What are the new Hall batteries for?
The recent installation of some brand-new Tesla batteries just outside the Hall entrance has prompted many questions regarding what they’re for!
The answer is that they form the final piece in a long-running project to increase the self-sufficiency of Pelham Hall by maximising the use of the solar energy we collect.
Some 6 years or so ago, a project led by Janice Harrhy looked into installing solar panels on the Hall’s south-facing roof overlooking the cricket field. No grants were available at the time, so the Hall had to fund the £14k cost of the 48 panel array itself and they were installed in early 2019.
These can generate up to a maximum of 10 kW of electricity when the sun's output is at its highest. But the average daytime output is much less, between 2 and 3 kW being typical.
This is because generation depends on height of sun and on cloud cover so, on a typical day, output power comes in “lumps” when the sun is out, dropping to much lower values in full cloud cover. The chart below shows what happened on April 8th this year (2024) and shows a peak of about 8 kW around midday, dropping to under 1 kW at about 2pm. About 24 kWh of energy was generated that day meaning that, for the roughly 12 hour period shown, the average power output was 24/12 = 2 kW.
Unlike offices and homes, the Hall requires power at random times, often in the evening, and these regularly do not coincide with the times when good power is generated. Luckily, the energy generated which we don’t use is exported back to the grid, earning the Hall about 7p per kWh. At the same time, the Hall did not have to pay for the generated electricity which it did use and was saving money that way. In total, it’s estimated that the solar panels have saved the Hall some £5000 since installation so far.
To better use the energy generated, the Hall began a new project led by Simon Angell to install Energy Storage batteries. These store the excess energy and then use it to meet the energy demand of the Hall when solar generation dips.
The initial cost of these batteries was circa £25k and so a grant application was made to the National Lottery and National Landscapes Wales for the funding. We learned that this was successful in October 2023 and a process of evaluating and selecting the installer and solution was started. In January 2024, Green Park Power in Abergavenny was chosen as the installer and 3 Tesla Powerwall 2s were selected, providing a total energy store of 40.5 kWh.
Coincidentally, the UK government then changed the VAT rate on Energy Storage Batteries to a zero rate and so the savings of around £5k were used to install energy monitoring and improve the weather protection for the batteries. Both of these were identified as original requirements to be included if funds remained and will maximise the performance and management of energy throughout the Hall.
The Tesla batteries have the additional benefit of providing energy for the Hall during power cuts, which will enable it to be used by the community during future outages.
Some technical data
The solar panels went live on 24th February 2019
They comprise 48 Perlight Solar Plus+ 4th gen 285W panels and two Solis 5 kW inverters
They have generated on average some 10.8 MWh of energy per year, or nearly 30 kWh per day – about 2.5 times the typical electricity use of a UK 4 bedroomed house
The battery consists of three Tesla Powerwall 2 units, each capable of delivering up to 5 kW, or 15 kW in total