QUESTION
Does anyone know about an inverter for a solar system that will supply power to an installation, but if more power is required it gets it from the grid?
I am an electrical engineer, but I haven’t had a lot to do with solar. Typically what I have seen is things like houses with solar panels, continually feeding power into the grid. But where I live the power authority can be hard to get on with. They won’t approve anything over 5kW. I know some people who use around 30kW of power and would like a solar system.
They don’t care about putting power back into the grid, they just want the solar to help reduce their power bills (they use most of their power during the day).
- The network provider doesn’t allow backfeed of any more than 5kW in this area. The site is grid connected.
- This is for a very small factory that makes organic fertilizer (so not a residential load)
- The current draw is around 30kW of power during daylight hours, and nothing at all during the night
REPLIES
FreddyNurk
There are quite a few inverters around that can integrate with solar, and depending on inverter and function, can also limit the export requirements. Selectronic is one company that advertises this capability, Outback Power is another one. Depending on requirements and so on, batteries may be able to be integrated in order to balance power requirements and solar output as needed. The local power authority generally has the consideration on whether or not to allow for connection to their network, along with certain standards for anti-islanding requirements and network protection. 30kW isn’t really a small system for residential applications though.
There are means to get around the problem, although admittedly part of the problem is still getting the utility to accept the proposal.
If the inverter is capable of generating more than what the site requires as load, then it either needs another means to accept its output (say, batteries), or it needs to be able to reduce its output to suit both the site load and the utility requirements (which might be nil export to network, or 5kW export to network). I expect that a lot of the solar only inverter systems currently installed don’t have that ability by themselves, if the network is present and within appropriate parameters, then they will output as much as they can.
Some solar inverters will have the capability to monitor the connection point (not all have the capability to do so through external instrumentation though!) and thus regulate the output based on available solar energy and grid requirements. There are also anti-islanding requirements for inverter systems that prevent the inverter from operating when the network disappears (UL1741, AS4777, other IEC standards).
In Australia some of the utilities have been more accepting of the issues in terms of connection of inverters to their network and the associated requirements, and will permit systems on the sort of scale mentioned by the OP subject to installation of appropriate protection schemes and/or use of standards compliant equipment (AS4777).
Its all possible, it might not be as cheap or easy as expected though, and subject to location and utility requirements, there may be equipment already available to do it.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=378162
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