Storage

Storage systems have fallen in price recently, and now include management systems which can provide a number of benefits. You can store excess power from your renewable system, buy cheap electricity at night and store it for use during the day and provide back-up supplies for use in a power cut.

This is possible because of the introduction of smart meters which enable two-way metering of electricity (import and export) and time-of-use tariffs like Economy 7, whereby customers pay different rates for electricity purchased at different times of the day.

Storage systems fall into two categories: thermal stores and batteries.

Thermal stores

Thermal stores are highly insulated tanks that can store heat as hot water for several hours. They vary in size from around 120 litres up to very large stores of 500 litres or more and can be used with solar, wind, biomass and hydro renewable systems.

According to the Energy Saving Trust, the cost of a 500 litre thermal store is around £2,500, and installation costs can be up to £450.

Batteries

Electricity batteries can also help you make the most of electricity generated from solar, wind or hydro systems. For example, your solar PV system will generate electricity during the day when you are out at work, which can be stored in your electricity battery to use in the evening.

Or, your business can reduce energy costs by charging the battery when energy is cheap – either at night via the grid when tariffs are low and/or during the day with excess solar – and ‘shifting’ this power to periods when energy is expensive ie during the day and peak periods. Operating the battery this way will typically flatten out your company’s demand for energy from the grid

The cost of electricity batteries currently ranges from £4,000 to £6,000 for a fully integrated 4kWh system, but this is likely to fall in the future.

It’s important to consider if using a storage system will be cost effective for your installation. Good quality systems are expensive and will need replacing every five to ten years depending on how much they are used. In addition, batteries are not 100% efficient, so you will not get all of the energy out that you put in.

Using your electric vehicle to store energy

There are plans to make home electric vehicle charging two-way, a facility which is already widely used in Japan. By using the batteries inside electric cars as storage for the national grid, drivers could charge up when demand is low and power is cheap, and sell energy back to the grid during peak hours when it’s needed most.

Commuters could drive to work in the morning, plug in to charge their car battery while working, then draw power from their cars to save on their electricity bills in the evening. Later, they would use a timer to charge it back up again in the early hours when the price of electricity drops. In this way, a car’s battery could supplement the grid by providing additional energy for home appliances.

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