With the big growth, or planned growth, in wind and solar in many countries you need to connect up new windfarms and solar arrays with people. This requires power transmission lines.
Electricity grids also have to match supply and demand on a second by second basis. This presents a problem, especially with renewables like wind or solar which may produce 1 GW during a sunny windy day and 0.01 GW during a calm night.
One solution put forward is “affordable storage capacity”. Let’s say for now, along with everyone (serious) writing reports, papers and feasibility studies, that there is no “affordable storage capacity”, except for hydroelectric storage, which is mostly “tapped out” in developed countries. There might be – via some as yet unknown technology breakthrough – but until then storage isn’t an option. If this happens – problem solved – and the world has a major breakthrough.
So we need baseload supply for times when intermittent renewable supply is not available (at the moment this requires a conventional power plant, as we saw in earlier sections, e.g. Part IV)
Or maybe not.
Perhaps instead we can put massive solar arrays in Arizona, massive windfarms in South Dakota, more massive solar arrays in Libya and connect up the supply to Germany, or any country that wants to transform its electricity supply into renewable energy.
Kind of a massive outsourcing exercise. After all, why put solar arrays in Germany when there is so little sun? Why put windfarms in Germany when it really doesn’t have that much wind? Why not put up windfarms in places with lots and lots of wind and not many people, and solar into places with the highest solar insolation and not many people?
All you need is to connect them up with transmission lines. Not very difficult. Not a technical challenge at all. As one commenter said in an earlier article “An Atlantic interconnector may sound fanciful, but a UK Norway link is a live project, and an Iceland project is under feasibility.”
So, it’s clear, we can get power from A (source) to B (population). It’s just a piece of wire.
But what does it cost? That’s the real question. Generally the answer is “pricey”. Because it’s very substantial pieces of heavy wire with large support structures to get it from A to B, and massive transformers or large banks of thyristors.
In one paper (Osmani et al 2013) I read the costs of building new transmission were quoted as $/kWh. Yes, a paper with a sense of humor..
Think of building a railroad. Your cost depends on the terrain, cost of material, and cost of contractors. And very important: the length – whether you are running from Washington DC to Richmond, Virginia or from Portland, Oregon to Fort Lauderdale, Florida. At the end you’ve built the railroad. If one person a day or 10,000 a day travels the railroad the cost invested will still be the same. So quoting $/passenger isn’t exactly useful for an overall idea of what it costs to build a railroad. Better to quote $/mile for construction across a few different terrains and let everyone else do the maths for different passenger numbers.
Quoting $/kWh for power transmission is about as useful as saying the average cost of a journey = $7.46, when averaging domestic & international plane flights, train & bus journeys, dinner with friends, and all those trips to the local 7-11.
There are two options with transmitting lots of power – a.c. (alternating current) or d.c. (direct current). AC is what you have in your homes, it is what is supplied by the grid, and it is how most power is moved around.
Once you get past a certain distance, DC is a lower cost option. The “break-even point” is always changing but in essence the actual transmission costs are always less with DC, but the conversion costs (from AC to DC and back to AC at the other end) are significant.
The crossover point is around 800km for overhead lines, and 50km for subseas lines (Electric Power Systems, Weedy et al, 2012 – and see extract for more details in note 1).
There is another important point – if you just want to get power from say Innamincka in central Australia to Melbourne, Australia (see Part VII where we looked at the failure, so far, to obtain power from 4km deep geothermal sources) then HVDC is a good choice. But if you want to add in the power from lots of wind farms or solar arrays on the way, then all those conversion stations will start to cost and using AC transmission would be better:
Figure 1 – Thyristor (top) and Thyristor Bank for AC-HVDC conversion (bottom) – these babies ain’t cheap
Finding quality data on transmission costs is not so easy. The people who really know are in companies that provide these construction services and their data is confidential, like any business.
For example, if you want to find out what an LNG plant costs you might be able to dig through some annual reports of a few customers of LNG plants and see their capex costs revealed in expenses lines or in notes/discussion, but then you wonder why one plant of the same capacity was 20% more than the other. Maybe one of them negotiated a better deal with Bechtel. Maybe one customer provided some of the key services themselves and that reduced the price. Maybe another customer insisted on a given subcontractor or technology because of their view on the long term O&M costs and that increased the price. Maybe Bechtel was stretched on the last plant and gave a higher price and the customer didn’t have a better EPC to build it.
Onto power transmission costs which has similar challenges for the outside observer.
In reviewing the AEMO report for Renewables VI – Report says.. 100% Renewables by 2030 or 2050 – I found a link to a transmission costing report – Network Extensions to Remote Areas Part 2 – Innamincka Case Study – which was very useful (I have lost the link where I downloaded this report, I can email the pdf report to anyone interested). This looked at the cost of power transmission from a possible geothermal source in central Australia to a few population centers.
The costs are given in Australian Dollars, but the report was 2009 and the conversion from the greenback was at US$1 = A$1.20 so the costs are basically similar in US$, given the lack of hard data, changes in costs of various materials, and so on.
My summary of their table, followed by the table itself:
- AC transmission of 5GW – 1000 km (620 miles), 765kV double circuit line with series compensation – $3.3 BN to $5.1 BN
- as above but with two cities as stop off points – $3.9 BN to $6.1 BN
- DC transmission of 4GW – 1100km (680 miles), +/- 800 kV bipole – $2.5 BN to $3.5 BN
Click to expand
The report states:
Note that this study has not taken into account the following routing considerations which could add to the cost of the transmission options :
- a) Excessive wind and ice loading (the study assumed moderate winds with no allowance for cyclonic conditions and no ice loading)
- b) Minimization of visual impact
- c) Complexity of terrain
The indicative costs in this report exclude :
- a) Allowance for difficult terrain such as forested, hilly ,or mountainous
- b) Costs for access roads
- c) Statutory compliance costs
- d) Consenting costs
- e) Allowance for project scope accuracy
- f) Price contingency for exchange rate variation, manufacturing market pressures, and price of materials
- g) Interest During Construction
- h) Operating and maintenance costs
- i) Cost of losses
For example, if this was Europe or most parts of the US you would need to add “a lot” (maybe 25%) for additional costs to support the ice loading. If you have to consider very high wind conditions – that’s more cash. If you need to go through cities or over mountains, add “a lot more”.
So from this report, as a rule of thumb, think $1BN per 1GW per 1000km as the likely minimum. From the scaling in their calculations increasing the power by a factor of 10 increases the HVDC costs by a factor of around 4, but I can’t say whether that holds true if you want to increase by another factor of 10 (they weren’t trying to design for 10x the power).
If you live in a country which has an environmental lobby with political power then you can add “even more” due to costs of ensuring the lesser-spotted green frog is not at risk when putting up the necessary support structures:
If you want to ensure that a tower coming down doesn’t bring down the power transmission then you need two of the above for the whole journey, adding “a lot” to costs:
The cost of land access can be high, depending on the country and the right of easements given to utilities.
In future articles we will try to find other pricing points to see how this compares.
These costs also worked on the basis of keeping the losses below 10% for the 1000km distance. If you want to reduce losses then you need to spend more – bigger conductors (more cash), stronger support structures to support these heavier conductors (more cash).
Route 66 and Relocation Relocation
The US used 4,500,000 GWh of electricity in 2011 (Osmani et al 2013). This equates to an average (but not a peak) of just over 500 GW.
So if we wanted to bring 50GW of solar power from Arizona to the North East then we are looking at a distance of something like 3,500km and a cost (assuming the scaling holds from the report) of $100 BN, plus all the exclusions listed above. Maybe with economies of scale this might be $50BN, on the other hand it might be $300BN.
I’m just trying to some perspective on the order of magnitude of the costs.
And for this distance, at the efficiencies noted, this would include a loss of at least 35% of the source energy. So multiply the cost of 50GW of solar in Arizona x 1.5 to cover the losses. And don’t forget to increase the AC-HVDC conversion costs at the source end by 1.5 – and so on. (Depending on the relative costs, it might be more cost-effective to spend less on solar arrays and more on transmission).
If we have distributed wind farms through the midwest and solar arrays in the southwest and we want to take that power around the country it’s clearly going to be a lot more. It all depends on the amount of power, the number of feed-in points, the number of extraction points, the distance, the terrain.. To do this we would probably have a mix of DC and AC lines. If the whole network was AC the cost might double.
We can see that locally-produced power has a large benefit over long-distance power. Moving, or outsourcing, power production has a significant price tag and a significant power loss.
Still, it’s a price point. When we have some approximate costs and efficiencies of local wind and solar production we can see whether the transmission costs justify the relocation.
Maybe someone has already done a detailed cost analysis of a “massive inter-state power transmission” project.
Articles in this Series
Renewable Energy I – Introduction
Renewables II – Solar and Free Lunches – Solar power
Renewables III – US Grid Operators’ Opinions – The grid operators’ concerns
Renewables IV – Wind, Forecast Horizon & Backups – Some more detail about wind power – what do we do when the wind goes on vacation
Electricity generation from renewables in the United States: Resource potential, current usage, technical status, challenges, strategies, policies, and future directions, Atif Osmani et al, Renewable and Sustainable Energy Reviews (2013) – paywall paper
Electric Power Systems, John Wiley & Sons Ltd, Weedy et al, 5th edition (2012) – textbook
Network Extensions to Remote Areas Part 2 – Innamincka Case Study, by Power Systems Consultants Australia Pty Ltd, for Australian Energy Market Operator Ltd, 2009
Note 1: Electric Power Systems, 5th edition (2012) has a good summary on AC vs DC: