The Magic of Solar Power

 

The Magic of Solar Panels

I used to play Magic the Gathering card game.  Some thirty years later the original cards from 1993-1994 turned out to be worth quite a lot of money.  In fact they were worth so much I sold my collection of old cards and got enough cash for an entire solar array on my house!

My full system cost just over £15,000.  The main part was on the panels, inverter and battery.  There were additional costs for scaffolding and a Solar iBoost for hot water (more on that later).  What I had installed was a 4 kilowatt peak (kWp) system consisting of: 

• 10x QCell 395 Watt panels with SolarEdge optimisers and SolarEdge inverter £6300
• An integrated SolarEdge StoreEdge 10kWh home battery £8000

What can you expect from a Solar system?

According to Ofgem the 'average' British household uses 242 kWh of electricity per month.  This is only household consumption and does not cover anything for an electric vehicle.  Fortunately my friend was kind enough to share data for the last five years from his 3.85 kWp system.  Using that as a guide we would expect a standard installation in the UK to cover our need for 7 months of the year and have another 2 months with at least 50% covered.  We also have 5 months in the middle of the year where selling our excess generation back to grid can offset winter costs.

Solar Panel Selection

There are new and better panels coming out all the time.  Already you can buy 400 w and 440 w panels.  There are a lot of brands available and it probably does not matter which manufaturer you select as they all have excellent levels of robustness.  What you want to look for is Monocrystalline panels as they offer the best efficiency rating available at the moment.  Most of us have a finite roof space.  Within a few months of having my system installed my first regret was not having more panels installed as it would all add to the savings I am making.

The European Commission has a website where you can calculated the expected solar generation of your system.  Enter your postcode at the bottom of the map on the left and then the peak PV you are looking to get on the right and you will get a graph at the bottom showing expected output based on information from the solar radiation database.

Inverter and connection method

The beating heart of the system is an inverter.  This change the DC current from the panels into AC current making it compatible with everyday appliances in your home and allowing export to the national grid.  The second part is how the inverter and panels are connected.  You can have simple string inverters, Microinverters or Power Optimisers.  I found a good graphic on this webpage, image below.  The main weakness of of using a string inverter is that any shading on a single panel will effect the output from all panels connected to that string.  Microinverters and Power Optimisers give you an answer to this as they adjust the current to maximise output.

Most installers will offer a 4 kWp system as a standard installation as anything more can require approval from the Distribution Network Operator (DNO) and uses different forms, G98 and G99, depending on the expected export size of your system.  There can also be additional costs depending on where you live.  One counter to this extra cost is clipped solar power.  All inverters have a maximum output, meaning that if there is more electricity being generated by the panels, the inverter is only able to convert to the set capacity clipping the leftover electricity. While on the one hand this is a waste there may only be a few days of the year where you reach full capacity and it means that for the months of the year where you are not near capacity you get more power generated.

Battery Choice

The main benefit of a battery is being able to store your excess generation to keep the house running over night or on cloudy days.  They can also be used to charge up overnight with cheaper rate electricity and, if you are allowed to force discharge, sell back to an energy company during peak periods for a profit.  The other consideration is location as not all batteries are suitable for external mounting.

Unfortunately batteries are expensive.  Unless you have real high usage you can probably get away with a small battery to just keep the house running overnight.  If you are also wanting to swap to electric heating or maximise earnings on solar export you are likely to want 10-15 kWh of storage.  SolarEdge, GiveEnergy, Tesla and others all offer batteries of various sizes.  There is also a mix of AC or DC coupled batteries.  This makes a difference as there is some efficiency lost with cycling energy through the battery and back out again.  Another factor is what sort of control do you want over setting the battery configuration?  Tesla Powerwall is probably still the best battery available but depending on where you live you may not be allowed to force export due to the shear power of the system.  SolarEdge has the battery configuration locked down to installer level but has recently relaxed this so that end users can set the charge/discharge times.  

It took me quite a bit of time and hassle to get myself setup as installer for my own SolarEdge system so that I could change the battery charge cycle and have it charge from the grid during the cheap off-peak time and force discharge during peak times.

Income Tax

The HMRC Business Income Manual, BIM40520, states there is an Income Tax exemption for domestic microgeneration (solar power) systems.  The exemption covers occupied domestic premises where the amount of electricity generated will not significantly exceed the amount of electricity consumed in those premises.

The term ‘significantly exceed’ is not defined in the act. However the webpage states a householder who does not intend to generate more than 20% in excess of their own domestic needs is unlikely to be regarded as intending to significantly exceed their consumption.  At the moment it is unclear how EV's factor into this.  Does home charging count as being consumed on the premises?  As more people swap over to electric transport this is an area of taxation that may get changed.

Solar Energy Tariff

Octopus Energy offer some specialised tariffs for customer with solar system as well as EV's and Heat Pumps.  Their Flux tariff offers three hours overnight for charging my battery at a cheaper rate as well as an increased export price during peak period of 4pm to 7pm.  I have a referral link that will get us both £50 if you use it to join up to Octopus.  If you are phoning them then please quote "Pure Lord 584" as the referral.  At the moment I am charging my battery at a cost of 17.69p/kWh and selling it back later in the day for 30.28p/kWh a profit of 12.59p/kWh.  While that does not sound much it adds up to £75 over the summer which is on top of selling the excess generation during the day.

Summary and future power use

Initially I was using a solar diverter to generate hot water however as the export price increased over 12p I have stopped using it for the moment.  Eventually I want to replace the immersion tank with a heat pump cylinder for even more efficiency at which point I will be heating water with solar power again.  As heat pumps, EV's and other options become more popular the average amount of energy used in a home will increase.

I would recommend people get as many solar panels as they can afford to try and future proof expected need.  At the end of the day though whatever you can get will help to reduce your ongoing bills as well as helping with the environment.