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Hybrid Inverters and Submeters


gooseberry
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I have a property I'm going to rent out and then probably live in myself after a few years. I have installed 3.6kWp of panels there and I want to offset my capital layout by having the tenant use a prepaid submeter (see Recharger.co.za) to pay for their usage. In simple terms, I then get the difference between the municipal meter reading and the total electricity used.

This is all very simple to do with a grid tied setup, or with a hybrid that's running without a battery. I do lean towards getting a hybrid because of the flexibility it provides. If the tenant wants a loadshedding/backup solution I can add a battery. I could even set it up for self-consumption at night and pay back the battery over time. The issue then becomes where do I put my submeter? As soon as I add a battery, if the meter is on the grid side it will flow in reverse when the grid charges the battery or powers the backup loads. If I put it on the backup loads, all the non-essential load usage is not metered. If I were to switch the non-essential loads to the Aux port (Sunsynk) can the submeter measure two conductors at the same time? Will a clamp work if you put it around both?

The alternative is to go grid tied and then add a UPS inverter. This will make self-consumption tricky though (for that you want to be sure you're using excess PV to charge the batteries) so you won't get the full benefit. When I move in myself and remove the submeter I will curse it and wish I just had a hybrid.

Which option would you go with?

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1 hour ago, Tariq said:

Assume you will not be feeding into the grid, then put the sub-meter between the grid and CT clamp

But that way I will only meter grid usage, and not total usage? In case it's not clear, I want to sell the PV I generate to the tenant, same as they would have paid for normal electricity.

Edited by gooseberry
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@gooseberry I understand your logic.

Batteries won't save you money the costs are not on your side.

So that leaves a grid-tie inverter.

Legalities aside, some practical economic considerations:

If your array is uniform all your power will be delivered in about one 4-5 hour mountain sometime during the day.

If your tenant is at work no-one will use it and your inverter will throttle. (No sales)

If your tenant is home and doesn't need it at the time you produce it your inverter will throttle. (Minimal sales)

When a user uses his/her own solar he/she has an incentive to schedule his/her loads to match production to save money.

What incentive does a tenant have for scheduling their usage to make you money? 

 

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I wouldn't sell the electricity generated by PV, it's illegal and the moment you have a dispute (which happens quite often), you won't only have the rental housing tribunal on your back, but  NERSA too.

The tenant obviously gets the benefit, and is the one in control of their own usage. I'd just inflate the monthly rental instead, with an amount that an average tenant would use, like the cost of say 500kWh (two people) or more if the home is big. You can then install the submeter on the grid side, and the tenant pays for the full utilisation. Far simpler and easier. 

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It is absolutely not illegal. It happens everywhere - in office parks to housing estates. As long as you're below 1MW you're allowed to sell your own electricity. 

And submetering is common where people rent out additional units on their property.

 

I get the point about there not being large loads during the day, but I plan to put timers on the geysers to heat them with PV at least. Having the upside of backup for power failures would be nice for the tenant and let them feel they get some benefit from the system too. I just don't know how I'd do the metering with a hybrid.

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With grid tie there is no risk of overloading anything. It looks like a normal prepaid meter and they buy their tokens at Spar or their banking app like they're used to. Only difference is I get paid by the meter company at the end of the month and I pay the Eskom bill. I'd rather not add money to the rent as then the rent 'looks' high. People are used to prepaid electricity.

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11 hours ago, gooseberry said:

t is absolutely not illegal. It happens everywhere - in office parks to housing estates. As long as you're below 1MW you're allowed to sell your own electricity. 

And submetering is common where people rent out additional units on their property

Sub metering, even with the tenant paying extra, certainly is legal. Your case is more unusual and more interesting because you're proposing to sell electricity that you made yourself. 

You'd think that would be legal for tenants on the same property, but I wonder if there's not some limits to stop you becoming a mini Eskom. 

But how do you explain it to your tenant? If you just put a grid-tie system in you have to tell them that they're not protected against load shedding. They will then ask about the panels on the roof and that box with the flashing lights on it and they will realise what is going on. They will feel exploited. 

I think the best thing to do is just install a sub meter and don't install any solar. Then put any capital you were going to inject now and a portion of the rental into a savings account. Then in a few years time you will have money for a new system, better than what is available now and with brand new batteries with plenty of life in them. 

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You're quite right, there are limits to stop me becoming Eskom. I can't generate more than 1MW and I can't sell to neighbouring properties. I'm not sure how someone can feel exploited. If I didn't have solar they would have paid for electricity too, it makes no difference to them. I might just install my 3kW Axpert as UPS so they're convered for load shedding at least.

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10 minutes ago, gooseberry said:

If I didn't have solar they would have paid for electricity too, it makes no difference to them.

I think this depends on how the whole scheme of them buying tokens and money getting into your account works. There'll be a service charge somewhere along the line - even buying COJ tokens via my bank there's a 2.5% charge. Most sub-meters that I've seen apply a service fee of 10 to 15%, which is added on at transaction time and thus would be for your tenant's account. So if they buy 500 kw/h in a month they will pay more for that than if they bought direct from the municipality, but if they figure out that you only actually used 50kw/h from the grid then... well I would feel grumpy about that. I might not use the e... word, but I'd be a bit sullen.

BTW It strikes me that depending on which tariff you use you may not recover your entire charge in the month. If I were to do this where I live now then I would have to be continually feeding the municipal pre-paid meter that I have, because it's no use the tenant buying tokens if the main meter runs out. So I'd have to barge in at least once a month to feed the meter. Life would be easier if I switched to the post-paid tariff. I wouldn't have to feed the meter and my price per kw/h would be lower, but I'd be in for a few hundred a month in fixed charges. Oh well, I suppose that's built into the rent.

But then, to come back to my point, your tenant may not feel so hard done by because if they were settling the electricity amount on your municipal bill they might be in for more. So maybe I'd be grumpy for just a short while and the figure out (or have it pointed out) that I'm still ahead of the game. 

I'd think you a very nice landlord if you installed a UPS.

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  • 2 weeks later...
On 2021/05/14 at 9:53 PM, gooseberry said:

It is absolutely not illegal. It happens everywhere - in office parks to housing estates. As long as you're below 1MW you're allowed to sell your own electricity. 

And submetering is common where people rent out additional units on their property.

 

I get the point about there not being large loads during the day, but I plan to put timers on the geysers to heat them with PV at least. Having the upside of backup for power failures would be nice for the tenant and let them feel they get some benefit from the system too. I just don't know how I'd do the metering with a hybrid.

The fact that it happens everywhere does not make it legal. Here is a link to the Electricity Regulation Act https://www.lawexplorer.co.za/StatutoryDatabase/Statute/StatuteDownload/81

Take a look at Section II which covers the conditions for exemptions in the obligation to obtain and hold a license as defined in Chapter III 7:

Quote

 

The trading of electricity by a reseller in circumstances in which-

3.6.1 the price charged by the reseller to customers does not exceed the tariff that would have been charged to such customers for the electricity if it had been purchased from the holder of a distribution licence for the area in which the electricity is supplied to the customer; and

3.6.2 the reseller has entered into either a service delivery agreement in accordance with the Municipal Systems Act, (Act No 32 of 2000) (where the licensed distributor is a municipality) or a similar agreement with the distributor (where the licensed distributor is not a municipality) that regulates the relationship between the reseller and the holder of the distribution licence and the obligations of the reseller in respect of the quality of supply to customers; and the Regulator has ratified the general terms and conditions of such service delivery agreement.

 

It seems from what you have previously stated, 3.6.2 applies to your situation.

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