Renewable Energy

Dr Duncan MacLennan

Principal Engineer

Max Fordham LLP

Clean Renewable Energy

The Committee on Climate Change and National Grid ESO expect that renewable power generators, including offshore and onshore wind farms, hydropower and large-scale photovoltaic installations will be needed to provide a significant proportion of our future electricity supply. These renewables would be supported by other low carbon technologies including Nuclear Power Stations and Carbon Capture and Storage (CCS) Schemes. The CCS schemes are expected to capture emissions from biomass, “Bio Energy Carbon Capture and Storage” (BECCS) or from the continued combustion of natural gas or the reformation of natural gas to produce hydrogen. It is expected that these national scale initiatives will be implemented between now and 2050.

The rapid deployment of renewable energy generation over the last decade, in particular of wind power, along with the closure of older coal power stations has led to the rapid decarbonisation of the UK’s electrical grid. This is expected to continue but with a move towards electrification and away from natural gas for heating and the increased use of electric vehicles a significant increase in generating capacity is required.

The Role of Renewable Energy in NZC Buildings

Renewable energy generation has a big role to play in the delivery of net zero carbon buildings. Integrating renewables into existing and new buildings allows them to meet a proportion of their own energy needs and minimise their carbon emissions beyond that which can be achieved by efficiency measures alone.

In addition to the benefit to the building emissions that on-site zero carbon electricity generated brings, widespread adoption of building integrated renewables could help reduce demand on centralised generating infrastructure. At least 3 GW of wind and 1.4 GW of solar need to be built every year from now until 2050 if the UK is to reach its net zero goals. Building integrated renewables could contribute partly towards this target.

It makes sense to maximise energy efficiency before incorporating renewable energy generation in a building and for most projects solar PV panels will be the most appropriate form of renewable technology available. Solar PV panels convert natural light, both indirect and direct sunlight into electrical energy. The electricity generated is direct current (DC), but usually this is converted into alternating current (AC) via an inverter for use in the building’s electrical network. Many new build projects now incorporate significant PV installations, often covering more than 70% of their roofs. Rural projects might make use of other generation technologies such as wind turbines, or water turbines dependent on their site and availability of local natural resources.

Simple Payback of PV, Capital and Carbon

The cost of PV panels has reduced significantly over the last 10 years as a result of widespread adoption and PV prices are typically around £200/m² and £1,000-£1,500/kWp when installed in larger arrays. It is common for PVs to repay their cost of installation through energy savings within around 10 years.

A 1kWp (around 7m²) PV array in the UK can generate around 900 kWh of electricity, depending on its location. The zero carbon electricity generated displaces (or saves) around 180 kgCO₂ of emissions which would have arisen from the national electricity grid. The reported embodied carbon of a 1kW PV array can vary widely, however it is typically in the range of between 1,000-2,000kgCO₂, and so it takes around 6-12 years for the PV panels to offset the carbon emissions arising from their own manufacture before they start reducing the lifetime emissions of a building.

Biomass Heating

Current regulations assign a very low CO₂ emission rate to the burning of biomass, therefore the use of biomass to heat our buildings has commonly been viewed as a renewable low carbon heating source. However, in the short-term burning biomass results in a rapid release of CO₂
and other combustion by-products such as NOx and particulate emissions, which contribute to climate change and local air pollution. The world needs to end carbon emissions and start work to reduce atmospheric CO₂ levels as soon as possible, by 2030 if we are to avoid the worst effects of climate change. Burning biomass might be carbon neutral over a certain time period, e.g. 100years, but it is unlikely to be climate change neutral without significant advances in carbon capture and storage technology. Bio-energy carbon capture and storage (BECSS) is likely to be a technology which is only ever suitable for a small number of grid connected power stations, not individual buildings.

There may be a place for limited use of biomass in remote or off grid locations where local forestry can provide small sustainable stocks of biomass with forest growth or planting in excess of the timber consumed, however in the majority of cases and against the short timescales of the climate emergency it may be best that an alternative low carbon approach to heating is considered for use in buildings. Firstly, by reducing heating demand and secondly utilising electricity efficiently through heat pump technology.

Smart Energy Management, Demandside Response and Energy Storage

High electricity consumption at peak times, typically between 4pm-7pm, when domestic usage coincides with industrial use can put strain on the national grid and result in an increase in the carbon intensity of the electricity produced as additional generation from fossil fuel power stations becomes necessary. Peak time electrical energy is the most expensive on the wholesale electrical market and also the most polluting.
Buildings which can modify their consumption of electricity in response to changes in the availability of power in the national electrical grid can further reduce their carbon emissions and generate energy cost savings or additional income.
For industrial or large electrical energy consumers, working with a demand side response provider/aggregator can enable a building’s generating plant, energy storage installations or large M&E plant loads to be controlled to provide:

Balancing services for the national grid, i.e. turning major loads off or exporting power to the grid on to assist in balancing grid supply and demand.
Capacity market access, i.e. providing electricity to the grid during times of low generation capacity (perhaps the wind is not blowing)
Peak rate avoidance i.e. shifting building loads to make use of lower cost off peak grid electricity

On a domestic scale, the roll out of smart meters is enabling energy suppliers to offer agile tariffs which offer variable priced electricity depending on the availability and cost of energy at any given time. Domestic consumers can benefit from reduced electricity prices overnight, for example, or during times of oversupply of wind power during stormy weather.
Industrial and domestic energy storage either in the form of heat or electrical batteries can help flatten peaks of consumption or increase a building’s self-sufficiency by increasing its utilisation of its own renewable energy generated and reducing exported energy.
National Grid ESO’s new API tool offers predictions of grid carbon intensity up to 96 hours in advance, the aim of which is to provide smart device developers a means through which they can use to control their equipment to align energy consumption with times of lowest carbon emissions. For example, all new EV chargers now need to be smart and are controlled via apps. If you need to charge your EV once a week, then the use of this tool would allow the app to pick the optimum time at which to charge the vehicle to minimise either carbon emissions, costs or both. Similar functionality could be built into domestic appliances such as washing machines, dishwashers, fridges and freezers further reducing carbon emissions in use.