Helpful video reference. We use Artisan Electrics' UK video "DC vs AC Electricity Explained for Solar & Battery Owners" as the video reference here. Artisan Electrics is a Cambridge-based firm with one of the larger UK electrical YouTube channels. Their explanation covers the grid-tie context that American tutorials tend to miss, and they get the BS 7671 wiring colour conventions right throughout.
1. What DC electricity is
DC stands for direct current. Electrons flow continuously in one direction from negative to positive. A car battery, a phone charger output, and a solar panel all produce DC.
A single residential solar panel typically produces around 30–45 V DC at its maximum power point in full sun. Panels in a series string add their voltages together, so a string of ten panels can reach 350–450 V DC at the inverter input terminals. That is a genuinely dangerous voltage, which is why solar work is reserved for qualified electricians even for tasks that look straightforward.
Batteries also store and release DC. Whether it is the small 12 V battery under a car bonnet or a 48 V home storage unit, the internal chemistry works in DC.
2. What AC electricity is
AC stands for alternating current. The voltage repeatedly reverses direction, cycling from positive to negative and back again. In the UK that cycle happens 50 times per second, giving us 50 Hz at a nominal 230 V.
The National Grid transmits electricity as AC at very high voltages (up to 400 kV) to reduce losses over long distances, then step-down transformers bring it to 230 V for homes. Almost every mains appliance in a UK home runs on AC.
One important consequence for solar: because AC reverses direction 50 times a second, there is a zero-crossing point where the voltage briefly passes through zero. This means an AC arc naturally extinguishes at each zero-crossing. DC has no such mechanism, which is why DC faults and DC wiring require different protection devices to AC.
3. What a solar inverter does
The inverter is the central component of any grid-tied solar system. It takes the DC from your panels and converts it into 230 V / 50 Hz AC that your appliances and the grid can use.
Most modern inverters also include MPPT - maximum power point tracking. Solar panels have an optimal voltage and current at which they produce maximum power, and that point shifts constantly as light levels change. MPPT electronics continuously adjust the panel operating point to extract as much energy as possible.
There is one more function that matters for safety. A grid-tied inverter monitors the live grid signal. If the grid voltage or frequency goes outside tolerance - because of a power cut or a fault - the inverter shuts down within milliseconds. This is not a flaw; it is a legal requirement under G98 and G99 to protect engineers who may be working on the network. Without this protection, your inverter could feed voltage back into a line that an engineer believes is dead.
4. How a battery stores and releases electricity
Home batteries - GivEnergy, Tesla Powerwall, Solax HV, and similar - store energy as DC internally. A typical residential battery bank holds 5–15 kWh. Most systems use a 48 V or high-voltage DC internal architecture.
When the battery discharges to power your home, an inverter built into the battery unit converts the DC back to 230 V AC. On charge it does the reverse.
Energy capacity is measured in kilowatt-hours (kWh). A 10 kWh battery fully charged could - in theory - run a 1 kW load for ten hours. In practice, most batteries can only be discharged to around 80–90% of their rated capacity to preserve cycle life, so usable capacity is slightly lower than the headline figure.
5. AC coupling versus DC coupling
When you add a battery to a solar system, there are two ways to connect it. The choice has practical consequences for cost and efficiency.
AC-coupled means the battery connects after the solar inverter, on the AC side. Solar panels generate DC, the solar inverter converts it to AC, and the battery's own inverter/charger converts that AC back to DC to store it. When the battery discharges, its inverter converts DC back to AC again. There are two conversion steps between panel and battery. Each step has losses - typically 3–5% per conversion - so the round-trip efficiency of an AC-coupled system is a little lower than a DC-coupled one. The big advantage is flexibility: you can add an AC-coupled battery to almost any existing solar installation without replacing the solar inverter.
DC-coupled means the battery connects on the DC side of the system, before the main inverter. A single hybrid inverter handles both the solar panels and the battery. Solar energy goes straight into the battery in DC, with only one conversion step when it eventually discharges as AC. Round-trip efficiency is typically 1–3% better. The limitation is that DC coupling normally requires a hybrid inverter from the outset - retrofitting it to an existing string inverter installation is usually uneconomical.
In practice: if you already have solar panels and want to add a battery, AC coupling is usually the right choice and lower cost. If you are fitting a brand-new solar and battery system together, a hybrid inverter with DC coupling is worth pricing up.
6. What changes when there is no grid
A standard grid-tied inverter shuts down in a power cut because of the anti-islanding protection described above. Your solar panels and battery will not power your home during a blackout unless the system specifically supports islanding (also called off-grid mode or backup mode).
Some battery systems - the Tesla Powerwall and several GivEnergy models - can island a subset of circuits. This is more complex to install because the electrician has to wire a gateway or changeover switch to separate those circuits from the grid supply. It adds cost and requires additional DNO notification in some cases, but it is the only way to keep lights on during a grid outage.
When to call us
Richard is qualified for solar battery storage and EV charger work, covering Sandwich, Deal, Dover and east Kent generally. Whether you are adding a battery to an existing system or pricing up a new solar installation, he can assess whether your current setup is suitable, advise on AC or DC coupling, and carry out the notifiable installation work. He can also deal with DNO notifications via G98 for systems up to 3.68 kW per phase.
Thinking about solar battery storage in Kent?
Richard can assess your existing solar installation and advise on whether AC or DC coupling suits your system. Based in Sandwich, covering east Kent.
Contact Richard