Energy Matters Forums

[JohnC]

I'm about to start discussions with a PV installer regarding the placement of 8 new PV panels and inverter at my home and wanted some 'independent' thoughts to get the best outcome. My home is a single fronted Vic cottage with colourbond roof of a standard pitch. The northerly aspects of the roof are split between NW (front) and NE (left side looking from the front). In the mornings during winter the NE side is progressively unshaded by the shadow of the roof of the neighbouring property. This means the peak of my roof gets the first sunlight and the rest is exposed as the sun rises and the shadowing reduces down past the gutterline. I think it would make sense for the panels to be placed on the NE side as close as possible to the roof peak. Any issues to consider with this? Would it be better to split the panels over NE and NW (allowing for the fact that by the time the sun is on the NW face, any panels could be located closer to the gutter line, and that the width of the house front could probable accommodate 3 panels at most). Would splitting the panels improve the overall energy generation or would this be insignificant compared to all panels on the NE? Do you think further angling is required for panels on NE/NW faces so they face N more directly? The inverter is a CMS 2000 (no fan). I thought I would put it on the wall in my entrance hall near the front door. Any tips with this?
Thanks in advance for your responses.

[ianthepostie]

Gday Bloke. Just on the placement of the inverter, put it as close as posible to the pannels for efficiency and nowhere near anywhere anyone wants to snooze. My inverter would drive me crazy humming away if I wanted a kip in the shed. Noise IS a consideration.

[Bthree]

An array seems to give more output in Kwh in the afternoon past midday (sun directly overhead not 12PM)

Although the output of the sun is a cosine, solar panels appear to nearly peak out about 3 hours past sunrise and start falling off about 2 1/2 to 3 hours before sunset (my roof is 25Degree pitch and is facing directly north). It is therefore important if you have got any shading to keep the panels in the sun in the middle of day.

Your consultant will have a really good idea were to install the panels with your input on shading

Inverters do make a humming sound and does transmit through walls so keep it away from bedrooms

[micke]

With regard to panel placement the installer should have a solar pathfinder type device which they will be able to set up in the intended panel position to determine any shading issues throughout the year.

Mounting the array no more than 45 degrees from north will reduce system output by between 3 - 6%.

It is also advisable to have the whole array facing in one direction, as splitting the array between NE and NW roof will reduce output further. Because the panels are series connected the system is only as good as the weakest link, therefore in the morning the NE panels will perform well but the system is limited by the NW panels and vice versa for the afternoon. Another factor to consider is morning fog, if you do get heavy fog then the NW placement would be better than NE.

Inverters do tend to be noisy and placing them outside can be a better option, the CMS2000 inverter can be ordered in a weatherproof enclosure, which would allow it to be placed on any external wall. It is good practice to try and mount the inverter in the shade if possible. The usual location is on the external wall above existing electrical switchboard under the eave.

[Orf]

Do the inverters make a noise both day and night or only when the panels are collecting during the day?

[Bthree]

Do the inverters make a noise both day and night or only when the panels are collecting during the day?

Only during the day and only when they are producing significant output

[SR76]

My SMA1700 makes a very slight electronic noise - kind of like a TV turned on but with the sound down. It probably wouldn't stop me sleeping in the garage.

Splaying an array can make good sense in a stand-alone system with a few strings in parallel, but with an 8-panel grid connect system they will probably all go in one string so splaying them could be a very bad idea - will probably work OK at mid-day but you will lose a lot of power in the early morning and late afternoon when only half the array is in good sun. The full string voltage will need to get up to a minimum point before the inverter will start producing power, if half the array is shaded the whole array will suffer.

Circumstantially I've heard suggestions that afternoon sun is often better than morning sun because the day has heated up, less water vapour likely to be in the sky diffusing light etc. On the downside, panels may be a bit hotter and perform slightly worse. I'm not 100% convinced that this is a real consideration.

However in WA we have a much better reason. SmartPower (our time-of-use tariff) charges / pays the peak rate from 11am-5pm in summer. We are allowed use SmartPower to sell back to the grid, don't know if this is true for other states / other utilities. If you are able to use a time-of use tariff, and it is biased towards the afternoon (likely so - summer air con demand would peak in the afternoon), then definitely look at NW rather than NE - collect more power in the afternoon and sell it at higher rates!

Cheers,

-SR