which is what I'm still doing.
This entry was posted in Energy Efficiency, Renewables and tagged , , , , , , , , , , . Bookmark the permalink.

Leave a Reply

Your email address will not be published.


This site uses Akismet to reduce spam. Learn how your comment data is processed.