Your Battery Stores the Power, But the "Inverter" Makes It Useful

When customers first chat to Household Energy Solutions (HES), their main question is: how much battery storage do I need to avoid using expensive electricity during the day so I can slash energy costs by buying only 9p per kWh of cheap nighttime electricity?

The initial discussion often focuses on whether they need a 10kWh, 20kWh, or perhaps even a 40–50kWh battery system; however, HES's guidance on the right inverter is just as important because it critically controls how quickly electricity can enter and leave those batteries.

The simplest way to understand it is to imagine the battery as a water tank and the inverter as the pipe connected to it. A large tank may hold plenty of water, but if the pipe is too small, it will take longer to fill and cannot supply water fast enough to provide a decent shower, a pet peeve of mine. Your household energy system works in much the same way.

What does an inverter do?

Electricity supplied by the National Grid arrives at your home as alternating current (AC). Household batteries store electricity as direct current (DC). The inverter converts AC to DC when charging the batteries and then converts it back to AC when your home needs to use the stored power.

However, critically, the inverter also controls the rate at which your batteries charge overnight and how much stored electricity can be supplied to your home at any one time.

That makes getting the choice of inverter right at the start, whilst allowing for likely future changes and battery upgrades, crucial.

For a normal household installing a battery of around 20kWh, HES would recommend 3.68kW as a cost-effective starting point; it can nearly recharge a 20kWh battery from 10% during the normal five-hour cheap-rate night period.

But for larger households, the calculation can be very different. A home with electric vehicles, a hot tub, a sauna or high daytime electricity consumption like my own house will need a 40–50kWh battery array. To charge this size kit in the 5-hour window, you'll need a larger, more expensive 9.8kWh inverter.

An inverter that is too small means the batteries won't fully charge before the cheap tariff ends, but choosing one that is unnecessarily large could increase costs and complicate the approval process without delivering a worthwhile benefit, so getting HES experienced advice is important.

DNO paperwork and why it matters

Your local Distribution Network Operator, or DNO, is responsible for the electricity network serving your property. It needs to understand what equipment is being connected and whether the local network can safely accommodate it.

HES has found that simple 20 kWh installations that most medium-sized houses need require only a 3.68kW inverter, which can be installed under the simple G98 process. This allows the equipment to be installed first and the DNO notified afterwards, simplifying the process

However, larger inverters fall under G99 and require an application to the DNO before installation begins. The DNO may simply approve the proposed system but may request changes or impose an export limit on what you can send back to the grid, which is not a major issue as HES always recommends basing your battery need on just what your house needs to power itself during the day. However, the process involves technical specifications, equipment certificates, site details and electrical diagrams and is a nightmare unless you know what you're doing. That's exactly why the experts at HES do it for you under delegated authority.

Understandably, most homeowners don't want to become experts in grid-connection rules just to buy a battery.

HES makes the process simple

Household Energy Solutions will assess how much electricity your home uses, your overnight tariff period, the size of the battery under consideration and the amount of power your house will normally need at peak times.

We will then explain your options in plain English and help you choose an inverter that suits your home, rather than simply selling you the biggest or most expensive system available.

Most importantly, HES will manage the relevant DNO paperwork for you. Whether your installation requires a post-installation G98 notification or a pre-installation G99 application, we will gather the required information, prepare the documentation and work with the installer and DNO throughout the process.

The inverter may be the least understood part of a household battery installation, but it is one of the most important.

With HES, you will not have to work it out alone, as we guide you through the decision, handle the paperwork and help ensure your battery system is designed around the way your household actually uses electricity.

Back to the blog