Expanding solar generation

greenbee

I currently have 6.16kW of panels installed on a south-facing garage. There is some shading from the east, and as it is a single-story building, also when the sun is low in the winter. I also have a 5kW Libbi Inverter with a 10kW battery and and Eddi for the hot water tank (I don't want to debate the value of the Eddi - it means I can turn off the oil boiler in the summer).

I have a proposal to add the same capacity again, but using the higher (small) south-facing roof on the house, and and the west-facing house roof. This will provide some earlier and later generation most of the year. The new proposal includes optimisers (Tigo) and another 5kW inverter (Solis) 

Before I agree to the proposal, I think I need to understand a bit more about how I can optimise this in the summer. In the winter I'm likely to consume pretty much all the generation - and with the battery, exports is likely to remain below the 5kW inverter capacity. 

In the summer, it'll clearly be very different (although the heating and hot water will be off, so towel rails and water will be reliant on solar generation). 

The proposal for the additional capacity was at my request, from the original installer who is also sorting out the house electrics (which are a mess, hopefully being resolved when we put a new consumer unit in), so I don't want to change installer, but I do want to work with him to get this right. 

My question is (assuming DNO approval for increased export), can this be achieved using two separate inverters, or do I need the new inverter to be larger, and how should they be set up?

nologo

My 2 systems have 2 separate inverters (growatt and solar edge) although I don't have a battery..

Petriix

Nothing wrong with two inverters but there are some potential complications with what the battery inverter and eddi 'see' as import/export/generation/consumption. Very careful thought has to be put into where CT clamps are placed and how things are configured. I believe the Myenergi hardware is designed to cope with this kind of setup, it would only really become an issue if you add another battery elsewhere.

Without wanting to disrespect your desire to not debate the Eddi, an oil boiler is one of the scenarios where solar hot water diversion is probably sensible.

Do you have a working smart meter to get export payments (assuming your original array was installed after the FIT scheme ended)?

greenbee

Thanks.  I have a smart meter - I'm currently on Agile incoming and Fixed outgoing at 15p/kWh. 

Hopefully my installer will have worked out exactly what he needs to do... I can't see that we're likely to need another battery, although who knows whether that will change in future. 

Screwdriva

greenbee said:

Before I agree to the proposal, I think I need to understand a bit more about how I can optimise this in the summer. In the winter I'm likely to consume pretty much all the generation - and with the battery, exports is likely to remain below the 5kW inverter capacity. 

My question is (assuming DNO approval for increased export), can this be achieved using two separate inverters, or do I need the new inverter to be larger, and how should they be set up?

A few thoughts:

1) I would definitely skip Solis and Tigo. If optimizers are required, I recommend a SolarEdge inverter with their optimizers. Recent price reductions have made them more competitive (10 panels + SE system = ~£5K) and the software, performance, 20 year warranty and aftersales are in a different league.  

2) I normally advise against two inverters (twice the failure points from different brands) but in this instance, I see no way to avoid it other than replacing your 5kW Libbi inverter with a larger 10kW SolarEdge inverter to handle the entire household. You can AC couple the Libbi battery to the SolarEdge inverter, and sell the 5kW inverter on. All panels will be optimized so shading will be dealt with in the best way possible. 

3) Your installer (assuming they still have MCS accreditation) can reapply for a higher G99 export allowance spread across two inverters, before you have paid for the system expansion. The highest approvals I've seen for projects I’ve helped with is 22.1 kWh for 2 x Tesla PW3s & 16 kWh for dual SolarEdge.

I would wait till the G99 result before deciding on specification, as some DNO's can disappoint with increases. If you get a 10kW export allowance, option 2) above becomes more appealing. 

4) I recently expanded my 4 kW system to a 7.3kW system, including a larger inverter. It wasn't a straightforward decision but it has resulted in a substantial increase in annual generation. Summary: You won't regret your decision. Details here.

Hope these help. Apologies if I've disrupted the apple cart! 

Martyn1981

greenbee said:

My question is (assuming DNO approval for increased export), can this be achieved using two separate inverters, or do I need the new inverter to be larger, and how should they be set up?

Have you been given any indication that you will get DNO permission. 5kW is already a decent size/export allowance, so to double it is quite an ask. Not being negative, hope you get it and can have a monster PV system.

ispookie666

We are a heavy electric household on an E7 tariff and we charge the battery overnight depending on forecast/predicted solar, all hooked to HomeAssistant. 

We did expand my system, and my DNO export limit is 10.96kW. They added the additional 2.16kW to the original 8.8. 

I have an enphase system. I do know that, enphase can do custom grid profiles depending on your export limitation. Eg: if you have a total generation of 7kWp and export limit of 5.5, the grid profiles can be matched to limit to it. But this assumes you do not have battery system which not enphase. 

If you have a system with tow inverters, you might need to decide which one gets export limited so that the total stays below, realistically it will be the new inverter/system 

greenbee

Oops... forgot to come back. I got the DNO permission for 10kW export, and we've got ahead with the additional installation. So eight panels on the south-facing house roof (with Tigo optimisers, as this is the bit of the roof that gets most shade), seven panels on the west-facing house roof, and a Fox inverter. All panels are 445W bifacial, the same as the existing ones. The inverter is in the attic (Libbi inverter is in the garage) with a cabled connection to the Libbi and a dongle connecting it to the Fox app to avoid wifi issues. 

The installation went live yesterday, and despite being turned on and off multiple times during the morning as it was set up, generated 64KwH. Today we're up to 36kWh so far. I'm seeing both earlier and later generation so far, which was the main objective. I'll need to do some analysis, but clearly have enough to charge and EV/run a heat pump (and currently I'm being lobbied to use the extra generation in summer to heat a swimming pool... I'm not sure who is going to pay for the pool to be installed, or do the maintenance though ).

Solarchaser

Great news on your extra install.

I have an eddi, and while i understand you don't want to debate the solar aspect, assuming you are now being paid for export, perhaps its worth looking at an off peak tarrif.
I am on octopus intelligent which is 7p for 6 hours, and I use this to charge batteries and charge the ev, but I also use this to heat my water tanks with the eddi, so Heating it with 7p electricity and exporting the 15p solar you would normally use to heat

greenbee

I'm only eligible for Flux, so not really worth it with 3 hours at 16.4p - if I do ever bite the bullet and get an EV then clearly that's worth doing. I hate buying cars and the current one is relatively new and reasonably well-behaved. 

66kWh generated today of which 46.6kWh were exported. It makes a change from winter on Agile!

Apparently you can use an Eddi to heat a swimming pool  

QrizB

greenbee said:

I'm only eligible for Flux, so not really worth it with 3 hours at 16.4p

You might want to see whether E7 is worth it during the summer months, when you expect to be exporting for 10+ hours a day.