Solar Energy and saving money

[Switchornot]

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.

Conor - thanks for input above. Just one query on your analysis - the estimated payback term seems to jump quite a bit when the battery is factored in whereas I would have thought that by adding a battery, the payback term would be similar to solar only as the battery makes the system more efficient. Is this the case or are the cost of batteries still relatively high compared to the potential savings?

I have received a few quotes for my house over the past few weeks - I am looking at an average cost of 9k excluding battery. This includes 22 panels, an inverter and optimizers. The price including a 5kwh battery and power module jumps to an average of approx. 12.5k so it is an extra 3.5k for the battery option.

I guess my question is how do I analyze the daily/annual saving that a battery can generate? Is it by looking at the daily usage x the differential between the daytime and nighttime rate? Our average daily usage during summer months is 16kwh and anywhere between 25-30kwh during the winter months.

 

[Leo]

the estimated payback term seems to jump quite a bit when the battery is factored in whereas I would have thought that by adding a battery, the payback term would be similar to solar only as the battery makes the system more efficient.

Can you see the workings of the calculation? Some of the older ones just assumed you'd only charge the battery using excess solar when available so the savings were negligible when you factored in the alternative of getting paid for that excess solar. However, with some of the smart plans now targeted at EV owners, it's possible to charge the battery fully overnight and sell excess solar, making for a more compelling case.

 

[Switchornot]

Can you see the workings of the calculation? Some of the older ones just assumed you'd only charge the battery using excess solar when available so the savings were negligible when you factored in the alternative of getting paid for that excess solar. However, with some of the smart plans now targeted at EV owners, it's possible to charge the battery fully overnight and sell excess solar, making for a more compelling case.

The workings are pretty basic as they just show any excess being pushed back to the grid for a fixed price. My guess is that the payback on the battery is much shorter than I was thinking it was if it is used efficiently and if the right smart plan is chosen.

 

[Leo]

My guess is that the payback on the battery is much shorter than I was thinking it was if it is used efficiently and if the right smart plan is chosen.

Up until the smart tariffs came along with the potential to charge overnight at super cheap rates, the consensus was that batteries didn't make financial sense. Remember, the battery will have a shorter life than most of the rest of the solar system components. As a result you need to be sure you can make full use of it to ensure you get payback before it requires replacement.

 

[misemoi]

Does the battery operate on an age life span or usage life span? Though assume that you would not buy it if you are not going to use it efficiently!

 

[Switchornot]

Does the battery operate on an age life span or usage life span? Though assume that you would not buy it if you are not going to use it efficiently!

The battery in question has a 10 year warranty so would imagine life span won't be too much longer than that.

I think the question on using it efficiently is what I am struggling with because what I am trying to understand is the payback term. Firstly, our annual requirements are about 35% greater than the maximum amount of solar energy that the panels can supply so in most months, I would expect us to utilize the majority of the solar power we generate as we use quite a lot of power during daylight hours. If we don't use it, it gets sold back to the grid at a certain price - around 15c per unit.

What does using it efficiently mean in my scenario if we are already using most of the solar or selling it back to the grid? Does efficient use come down to something like charging early morning to avail of a very low rate (say 6c). If that is it, the payback term becomes very long and it doesn't seem like a good investment at this time.

 

[misemoi]

Using the battery to charge overnight on an EV rate and then selling your solar back to the grid at FIT rates and minimise your purchase of grid units....you pocket the difference. There are so many permutations to this and it replies on the EV rate being much lower than FIT. You would need to do up a file with all your inputs costs and make assumptions about all rates etc. Then layer in potential other income you could earn from the battery money! I think using solar/batteries etc relies on the user being savvy with usage which a lot of people tend not to be - though anyone I know who has gotten solar def gets stuck into it!

 

[Marsupial]

Does the battery operate on an age life span or usage life span?

A combination of both really. My warranty guarantees that the battery will still retain at least 60% of its original capacity after 10 years of normal use. (Normal isn't defined!)

 

[Switchornot]

Using the battery to charge overnight on an EV rate and then selling your solar back to the grid at FIT rates and minimise your purchase of grid units....you pocket the difference. There are so many permutations to this and it replies on the EV rate being much lower than FIT. You would need to do up a file with all your inputs costs and make assumptions about all rates etc. Then layer in potential other income you could earn from the battery money! I think using solar/batteries etc relies on the user being savvy with usage which a lot of people tend not to be - though anyone I know who has gotten solar def gets stuck into it!

Thank you - I think this is the answer I was looking for. I am not overly tech savvy - I think the solar aspect is relatively straight forward but the battery optimization seems complicated. I think the key point you make about using the battery money elsewhere is key - I am pretty confident I could earn more each year investing in stocks via my DeGiro account than I would save on the battery so I might just stick with solar.

I suspect that over the coming years, the amount we can sell back to the grid for will drop off as more people sign up to solar - that seems to be happening already in some countries - that might be the tipping point to move to a battery for me as using excess to fill a battery would be more attractive than selling back to the grid for a low rate.

 

[mugsymugsy]

I would strongly suggest if you go without a battery to ensure that you get a hybrid inverter and not a string inverter. A hybrid inverter can future proof if you want to get a battery at a later stage.

Also be careful as currently you pay no vat on battery if you get a battery installed at same time as panels. I believe you would pay vat if you got the battery purchased /installed at a later date.

 

[conor_mc]

Conor - thanks for input above. Just one query on your analysis - the estimated payback term seems to jump quite a bit when the battery is factored in whereas I would have thought that by adding a battery, the payback term would be similar to solar only as the battery makes the system more efficient. Is this the case or are the cost of batteries still relatively high compared to the potential savings?

I have received a few quotes for my house over the past few weeks - I am looking at an average cost of 9k excluding battery. This includes 22 panels, an inverter and optimizers. The price including a 5kwh battery and power module jumps to an average of approx. 12.5k so it is an extra 3.5k for the battery option.

I guess my question is how do I analyze the daily/annual saving that a battery can generate? Is it by looking at the daily usage x the differential between the daytime and nighttime rate? Our average daily usage during summer months is 16kwh and anywhere between 25-30kwh during the winter months.

3.5k for a 5kWh battery is ridiculous. I "priced" mine by asking for a price if it was removed from my similar-sized 22-panel quote, it was €1250 less. When I said "cool, give me 2 then please!" it was plus-€2,200.... go figure! In the end, I kept the one 5kWh battery in but I've just ordered a 15kWh, 10,000-cycle battery from GobelPower in China for €2,300 to my door, duty/taxes paid. I'll then sell off the 5kWh battery for about what I paid for it, give or take. I was very, very tempted to order two and might yet add a second after I've gotten my head around wintertime payback vs a second 15kWh battery being largely redundant during the summer.

In terms of analysing payback for a battery, I went with a fairly simple cost avoidance model, i.e. daytime-rate electricity less nighttime-rate charging, multiplied by an 80% cycle by 320 cycles a year. I then also estimated a higher self-consumption percentage to my solar PV payback model due to solar top-up during the day.

 

[conor_mc]

Thank you - I think this is the answer I was looking for. I am not overly tech savvy - I think the solar aspect is relatively straight forward but the battery optimization seems complicated. I think the key point you make about using the battery money elsewhere is key - I am pretty confident I could earn more each year investing in stocks via my DeGiro account than I would save on the battery so I might just stick with solar.

I suspect that over the coming years, the amount we can sell back to the grid for will drop off as more people sign up to solar - that seems to be happening already in some countries - that might be the tipping point to move to a battery for me as using excess to fill a battery would be more attractive than selling back to the grid for a low rate.

Just on this - I think we are more likely to move towards a time-of-use model eventually, which for those signed up to such tariffs could mean filling batteries for next to nothing and avoiding penal electricity rates at tea-time. In short, I think a battery is actually the most useful part of a solar PV install and is genuinely worthwhile even without solar panels, at the right price.

 

[Switchornot]

I would strongly suggest if you go without a battery to ensure that you get a hybrid inverter and not a string inverter. A hybrid inverter can future proof if you want to get a battery at a later stage.

Also be careful as currently you pay no vat on battery if you get a battery installed at same time as panels. I believe you would pay vat if you got the battery purchased /installed at a later date.

Yes, thanks - that makes sense. The inverter included in the quote is a Huawei Sun2000-5KTL-L1 Smart single phase 5kw Hybrid Inverter. That should give me flexibility to go to a battery if I decide to go down that route at some point in the future.

 

[Switchornot]

3.5k for a 5kWh battery is ridiculous. I "priced" mine by asking for a price if it was removed from my similar-sized 22-panel quote, it was €1250 less. When I said "cool, give me 2 then please!" it was plus-€2,200.... go figure! In the end, I kept the one 5kWh battery in but I've just ordered a 15kWh, 10,000-cycle battery from GobelPower in China for €2,300 to my door, duty/taxes paid. I'll then sell off the 5kWh battery for about what I paid for it, give or take. I was very, very tempted to order two and might yet add a second after I've gotten my head around wintertime payback vs a second 15kWh battery being largely redundant during the summer.

In terms of analysing payback for a battery, I went with a fairly simple cost avoidance model, i.e. daytime-rate electricity less nighttime-rate charging, multiplied by an 80% cycle by 320 cycles a year. I then also estimated a higher self-consumption percentage to my solar PV payback model due to solar top-up during the day.

I thought 3.5k seemed high alright - I guess its 3.5k for the battery plus the power module. It can definitely be found on-line for much cheaper but then I still need someone to fit it.

I am waiting on another quote so I will see what they price for it.

 

[conor_mc]

I thought 3.5k seemed high alright - I guess its 3.5k for the battery plus the power module. It can definitely be found on-line for much cheaper but then I still need someone to fit it.

I am waiting on another quote so I will see what they price for it.

ah, you're Huawei - they're locked in to expensive Huawei batteries. Is this a quote or already installed? If it's just a quote, I personally wouldn't go down the Huawei route for that vendor lock-in=very expensive reason.

 

[Switchornot]

ah, you're Huawei - they're locked in to expensive Huawei batteries. Is this a quote or already installed? If it's just a quote, I personally wouldn't go down the Huawei route for that vendor lock-in=very expensive reason.

Just a quote - I haven't done anything yet. I am waiting on 2 or 3 more quotes before I decide who I will go with. If all the batteries are broadly similar and carry out the same function, why are Huawei charging so much for theirs?

I might be in the market for a 2nd hand 5kwh battery yet so let us know when you decide to sell it!!