Solar Energy and saving money

[Radioman]

First you can buy electricity at the low rate once you have a smart meter and agreed a tariff
Next you can store this energy and use it during the day
You need just two items to do this
A A storage battery
B An hybrid Inverter
Next and later if you wish to install solar panels it’s relatively a simple job to add these benefits are keep the batteries full and sell any surplus to grid
Finally to get the best elevation angle and compass direction ground mounting of solar panels makes the most sense if unshaded space available
Maintainence is simpler and potential roof damage avoided

 

[Marsupial]

A year ago today my PV solar system was installed. It's a west facing, roof mounted, 10 panel 4.15 Kw system with a 5Kw battery.

I received three quotes from well-reviewed installers in Munster (I live in West Cork) and as the two lowest were virtually identical, I went for the local man. Net of grants, it cost 9k to install, including the necessary BER survey.

The following two websites were consulted to calculate the estimated power generation for a year:-

https://pvwatts.nrel.gov/index.php ................. which predicted that I'd generate 2,990 kWh annually. and https://www.clare-energy.ie/calc_PV_production/ ...................... which predicted that I'd generate 3,450 kWh a year. My actual production was 3,365 kWh, which suggests that the second site [which uses one's Eircode] is more accurate.​

In the past 12 months I have sold 76% of the units produced to my energy supplier, generating an income of €540 and using the remaining 24%, thereby saving an estimated €250.

Further savings have been realised from charging my battery fully every night at the cheap night rate and using the stored power during the daytime. I estimate that this has saved me at least €380.

In summary, my outlay of €9K has resulted in savings in the region of €1,150, after tax but excluding depreciation.

I am very satisfied with this outcome and hope that the above may be of assistance to anyone contemplating a similar installation.

 

[_OkGo_]

Further savings have been realised from charging my battery fully every night at the cheap night rate and using the stored power during the daytime. I estimate that this has saved me at least €380.

Curious as to the breakdown on the costs of the battery were here?

Is your estimate based on 1825kwh (365 x 5kwh) moved from day to night rate? If so, how much was the battery to install with/without grants?

I've often wondered if the payback on a battery alone made sense or even if it is better than the solar

Or in your case, had you chosen not to install the battery, would you have been able to consume all or most of what was exported?

You exported 2555kWh so instead if you consumed an additional 1825kWh and only exported the remaining ~730 units you would have saved €815 from your day rate and generated €150 from export. You could be saving €965 with solar install only

 

[mugsymugsy]

Apologies if I am missing your point but the issue with not having a battery is consuming power at an expensive rate in the winter. By having a battery and charging it at night rate of say 8c then during the day if there is solar power generated then this can be consumed / refill battery so it can the be reused in the evening when no solar being generated.

If you don't have a battery you will then have days where you are taking from the grid at peak rates.

 

[Marsupial]

Is your estimate based on 1825kwh (365 x 5kwh) moved from day to night rate? If so, how much was the battery to install with/without grants?

It's not quite as simple as that. In the summer, the battery often retains a significant amount of charge at midnight, so it doesn't need to recharge fully overnight. Furthermore, in the daytime, particularly in the afternoon/evening (because it's west-facing) it is constantly being topped up by the panels, leading to a situation where, in the 153 day period between 1 April and 31 August, I drew down only 10 daytime rate units!

I've often wondered if the payback on a battery alone made sense or even if it is better than the solar

Me too! It's certainly becoming a lot more viable as the price of batteries keeps falling. .

Or in your case, had you chosen not to install the battery, would you have been able to consume all or most of what was exported?

Definitely not! In the last 12 months I have only used 355 day rate units.

Before PV, my day/night unit ratio was 45:55; since PV (and battery) this has changed to 10:90.

Incidentally, 78% of my total yearly PV energy was generated in the 6 months between 1 April and 30 September.

 

[Switchornot]

Hi All,

The above thread is very interesting. I am far from an expert in these matters so I would appreciate any guidance provided on my situation.

I recently renovated our house in Galway - we gutted the house as part of an extension project which involved changing the heating system to a heat pump. As part of this, we moved to UF heating, new rads etc. BER is now A1 rated. We are high energy users (even more so since we installed the heatpump as electricity powers everything) - 4 teenagers plus there is someone in the house most of every day. I estimate that we use in the region of 8k-9k kwh per annum. Our usage tends to be 70% daytime/30% nighttime (based on 12 months of data).

It seems like moving towards solar should be a no brainer but I want to understand if it makes sense for us. I have the following questions:

-We are in the house very little over July and August which seems like peak season for solar. Does this negate the benefit?
-If we could get a solar unit to generate say 4kwh per annum, that in theory should cover 50% of our costs but it is probably not that straightforward given a lot of the production will be during a time of low usage for us. In terms of payback, can I just sell the excess from those months back to the grid?
-We are on the west coast which means it is a bit cloudier most days than on the east coast - does this matter?
-Now that electricity prices seem to be dropping again, it extends the payback period. What lifetime should I be using for the solar system to calculate the payback?

Thanks.

 

[Leo]

-We are in the house very little over July and August which seems like peak season for solar. Does this negate the benefit?

It certainly reduces it.

In terms of payback, can I just sell the excess from those months back to the grid?

Yes, but the rates they pay you are much lower than they charge.

-We are on the west coast which means it is a bit cloudier most days than on the east coast - does this matter?

Yes. There are tools online that will help you calculate the likely output from a system based on your location and roof orientation.

What lifetime should I be using for the solar system to calculate the payback?

You want to work out the payback period based on the cost of the proposed system versus what you would likely spend on electricity in that time. Factor in some maintenance costs and see how many years it will take and compare that to the warranty period of the system.

Bear in mind the solar will be producing least when you use most electricity. So ensure that is factored into your calculations.

 

[conor_mc]

Regarding your westerly location, you can use PVGIS to estimate the generation at your specific location for a specific size install (kWp) pointing in a specific direction and roof angle. It's very accurate and if anything, under-estimates a little.

Regarding being away in July/Aug, most folks put multiple names on the bill, each of whom is entitled to an allowance of €400 solar feed-in tariff tax-free. The grid is effectively your big seasonal battery, you build up credit by exporting during summer months.

Your payback should be in and around 6-8 year mark, and system lifespan is generally 25-30 years for panels, and 10 years for inverter/battery. Imo, falling electricity prices have stabilised for now as YoY wholesale prices across Europe are creeping up again.

In short, solar is a no-brainer if you have the roof space and funds to do it.

 

[Switchornot]

Leo/Conor_Mc,

Thanks for the feedback. Based on the estimate tools you recommended, for a 6kwp installation, I could generate approximately 4.3 kwh's per year in my location (albeit approx. 1,100 of those are across July and August) which would meet approximately 47% of my requirements for the year.

I have worked out that my average cost per kwh per my current smart plan is 23c. With the electricity company I am currently with (SSE), I believe I could sell back to the grid for 19.5c per kwh so current in v out prices are not that far apart for purposes of calculating payback.

I have forecast that I will spend approx. 2.1k on electricity this year (excluding standing charge and any move to solar) so a move to solar should save me 1k per annum between reduced electricity costs plus feed in tariffs.

Allowing for maintenance costs etc, that would indicate around a 10 year payback but it is also a good hedge against prices going back up.

 

[conor_mc]

You should probably also consider adding a battery since your inverter is likely to be a hybrid inverter. A battery may allow you to switch to a day/night rate and so you might absorb a higher day rate (maybe by 2c or so) for the benefit of loading up a battery (say 5kWh) at ~14c overnight. As the solar tops up the battery throughout the day, you are also improving your overall solar consumption rate.

For a heat-pumped house though (i.e. with a larger consumption of electricity, particularly in winter), it may even be worth looking at a bigger battery than this - the economics may stack up for something as large as 2x15kWh even if it requires reducing the solar array size to fund it.

As a non-heat-pumped household with pre-EV usage of ~5,500kWh per year, I'm already looking to upgrade my 5kWh battery.

 

[Blackrock1]

You should probably also consider adding a battery since your inverter is likely to be a hybrid inverter. A battery may allow you to switch to a day/night rate and so you might absorb a higher day rate (maybe by 2c or so) for the benefit of loading up a battery (say 5kWh) at ~14c overnight. As the solar tops up the battery throughout the day, you are also improving your overall solar consumption rate.

For a heat-pumped house though (i.e. with a larger consumption of electricity, particularly in winter), it may even be worth looking at a bigger battery than this - the economics may stack up for something as large as 2x15kWh even if it requires reducing the solar array size to fund it.

As a non-heat-pumped household with pre-EV usage of ~5,500kWh per year, I'm already looking to upgrade my 5kWh battery.

does anyone do battery installs only? i have a heatpump and an ev, if i could shift a lot of the winter HP usage to night rates it would be a good saver but id need a large battery.