I live off-grid, so my system is the complete process of PV panels, batteries, controllers, diesel generator, and solar water heater.
My suggestion is to go direct to a suitable system installer in your area and ask for advice. They can advise as to the load you may want to generate for (frig, freezer, washing machine, etc.) and consider the panels and inverter that you already have. The previous owner may not have installed a system that could cope with a household.
The simplest option that will save the basic 40% or so of your household energy usage, would be to connect the inverter directly, via a switching system, to your hot water. There would be an obvious saving there. If connecting to the household in general, make sure the inverter is a full-sinewave model or your electronics will play up.
If you're not sure what the overall process is, ask someone who does.
The Electricity Authority just made it clear that they want people to be discouraged from installing solar, and that they're prepared to allow changes to tariffs to let it happen. Their rationale is that by avoiding lines charges, people without solar will end up subsidising those with it. http://www.ea.govt.nz/development/work-programme/transmission-distribution/distribution-pricing-review/consultations/#c15642
At the same time they're signalling that cutting peak loads is good (so that lines don't need to be upgraded) and that in-home batteries can be used to spread your use out over the day to cut the peak demand. So batteries are likely to work out better.
The outcome they're looking for is for the variable rate to drop from 25-odd c / kWh to more like 15-20c / kWh. The income would then be made up by more fixed charges, based on either capacity or peak demand.
For an average house with an average solar setup you could be a few hundred dollars / year worse off, because the electricity you don't buy will be cheaper per unit, and your fixed charges will go up. If the variable charges become peak demand charges and you can avoid them by spreading your load with a battery, and if a 10kWh Tesla PowerWall can do that for $3000 the payback time on batteries might be really good. You won't need solar to do it, just the battery.
It'll be different in every region with different lines companies but there's a strong possibility that solar will be financially a lot worse off within a couple of years, and batteries will be a good investment.
fortydayweekend: The Electricity Authority just made it clear that they want people to be discouraged from installing solar, and that they're prepared to allow changes to tariffs to let it happen. Their rationale is that by avoiding lines charges, people without solar will end up subsidising those with it. http://www.ea.govt.nz/development/work-programme/transmission-distribution/distribution-pricing-review/consultations/#c15642
At the same time they're signalling that cutting peak loads is good (so that lines don't need to be upgraded) and that in-home batteries can be used to spread your use out over the day to cut the peak demand. So batteries are likely to work out better.
The outcome they're looking for is for the variable rate to drop from 25-odd c / kWh to more like 15-20c / kWh. The income would then be made up by more fixed charges, based on either capacity or peak demand.
For an average house with an average solar setup you could be a few hundred dollars / year worse off, because the electricity you don't buy will be cheaper per unit, and your fixed charges will go up. If the variable charges become peak demand charges and you can avoid them by spreading your load with a battery, and if a 10kWh Tesla PowerWall can do that for $3000 the payback time on batteries might be really good. You won't need solar to do it, just the battery.
It'll be different in every region with different lines companies but there's a strong possibility that solar will be financially a lot worse off within a couple of years, and batteries will be a good investment.
The problem is that total power use is not a good proxy to the amount of lines capacity required to serve a customer. So they are just proposing separating those 2 charges to make it fair. Have a look at The Lines Company website for an example. (they operate the power network in the King Country area).
Myself for example. I have been With Flick electric for only about 1.5 weeks. So far my biggest usage peak was 1.72 units in 1/2 an hour. And that was only because there wasn't much sun that day. Meaning my solar hot water system didn't provide much heat. Then someone had a shower which caused the 3kW boost element to stay on for that whole 1/2 hour period. I could easily take steps to further reduce my peak demand. So capacity based billing would save me heaps.
As for capacity charges and solar. That is only because peak loads occur in the morning and evening. And solar peak generation is around midday. So someone getting solar panels installed probably won't reduce their peak load by much. Yet their total power use will go down. Which will mean that capacity costs will have to be spread over a lower total number of units used. This will mean a power price increase. So it is only fair that the pricing structures are changed to accurately reflect where the costs are.
As people who rent and people who are poor are unlikely to be able to get solar installed. So this alone is a big reason to remove any solar subsidies. (both direct and accidental) As otherwise you are forcing poor people to give their money to rich people.
The installation sounds unusual but there is probably a good explanation. Contact the company that installed it in the first place or the previous owner, he sounds like the type that is very interested in this stuff. They will know the logic of why it was done as it was.
Usually you want to use the solar PV to offset your energy use during the day then you are saving the retail rate of buying the electricity (say 15 cents a kwh) but only get paid say 7 cents an hour.
It sounds like there are separate meters and more than one connection to the grid so are you paying for more than one power account, therefore daily charges etc? If so consider getting rewired to the house and try to use as much electricity during the day, set your hot water heat pump so it only runs during the day etc.
There are systems available now that divert excess electricity directly into your hot water cylinder so you get a better payback. Here's an example.
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