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5 kWh Solar Photovoltaic Installation


Just a bit here about my experience with using solar panels in South Ayrshire, Scotland

Solar Panels


Using a 5kWh photovoltaic setup with 13 panels total. Note: 1 kWh (KiloWattHour) = 1 unit (consumption of 1 kilowatt for 1 hour)

:: Setup ::

13 x 395W Black Monocrystalline panels (JA Solar 395/MR)
Solis inverter (& dongle) (RHI-3.6K-48ES-5G)
Emlite generation meter
Schletter mountings
5 kWh PureDrive PureStorage II DC battery


Panel Layout

The panel arrangement is split across 2 strings - 3 panels facing South-East and 10 panels facing South-West (the roof ridge actually points South).

The panels generate DC voltage which feeds into the dual-string inverter. The inverter then distributes the generated power to the house and battery with any excess being exported to the grid. The battery is a 5kWh model and any power not used by self-use (household consumption) will be used to charge the battery before any excess is exported to the grid.

Unfortunately at the moment there is a big supply issue with batteries so I have yet to see ours installed (4 months and counting).

Initial impressions:

Seems to be working well but without a battery (during summer) some power was always being imported from the grid albeit much less than would normally be the case.
With a battery I would anticipate not having to import any power at all during summer since the battery would have enough charge to cover reasonable usage spikes during the day and the low level ambient overnight draw.

Important to note that the heat of the sun does not make any difference in generation capacity and in fact if the panels get too hot it can be detrimental however in Scotland it is often the case that even with a hot sun there is a cooler breeze present which should help the panels. The amount of light available is crucial and it is very noticeable that generation drops away markedly if clouds are present over the sun.

At the moment the present arrangement looks like it will provide c. 34 units/day on a perfect clear day at the height of summer and although winter is still to arrive it looks like generation will be c. 1 or 2 units/day for a wet rainy day.

The split panel arrangement is working pretty well with the generation of the panels following a bell curve very similar to the track of the sun. The smaller string of panels (3) starts the day off and about mid morning the larger 10 panel string will handle the rest of the day.

It should be noted that the experts say that the generation output will never be the same as the rated output due to losses in the system and I find this with the 5 unit system however the losses are not huge and since there is space for one more panel on the second string the output could be boosted a little bit again. The panels themselves are not hugely expensive and if the roof space allows there is not a huge price difference between a 4 unit and 5 unit array.

At this stage I still need a full year of data to see the actual impact but I reckon that once the battery arrives I would expect hugely significant savings on electrical energy costs with the summer production offsetting to a large extent any impact from the winter performance.
I reckon that the average monthly consumption will end up at around 350 units or so which is easily covered for two thirds of the year and probably a bit of shortfall in the four months around winter - we'll see.

Update: Finally got a battery (Feb 2023 waiting since May 2022). Won't know the true effect until summer where grid import should be zero or near enough and there will still be a good bit of export. Interestingly it almost looks like the grid import during winter will go up a wee bit because the panels will not generate enough to cover the self use or charge the battery on cloudy/rainy days. The batteries are not allowed to completely discharge so at a certain threshold (default: 20%) grid import will occur to boost the battery charge as well as supply the ambient overnight usage - this is not a major issue since the power imported will still be used from the battery but for about 4 winter months in the UK there will be insufficient panel generation to charge the battery as well as normal house usage.

Not sure at this stage whether additional batteries are desirable (they are expensive and need to be kept at a minimum charge) - in summer of course there will be enough generation to cover more than one battery but having more batteries means that more grid power will be imported to supply the batteries during winter so it is a bit of a juggle. It will be interesting to see if one 5 kW battery will work and how the high draw spikes (eg: electric showers/kettles/ovens) will be handled given that the inverter output is limited to 3.6kW. In theory the battery should cover a good bit of the evening usage and maybe some of the overnight ambient usage.
The main advantage of summer generation is that the peak morning/evening usage times are within the solar generation curve whereas in winter they occur in darkness.

Configuration Note: Although the number of panels installed gives 5kWp capacity on the DC side the inverter fitted is a 3.6kW model which does not sound entirely logical - normally one would expect the inverter to be 5kW however this arrangement is known as overclocking/oversizing and can produce some operational efficiencies to the generation process. In the UK the max size for standard grid connection is 3.68 KW (based on inverter AC output) and is classified as G98. Any connections exceeding this limit require G99/100 compliance and can involve more hassle getting grid connection permission.

The charts below give an indication of the sort of generation performance that can be expected in SW Scotland.

Typical output for 4 unit array in Glasgow area.

4 Unit array





Current output for 5 unit array in South Ayrshire (slightly better latitude)
(Install done halfway through May)

5 Unit array


Typical of a good high summer day - good solar curve

34Uday

Example of day with poor light in the morning and sunny intervals in the afternoon - effect of sporadic cloud cover can be seen in afternoon.

18Uday

Good summer month - shows in excess of 700 units possible (May was better but system was only installed halfway through).
The anomaly for the last 2 days was a problem created by the installation of a 'smart' meter. The magnetic current sensor for the solar had been reversed on the grid supply so the polarity was wrong for the import/export data. The panel generation data is accurate.

June Daily

Anomaly Note:

As shown in the above graphic the last 2 days of the Consumption bar chart are too high and the export level of the Generation bar chart is too low.
Essentially this happened when a smart meter was fitted by the grid provider and it highlighted a problem I have seen many times in the technical industries.

The fix was easy because the mains clamp had been reversed but it took c. a week to be resolved. I got the problem of the grid folk saying it wasn't them and the solar saying it wasn't them (good ol' fingerpointing rather than just trying to find the issue).
The smart meter guy eventually was sent back out and reversed the clamp which fixed the problem but he didn't understand why it had been reversed because he used a technique of marking the clamp before removing and replacing it the same way after the meter install. He placed the clamp on the consumer side of the smart meter which would be logical since the grid side should only have gear connected that is owned by the grid (solar inverter etc should be classified as consumer side equipment). Using his technique of marking and replacing in same orientation it means that prior to the smart meter install the clamp must have been placed on the grid side of the old meter and the grid installer would naturally place it back on the consumer side thereby creating a polarity reversal.

So if the grid installer had used the polarity arrow marking on the clamp the problem would not have occurred and likewise if the clamp had originally been on the consumer side of the meter all would have been OK.

Lesson:

Always think twice when trusting the professionals (both sides in this case demonstrated faulty technique) and be aware that for many solar providers Sales and Installation is the focus, Maintenance is an afterthought. Also there appears to be a lack of focus on service in the solar industry - most installs appear to be left in default state and a lot of technical data goes from the inverter to the remote servers of the manufacturers. Optimisation of solar setups appears to be left to enterprising folk who try to figure out how it should all work (via forums, etc). Any apps provided by the manufacturers appear to be quite limited with changes to the settings needing to be done at the inverter.







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