Solar PV - thinking out of the box?

[JamesPa]

I have recently been working on PV for my (leisure) narrowboat.  The requirement is essentially winter-only, because in summer the engine tops up the batteries when we are cruising.

 

This led me to look more closely at the relationship between output and panel slope by month, and I come to the conclusion that, if we could somehow build to maximise winter output rather than maximising annual output, we might, in many cases, have a better trade off.  Its often lamented that solar panels generate least when we need the energy most.  This is true but it needn't be as bad as we assume...

 

According to pvgis a south facing 1kWpeak array set at 75 degrees to the vertical generates (in the South of England) about 44kWh in the worst month, ie December.  Interestingly its only marginally worse at 90degrees (ie vertical) - 43kWh - graph below.   So a 4kWpeak array set at 75 deg or mounted on an unshaded wall will generate 5.7 kWh per day in December, more than enough (based on a CoP of 3 or better) to heat most houses, with energy left over for domestic use.  The annual production at this angle is reduced by about 30%.

 

There are of course practical considerations, roofs aren't at 90 degrees and many house walls are shaded, but perhaps, just perhaps, we should be spending more time looking for opportunities for vertical or near-vertical placement of solar panels rather than defaulting to roof angle?

 

Unfortunately the output falls off quite rapidly north of the Wash, but that's no reason to ignore the opportunity if you live further South.

 

Just a thought!

 

 

 

 

[ProDave]

I am surprised the figures are so high in the south.  Up here in northern climes, 1kWh in december is good, and 0 is not unusual.

 

I did mine on an East / west split at a low angle to try and prolong the generation throughout the day with less of a big mid day peak to make self use of the electricity easier.  Perhaps if you are installing batteries and they can charge at a rate to use all the peak generation, then optimising for mad daily output would be better.

 

The real boffins would of course have tracking panels, or at least a manual summer / winter adjustment to elevation.

[JamesPa]

As well as a more favourable angle and longer days, there is probably less cloud here also.  I'm in the South East so there are quite a few sunny days even in winter.  The figures are from PVGIS,

 

I haven't verified the figures by experiment.  My panels are at 15degrees on a flat roof.  However I'm now thinking that its a roof we only really look at during summer, so tilting them seasonally is by no means out of the question.

[Ajn]

before we moved we had a south facing 3.5kw system and my son half a mile away had an east west 3.5kw system split both sides of the roof on a dual input inverter. interestingly his produced no less than ours during the winter months.

Edited May 28, 2022 by Ajn

[SteamyTea]

The steeper the angles, more 'land' area is needed because of shading other modules.

This is OK if you can moor the narrow boat with the bow or the stern pointing east, with ne set of optimally angles modules running the length.

No good if it is turned 90° and al but one modules are shaded.

 

You may have noticed that some large solar farms are set at quite shallow angles, the overall annual yield is greater, even though peak power is clipped.

This has two benefit to the operator, they get paid more and can often keep below an export limit, which is based on peak power, not energy exported.

 

One of the Birmingham universities made a solar powered narrow boat.

[JamesPa]

 

3 hours ago, SteamyTea said:

The steeper the angles, more 'land' area is needed because of shading other modules.

This is OK if you can moor the narrow boat with the bow or the stern pointing east, with ne set of optimally angles modules running the length.

No good if it is turned 90° and al but one modules are shaded.

 

You may have noticed that some large solar farms are set at quite shallow angles, the overall annual yield is greater, even though peak power is clipped.

This has two benefit to the operator, they get paid more and can often keep below an export limit, which is based on peak power, not energy exported.

 

One of the Birmingham universities made a solar powered narrow boat.

The boat is moored (in winter) pointing either North/South or South/North.  There are various proprietary solutions for Narrowboats so that you can tilt the panels either one way or t'other.  In this case I'm only looking to harvest enough energy to recharge domestic batteries in 2 weeks after they have had about 3 days of use - about 2kWh in total.  heating and propulsion are both diesel.  A couple of 120W panels should do this and narrowboats are also long, so with a modest number of panels shading isn't a problem even in winter. 

 

I think this branch of the discussion probably belongs in a boating forum however!

 

 

[SteamyTea]

You may find that you are better off with a 200W wind turbine on a long pole.

My sister runs a narrowboat business.  I think she just has extra batteries to cover the times the boat is not used.  They charge up pretty rapidly once the old motor is running.

[Ronski]

Perhaps I should glad the rear of my almost south facing house in solar panels.

[SteamyTea]

1 minute ago, Ronski said:

Perhaps I should glad the rear of my almost south facing house in solar panels.

If it is by the canal, sell the power, and mooring rights, to @JamesPa