Solar

dormermike · 23 Mar 2020

Hi

Got a few solar panels kicking around and found a 3kw inverter so am interested in putting these to safe use.

Is it just a matter of connecting the 240v output to the mains circuit in my house?

I doubt it's that simple and fully expect a roasting but if it is near enough that simple I'll do it. Am not sure which circuit it should be fed into, and don't fancy playing about with the CU.

If I need a competent electrician to do some CU work so be it. I just want to under stand what is needed first.

Thanks
Mike

ericmark · 23 Mar 2020

Basic idea is the DC from the solar panel is converted to AC with the waveform tied to the mains plus some safety measures so if the frequency varies, or the voltage goes over or under a set limit it will auto disconnect, so if some one hits the mains in the street, when the suppliers fuse ruptures all solar panels will close down making it safe.

There is no way you can DIY this, you have to use approved equipment, and anyway without the approved equipment you could end up being charged for the power you export rather than being paid for it.

However you can use solar panels to charge batteries, and then use batteries to power some thing else, or use solar panels to heat water, so if you have something like for example a freezer that the inverter can power then you could in theory use solar panels, however when using a 3 kW inverter on the narrow boat the 3 x 160 Ah batteries were not big enough, and you would need another inverter to control the solar panels.

So solar panels to work efficiently have a variable voltage, so first thing in the morning it may be 6 volt and mid day 24 volt so you use an inverter which alters the input voltage to match the amount of sunlight, and keeps a constant output voltage to charge a battery, well not even constant the battery is charged with pulses and after each pulse the voltage of the battery is measured and using the rate of volt drop the unit works out how charged the battery is.

So again not some thing one can really make DIY wise, again you have to buy the bits, you could try charging using a simple diode, but you would only get half the output the panel should give.

A simple solar panel to keep a caravan battery topped up yes, but at 3 kW some where some how you will need to buy something to do it with.

flameport · 23 Mar 2020

dormermike said:
and found a 3kw inverter

What kind of inverter?
Unless it's one specifically designed for connecting solar panels to the grid, then forget it.

Even if it is suitable, installing it properly is far beyond the scope of DIY.

dormermike · 23 Mar 2020

Hi all

Thanks

Not interested in grid tie in the sense of FIT just to feed into the house when the sun's shining so appliances use the produced power rather than the grid power.

If that's not trivial (I've seen plug in solar being offered) then I will think along the lines of charging car batteries or dump into immersion.

Is only 700 watts or so of power anyway.

Yes the inverter is a solar one.

Thanks

JohnD · 23 Mar 2020

if the house is connected to the grid, then connecting your inverter to a house circuit will connect it to the grid.

which you are not allowed to do

dormermike · 23 Mar 2020

Ok so I need a grid tie inverter, which presumably is what does all the AC synchronisation.

Thanks.

Btw I'm all for standards etc (my job involves writing them, different industry) but after have two separate niceic electricians in and having a mess made, dangerously so in both cases, and then BC not giving a toss, and then niceic themselves pretending to look at the technical aspects and then assessing it was out of their control - didnt care at all - screw it, I'll do what I like within reason and within my skillset. I used to think niceic were about protecting the public but its for protecting members interests, about as useful as checkatrade or trustedbuilders. They are REALLY in my bad books haha.

dormermike · 23 Mar 2020

ericmark said:
Basic idea is the DC from the solar panel is converted to AC with the waveform tied to the mains plus some safety measures so if the frequency varies, or the voltage goes over or under a set limit it will auto disconnect, so if some one hits the mains in the street, when the suppliers fuse ruptures all solar panels will close down making it safe.

There is no way you can DIY this, you have to use approved equipment, and anyway without the approved equipment you could end up being charged for the power you export rather than being paid for it.

However you can use solar panels to charge batteries, and then use batteries to power some thing else, or use solar panels to heat water, so if you have something like for example a freezer that the inverter can power then you could in theory use solar panels, however when using a 3 kW inverter on the narrow boat the 3 x 160 Ah batteries were not big enough, and you would need another inverter to control the solar panels.

So solar panels to work efficiently have a variable voltage, so first thing in the morning it may be 6 volt and mid day 24 volt so you use an inverter which alters the input voltage to match the amount of sunlight, and keeps a constant output voltage to charge a battery, well not even constant the battery is charged with pulses and after each pulse the voltage of the battery is measured and using the rate of volt drop the unit works out how charged the battery is.

So again not some thing one can really make DIY wise, again you have to buy the bits, you could try charging using a simple diode, but you would only get half the output the panel should give.

A simple solar panel to keep a caravan battery topped up yes, but at 3 kW some where some how you will need to buy something to do it with.

Thanks for this detailed post. I do have the inverter lined up, so can produce ~750 watts of 240v on a good day. I'm thinking of just sticking underfloor heating in my garage or something.

I did get two panels in parallel to heat a 8kw shower boiler to boiling point earlier this year when the sun was shining. That was two 90v panels connected straight onto the heater element connections. That was enough for a cuppa

ericmark · 24 Mar 2020

To heat domestic water using electric solar panels likely better that using water direct, electric panels convert light, water ones don't and the losses with water are too high, so connected direct to an immersion heater likely work OK, but need to make sure they will not go over voltage, but feeding 180 volt into a 230 volt immersion is no real problem.

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