This webinar was arranged by the IET's Electrician EngTech programme in association with Wiring Matters. Electrician EngTech helps electricians gain recognition of their professional competence.
Your questions answered
Can our present electrical supply infrastructure deal with Electric Car charging even taking into account what renewables give?
In a few areas Yes. In most areas, the DNO network will need to be upgraded and/or renewed for the additional loading.
What is the full meaning of MPPT?
Midpoint power tracking is the relationship between the speed of the wind turbine and the power coefficient. The aim of the tracking is to ensure the maximum power can be generated from the suns rays or from the wind by controlling the rotor angle/position/tilt of the wind turbine, or the position and orientation of the PV panel.
Why should we use the DC/DC inverter for PV system?
A DC/DC converter is used in a PV system to counteract the voltage drop on long cable runs to the substation. It allows the voltage to be boosted. This helps reduce the cable cross-sectional area of cables in the installation. Prior to the DC/AC (Inverter) being used to convert the PV output voltage to AC for connection into the network.
How do the power densities for wind, photovoltaic and tidal compare to hydrogen fuel cells for integration with batteries?
The energy storage system required for a renewable energy system has to be carefully chosen depending on the power output of the renewable system. It has to be appropriately sized depending on the requirements. Lithium-ion batteries are typically used for energy storage systems and demand-side response.
Which renewable method is most value-for-money cost-effective: wind, photovoltaic, concentrated sun, or other? In other words which method brings the most Return-On-Investment?
This all depends on the installation, size of the installation and the technology used. Each has to be evaluated on its own merits depending on the application.
Our PV Solar Design & Build Supplier regularly install inverters that are approximately 10% smaller than the PV Solar system output, on the basis that the system rarely exceeds the inverter output and that the inverter can manage this overload for short periods. I would be very interested to hear your view on this practice.
Inverters do have a short time overload capability, which allows them to deal with small overloads for a set period of time within the manufacturer's guidelines. Without knowing the exact details of the installation and the power requirements and sizing of the inverters with the PV panels, it is not possible to comment on the installation.
What is DPC?
The Draft for Public Consultation. The DPC for Amendment 2 of BS 7671 was published last year for the public to feedback their comments on the new provisions in the publication.
How do we get the size of Solar PV to power a home?
To install solar on a home the angle and pitch of the roof need to be considered to ensure the best arrangement. As a basic rule to calculate the number of panels required, the average hourly energy usage of the home should be divided by the power rating (watts) of the solar panel model available for installation.
Would a prosumer automatic disconnection device be similar to that of a G99 relay used in commercial generation schemes?
Yes. Although a suitably rated contactor would be all that is needed.
On the prosumers slide - why switch the DNO's Earth? Isn't attempts to do so likely to be defeated by bonding to extraneous-conductive parts shared with other installations?
It may be a DNO requirement. AMD 2 of BS 7671 may allow the DNO earth to remain connected. It would seem sensible to have as many connections to the General Mass of Earth as possible.
Why use Heat Pumps instead of just using electricity with simple convection resistive heaters controlled by high-spec, modern and extremely efficient controllers/sensors? I know heat pumps can give a bit of energy savings (probably around 20%) but the high cost of equipment, installation, labour and ongoing servicing costs of heat pumps are hardly convincing.
A cost-benefit exercise would need to be undertaken. A discounted cash flow exercise would be useful to do. Modern or upgraded premises with a high level of thermal insulation may need only supplementary electric convector heaters for use in very cold weather.
Tidal energy derived from floats moving up and down rather than turbine type tidal?
A tidal turbine sited on the sea bed allows for energy to be captured from both the incoming and receding tides. It also allows for the cabling installation to shore. This method also does not disrupt shipping as they are sited on the floor of the sea bed. A float moving up and down with a lever technology could provide potential implications to shipping and marine life.
If the earthing system is TT, is it required a separate earth electrode when operating in islanding mode?
No. With a TT system, there will already be a consumers earth electrode.
If smart meters are going to be installed with Pay As You Go or power control with external control, what extra security is going to be provided to prevent hackers from disrupting a country's national supply?
As we said in the webinar, smart meters already have a high level of security but, no doubt on the basis that anything is possible this could be done.
In a prosumer installation, is the independent earth electrode connected all the time, or is it just switched in when the DNO supply is disconnected?
Yes, the consumer's electrode should remain connected to the MET at all times. The DPC for AMD 2 recommends all installations have a supplementary earth electrode.
Where PV solar is installed owned by a third party which doesn't want to provide surge what then?
The owner of the installation may wish to install surge protection to their installation. AMD to BS 7671 may mandate the use of SPDs except in extreme circumstances.
PV's are currently around 20% efficient, is this going to improve by using multi-layer?
Silicon panel typically have an efficiency of 20%, research is being undertaken into multi-layer technologies, with the ambition to increase the efficiency to 50%.
Electrification of heating will add considerable load and demand on the network - some people need heat when they need it and variable tariffs may impact them negatively. How might the network be configured to prevent heat/energy poverty?
This is not known and would be a political question. It could be that this could be done with a sliding tariff to encourage consumers to manage their demand.
What percentage of nuclear power will be required by 2050?
We don't know. It would depend on the politicians and the time scales to build and commission new nuclear power stations, although it is predicted that Nuclear power will supply 31% of the UK's demand by 2050.
Does the independent earthing system for the home need to be installed away from the proximity of the grid earthing connections such as extraneous pipework connected to the incoming PEN?
Yes. To avoid a transfer of potential from connected metallic pipework from adjacent premises the earth electrode may need to be some 3m from any underground pipework. It depends on soil earth resistance but DNOs have recommended distances e.g. WPD say 3.6m.
What are the different kinds of photovoltaic panels, I'm referring to the different kinds of crystalline structure, are some more suitable for different kinds of light quality (ie overcast days as opposed to sunny days).
The solar cells type mainly depends on the efficiency requirements and the available budget for the installation as the technology chosen affects the efficiency which can be gained. There are several solar cell types that can be chosen:
- Monocrystalline Solar panels have a high-efficiency rate of around 20%, these however have a higher installation cost.
- Polycrystalline Solar Panels have a lower cost but are sensitive to high temperatures, are larger and their overall efficiency is around 15%.
- Thin Film: Amorphous Silicon Solar Panel are lower cost, but have a shorter lifespan. These are only 7-10% efficient.
- Concentrated PV cells have a higher performance and efficiency rate, however, these require a cooling system and solar tacker and are overall a more costly installation.
I have seen a lot about new grid storage technologies for renewable sources, such as insulated thermal and concrete flywheels, is this something that we are looking to invest in?
We are not aware of any proposals to invest in this technology. A question for the politicians we think?
Future-proofing - what is your view on power over Ethernet (instead of WiFi) instead of fibre optics? I.e. utilising the same cable for data and power say for individual light fittings etc.?
POE is used now for things like cameras. It would seem sensible for supplying any low consumption electronic loads. We understand there is a TV on the market that uses POE for a power supply.