Sizing solar & battery requirements and selecting a supplier

PGammage

Knowing what was likely to happen with electricity prices I started looking at a solar & battery solution last year. Now I've had my electricity renewal in and it's gone up by over 40% I'm glad I started when I did.

I've documented the steps I took to size and choose my solution at the link below. If you're considering a solar and/or battery solution have a read as it includes tips on sizing what you need and on selecting a supplier. 

My next step is to investigate how best to use excess solar for hot water heating (ie through I-boost or Eddi) and solar coupled EV chargers (I already have a 7kw Rolec). 

Hope it helps others to size and select a system

https://pghintsandtips.blogspot.com/p/my-contribution-to-net-zero.html

QrizB

An interesting blog article, thank you for sharing it!

Havre you done any calculations of payback time or return in investment over eg. 25 years? Did you compare the case with and without a battery, and how did you decide in favour of storage?

PGammage

QrizB said:

An interesting blog article, thank you for sharing it!

Havre you done any calculations of payback time or return in investment over eg. 25 years? Did you compare the case with and without a battery, and how did you decide in favour of storage?

For me it was not so much about ROI, it was more price protection for potential energy price hikes and investing in my property (a good/solar battery system will increase house value) rather than putting money into the big six profits.

That said I did do an ROI calculation and based upon my consumption and post price cap increase prices, my system should pay back in 7-8 years or less if my consumption increases

I did compare battery alone with solar + battery. I worked out a battery solution alone (7.2kwh battery for £5,250 or 9.6kwh for £6,250 - both from Moixa) would reduce my bills by about 60% - charging overnight at the off-peak rate of 5p and then using it during the day instead of paying 25p for peak power. As I mentioned in the blog, the main reasons for not just doing battery was the vat benefit of doing both together and that the Home Energy Scotland loan (0% over 10 years) was only available if you did solar + battery.

Magnitio

I noticed that your link contains "my-contribution-to-net-zero", but that your ROI refers to financial payback. Is it not worth looking at the timescale for achieving net-zero in your calculation i.e. how long does it take to generate the savings in CO2 to compensate for the manufacture, transport and installation of the equipment you are choosing?

PGammage

Magnitio said:

I noticed that your link contains "my-contribution-to-net-zero", but that your ROI refers to financial payback. Is it not worth looking at the timescale for achieving net-zero in your calculation i.e. how long does it take to generate the savings in CO2 to compensate for the manufacture, transport and installation of the equipment you are choosing?

It's a good point. When I started the blog I wanted a catchy headline and I thought "my contribution to net zero" fitted the bill. In practice calculating net-zero is a bridge too far for me, I'm primarily looking to manage my electricity costs and hoping that the headline of solar being good for the planet is true.

NoobSolar

"During winter it would get most of its charge from an off peak energy tariff, during summer it would fully charge in 4-5 hours of full sun from the 1.5kw solar panels."

No it wouldn't. It would be providing energy for your house, immersion and I assume EV.  You would be aiming to get your dishwasher, washing machine and cooking into this time too. I would say

1 get a bigger array, at least 6kwh

2 get a bigger battery

3 get off grid or Uninterrupted Power Supply functionality built in.

4 definitely get optimisers if you are going to be limited about the amount of generation and cannot get near to 6 kwh minimum.
This is one way to ensure better generation if you cannot install more due to space. With such a small array, you will be getting most fo your power during the day from the grid.

Very best of luck.

PGammage

NoobSolar said:

"During winter it would get most of its charge from an off peak energy tariff, during summer it would fully charge in 4-5 hours of full sun from the 1.5kw solar panels."

No it wouldn't. It would be providing energy for your house, immersion and I assume EV.  You would be aiming to get your dishwasher, washing machine and cooking into this time too. I would say

Why wouldn’t it?

During summer solar generation would be up to 1.5kw per hour for say 10 hours in summer, which means even after base load (150w for 10hours = 1.5kw) I’d have over 10kwh. I don’t intend to charge EV from solar (I’ll be using off-peak grid charging) and I’d be prioritising battery recharge over other schedulable loads like immersion hot water (via Eddi or I-boost) which would only kick in when there’s excess solar once battery is charged and if no excess it will heat during off-peak as well. If I did have an energy hungry load like washing or dishwasher I’d manually put it on when there’s excess or again set it to run overnight during off peak.

All that said, I am getting a bigger array - 5.2kwp. The purpose of my blog was to estimate the minimum I need to help me with an affordability calculation

QrizB

PGammage said:

NoobSolar said:

"During winter it would get most of its charge from an off peak energy tariff, during summer it would fully charge in 4-5 hours of full sun from the 1.5kw solar panels."

No it wouldn't. It would be providing energy for your house, immersion and I assume EV.  You would be aiming to get your dishwasher, washing machine and cooking into this time too. I would say

Why wouldn’t it?
During summer solar generation would be up to 1.5kw per hour for say 10 hours in summer ...

Check out the typical reports over in the "my generation" thread. The best anyone has ever reported is, I think, 7 O's (7kW generated / kWp) and 4-5 O's is far more common.

1.5kW x 4 = 6kWh.

Or look at the "how low can you go" thread. In July last year my 2.72kWp array generated 319kWh; an average of just over 10kWh/day.

PGammage

QrizB said:

PGammage said:

NoobSolar said:

"During winter it would get most of its charge from an off peak energy tariff, during summer it would fully charge in 4-5 hours of full sun from the 1.5kw solar panels."

No it wouldn't. It would be providing energy for your house, immersion and I assume EV.  You would be aiming to get your dishwasher, washing machine and cooking into this time too. I would say

Why wouldn’t it?
During summer solar generation would be up to 1.5kw per hour for say 10 hours in summer ...

Check out the typical reports over in the "my generation" thread. The best anyone has ever reported is, I think, 7 O's (7kWk/kWp) and 4-5 O's is far more common.

1.5kW x 4 = 6kWh.

Or look at the "how low can you go" thread. In July last year my 2.72kWp array generated 319kWh; an average of just over 10kWh/day.

Thanks, I’ll have a read of that thread. As I said above I did actually go for a bigger array (5.2kwp) - the blog was about calculating the minimum I could get away with to be able to understand affordability. 

Verdigris

Depending on your pocket, you can't really have too much solar, these days, what with batteries and TOU/export tariffs. The size and orientation of you roof are the fixed limits.

JKenH

Verdigris said:

Depending on your pocket, you can't really have too much solar, these days, what with batteries and TOU/export tariffs. The size and orientation of you roof are the fixed limits.

..and the DNO.