Hi novemberRomeo,

Welcome to the forum.

I have had a 4kW solar PV system for the best part of 10 years, and as I stated in previous post, deem it to be one of the best investments that I have made.

Your proposed system of 18 x 320W panels would give a maximum possible output of 5.76kWh, though the actual output will only approach this value on one or two occasions during a year, if at all. The maximum output could further be limited by the size of the inverter. Do you know what size inverter is to be supplied? Maximum generation obviously occurs during the Summer months when the days are longer and the Sun is higher in the sky, though Spring and Autumn also gives quite reasonable generation.

Here are the important factors that should be considered.

1) Ideally the panels should be mounted on a South facing roof, though South-West or South-East also works quite well.

2) The roof angle is not too critical. Much more critical is the possibility of shading of even part of the panel array, which can reduce generation quite considerably. In Winter the Sun only rises 13 degrees above the horizon at midday, though the arc is much smaller than other times of the year.

3) Maximum generation is likely to occur during the Summer months, when heating demand will be low or not required at all. Solar PV can be used to provide most if not all hot water demand from Spring through to Autumn, though it would be better to install a solar power diverter to control the water heating.

As far as how best it is to use the available solar energy, is very much down to the individual requirements, and will probably vary from day to day. In Spring and Autumn there may be days when heating is required and you do not need to charge your EV's.

There will be a limited amount of solar power available, so to maximise its use may require some pre-planning, and possibly additional control equipment. Let me give you and example.

If your solar PV system is generating 2kWh and your heat pump requires 3kWh, then you would need to import 1kWh of energy from the grid. If you also start to charge an EV requiring 7kWh of electrical energy, then your import will increase to 8kWh. If instead, you could wait until your heat pump stops running before charging your EV, the imported energy would increase from 1kWh to 5kWh, rather than 8kWh.

I hope this makes sense, but if not then please ask for clarification.

Welcome to the forums @novemberromeo.

When we put our array up, one of the quotes we got was from a "Google Maps" provider, and I have to say that it was worrying that they quoted us for solar system in this manner, when compared to an on-the-ground site survey. When a survey is conducted, they look at a number of things that you simply can't pick up from a satellite image, such as the pitch of the roof and the materials used. This is all very important, especially the fabric of the roof because it'll determine what fixings the installers will use. In addition to this, when a survey is carried out, the installer also looks at potential shading that won't be picked up on the satellite, which will impact your production - things like trees, hills and general topography. 

The price quoted is competitive. I would ask about the brand and size of inverter, and would definitely invite an established solar installer to visit your property. 

I hope that helps.

Thanks for your thoughts.  I will ask more questions of the supplier and also obtain a quote from a local installer for comparison.

One thing I still don't quite understand though, is how the output of the energy generated by the solar system gets used.  All this talk of using it to heat your hot water is confusing me.  Why or how do you prioritise what devices use the energy? Can't you just feed it all back in to the house mains and  have it be used by anything?

@novemberromeo you need to think of it as a flow. Let me explain how my system works, but its important to know this is variable.

Your panels will generate a varying level of power over the day. From zero at night, to lots at 1pm. This also varies by season, loads in the summer and very little in the winter. Your house will use this power and any extra will be "exported" to the grid. For example if you are using 500W and your panels are making 1000W you will buy no power and you will export the unused 500W (500W for the house + 500W export). If you are making 250W and using 500W then you export zero and buy 250W from the grid.

When people talk about diverting power to hot water they are talking about turning on an immersion heater automatically. This just increases the houses' demand and reduces the export. In my earlier example if you are making 1000W and using 500W a solar diverter would see this and turn on the immersion to use 500W. This would mean you use 100% of your generation and export zero back to the grid. These diverters scale (usually up to 3kW) to meet excess demand. This saves you money as you would otherwise heat your hot water by other means.

Some people (myself included) go even further. I have batteries, so my setup has a different design. If my panels are producing, my system follows these rules,

1. Do I need the power to cover whats running?
2. If there is excess power, charge batteries
3. If batteries are full or charge is at max, divert to hot water
4. Export to grid

How you build these priorities is by using CT clamps to track power though your system. Any electrician (the people installing your solar) will be able to do this.

@novemberromeo 

Yes, you can just feed it into your electrical system, but most times you will not be using most of the electricity generated and so it will be exported back to the grid.

Let me give you an example. Your home will have a base load, the electrical items that are switched on 24/7. Things like your your router if you have one, your refrigerator and freezer, though they will actually be switching on and off. Dependent upon all your devices your base load will probably be in the order of 200W to 300W. So if your solar system were to be producing say 2kW (2000W), and your base load was 300W, then you would be exporting 1.7kW. If you were to now switch on your immersion heater, which is normally rated at 3kW, then instead of exporting 1.7kW you would now be importing 1.3kW. By installing a power diverter such as an i-boost, immersun unit or similar, the diverter would limit the power to the immersion heater to approximately 1.7kW, so your system would neither be importing or exporting. If you were to now switch on your 3kW kettle, the power to the immersion heater would be switch off and you would be importing 1.3kW. When your kettle switches off, the power feed to the immersion heater would be restored and you would once more be neither importing or exporting.

A power diverter therefore automatically allows the use of any excess generation, without causing energy to be imported whenever your solar PV system can meet demand. Obviously your hot water will heat up slower, unless your solar PV is generating an excess of 3kW or greater, but normally this is not a problem. On low generation days you will need another heat source to provide hot water, but that would be the case if you did not have a solar PV system.

@novemberromeo 

I forgot to mention. A power diverter will only work if you have a hot water tank with immersion heater.

Thanks both - think I get it now.

So as well as an immersion heater, I see another potential application of a diverter is for EV charging, right?  Instead of plugging in the car, at say 7am and drawing a full 7kWh until fully charged at 7pm (using solar and paying for import), by using a diverter it would ensure that the EV only charges at a rate that means you only use solar power, which perhaps might vary from say  0 - 3kWh during the day. Thus it will charge slower and take longer but you wont have paid for any import from the grid.

Do you buy a diverter for specific applications (such as hot water and ev charging) or are they just a standard box and can be wired to anything?

@novemberromeo 

Diverters are a standard box so to speak. The i-boost can apparently feed a maximum of two individual loads of up to 3kW, though not at the same time. I personally have an immersun unit which can feed up to three individual 3kW loads. The stipulation for the immersun unit and probably other diverters is that they can only be used on resistive loads. i.e. heaters and the like.

As far as using a diverter to charge an EV battery is concerned, I am not certain if it would work, you would need to look at the power requirements for the EV charger.

@novemberromeo There are a number of EV chargers which use this function. Below is a link to the Zappi. I am sure you can find others

https://coolenergyshop.com/collections/myenergi-smart-ev-charger-solar-power-diverter/products/myenergi-zappi-ev-charge-point-ce-zappi-207

@novemberromeo 

From the information kindly supplied by Batalto, it would appear that the Zappi charger has an ECO+ charging mode which could be used to limit the power drawn from the grid. It would therefore use any surplus solar PV power to power the charger provided that it meets the minimum requirement. In ECO+ mode though, if there is insufficient solar power the EV would not get fully charged. From my understanding ECO mode could be used as an alternative, and would fully charge the EV, though it may draw power from the grid to do so.

My comment in my previous post about charging via an energy diverter unit, is because it is possible that the diverter unit could be damaged if the load presented to it by the charger is not resistive. I can provide a more detailed explanation if you require one.

Does anyone have any experience of solar PV panels which replace the slates on a roof, rather than sitting as a panel on top of it?

The rising price of electricity has me re-considering the solar PV decision. Aesthetically these are prefereable, in a conservation area, to traditional panels but I wonder what the price and performance trade-off might be

https://www.gb-sol.co.uk/products/pvslates/default.htm

Mike