Solar in the UK is probably a doubt for many, but it does work and can save you money. If you have been reading our posts about the different types of solar then you would know that its not the more the merrier and there are price points as well as power points that make sense to a point, here we will look at what could be the minimal solar panels and type which will give you the best bang for your pound..
Going grid tied is a cheap option and its does have draw backs, I have said a million times, you only save what you use. So here the premise is that your solar should be smaller in size to make the most of the solar production, which will relate to the load ( power use) that you have. going too big is a waste of your money and only give profits to the electric companies.
Grid tied also has no buffer, which is where battery storage comes into play, solar is so up and down that you will draw power from the grid fairly often and this will give some sense that its not that effective if you di not size the solar array large enough to account for the clouds, weather conditions and seasonal change. You would want to size around 40% over the load.
Mounting the solar can play a large part in how well or not your solar will perform. Our Tilt and angle post explains this in more detail. A fixed south facing roof is fairly standard and claimed to be the best, this is not true. Solar power is higher in the summer than the winter, and you will tend to use more power in the winter than the summer, so it makes sense to optimise for the winter, a roof mounted solar panel would need to almost stand up right to be good for winter, and lay flat for summer. A roof install or around 45 degrees would clip power in both summer and winter.
While it is true that the panels should face south, that only relates to winter where the sun arch is smaller and you have less sun hours, here in the south, the sun rises at 11 until 15:30 in winter, so you want to keep this in mind.
You could mount with a solar tracker, you will get about 40-50% more daily production from a tracker meaning that you will buy less panels and don’t have to worry about seasonal alignment. fixed solar in summer starts behind south facing panels and finishes behind them too. you will lose about 5 – 8 hours of better performance just south facing.
East and west facing solar (30 degrees off set) will start your summer solar much more early and later in the day, making the grid load lower, or if you have a battery, setout a wider charge time frame through the day. You would have a more vertical angle on these panels, and the south double stacked with the winter alignment to a summer alignment under those.
Summer time solar panels less power.
Solar panels get hot and the production of power drops, sunny days tend to give less power output. you can find information on the panel data sheet or follow the NOCT data from them. expect around 10-20% drop in power. as you will also get dirt and dust on the panels.
Systems with a battery should always be sized for the battery size divided by 5 hours and include the loads. this will ensure that the array is sized to charge the battery and have ample power to supply the load over the day. you will fall short in winter and have too much in summer.
The array size for winter in the UK will usually be too much in size and current to be safe for the battery.
This is mostly due to the fact that you wouldn’t be able to charge in 2 hours – that’s around 108 amps continuous charge, and the array would been to be around 46.6kw
Grid tied off set array size.
120V 1kw array would be good for a starting point, but you will suffer in winter with power around 65w rising to 120w.
1.7kw will see you have surplus power in the summer for much of the day. in winter with the correct alignment, around 200 watts but generally the four or five hours of sun wont cut it for any good dent in the power cost. for this you would want to energy trade by getting cheap rate ( eco7/10 EV rate) to charge a battery. The working times frame would be between March and October.
Micro inverters.
Having a micro inverter may work for you, these are small and you can mount them in most places, but you can also have independent panel alignment. this means that you could have two winter and two summer, a east west off set all from one single inverter.
Micro inverters can be deceptive to the power as they are rated for commercial panels which have a higher voltage, and are slightly bigger (2.1×1.3meters) the difference comes in the form of voltage to current.
If you have a 38 volt panel, with MPP being around 32, then the current plays a big roll in the power production lets say 14 amps.
32×14 is 448watts of power where as 41×14 would be 714w a factor of 1.6 in power production. you may find the inverter rated to 3000w (3kw). while in the real world you may only see a peak of around 1.8 kw from the system.
You have by now gathered that the size will be related to how you mount your solar and what the tilt and angle is. Then there is the battery or and load to consider, so that is no real answer to the question.
Small GTi 800w – 1.7kw.
Series GTi for a more flexible use 4kw
Hybrid and off grid starts at 4.6kw
Flexi 5.6kw
Take a look at this winter vs summer array video to get an idea of the difference in the array output power.
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