Solar Panel System - What spec do I need?

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Mettmo

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Hello, we're looking to get a solar panel system installed and have received a number of quotes.
Our average household usage the past 2 years has been 6,500 kWh per year. We'll likely get an electric car at some point soon and want to include an EV charger as part of the system - Google tells me to allow roughly a 3,000 kWh usage per year for an electric car. So our total then would be 9,500 kWh per year.
The spec in the quote we're most interested in is for a 6.6kW set of 14 solar panels - a 5kW inverter - an 8.3 kWh battery and a 7kw EV charger. Would anyone be able to give me an opinion on whether we're getting the best out of the panels 6.6kW output for our needs with this setup e.g. should the inverter and/or battery be a higher capacity? Finding it a bit complicated and as it's a big investment we'd like to be sure we're getting the best system for our needs. Thanks.
 
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suzie said:
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Someone else just told me that too. I'm thinking that might be better as it's the correct spec I need. It's all about the money in the end, but as the VAT is off everything you get with the initial install, we want to invest what we can now.
 
Mettmo said:
Our average household usage the past 2 years has been 6.5kWh per year. We'll likely get an electric car at some point soon and want to include an EV charger.
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Download your usage file and go to kilowatt.ie or a similar website. You can alter the settings once your file is uploaded to work out your daily usage during the winter. For example, in my case, I use about 9kWh per day during the winter, so a 10kWh battery was sufficient for my household. It allows me to use less than 1kWh of full-price electricity per day.

If you intend to charge an EV, you will probably need a supplier with a 3-hour night EV window.

The Clare Energy Agency website is a great resource; it can estimate what you can expect from a system based on its size and your exact location.

With the most recent reduction in FIT rates, you may want to spec your system accordingly. I have 15 panels with a total output of 6.4kWp, south-facing. In the last twelve months, they produced 6,700kWh, of which 5,000kWh was exported back to the grid.

If you are south-facing or similar, you could possibly get 7,000kWh from your system, but with a 5.5kWh inverter, you will be clipping. Having an EV charger is a great advantage, as you can charge your car with the excess solar production that your house doesn't use.
 
Mettmo said:
Finding it a bit complicated and as it's a big investment we'd like to be sure we're getting the best system for our needs.
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I've had solar panels for a few years. Whenever asked for advice, I always tell people to get the biggest system they can fit/afford - including total panel kWp and battery. My system was installed when supply chains were still constrained post-covid, so it was a matter of getting whatever the suppliers could get their hands on.

I have never met a person who thought they bought too big a system, generating too much free electricity. I've met loads of people (myself included) that wishes they could have installed something bigger.

To me, 6.6 kWp sounds good, as long as most of your panels are south facing, with some allowable on east and west. Get the Sun's Path app to give you an idea of where your panels would ideally be located.

6.6 kWp should also give you a good bit of excess during the day, if charging your (future) car from the sun is a goal. Remember, you need a minimum of 1.4 kW excess for charger to be able to work, but 1.4 kW alone will give you very little in terms of increasing the %charge of your EV. More is better.
 
As others have said its best to max the number of panels you can. Be careful calculating it on current usage. Very few people have the electrical consumption stay the same or reduce over time. More and more items are becoming smart, coming with a plug, houses may have two EV's in the future, fossil fuels will be replaced with electrically powered heat pumps, if you retire you're in the house longer using more electricity, etc.

Adding extra panels will only add circa €200 each fitted so if you've a quote of 14 panels I'd consider 16 or 18 if they fit. That's not going to greatly increase the quote but will future proof you.

I've a huge roof with a huge energy use so I'm just posting the below for others as the ESB have a max limit I wasn't aware of when getting mine.

ESB allows a connection of 25 amps. This works out circa at just under 6kw so most inverters sold in Ireland are 5kw. You can get ones that are 5.75kw designed for the Irish Market. Therefore you shouldn't get too much difference in the inverters you're offered.

Most inverters allow you you to have double the amount of the size of the inverter in PV panels. Therefore if you've a 5kw inverter you can have 10kw of solar panels. If you get a 5.75kw inverter you can have 11.5kw total size of panels however the limit of the grant is 11kw. This means circa 24 max panels (depending on brand, size, etc).

In summary, if you have a large roof area, max the system to what the ESB allow. If you want to go bigger than this its an NC7 commercial connection or three phase.
 
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