Having invested in a roof-top solar PV system it's important to make sure you get the best from your system. This guide provides some tips for using the system as installed, and some additional options you can add to get more benefit from the free energy you are generating.
Maintenance
Solar Panels (PV) require minimum maintenance and should be productive for more than 25 years. As panels age there is a slight degradation in output each year, but not sufficient to worry about replacing panels
However, periodically cleaning the panels, to remove the residue from bird droppings and dirt from the rain will ensure maximum output. Don't attempt to clean rooftop panels yourselfyou should be able to find local specialist contractors online
Shading
If trees and shrubs around your property have grown up since you first had PV installed they may now be causing shading, reducing the amount of electricity being produced. Dependent on the configuration of your panels, a small amount of shading can have a big impact. Trim back overhanging branches to ensure your panels aren't shaded throughout the day (If they are not on your property, get permission first!)
Use the power
Make sure that you make good use of the free electricity generated during daylight hours, especially during the summer months, and ensure your home is as energy-efficient as possible
When the sun is shining, you should change your routines and plan ahead. For example, using your washing machine or dishwasher during the day rather than in the evening. Use a slow cooker for your evening meal rather than the electric hob or gas stove
For high-wattage appliances, use the in-built delay programmers or fit timer switches so that you can let the washing machine finish before starting the dishwasher.
Energy Storage
Technology to store any excess electricity you produce is becoming more affordable There are two routes to consider:
convert it to heat to boost your hot water system; or store your power as electricity in a battery.
A home battery storage system allows you to store electricity for use at a later time. Houses that have renewable energy, such as solar PV panels, can store excess generation in a battery, and then rather than export it to the grid, use that stored power to reduce consumption of higher priced grid electricity
The effectiveness of a battery used in this way is determined by how quickly it can charge and discharge, measured in kilowatts (kW), and its overall energy storage capacity, in kilowatt-hours (kWh).
Convert excess electricity to heat to boost your hot water system
Put the power into heat with a solar diverter
If you have a hot water cylinder with an immersion heater, then a solar diverter may be able to reduce your hot water costs and increase consumption of your solar generation It does this by diverting excess generation into your hot water cylinder's immersion heater, rather than exporting it to the grid. These are relatively low cost devices, compared to batteries, and are easy to fit.
To make sure this could save you money, check to make sure the unit cost of heating your hot water with your existing heating system is higher than the unit rate you sell your solar electricity for, otherwise a solar diverter won't save you any money.
Thermal stores
Heat batteries provide hot water just like a hot water cylinder to use for hot water at a later time or as a buffer for a heat pump
Heat batteries can take inputs from several sources, e.g. solar PV and a heat pump. They use phase change materials that change from solid to liquid and back again, as heating is needed. The technology means that the heat can be stored for a long time, and they don't lose heat lilke a hot water tank.
They are compact so can fit alongside a washing machine or under the stairs, and there is no need for a hot water tank.
Thermal heat stores cost about the same as a new gas boiler
Electric batteries
Battery storage is still a relatively new technology for use in homes It is a market that is changing rapidly, with new products regularly being launched. As a result, batteries are still a costly option and whether they are right for you depends on what you are trying to achieve:
If you are looking for a return on your investment, with a quick payback, then batteries probably aren't right for you.
If you have a solar PV system and are at home for most of the day, then you can make sure that you use the electricity generated by your panels immediately, by running the washing machine, dishwasher, or high consumption appliances in the middle of the day, at times of peak generation. Therefore, you might not necessarily use much of the stored electricity that a battery can discharge, and in this case, a battery system may not be worthwhile
If you and your family are out o the house during the day and most of your consumption happens at times when the solar PV isn't generating, e.g. in the evening, then a battery may work for you.
If you want to increase the amount of renewable energy you consume, or if you want to get 'off grid', or if you want a technology that can help stabilise the electricity grid whilst reducing peak time carbon emissions, then a battery is worth investigating.
Before making a purchase, it's important to have a thorough understanding of your household's consumption patterns across a whole year You will need to know how much electricity you use and when. Additionally, you need to know what your solar PV system generates in a year to be able to assess the appropriate battery system you need. Batteries for homes come in different sizes from under 3kW up to 20kW and the cost increases with size, so it is important to specify the right size.
Common types of batteries
Lithium-ion batteries are the most common type of domestic battery. Compared to lead-acid batteries, they are lighter, have a higher energy density, a longer lifetime and can charge and discharge at higher rates. Lithium batteries are more expensive than lead-acid, which is why lead-acid batteries are more common in off-grid installations.
As with other renewable technologies there are a lot of complex terms used. The key concepts to understand are:
Usable capacity
This is how much energy can be stored in the battery, measured in kWh This is typically less than the total capacity, in order to maximise the battery’s life, e.g. an 8kWh battery might have a usable capacity of 6.5kWh.
Charge and discharge rate
This is the maximum power of the battery, in kW You will have to make sure the power rating is high enough for your requirements, i.e. if a battery can charge at 1.5kW but you have 4kW of solar PV, then some electricity will still be exported.
Battery cycles
A cycle is one full charge and discharge, and most batteries will only go through partial cycles each day Lithium-ion batteries are typically warranted for up to 10,000 cycles but lead-acid tend to be warranted for significantly fewer. After this number of cycles is reached, the usable capacity of the battery might start to reduce. Note that this is different to the product warranty which is typically around ten years for lithium-ion batteries
Direct Current/DC or Alternating Current/AC coupled
Batteries need an inverter to charge and discharge. Some batteries can be DC coupled where they share an inverter with a solar installation, while others have their own inverter connected to the main electricity circuits in your house. DC coupled inverters can be cheaper and are 1-3% more efficient than AC coupled inverters, but charging and discharging can be limited by the operation of the solar PV and faults with the solar PV or battery can cause both to stop working AC coupled inverters work independently of the solar generation, so the combined power of both can be used and faults in the PV won't affect the battery.
Back-up power
Some batteries can provide a backup in the event of a power cut. This often comes at an extra cost and depending on the discharge power of the battery, it may not be able to supply all appliances in the house, but will be sufficient for lighting
Prices
Prices for lithium-ion batteries are dropping all the time and, currently, start from under £5,000, up to £14,000 fully fitted, depending on the storage capacity and model of battery It is cheaper to install a battery at the same time as a solar PV system which is subject to a 5% VAT rate. If you receive the feed-in tariff for your solar PV generation, this should be unaffected by installing a battery.
Smart grid tariffs
Some companies are creating 'Virtual Power Plants' (VPPs) which use the combined power of many simultaneously controlled domestic batteries to help keep the grid stable and reduce the carbon emissions from peak-time electricity In return there can be significant savings, in some specific cases up to £1,000 per year on your electricity bills. You would need to buy a battery and in some cases solar PV, before becoming eligible for these tariffs
To be eligible for tariffs, the battery and solar would need to be installed by an MCS registered installer.
Store your power as electricity in a battery
EV cars as batteries
As electric vehicles become more popular, many owners are realising that they have a large battery parked outside their house Solar PV can be used to charge electric vehicles, however you need to make sure that the charger will use the excess generation, rather than total generation, so that you don’t import any electricity from the grid.
If you have off-road parking and charging, with a EV battery parked outside, using this as a storage device for your home is also now feasible. Vehicle to Grid compatible cars and chargers are now available and worthwhile investigating if you are considering an electric car
Some electric vehicles have the capability to power your home or export to the grid using vehicle to grid (V2G) technology. Currently some Nissan, Mitsubishi and Toyota models can do this, with many more manufacturers developing V2G compatible cars. A V2G compatible charger and a V2G tariff are also required. V2G tariffs are being developed which offer discounts on electricity bills or electric vehicle leases and will become more widely available over the coming years
