Comparing solar/battery ecosystems

[lookseehear]

I've had a couple of quotes for solar + battery + associated hardware and have three options on the table. We're looking at a 5kW array and probably a 10kWh battery. The options are SolarEdge or Libbi from one installer, or GivEnergy from another. The main difference that I can see is the first installer is offering a 3kW or 5kW inverter whereas the GivEnergy is 8kW.

 

We have a small EV but we'll likely get a bigger one when all the work is done, so I'm leaning towards the GivEnergy. We're also expecting to put in a 10-12kW heat pump as part of our renovation and a >200l UVC. We're on Intelligent Octopus Go at the moment with a SyncEnergy 7kW charger, which I'd rather not replace but would do if it meant managing the whole system was easier.

 

I'm not really sure how I'm meant to choose between these three options. Are there any obvious good or bad choices here? Ideally I'd like a system that can manage import/export, dump excess solar into EV/DHW and be as future proof as possible.

[JohnMo]

11 hours ago, lookseehear said:

dump excess solar into EV/DHW

Why - you are laying for the system to be installed so it will come with MCS certificate, which means you get paid for export, so why not sell the electric. DHW heating is fine if you don't get paid for export. Gas or heat pump DHW heating is around 6p per kWh, export around 15p on the correct tariff.

 

I would look at a system that doesn't demand internet connection - GivEnergy does require internet, others no idea. 

Edited 15 hours ago by JohnMo

[Dillsue]

A 5 or 8kw inverter will need DNO consent. What does your installer say about that?

 

As JohnMo says you'd be better off charging your EV on the overnight go tariff and let your daytime solar generation run to the grid after you've used what you need. Charge the EV and battery overnight

 

Solaredge doesn't need an internet connection to generate but it does for remote monitoring. I think scheduling of battery charging will need an Internet connection.

 

Why does having a larger EV make you lean towards the larger Givenergy inverter? Our 3.68kw inverter has an integrated 7kw EV charger which charges overnight from the grid so isn't linked to the inverters 3.68kw solar generation capacity

[Marvin]

Hi @lookseehear

 

For me it would depend on the how shaded the panels are, the pitch of the roof and if the panels will face due south because I am more interested in how much energy is produced during the winter months.  This is because winter is the time when the system produces about one fifth of the energy compared with the summer and we use about 5 times the energy heating the house.

 

My assumption is using "packages" from energy suppliers which give you lower and higher rates at different times will slowly change to different periods of the year as well. I know in some other countries that, as more and more people have PV, the power generated during more and more days in the summer has become almost worthless because more is being produced than used.

 

This "changing the game" or "moving the goal posts" means long term that anything that is in someone else's control will change as has happened with Electric Vehicles (EV): The benefits of having an EV have diminished so far that it now makes little financial difference. 

 

The breakthrough will be when the energy can be stored long term in a cost effective manner when the more PV you have the better off you will be.

 

If you have more than I think, a 3.6 kWh system, you have to obtain permission from your power supplier. 

 

 

 

 

 

[lookseehear]

3 hours ago, JohnMo said:

Why - you are laying for the system to be installed so it will come with MCS certificate, which means you get paid for export, so why not sell the electric. DHW heating is fine if you don't get paid for export. Gas or heat pump DHW heating is around 6p per kWh, export around 15p on the correct tariff.

 

I would look at a system that doesn't demand internet connection - GivEnergy does require internet, others no idea. 

 

Maybe I need to look more at tariffs. My assumption in the future is that export rates will reduce as more people get solar, because they'll all peak at the same time and at that time the generation will greatly exceed energy requirements.

 

Other than being future proof, why look for a system which doesn't require internet? I imagine internet is only for some smart features, not for basic functionality?

 

2 hours ago, Dillsue said:

A 5 or 8kw inverter will need DNO consent. What does your installer say about that?

 

the one who offered 3 or 5 said the 5 would be a 'small additional cost' and the 8kW one didn't mention but I assume would get consent as part of the install.

2 hours ago, Dillsue said:

Why does having a larger EV make you lean towards the larger Givenergy inverter? Our 3.68kw inverter has an integrated 7kw EV charger which charges overnight from the grid so isn't linked to the inverters 3.68kw solar generation capacity

 

In the event we want to charge during the day (and if we have 2 EVs that might be more of a common occurrence), it would make sense to use stored energy in the battery wouldn't it? If I have a 3kW inverter and charge at 7kW I need to import 4kW from the grid at peak rates. Sorry if I've misunderstood.

 

2 hours ago, Marvin said:

The benefits of having an EV have diminished so far that it now makes little financial difference.

 

Not sure I agree - charge at 7-8p/kWh, get ~3miles/kWh efficiency means ~2-3p/mile plus 3p new tax still makes it probably half the price per mile of a petrol or diesel. Things will change though over time. Personally I hope someone manages to reform the UK energy market to enable cheaper electricity from renewable sources.

[Thorfun]

I’m confused. If you’re getting a 5kWp array why would you need an 8kW inverter?

[lookseehear]

My understanding (happy to be corrected) is that if I have a fully charged 10kWh battery and a 5kW inverter, I can only draw 5kW from the battery. This would mean that if I plug in my car to the 7kW charging point, I would have to 'buy' 2kW from my electricity supplier rather than use what I have in the battery. Another scenario is that it's full sunshine and the panels are generating 5kW and I plug the car in, I can't do 5kW from the panels and 2kW from the battery without a bigger inverter.

 

I believe the panels and battery are DC, but the inverter is required to convert to AC for use in the house or for selling back to the grid.

[JohnMo]

2 hours ago, lookseehear said:

future is that export rates will reduce as more people get solar, because they'll all peak at the same time

 

2 hours ago, lookseehear said:

charge at 7-8p/kWh, get ~3miles/kWh efficiency means

Aren't both likely to change at the same, everyone with an EV charging at the same time, lo tariff becomes a high tariff period. You can't use one as justification and not the other etc.

 

Not sure you would charge your house battery to then dump into your car. Then 5 mins later end up with a flat home battery.

2 hours ago, lookseehear said:

Other than being future proof, why look for a system which doesn't require internet? I imagine internet is only for some smart features, not for basic functionality?

Some require it for anything other than basic functions. Some require for warranty, if control is from china who knows what will happen.

[lookseehear]

It's really hard to tell whether these things will happen at the same time. Low overnight rates is a product of low demand vs peak hours, but I don't know how much more the adoption needs to increase until it becomes relatively higher demand and therefore has a cost impact to the consumer. The good thing is demand is predictable and relatively stable (and growing) which I think will contribute to keeping prices lower.

 

Solar's problems are that it's seasonal and unpredictable and peak generation is rarely when consumers want to use it. Without the demand from consumers, it's more likely to be that we see a lot more 'free' energy during the sunnier seasons to balance the load, which will likely have a greater impact on the feed in rates because you can only buy something for 15p and sell it for nothing to a certain point.

 

My guess is that feed in rates will drop before overnight rates increase, but who knows.

 

I'm not proposing to dump all the power from the battery into the car, but I'm thinking that with some moderate sun it would make sense to supplement solar production with a battery for a short charge during the day.

[mjc55]

12 minutes ago, lookseehear said:

I'm not proposing to dump all the power from the battery into the car, but I'm thinking that with some moderate sun it would make sense to supplement solar production with a battery for a short charge during the day.

 

Isn't the future the ability to store in car as well as house batteries and then pull back stored power from car if necessary.  Cars contain a lot of storage (40-60 kWh according to AI 😁)

Edited 8 hours ago by mjc55

[lookseehear]

You're right I'm probably looking at this the wrong way round. I'm likely being swayed by the fact our current EV only has a 24kWh battery and needs charging often and sometimes during the day, whereas most newer EVs have bigger batteries and can be charged overnight almost all of the time. There are definitely times during the day where someone would want to 'top up' an EV with a larger battery, for example just before a long trip where you want to have max range to start with.

 

The issue with using the car battery to buffer the house demand or grid is unnecessary battery cycling - no one will want their car battery devalued or degraded. But I agree that having an 80-100 kWh battery sat on the driveway seems a bit of a waste if you can set it to better use.

[Thorfun]

5 hours ago, lookseehear said:

My understanding (happy to be corrected) is that if I have a fully charged 10kWh battery and a 5kW inverter, I can only draw 5kW from the battery. This would mean that if I plug in my car to the 7kW charging point, I would have to 'buy' 2kW from my electricity supplier rather than use what I have in the battery. Another scenario is that it's full sunshine and the panels are generating 5kW and I plug the car in, I can't do 5kW from the panels and 2kW from the battery without a bigger inverter.

 

I believe the panels and battery are DC, but the inverter is required to convert to AC for use in the house or for selling back to the grid.

Ok. That makes sense. 

[WisteriaMews]

When selecting our system I wanted the option to be able to use it with smart tariffs. Octopus seems to be the leader in this space so I checked which systems they are compatible with. We're a way of installing but I've specified a GivEnergy battery on this basis currently.

[Dillsue]

7 hours ago, lookseehear said:

My assumption in the future is that export rates will reduce as more people get solar, because they'll all peak at the same time and at that time the generation will greatly exceed energy requirements.

 

the one who offered 3 or 5 said the 5 would be a 'small additional cost' and the 8kW one didn't mention but I assume would get consent as part of the install.

 

Have a look at gridwatch to see how little solar we produce even in the summer. We're a million miles off generating more PV than the countries energy demand.

 

Your DNO decides what export capacity you can connect to the grid so don't assume that will "be part of the install". Speak to your installer as they may have already made enquiries on your behalf, or they may be winging it.