Can a Battery Help Me Get the Most From My Solar Panel System?
Updated October 26, 2023
By Morgan Pierce
You and your family have made the big decision to go solar.
Now you want to be sure you’re going to get maximum efficiency and cost-savings from your investment. You’ve heard other homeowners talking about “batteries” in connection with their own solar panel system, and you’ve got lots of questions.
Our Irish Solar Energy Advisors have heard a lot of those questions, so we thought it would be helpful to answer the most frequently asked ones here. That way, when you start looking for a company to install a Solar PV system, you can be prepared to follow up with any questions specific to your personal situation.
Does my solar panel system need a battery?
If you’ve got this far, you already know the basics of how Solar PV works. Panels installed on your roof generate electricity during daylight hours – most of that when the sun is shining, but even on some cloudy days.
Irish government guidelines make it possible for anyone who generates electricity – they call us “microgenerators” – to sell any excess they don’t need to the National Grid through their energy provider.
That’s great for consumers, but there are times a system’s ability to generate electricity doesn’t match up with a homeowner’s need. Even with more of us working from home, electricity demand still goes up at night when families turn on lights and switch on domestic appliances like washers, dryers and televisions.
That’s where a battery comes in – allowing any surplus electricity generated by solar panels during the day to be stored for later use, rather than sold to the grid. Given the difference in price between what energy suppliers charge for electricity, and the amount they are willing to pay for what we microgenerators sell them, you can save money by relying as much as possible on electricity you’ve generated yourself.
Does having a battery attached to my solar panel system mean I’ll be able to use it to charge my electric car at home?
With the growth in numbers of EVs on the road, this is something we get asked a lot. The simple answer, unfortunately, is “no”.
An EV charger requires more electricity than a battery can discharge at any given time, so charging your EV will require electricity both from the solar panels and battery system, and the grid.
We’ve already got solar panels. Can a battery be installed to an existing solar panel installation?
Yes, it can be a pretty straightforward matter to retrofit a battery to an existing system, provided you have a hybrid inverter – an inverter capable of communicating with a battery.
Battery size will depend on the generating capacity of the system in place, and how much storage capacity is desired. Some manufacturers (Huawei, for instance) allow for the possibility of as many as six 5kWh batteries being installed “in line” for a total of 30 kWh of electricity storage. One of our Solar Energy Advisors will be able to liaise with you about what your system may require.
If you don’t have a hybrid inverter, installing a hybrid inverter while adding a battery is a simple swap of your existing string inverter, which probably only has a 5-year warranty anyway.
How much does it cost to add a battery to my solar panel installation?
Adding a battery to your solar panel system adds about €3,500 to the initial purchase price. That said, adding a battery will save the average homeowner some €700 a year in electricity costs – doubling the amount of savings from a system without a battery.
Something else to keep in mind is that the 0% VAT exemption only applies to the initial solar panel system installed, so deciding to postpone the battery purchase will run approximately €1,500 more, if you chose to add a battery at a later date.
What kind of battery is it?
Most batteries used for solar panels are lithium-ion (like those used in consumer electronics). They have a high energy density (kWh/kg), so they can store more electricity for their size, and can discharge a larger amount of power at any one time. Lithium-ion batteries are more efficient than lead-acid batteries, and easier to maintain. At SolarSmart, we use batteries made by Huawei, PureDrive, Soluna, SoFar and Dyness.
Do those types of batteries pose a fire risk?
There will always be doomsayers spreading those “My uncle’s best friend’s neighbour said….” type stories. Studies show, however, that while the threat of energy storage systems causing or contributing to building fires is real, they are incredibly rare.
If a battery is going to catch fire, the most likely cause is something called “thermal runaway”. This happens when a battery’s temperature increases rapidly and to such an extent that it eventually leads to cell short-circuiting or disintegration that can spark a fire.
If battery installers follow the manufacturer’s manual and adhere to local fire codes and standards, the chance of a fire starting is near zero.
One of the key benefits of the Huawei Luna2000 battery that SolarSmart uses is its AI-powered internal cell short circuit diagnosis to avoid fire hazards, cell-level temperature control to detect overheating, and cutting-edge technology to ensure rapid shutdown for safer installation and maintenance.
How big are they? Where are they installed? Are they noisy?
5 kWh batteries are the most commonly used type of battery for residential solar energy storage systems. The term “5 kWh” refers to the amount of energy that a battery can store, and it stands for 5 kilowatt-hours. The battery can supply a continuous power output of 5 kilowatts for one hour – or a much smaller amount for a longer period of time, for instance 500 watts for 10 hours.
The popular Dyness DL5.0C weighs in at 54kg, with dimensions of 558 mm X 545mm X 150mm.
Our premium battery, the Huawei Luna2000 (5kWh), measures 670 mm x 360 mm x 150 mm – that’s about the same as a large bathroom cabinet. The sleek modern design of the Huawei battery has even garnered an international design award. It weighs 50kg and can be mounted on either the floor or an interior wall.
While many lithium-ion batteries are cooled by an internal fan, this Huawei battery uses an innovative natural convection cooling system, which means that it runs almost silently.
How long do they last? Do they become less effective over time? What is the life-span of the battery?
All batteries lose capacity over time, including all of those used for storing solar energy.
Most batteries are warrantied for a certain number of cycles. A cycle is defined as a charge and discharge of the battery. Dyness is warrantied for 6,000 cycles, while the slightly more expensive PureDrive 5kWh battery offers a warranty for 10,000 cycles (worth the extra in our opinion).
The Huawei LUNA2000 comes with a 10-year manufacturer’s warranty that guarantees that the battery will still have at least 60% of its original capacity after 10 years of use. Huawei’s research suggests the battery has a working life-span of 20 years.
How long does it take to the battery to charge? What happens when the battery charge wears down?
The time it takes to charge a 5 kWh battery depends on several factors, the battery’s current charge level, the capacity of the solar panel array from which it is being charged, and the domestic load.
During periods of peak sunshine – long summer days – rooftop solar panels might recharge a 5 kWh battery in just a few hours.
Solar panel systems are intended to supply your home’s current energy needs first – and only send excess electricity to the battery. That means that during the shorter, darker days from October to May, your system might use more of the electricity the panels have generated on things like lights and heating. It would then have less excess electricity left, so would take much longer to completely recharge the battery.
What happens to batteries that have reached the end of their lifespan?
In Ireland, the Waste Electrical and Electronic Equipment scheme (WEEE) is responsible for collecting and recycling waste batteries, including those used for storing solar energy. Consumers can bring the batteries to any local authority waste collection site, or to one of WEEE’s regular electronic waste collection days.
An EU-wide sustainability target requires that 15% of critical raw materials – things like magnesium and cobalt – be sourced from recycled material by 2030. By using WEEE’s resources to recycle your old battery, you can contribute to meeting that target.
Isn’t it a waste of money to install a battery for my solar panel system if the system won’t be able to feed sufficient energy to the battery to charge it fully, at the very times of year I’m most likely to need it?
One of the hidden benefits of adding a battery to your solar panel system is that – if you do need to buy any electricity from the grid – the battery enables you to take advantage of the cheapest available rates. You can charge your battery on the cheapest night rates, then use the electricity stored to get you through the morning’s household chores, then recharge the battery with the energy generated from your solar panels during the afternoon. Our support team will streamline the process to meet your family’s unique energy needs, and help you make the greatest savings.
How long will I pay be able to power my home off the battery? Can my battery supply my home with power during an outage?
There are too many variables – the size of the house, the size of your solar system, number and house load, time of year, etc. – to say with certainty how long the power in a 5 kWh battery will last for your home. Industry sources suggest, though, that a fully charged 5 kWh battery will power the average home for 10-12 hours.
During a grid outage, you can access the electricity stored in your battery through the socket the SolarSmart team installs near your battery. This way, you can plug in specific appliances like your fridge or WIFI router, while the grid is down.
Unfortunately, a battery won’t power your entire home because the battery/inverter can only discharge a certain amount of energy at a time, and it is likely the house load requires more than today’s domestic inverters can handle.
So, is battery storage right for me?
If your electricity use is low, your budget is tight, or you have an EV parked at home during the day, adding a battery to your solar panel installation might not be something our Solar Energy Advisors would recommend.
On the other hand, those with higher demand or who want to maximise their household’s use of “self-generated” power will see real benefits from a battery.
While a battery will add significantly to your home’s energy self-sufficiency, the cumulative impact of your individual energy independence also reduces overall carbon emissions and will help Ireland meet its net zero climate change commitments.
Investing in Solar PV systems can bring many benefits, including reduced energy bills, increased energy independence, and a reduced carbon footprint. If you are interested in installing a solar panel system, it is worth exploring the different grant options available and seeking professional advice from one of our solar energy advisors.
Feel free to contact us for more information, we’re here to help.