Roof mounted Solar Photovoltaic (PV) Panels are becoming very much part of the modern landscape as more and more households try to lower both their energy bills and their carbon footprint. Are solar panels alone enough to achieve the maximum savings? The problem is that solar panels generate most electricity during daylight hours and because many of us are out at work during the day, we tend to use more power in the evening.

As Solar PV Panels have no inbuilt storage capability, we may actually be using very little of the electricity we generate. Unless we have an agreement to sell our spare capacity to the National Grid that electricity may well be going to waste. Thankfully, although the solar panels have no storage facility, we can add an external storage capability in the form of solar batteries.

A typical 4kilowatt (kW) Solar PV Panel installation will probably cost around £7,000 and a 4kilowatt-hour (kWh) Battery will add around a further £5,000 to the total system cost, which adds up to a considerable upfront investment. A typical domestic solar battery storage system size is around 4kWh, although In the UK, the average household uses around 8-10 kWh of electricity every day, so battery installations are scalable to suit your usage. You can start off at 4kWh and add capacity to suit your usage at a later date, but as you increase the capacity you also increase the cost. These batteries can be added to an existing installation or installed along with your panels.

Battery size, or capacity, is the maximum amount of energy in kilowatt-hours (kWH) that a battery can store at a given time, but to get a true figure for usable energy, you need to look at the figure quoted for Depth of Discharge which is the maximum percentage of a battery’s capacity that is actually useable on a day to day basis. If a battery quotes a capacity of 4kW capacity, you will never be able to use that full amount, because draining a battery completely can be harmful to the battery itself. This is why the Depth of Discharge figure is quoted to help you understand what percentage of the battery’s full capacity is safely usable. Most batteries will achieve a 90-95% Depth of Discharge.

The size of battery you will require is going to depend on your usage pattern, how much energy you use and when you use it. Peak electricity hours tend to be in the morning, around 7am to 11am when people are getting ready for work and school, and in the evening, from 5pm to 9pm when they are returning and making evening meals. On average electricity usage is 36% higher on a winter's day than on an average summer day. If you are at home during the day, it would therefore make sense to use the electricity you are generating by doing the laundry, running the dish washer and other appliances rather than storing power in the battery. If your property is empty and the power usage is low during daylight hours, the converse applies. Allow your battery to store the energy your solar PV panels generate during daylight and leave your power usage till evening allowing you to use your stored electricity. If you use more power in the evening than your battery has stored and you need to use power from the National Grid, evening tariffs tend to be lower than at peak time.

There is one other major factor that will dramatically change your energy landscape and that is an electric vehicle (EV). Most electric vehicle drivers take advantage of special tariffs aimed specifically aimed at EV owners and these are much lower than the normal domestic tariffs on offer. It is also true to say that the battery capacity of an electric vehicle is huge in comparison to a domestic battery, typically ranging up to 100kWh. Depending on how you use your EV, it may be prudent to charge it up from your solar PV panels during the day, as this electricity would be free, but this would only be beneficial if you then use the EV and the charge in its battery. If you are on a low EV targeted tariff, it may also be cheaper to use that to charge up your batteries in the evening or overnight, then use the stored power during periods when a more expensive tariff applies.

Solar power at home and electric vehicles are both relatively new and developing technologies and like many other such technologies, they start off simple and get more sophisticated as they develop. EV batteries are already improving as their technologies evolve, with the range available in many EVs increasing and shorter charge times being available. At present, charging a 100kWh EV battery from solar batteries is only a one way exercise, but as technology advances it is recognised that in the not too distant future, it will be possible to retrieve power from an EV battery for use domestically. This would give access to a store of electricity which would be much larger than the average household’s daily consumption.

There are a number of different scenarios available with regard to how and when to use battery power or when to take power from the national grid as tariffs vary to reflect national usage patterns as well as those of individual households, with or without EV tariffs. Thankfully, there is technology available to help us make these choices.

Many households now have smart meters which tell us how much electricity we are using at any given time and the same smart technology will allow us to check online to see when we should be charging our batteries and when we should be using the stored energy. With so many alternative models of how to manage our batteries and our energy usage or storage it is perhaps no bad thing that we now have the option to use a battery management system which is able to make the best use of both our batteries and the tariff options available to us, helping to ensure that we get maximum benefit of what is after all, a substantial financial investment.

Installing solar panels does not normally require planning permission as it can probably be done under permitted development, but do a quick check with your local authority. If you live in a listed building or a conservation area, you will however, need to obtain permission from the local authority.

Solar batteries can be installed either inside your property or in an outhouse or garage. When making that decision, bear in mind that the inverters associated with the batteries have cooling fans which make a similar noise to that of a fridge or freezer and they will also take up space in the property.

As with all investments in the home it is wise to engage with an experienced, qualified installer before making that investment. An experienced installer will carry out a site survey and make recommendations based on that and what you are looking to achieve. Should you be considering using the Smart Export Guarantee (SEG) then your system would require to be installed by a Microgeneration Certification Scheme (MCS) accredited installer.

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