So, it's been over eight months six since I had my photovoltaic (PV) array and battery installed on the back of grant aid from the Sustainable Energy Authority of Ireland (SEAI). As promised, here’s my follow up report with all the figures. Thanks for the requests on Twitter bright sparks.
I’ve emerged from the full blaze of a tropical Irish summer and a relatively bright, soft winter with more managed expectations of domestic photovoltaic. We’re not wholly disappointed. It’s shining feebly here at 11am on an early March day, and we are off grid with a tank of hot water from the water diverter and steadily climbing battery storage.
To remind you of what I bought into in April 2019 and installed from the 4-6th of June. We have: 14, 300w panels, so 4.2kWp on the roof. This is linked to a 6.3kWh battery and a hybrid DC/AC inverter, together with a diverter to use surplus power to heat our water tank. The diverter is prioritised over the battery.
After SEAI aid, the capital outlay was under €8,200 inc. VAT. The array was put in an East/West position on the determined advice of our technical designer who was keen for us to enjoy a longer yield over the course of a day on our higher, larger, steeper E/W roofs.
The retroactive grant aid was €3,800 (€2,800 for the array and €1,000 towards the battery).
Please note that grant aid for solar electricity from the SEAI has been altered since this project was carried out. You can find more details at: seai.ie/grants/home-energy-grants
Our project was audited by the authority which slowed our payment, but the SEAI were pert and in constant touch and finally the grant cleared and was dispatched to out bank account on the 28th of September.
So, here are the figures for June 2019 to February 2020 taken from our cloud software and my electricity bills. The E/W position has had an influence on our total yield, but it doesn’t tell the whole story.
We use in the area of 3,600kWhs per year and I am home most of the day, so we’re very well placed to use the yield from the array in real time. What there is of the sunshine, reaches us without interfering obstacles or a drop below the horizon by day in winter.
June - 256.30kWh (from June 7th after installation)
July - 360.50kWh
August - 319.10kWh
September - 227.40kWh
October - 140.50kWh
November - 68.10kWh
December - 60kWh
January 2020 - 68.10kWh
February 2020 – 120kWh
March 2020 – approx’ 7- 9kWh per day
November to January, the battery and water diverter idled on most but not all days. We knew with shorter, darker days, this fall-off was coming, and we had plenty of hot water from out dastardly, unsealed OFCH. The uptick in yield from mid-February was dramatic.
The killer (and it was a nonsense struggle) has been watching a south facing array from the same supplier of the same size and identical branding and components (4.2kWp) outstrip us in the summer. I can’t tell what happened from November as the user moved to charging their battery on NightSaver and those kWs then dropped into the inverter figures.
The south array serves a 40w EV car and on the best day in August he managed to gather 30% of his car’s 40kW charge from the PV – sipped up over a full day of blazing sunshine. This would appear to be exceptional — PV can generally offer only fractional help in charging a car. NightSaver is the norm’ (and the SEAI agrees) and my supplier tells me that they were impressed to see 20% charge from an array serving a car.
Tight comparison to any other array on a different roof material with a different pitch, or positioned near UV rich coastal light is impossible.
Our results are nuanced and cannot be judged by the kWh yield alone. Domestic PV is not a race to the largest kWh yield figure.
It’s moment to moment collection, and if you are at home, off-grid and using the power — higher yield figures don’t necessarily represent what you are saving.
If you are out all day, all you can do is run a washing machine on a timer, charge the Robomow, and fill the battery.
You could make 25kWhs over the course of the day in July with 4.2kWp and come home at dusk to just 4-6kWh sitting in the battery, a considerable surplus having been gifted to the Grid between 11am and 2pm.
By some strange alchemy, we used only 3kWs from the Grid one February day, and filled 47% of my battery. I was running my AA rated white goods sequentially and using the wattage coming from the roof rather than bleeding them it back to the grid — nibbling slices of bread, not banking loaves of bread at midday with a south facing array. We were still off grid at 9pm thanks to the remaining battery charge. The 3rd of March we consumed just 2.2kWh from the Grid.
So, what do we do over winter to cheer up the depressed figures from November to mid February? NightSaver electricity is approximately half the price of standard daytime units. Using a battery it can be stored and bled back to the house over the course of the day. So, if we used our 6.3kWh battery for the darkest months, we could enjoy 6kWhs of half price power every day.
This has proved to be a real comfort to solar PV users with larger batteries that otherwise sulk at 10%-20% in winter. A NightSaver draw can be easily programmed into your PV system.
The standing charge for NightSaver urban and in particular rural is around €60 higher per year, so it’s important to research whether this lateral move will work for you. The new meter is free.
We are estimating our total yield from our 4.2kWp array to come in a 2,600kWh pa tops.
Our supplier has been highly available, patient and listened to a lot of whinging and prodding. I’m projecting now around €500pa in savings on kWh units inc. VAT.
What about feed in tariffs? This was my dream — to use the FIT to obliterate my standing charges, PSO and 13.5% VAT — to wipe out my bills nine months of the year. We wanted to be true micro-generators, making as much as we need for nothing. Still, we’re now highly wattage aware and even leaner consumers.
If Electric Ireland buys back our surplus in 2021, rumour has it that the rate will be laughable. This further illuminates the advice of the SEAI to optimise high self consumption of your self-made power to at least 80% at 2kWp and 100% at 4kWp with battery storage when possible.
6 Bills (Bord Gais) 2nd January 2019 – Feb 2020:
kWh units 17.5c – 18.5c ex VAT/PSO/Standing Charge. *PV commissioned 7th of June 2019
2nd of Jan 2019 – 26th of Feb 2019. 55 days/701kWh/12.74kWh per day. €121.41/€2.20 per day
26th February – 30th April 2019. 63 days/640kWh/10.15kWh
€114.97/€2.21 per day
1st May to 2nd July 2019. 63 days/333kWh/5.28kWh per day
€60.27/95c per day
2nd of July 2019 - 29th Oct 2019 (had to be corrected for reading). 114 days/262kWh/2.29kWh per day
€46.70/40c a day
29th Oct 2019 – 6th Jan 2020. 69 days/550kWh/7.97kWh per day
€102.03/€1.48 per day
6th Jan 2020 – 26th Feb 2020. 51 days/393kWh/7.70kWh per day
€72.90/€1.43 per day
Changed supplier from Bord Gais to Panda Power for 28% discount 28/2/2020 – don’t forget to consider switching supplier every 12 months!