Power-Roof® as a Service
There is some benefit in thinking about Power-Roof® as a Service (P-RaaS), and about how such a system might be integrated into the local electricity distribution network. This introduces valuable potential economies for power provision in the local area.
Balancing technology and control systems
The Power-Roof® system can generate as much power as a house needs for pretty well 24/7 in winter, and deliver a reasonable surplus in summer. This will require consideration of energy (electricity and heat) storage. The simple option is a co-located battery, but questions arise around its overall cost and safety. This factor largely rules out co-locating battery storage within the house, and a potential solution is to look at houses equipped with Power-Roof® being linked, via the LV mains, to a local-area stand-alone battery (it’s appreciated this requires multiple connections to the local distribution grid and the co-operation of the DNO).
Notes: power here means electricity and heat, both from solar and ambient sources. On the battery point – if a lithium-ion (or sodium-ion) battery happens to ignite due to some overload condition or damage, the fire tends to be impossible to extinguish. We think this represents a safety and insurance risk.
We might consider a largish battery for every 20–50 houses that can provide for their needs. We would also like to be in a position where we can take energy off the grid when there is too much generation, and feed it back when there are shortages. Basically, we need a system that can balance generation with demand, hold sufficient energy for up to two days of overnight use, and support a number of EV charging points and air conditioning during the day.
A localised energy system
In all cases the local energy network will need to sit within an area fed by a single local substation, and the objective is to ensure load is never greater than it would have been prior to installation – the aim being to eliminate network reinforcement, both locally and upstream in the MV and HV mains. It would need to be sized to effectively balance the LV network as new systems are added to it. A number of possibilities are shown above for new build and end-of-street configurations, with many others possible across a DNO’s LV area.
Note: an ultimate objective would be to reduce or eliminate gas-fired combined-cycle power plants, and so bring the cost of energy down towards near-nuclear base-load cost.
If we regard this local energy system (LES) as an electrical load-balancing system, it can be used in a number of ways, each of which must be kept in balance so that, as far as possible, the whole system is as close to neutral as possible. The main periods of concern are winter, when there is limited PV generation combined with windless days, and summer, when there is too much PV generation alongside plenty of wind.
Note: there is already a considerable body of research and experience in localised energy systems, and much of this isn’t new. But the opportunity presented by Power-Roof® and the urban-area generation it can deliver stands to be a major change for energy supply in urban areas.
Benefits, opportunities and requirements are:
- The system batteries will absorb any excess electrical energy once the prime objectives of the system are met.
- The system batteries will contribute energy to the house when the PV is not generating. Ideally this should be sufficient to maintain house ventilation and temperature 24/7 for two days.
- EV charging will be a load the system can cover – directly from the PV during the day, and indirectly from the batteries when the PV is not generating – predicated on expected travel patterns and planned input from the user. V2G may also be integrated.
- The LES may supplement local demand for neighbouring houses connected to the LV circuit but not themselves part of the LES.
- The LES will need to help absorb excess energy from the grid when there is excess generation, and may even need to find ways to dump excess electrical energy.
- The LES may need to export energy to the grid when the grid has a shortfall.
- The LES will need to avoid taking energy from, or sending energy to, the grid when requested not to by the National Grid (NG).
- The prime objective of the LES will be to avoid excess energy flows within the local LV grid in the area covered by a local substation – and, clearly, upstream too.
- It will be essential to maintain grid connectivity to ensure frequency synchrony with the grid.
- The balancing software will need to control both import and export to the LV network in real time, and balance this with the combined input and output of the storage system, alongside any other network-control factor required by the grid or DNO.
The key to a localised energy system is its control system
It’s clear the LES will need a control system that can match the excess output from multiple Power-Roof® installations with the energy absorbed by the batteries, while at the same time managing the requirements of items 3 through 9 above. It will also need knowledge of future weather conditions, so that additional energy can be stored as necessary, or allowance made for future flows, expected demand from individual homes, and overall network demand – or, when local generation is insufficient, so energy can be imported at the least cost. It will also need to be able to access actual National Grid flows, so that the risk of excess renewable generation overwhelming “spinning reserve” and endangering grid synchrony can be managed, helping the NG by absorbing such peaks. In terms of the LES, it will be a large energy user, able to choose its source and timing of energy input or supply. For individual houses, these will be normal users on an ESO’s network, even if for most of the time the only charge is the standing charge. For an ESO to be involved, there needs to be a commercial incentive.
All control must operate in real time, to prevent spikes and surges.
This points to an AI system constantly drawing data from monitors and sensors in the houses, from environmental sensors and the wider environment, and from the Met Office – and points to the development of both a local network controller and linked house controllers to manage flows. While there has been a fair amount of research and development in this area, we’re not aware of any system where all of these requirements are met. This is an area of R&D that needs covering, which ACTL is aware of, and which will be researched and developed as Power-Roof® is rolled out.