The road to solar...

[philip]

I suppose 25m² is comparable to the amount of panels fitted on a typical house roof, so it that respect the path could be considered as equivalent.

[Kim]

There's a big difference between the area needed to meet the average consumption for a house, given sufficient storage and diversity to cope with peak loads, and the amount of capacity you'd need to actually power a couple of houses.

For this reason I think that the "could supply n houses" is a slightly less useful unit than the milliPirate-Ninja, and maybe it would be simpler if we all just used Watts.  File with London buses per Olympic swimming pool.

[Cudzoziemiec]

Another way to think of it might be "We're building a cycle path. Shall we surface it in tarmac, concrete, or solar panels? (Or for Sustrans, mud.)"

[philip]

If we ignore the peaks, how much would 25m² of solar cycle path generate? If it can produce about a kW in favourable conditions it could produce 10kWh in a day, that might power a house.

[Kim]

Another way to think of it might be "We're building a cycle path. Shall we surface it in tarmac, concrete, or solar panels? (Or for Sustrans, mud.)"

That's certainly the logic, but you also have to factor in the alternative of building a solar roof over the cycle path, with cheaper, cleaner panels inclined at a more productive angle.  It'd be brilliant: Not only do you get free electricity to power some inadequate lighting and an audio-visual art installation, but the shade helps keep the mud slippery and the puddles full even in the peak of summer.

Or, more pragmatically, building a normal cyclepath and installing some solar panels somewhere else.

[Beardy]

Dave on EEV has done a few YouTube videos on solar roadways. He holds them in almost as much contempt as he does wireless energy startups.

Here are the two most recent
Spanish pavement
US solar roadways

[Cudzoziemiec]

Another way to think of it might be "We're building a cycle path. Shall we surface it in tarmac, concrete, or solar panels? (Or for Sustrans, mud.)"

That's certainly the logic, but you also have to factor in the alternative of building a solar roof over the cycle path, with cheaper, cleaner panels inclined at a more productive angle.  It'd be brilliant: Not only do you get free electricity to power some inadequate lighting and an audio-visual art installation, but the shade helps keep the mud slippery and the puddles full even in the peak of summer. pragmatically, building a normal cyclepath and installing some solar panels somewhere else.

You forgot that it would also provide a pigeon perch in the optimum position for shitting on cyclists.

[Wycombewheeler]

I suppose 25m² is comparable to the amount of panels fitted on a typical house roof, so it that respect the path could be considered as equivalent.

I think the typical house with solar panels does not have 25m2 of panels.  I don't think the area of my roof is a large as that,  unless covering all faces,  which would be crazy,  very little sun falling on the north side.

[DuncanM]

The typical house install in the UK does not have 25m² of solar panels. The average panel is rated around 300W, and is about 1m² . IIRC, you need to apply to the DNO for permission if you want to install an array capable of more than 4.5kW peak, meaning you end up with about 14 panels or so. We have 15 on our house and because they are east/west the peak is probably around 3kW.
On a really good summers day, generation peaks around 28kWh. On really crappy winter days it can struggle to get to 1kWh.

There are other issues with sticking panels on the floor, like the effect shading has, and how the inverters can deal with it. I guess you would probably use micro-inverters so that each panel has it's own inverter, to avoid the effect where part of the roadway is in shadow so the whole thing isn't working properly, but this approach adds cost. 

[quixoticgeek]

The typical house install in the UK does not have 25m² of solar panels. The average panel is rated around 300W, and is about 1m² . IIRC, you need to apply to the DNO for permission if you want to install an array capable of more than 4.5kW peak, meaning you end up with about 14 panels or so. We have 15 on our house and because they are east/west the peak is probably around 3kW.
On a really good summers day, generation peaks around 28kWh. On really crappy winter days it can struggle to get to 1kWh.

Doesn't have 25m² of panels, but could. A 50m² house with a south facing pitched roof has 25m² of roof available.

A DNO is only required if you are exporting >4.5kW to the grid. If you are using the rest locally, then it's not a problem. This is also a UK specific requirement, in other locations it's different.

I heard a stat recently, but have been unable to confirm it, that in Australia, there is so much sun that panels on the south facing roof can yield more power than panels on a similarly pitched south roof in Germany. I need to confirm if that's true. Tho.

There are other issues with sticking panels on the floor, like the effect shading has, and how the inverters can deal with it. I guess you would probably use micro-inverters so that each panel has it's own inverter, to avoid the effect where part of the roadway is in shadow so the whole thing isn't working properly, but this approach adds cost.

Oh yes, I didn't get into that on my rants as I didn't want to get too technical. But yep, all those issues!

J

[jsabine]

I assumed that was QG's point.

[canny colin]

I wonder what will happen if a truck goes astray and gets a wheel on to  a corner of the  panel / path . Dutch trucks do have high axel loading for on / off road use . 

[mrcharly-YHT]

Most of this ignores another problem with wind/solar/tidal; building a grid that can cope with fluctuations.

It is entirely possible to have a 'local area' grid that also exports power. However, this is not often what is configured.

A perfect example of this exists in the Outer Hebrides. Tons of wind power. Turbines all over; lots of community groups invested in them.

Then the grid connection to the mainland grid was severed. The turbines had to be turned off.
Consequences:

• No income for community groups.
• Power supplied by (very) dirty diesel generators.
• Reduction in renewable power across Scotland

It will have taken 10 months to get the interconnector back up.

Have they learned from this?

No. There is a scheme to build several 180m tall turbines. Blade diameter 250m.

[ravenbait]

FWIW, people involved in infrastructure are VERY aware that the network just doesn't have the capacity to convert all power demands to renewables. What we do about it is another question entirely.

Sam

[DuncanM]

A DNO is only required if you are exporting >4.5kW to the grid. If you are using the rest locally, then it's not a problem. This is also a UK specific requirement, in other locations it's different.

I don't think it's possible to have >4.5kW generation capacity and limit the export so as to stay under that number for DNO purposes (legally, I'm sure it's technically possible).
You are absolutely right that it's a UK condition, and also that conditions in other countries may be much better suited to solar PV. One thing that people don't consider is that length of day is almost as important as sunshine - if the temperature gets too hot then the panels become less efficient.

[Kim]

Most of this ignores another problem with wind/solar/tidal; building a grid that can cope with fluctuations.

It is entirely possible to have a 'local area' grid that also exports power. However, this is not often what is configured.

A perfect example of this exists in the Outer Hebrides. Tons of wind power. Turbines all over; lots of community groups invested in them.

Then the grid connection to the mainland grid was severed. The turbines had to be turned off.
Consequences:

• No income for community groups.
• Power supplied by (very) dirty diesel generators.
• Reduction in renewable power across Scotland

It will have taken 10 months to get the interconnector back up.

Have they learned from this?

No. There is a scheme to build several 180m tall turbines. Blade diameter 250m.

To their credit, the Universiy of Birmingham actually learned this lesson:  After the Great Selly Oak Substation Fire of 2012 the campus was without power for a couple of weeks, while their half-megawatt natural gas CHP station sat there uselessly.  They had to bring in portable diesel generators to supply each building individually so they could make them safe for public use (lifts, lighting).

They've since installed a modest diesel generator and the control gear needed to boostrap and synchronise the turbine in the absence of grid power.  I've even seen them testing it.

(Bet their IT infra is still a single point of failure, thobut.)

It's one thing being in the middle of a city and not being aware that your electricity supply all runs through a single duct under a live railway line.  If you're on an island, it seems ludicrous to rely on an interconnector like that.  No doubt it saves a few quid on black start capability.  Turbines make money; resilience wastes it.

[SoreTween]

The typical house install in the UK does not have 25m² of solar panels. The average panel is rated around 300W, and is about 1m² .

I think you're a bit high there, 200w per m² is closer currently.

[DuncanM]

The typical house install in the UK does not have 25m² of solar panels. The average panel is rated around 300W, and is about 1m² .

I think you're a bit high there, 200w per m² is closer currently.

Good point - the panels are 300W, but they are more like 1.5m to 1m