Solar batteries & storage
A huge step towards energy independence: solar batteries let you store up power for when you really need it and support the grid at peak times for a profit.
Adding battery storage minimises your reliance on the grid, reduces the money you put in your energy supplier’s pocket and allows you to help the grid become more efficient. But what should you look out for when choosing a system? Below we list the questions you need to ask before making a decision.
The 6 ‘Watts?’ of Solar Battery Storage
1. What’s the ‘useable’ capacity?
Capacity is the amount of energy in kWh (units) that a battery can store. Batteries should never be drained completely. However, some are misleadingly sold quoting ‘total’ capacity. Check what’s being stated. ‘Useable capacity’ is the figure you need to know. Though Tesla Powerwall is 14kWh, it’s sold as 13.5kWh (its useable capacity). It will never fully discharge to prevent damage to the battery cells.
2. What are ‘cycles’?
A cycle is one complete discharge and one complete charge. In reality it doesn’t happen like that. A solar battery may only discharge 25%, then recharge 25%. This would be 1/4 of a cycle. So you need to know how many cycles a solar battery is warrantied for. Only then can you work out how many kWhs (units of electric) your solar battery will deliver over its warrantied lifetime.
3. What capacity do I need?
Like Solar PV, customer desires affect the answer. Planning an EV? A larger battery can keep the house running and charge your EV overnight. Grid trading: larger battery capacity means more charging on a cheap rate and more to sell back to the grid at peak rate. For high power devices larger batteries have higher output and will not be damaged by higher demand. Naked Solar can model everything to help you decide by using PV Sol software.
4. What’s Charge/Discharge power?
Some battery storage systems only deliver 800w (watts) of power. No good if you want a cup of tea (your kettle needs 2000 watts). Likewise, if you’re generating 4kW but the solar battery can only take on 3kW then 1kW will be heading to the grid, wasting your precious free energy.
So, it’s essential that you check the power output before you buy, otherwise you may find yourself drawing a lot of energy from the grid even though you have energy in your solar battery.
5. What’s the price per kWh?
As you’ll see from the table below, there are many solar storage solutions at varying prices. Checking the price/kWh of storage capacity is a fair and accurate way to compare different systems. What’s the right number of kWh for your property? That depends on you. The more kWhs you have, the more you can reduce your bills and take advantage of ‘Time of Use’ tariffs that are starting to emerge on the energy supply market. These allow charging on a cheap rate and selling back to the grid at higher rate periods. The greater the storage, the more you can sell.
6. What about power cuts?
Most systems are designed just for storage. However, some offer backup capability to provide power when there’s a powercut. Two things to consider:
- To prevent damage to your battery or appliances some of your circuits may need to be removed from the backed up circuits.
- You may want to consider a larger storage capacity to keep some power in reserve.
If backup is essential, let us know and we’ll design some bespoke solutions for you to choose from.
At Naked Solar, we ask these questions for our customers every day.
Compare Solar Batteries
Download this PDF to compare some of the battery systems available on the market. This information is for guidance only, it should be very close, so check with Naked Solar or the manufacturer for latest info before making your final decision.
AC Versus DC Coupling: Pros and Cons
When you buy a solar battery, you may come across the ‘AC coupling’ or ‘DC coupling’ question. Below we show you how each setup works and list the advantages and disadvantages.
AC Coupled
Requires separate inverters for your solar battery and panels.
Pros
- More juice: you get the combined power from both the solar battery and solar inverters at the same time.
- Flexible location. As solar batteries are best at room temperature and inverters are best at cooler temperatures, it’s easier to optimise both because they don’t need to be near each other
- Battery faults won’t affect your Solar PV & vice versa
- Works with any Solar PV system
Cons
- 2-7% more power losses than DC
- More expensive as requires more than one inverter
- The combined power of the Solar & Battery inverters may exceed your grid connections DNO power limit.
DC Coupled
Solar batteries and panels share the same inverter.
Pros
- More efficient power transfer than AC by up to 7%
- May be cheaper install as solar battery & panels share the same inverter
- Only one inverter, so more likely to be able to make the most of your DNO (Distribution Network Operator) power limit.
Cons
- Limited access to power.
The solar battery must be installed near the inverter. Batteries prefer temperatures around 20°C while inverters need to be in the cool, so there may be a trade off in efficiency.
A Deeper Dive Into Solar Battery Storage
TESLA POWERWALL 3
The Powerwall has transformed Solar for good. Tesla Powerwall 3 brings groundbreaking advancements that set a new benchmark for Solar Battery Storage systems, including unrivalled power output and exceptional flexibility to meet the needs of any Solar project.
SIGENERGY SIGENSTOR
SigenStor is an all-in-one smart energy solution designed to supercharge your home’s solar system. This single, sleek unit combines everything you need: a solar inverter, EV DC charger, battery pack, power conversion system, and energy management system.
Powered by AI, the SigenStor is a highly integrated and intelligent system that optimizes your home’s energy usage, making it an excellent choice for any homeowner seeking to upgrade their solar power.
GIVENERGY ALL IN ONE
GivEnergy is a British Owned Battery Storage Manufacturer with manufacturing/Research and Development facilities in the UK, Ireland, Australia and Shenzhen China (Shenzhen Givenergy Technology Co., Ltd). Their “All In One” Home Battery can power even the highest-demand households with maximum efficiency and minimum energy costs, making them a Tesla Powerwall alternative UK residents love.
How Solar Batteries Help You Night & Day
People often ask ‘Can solar panels work at night?’ The short answer is no. But with a solar battery, in effect they do. During the day, when solar panels are generating more power than your property is using, excess power is diverted to the solar battery for use later. When the sun goes down, or if you’re using more energy than your panels are providing, the solar battery will kick in to give you power and prevent drawing from the grid.
