Battery Storage

Batteries or Electrical Energy Storage Systems (EESS) are one of the best ways to increase the onsite consumption of your solar PV system; this has led to their increasing popularity in domestic installations over recent years. They are especially effective for households with a solar array who are not at home during peak sunlight hours (10 am-4 pm) as they can store the free energy being produced by their solar PV system for use when they arrive home after work.

The typical battery lifespan is between 5 and 15 years with warranties to match. This means you are likely to need to replace the battery during the lifespan of your solar panels which are typically warrantied for 20-30 years. This does increase the total, lifetime, cost of your system however, battery prices are expected to drop over the next 10 years as they become a more established technology.

At present, the cost of a storage system in the UK ranges between £1,200 and £6,000 depending on their capacity, battery chemistry, warranty and smart features. The high upfront cost of energy storage makes it more important to find the right storage solution for your situation. We will do our best to explain the key considerations so that you can make an informed decision.

Although a solar battery storage system is not inexpensive, the investment can pay itself back quickly if implemented and set up correctly. In addition, battery storage is the only possible way to become 100% energy-independent and self-reliant.

An overview

• Increase on-site use of solar generation – A correctly sized storage system can increase your on-site use of solar generation from 15-25% to 65-80%.

  • This is great as each kWh of free solar energy you use will save you around 28p compared to earning you 15p on the better SEG tariff rates.

• Emergency power supply in the event of a power cut.

  • A lot of batteries now provide either partial or whole-house backup providing you with an extra bit of comfort and security.

• The ability to buy cheap electricity off-peak and store it for use during peak times.

  • You don't just have to store excess solar energy in your battery. You can take advantage of the cheap electricity prices at night to charge your battery for use when electricity is more expensive. This is especially beneficial over winter when you have minimal excess solar energy to store.

• Potential to access future opportunities including the export and sale of electricity at peak charge times, and the provision of grid balancing services.

  • This is the next step when it comes to battery storage. Energy tariffs, like Octopus Agile, allow you to hand over control of your battery to be used to balance grid loads and provide you with great energy prices. (This is currently available just for compatible batteries.

The Key Benefits

There are 3 types of batteries

Batteries connected via hybrid inverter

Continue reading for the benefits and drawbacks of each type.

All-in-one battery

AC coupled battery

Hybrid Connected Batteries

This storage system is installed simultaneously with a solar PV array; it’s the most cost-effective and, therefore, the most popular way to add a battery to your solar PV system.

A hybrid inverter and battery allow the DC electricity generated by the solar panels to either be converted to AC for immediate use or sent directly as DC electricity to the battery, saving energy typically wasted in the conversion. This also allows for more system 'oversizing' (when your PV array has a higher output than your inverter) as the additional can be stored straight into the battery.

If you are looking for a new Solar PV and battery system, in most situations, your best choice is a hybrid one. It is cost-effective and will provide you with all the benefits that energy storage provides. However, if you are benefiting from one of the old Feed-in-Tariffs (FiT) or if you require high peak output, other storage solutions would be a much better fit.

How they work

Summary

Diagram of hybrid inverter system with a single string consisting of 2 panels.

AC - Coupled Battery

These storage systems consist of a separate charging unit and a battery. It's the easiest way to add a battery retrospectively to a system.

How they work

Summary

Since these batteries don't connect directly to existing solar PV systems they can be placed separately, making them great when retrofitting batteries. Another benefit of being a separate system is that they don’t affect meter readings on old FiT (Feed-in-Tariff) systems!

These systems are more modular, providing greater design flexibility. The additional charge/inverter unit means that your battery and solar can both be operating at maximum discharge, which is great for houses with high peak usage rates.

However, the need for an additional charge/inverter unit makes them less compact, more expensive and less aesthetically pleasing. Additionally, these systems suffer from greater losses by not having a direct solar battery connection. This is due to DC power from your solar being turned to AC and then back to DC before it can be stored in your battery.

AC Coupled Systems are great for retrofitting batteries or when you have a legacy Feed-in-Tariff system. They are a great way to ensure a higher peak output from your green technologies (solar and battery combined) and are necessary if you want to go down the micro-inverter route.

Hybrid system:

1 x 3.6kW inverter - max output = 3.6kW of AC electricity

AC Coupled System:

2 x 3.6kW inverter - max output = 7.2 kW of AC electricity

All-in-One Systems

These units combine the separate charge unit and a battery into a single unit. They have the same benefits and drawbacks as AC-coupled battery systems but are presented in a much simpler and aesthetically pleasing package. The Tesla Powerwall 2 and the new GivEnergy All-in-one are the most notable options.

There are now systems that take this to the next level and include a PV inverter. However, these are more similar to the hybrid inverter and battery setup. The Tesla Powerwall 3 is an example of this.