Tuesday, 4 August 2020

Does Solar still make sense ?

This is piece I created for a local  Facebook group and is based on estimates for our location in St Mary Bourne, Hampshire. If you would like to generate estimates for your location, we have a solar estimation tool here.

In 2005 I installed photovoltaic solar panels on our roof,the kind that generate electricity rather than the ones that heat hot water. There was not much information available in the UK at the time on how long they would take to pay back and there were no financial incentives.

After some searching for information on the amount of solar available, I worked out that they would pay for themselves in a little over 300 years. This was definitely a hobby project.

For 5 years my long suffering family put up with half of our house running off grid from a bank of batteries charged by solar panels during the day, and if we were lucky, powering the lights during the night.

The batteries were housed in the long wooden box in this photo and charged from the rooftop solar panels.

In 2010 the government introduced the Feed in Tariff. In October of that year, we swapped our home made installation (it was retired to power a narrow boat) for a system installed under the Feed in Tariff scheme. We had most of our SSE facing roof covered with panels, giving us a 3kW installation of 10 panels. In that year, I also started a small company to provide estimates on the cost and returns of solar and wind microgeneration RenSMART to installers and the public.

System Specification

  • 3kW peak output
  • HIT Panels 20% efficiency
  • Sunny Boy Inverter
  • Roof Direction SSE
  • Generated 23,800 Units (kWh) over 9 years
Financial Information
  • Cost £10,500
  • Pay back date - Two years ago
  • System life - 25 years

The Feed in Tariff, from the outset, was intended to be an incentive to help reduce the cost of solar to a point where it no longer required an incentive to make it viable. In 2019, the Feed in Tariff ended. Any new installation after that point would not receive the Feed in Tariff. I have been asked many times recently if it still makes sense to install solar panels. This is the result of my investigation.

While the Feed in Tariff was in place, the government recorded the cost of installations, and this information is readily available and published up until 2019. Using information from 2019, you can work out the average cost of an installation for a particular size. A 3kW system like ours, would have cost £6000 in 2019, so quite a reduction, but would it be financially viable.

Financial Estimates if the same system was installed this year
  • Estimated Cost - £6,000

  • Generation Forecast 23,800 Units (kWh) over 9 years [1]

  • 9 years - 50% of generation (deemed exported [3]) at 5.5p £650 feed in tariff [2]

  • 9 years - 50% of generation (deemed used on site [3]) at 18p £2,140

  • £2790 / 8 years = about £350 / year

  • Pay back date just over 17 years

  • £8750 over 25 year system life

  • About 5% return per year

[1] Taken from our current installations performance

[2] Although the Feed In Tariff has ended, many electricity providers pay you for exported electricity. In this case we are basing the figure on the Octopus Energy Outgoing tariff

[3] As the measurement of exported electricity is rarely in place, the amount used in your house is taken to be 50% of generation

So it seems that the Feed in Tariff did achieve its target of reducing solar installation costs to make them financially viable without incentive.

What about the green house gas reduction ?

Having calculated the financial returns of installing solar, I’ve calculated the reduction in greenhouse gas emissions such an installation would achieve.

Our 3kW installation was generating an average 8 Units (kWh) per day.

Using data made available from the National Grid, we can calculate that if we had used grid electricity, 8 kWh would have caused the release of 2kg CO2 per day. That does not really mean much unless you know what reduction we as a population need to make.

The average UK household has an annual carbon footprint of 20,000 kg CO2. To keep global warming to below 1.5 deg C, we need to reduce this by 50% with further reduction to 30% within ten years.

  • 50% reduction = 10,000 kg CO2

  • 2kg x 365 days = 730 kg CO2 = 7% of the required reduction for the average household

A solar installation in 2020 could offer a reasonable return on investment both in financial and carbon footprint reduction. If you would like to calculate estimated returns for your property try the RenSMART Quick Solar Project tool. RenSMART is a not for profit company and the tool is free to use and not linked to any kind of sales.

Sunday, 19 July 2020


Normally I would use this blog to highlight changes on the RenSMART site, however today I would like to concentrate on a very interesting TED interview with Nigel Topping, the UK high level climate action champion man tasked with organising COP26 Glasgow.

A link to the interview is here and my thoughts and a brief synopsis of the subjects covered follow.

TED Interview with Nigel Topping: We Need to Green The Economy While Restarting It

At COP21 2015 Paris countries agreed on their targets. The EU agreed a target of Net Zero emissions by 2050

In 2018 the IPPC released a report giving stark warnings of what will happen if global temperature rises above pre-industrial levels by 1.5C and 2C

COP27 Glasgow was to be where countries would report on their progress towards their agreed targets. It will now be held from 1-12 November 2021. Also in 2021 the IPPC  will release multiple reports.

"we are talking about the total re-engineering of the global social and economic system"

Nigel suggests that post pandemic the world needs to better understand the science of risk. Here is a start: BBC How to understand risk

Jobs need to be transitioned from carbon intensive industries such as coal mining. Coal is a dying industry propped up by governments due to the number of people who would be unemployed if it were to abruptly stop. Few investors want to put money into an industry that is causing global warming due to pressure from share holders (and their children). One of the key challenges in greening the economy is how to accomplish this without causing pain to those who rely on the industries that are carbon intensive.

Some companies have published plans of how they intend to transition to being carbon neutral, but it will take them time as a whole list of actions need to be taken to arrive at that point. For instance Maersk, the huge shipping company, have pledged to be a net zero company by 2050 and have hind cast their ship procurement to show how this can be done.

Transition and change can be faster than we, or forecasters, expect. Where there is a will, there is a way. We have just been through a pandemic (lets hope we are through) that has shown the whole world can change very fast.

What can we do as individuals ?
  • Halve our carbon footprint
  • Reduce flights
  • Change our diet - reduce our consumption of red meat
  • Make your next car an electric car
  • Ask your company or university what they are doing to transition to Net Zero
  • Ask your pension company what their investment policy is
  • Show our children what we are doing - talk to them about the decisions you are making 
  • Invest in renewable energy. Maybe take a look at Abundance Investment
  • Move to a green energy supplier
  • Check out RenSMART economyGREEN

What is RenSMART doing ?

Saturday, 25 January 2020

30 Million Waving Trees

During the election several of the parties decided to proclaim their intention to plant millions of trees a year to mitigate our green house gas emissions. I thought I would do some back of the virtual envelope calculations to see what difference this would make.

As a country we voted in a Conservative government with a manifesto commitment to plant 30 million trees a year to help reach net zero emissions by 2050[1]. Based on this and a simple model for capture of carbon by growing trees I got the following results:

  • Planting 30 million new trees a year, every year until 2050 will achieve about 9% of the reductions we would require to reach net zero emissions.
  • That would be 930 million new trees.
  • The same 30 million new trees a year, every year until 2030 would achieve about 1% of the reductions to reach net zero by 2030[2]


[1] Net zero by 2050 is a time frame that has a low probability of keeping warming  below a relatively safe 1.5C
[2] Net zero by 2030 a time frame that has a high probability of keeping warming  below a relatively safe 1.5C

Thursday, 9 January 2020

EconomyGREEN and Solar Micro Generation

Having begun the development of economyGREEN, a service to help you use electricity when it is at its greenest, and having an interest in home solar installations, I thought I would do some investigation into applying the same forecasting RenSMART uses for the UK to micro solar pv installations. The kind thousands of people have had installed on their roofs throughout the UK.

The idea would be to provide people with forecasts specifically for their location and installation. For example on a day with a sunny afternoon forecast, but cloudy morning, the economyGREEN service would suggest you delay your washing machine load until later in the day.

As a starting point I wanted to see what levels of excess are produced by solar pv in an average setting, and at what times of year.

I took a reasonably central point in the UK, Leicester, as the location of the installation, the electricity use profile of the average house, and a 4kW peak solar installation [1]

Key Points

The key information I discovered was:
  • 46% of generated electricity is excess to the average houses needs and is exported to the grid. This is close to the governments deemed value of 50% which was used to calculate the portion of the feed in tariff due for exporting to the grid.
  • This is almost 2000 kWh per year with a value of about £350 to the home owner if they could make use of it instead of using electricity imported from the grid.
  • This is saving of 1000kg of CO2 emissions per year. About the same as a return flight from the UK to New York.

The Data


What to do ?

The next question is what to do with this excess as an alternative to exporting it to the grid. With the end of the feed in tariff and no reliable replacement payment mechanism, using it within the house would seem like a good idea.

One option is to delay the use of appliances until the points in the day when excess is being generated. This is what the economyGREEN tag and app do, telling you the delay required for an appliance to use the greenest electricity.

For the wider grid, this just as likely to be at night than in the day due to the large amount of wind energy we, as a country, generate. However micro generation is mostly solar, and most excess is generated at midday, when the sun is at its highest, as you would expect. If you are about to do a washing load at 6pm, it is not helpful to suggest you delay it 16 hours to use the next days excess.

Battery Storage is expensive

One solution would be to install a battery storage solution[2]. This would cost about £500 per kWh.

At peak generation in the summer months, there is an excess of 14kWh to store, the mean excess is 5.6kWh. That would require a £7,000 battery installation to store each days excess for use later or £3,000 to store the average days excess.

Based on the excess electricity value of £350, that would take 20 or 10 years respectively to recoup the cost of installation.

Heat Storage is cheaper

A second solution would be to store the excess as heat and then release it throughout the cold parts of the day to keep the house warm and offset central heating.

Heat storage has a much lower cost than battery storage coming in at an estimated £20 per kW stored[3], That is almost 17 times cheaper than battery storage.

Also in the spreadsheet you will see that I have included average outside temperatures[4].
This shows that the average house wishing to keep an internal temperature of 19C is likely to need heating for all days on the year, as the outside temperature drops below this level. 14kWh of heat storage would cost £280 and £112 would store the excess energy as heat for most days.

economyGREEN for home solar PV

Based on this, RenSMART will be creating a specific economyGREEN service to control storage heaters for anyone interested who has (or intends to have) solar PV installed.

For more information contact nikcross@rensmart.com

[1] 4kW is the most popular installation size in the UK due to feed in tariff break points. The feed in tariff rate dropped significantly for larger installations.

[2] Based on price of a Lithium Ion battery backup installation

[3] Simple thermostatically controlled storage radiator storing for maximum of 12 hours

[4] Temperatures taken from the Metoffice weather station at Sutton Bonnington over the last 20 years.

Saturday, 28 December 2019

10 Renewable Energy and Green Songs

So its that period between Christmas and New Year where you are not sure what day it is, the diet is mostly leftovers and you are getting ready for the year to come. I spent a car journey between relatives coming up with a top ten songs related to renewable energy and green issues.

This is the list we came up with. Number ten is left empty, please feel free to suggest one in the comments. An obvious start, without need for much of an introduction. This is what we are fighting for and what we have to lose:

 1. Wonderful World.

Louis Armstrong  You can read more about it here 

The Wombles have been on message since 1968. Reduce, Reuse, Recycle. They were there and that is why they get number two spot in our list.

 2. The Wombling Song

The Wombles 

With solar panels on our roof (which have now paid for themselves in both money and carbon reduction), clear skies mean free electricity to us, so this one gets position three.

 3. I Can See Clearly Now 

 Hot House Flowers


However, as a country, our reduction in the use of fossil fuels can be put down to our building of wind farms, both on and off shore. As I write this, almost 30% of our electricity is being generated by wind turbines. I'll give the fire a miss, but I'll go with the wind :-)

 4. Fantasy 

Earth Wind and Fire


Now we get to the political ones. This gets into the list for the only Green Party MP, Caroline Lucas.
I won't go on about the fact the Green Party recieved 800,000 votes in the recent election and only have one MP. (Oh wait, I did)

 5. Sweet Caroline

Neil Daimond   

This one is really just dedicated by us to one American. The one who thinks wind turbines cause cancer and climate change is a conspiracy by the Chinese.

 6. American Idiot 

Green Day


And this is our message to him :-)

 7. Science Is Real 

They Must Be Giants


Now for probably our most tentative song. There is no real excuse for this except it came to mind and was part of my childhood.

8. Green Door 

Shaking Stevens 


John Lennon only gets a look in because I think if he was still alive, he would have written a good song for this list. As it is, this is the most appropriate I could find.

 9. Cleanup Time 

John Lennon 


I don't think I'll give up my day job and become a musicologist (A real job. I've worked with some before). The number ten slot is empty for you to suggest the final track. Please feel free to leave suggestions in the comments along with the reason for your choice if it is not obvious. Thanks.
Happy Christmas and a Green New Year to you all.

 10 ?

Sunday, 24 November 2019

Threat to Solar

The current government have removed most of the incentives for installing your own renewable electricity generators and in addition have increased the tax on new installations. This goes against all of their talk of tackling climate change. Under their watch micro wind generation has all but stopped and there is a risk solar will go the same way. Each roof top solar installation saves an average of 26 tons of CO2 emissions over its lifetime and if installed on the roofs of all new homes, would make a significant impact on our countries carbon footprint.

The tax rate on domestic coal is 5% The tax rate on domestic solar has been raised to 20%

The then environment secretary, Michael Gove, agreed that there was a climate emergency, but said he did not like the idea of declaring one. Telegraph

In April this year the MCS feed in tariff ended. The feed in tariff was intended as a reducing payment that would encourage solar installations while reducing year-on-year as the price of installation dropped due to economies of scale.

Payments were set by OFGEN each year with the payment having two elements, one payment was based on generation (the total electricity produced weather used or exported to the national grid) and a second payment for the amount exported.

Due to the lack of smart metering at the time the scheme started, the amount exported was deemed to be half of that generated. The amount paid was an index linked rate set yearly by OFGEN.

You could argue that it had done its job. Solar installation prices had come down to such an extent that they could payback their initial investment within a reasonable period of time without the need for incentives.

However, solar installations of a size suitable for most homes will produce more than they require at certain times of the year. At this point, the excess generated electricity is fed into the grid.

The government failed to provide a replacement for the feed in tariff, so it is currently up to your electricity provider to set a value on the electricity you supply them.

It is planned to set a minimum rate in January, but smaller electricity providers are exempt and the rate is likely to be considerably lower than the amount we pay to receive electricity into our homes.



Secondly, until October this year, solar panels had a VAT rate of 5%. The same rate as domestic fuel like gas, oil or coal. This has now been raised to 20%. This one piece of legislation will probably put an end to solar installations in the UK

This legislation was passed on 25 June 2019, the same day the UK House of Commons passed legislation to commit the UK to net-zero carbon emissions by 2050.

The rate increase was claimed to bring us in to line with EU rule, however this does not seem to be the case. The lower rate of VAT on solar had been discussed in 2016 and was deemed to meet EU tax rules at that point. Nothing has changed and yet here we are.



Saturday, 23 November 2019

Quick ! Solar !

I have been asked a few times recently, is it still worth getting Solar installed at home on your roof. I have gathered the data and completed the calculations, The answer still seems to be yes.

Despite the current governments lack-lustre support of micro renewable generation and the almost complete decimation of the micro wind generation market, a micro solar installation still looks like it will pay the initial outlay back within a reasonable time.

The following link will take you to a simple calculator for returns from solar installations based on average prices recorded as part of the official MCS certification process.

Based on our estimates, a 4kW installation (the average size) would cost about £7264 and pay for itself in about 10 years. The total value of savings over 25 years is an estimated £35,385 and over 26 tons of CO2.