NREL's Dr Debra Lew discusses the Western Wind and Solar Integration Study (WWSIS)

Beyond Zero Emissions' Matthew Wright and Scott Bilby speak to Dr. Debra Lew, project manager for the National Renewable Energy Laboratory in the United States, about the Western Wind and Solar Integration Study, the partner study to it's Eastern Counterpart.

Beyond Zero interviews Debra Lew of the NREL's Western Wind & Solar Integration Study

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Scott Bilby:

Hello, welcome to Beyond Zero, this is a show covering issues relating to climate change, including the latest news, science and solutions. Beyond Zero is producted in the studios of 3CR Melbourne, broadcast Australia wide on the community radio network, and syndicated internationally. This show is produced by Beyond Zero Emissions, an Australian based climate change campaign centre. It is our understanding that human-caused global warming has already exceeded safe limits and that we must act immediately to reduce our levels of green house gas emissions to zero and below. My name is Scott Bilby and with me in the studio is Matthew Wright, how're you going Matthew?

Matthew Wright:

It's a great day, Scott and a great day to be in the studio.

Scott Bilby:

Today we're speaking with Dr Debra Lew, from the National Renewable Energy Laboratories, she's their project manager on the Western Wind and Solar integration study. Now you may recall we interviewed about its partner study, the Eastern Wind Integration Transmission study a little while back so we're very interested to hear what Debra has to say. Thankyou for joining us on the show today Debra!

Debra Lew:

Oh no problems, thank you for having me

Scott Bilby:

Now the first question that we ask people is how did you get interested in renewable energy?

Debra Lew:

oh, I actually, I used to be a physicist, a solid state physicist, working on technologies, high temperature superconductors that were far off in the future and I decided that I didn't want to be working on things that were, say, 30 or 50 years off, I wanted to work on something that was going to affect people now, and I decided to work on something that a physicist could do to help the world, and I decided that renewable energy was the thing I could do that would help make positive change.

Scott Bilby:

You certainly chose the right place at the NREL laboratory. So this Western Wind and Solar Integration study, I really think it is going to help change America, can you tell us a little bit about the background to how that study came about and who paid for that etc?

Debra Lew:

Sure. It was paid for by the US Department of Energy and our lab, the National Renewable Energy Lab is one of the US Department of Energy's  labs that do research on energy, and our focus is renewables and efficiency. The way the study got started was, there were a lot of folks out there in the West who were trying to make decisions and answer questions about things like how can we integrate large penetration of wind and solar renewable energy into the grid in the West, how does geographic diversity of those resources help, what's the role of transmission, how does forecasting help, how can our existing hydro facilities help, what's going to be the impact of these renewables that are variable. The wind and solar fluctuate during the day, you can't perfectly forecast what the weather is going to be tomorrow and a lot of folks were thinking that you need a lot of storage or backup generation to help mitigate these resource variabilities. We undertook this study to try and help answer those questions, to try and help our public utility commissioners and our utilities and our developers and other resource planners make decisions.

Scott Bilby:

What was the major finding, what were the standout features of the study to you?

Debra Lew:

We find that we can integrate up to 35 percent, that was the maximum that we looked at, 35 percent wind and solar energy penetration in the grid, if some significant changes are made to current operational practice. We find that it is technically feasible to integrate 35 percent wind and solar energy, that is have 35 percent of our load served by those renewable energy sources and that it does not necessitate expensive additional infrastructure. It does require siginificant changes to how the grid is operated today.

Scott Bilby:

Which renewable technologies were you looking at? Can you list them?

Debra Lew:

Sure, we looked at large wind farms, we looked at solar photovoltaics, and concentrating solar power with thermal storage, the three technologies.

Matthew Wright:

What was your benchmark for wind farms, what was the hub height that you were using and were you using hub height wind data, or were you using met. stations?

Debra Lew:

This is a very good point. To develop the input to this integration study was a big research effort in and of itself; there is not that much wind and solar data available, measurement wise, to make up the inputs for this kind of a study, on the scale of a 35 percent integration, so in order to develop all these hypothetical wind and solar plants we had to undertake a large simulation of the weather of the Western half of the US and we historically modelled the years 2004, 2005 and 2006, so we essentially went back in time and historically made a three dimensional model of the atmosphere of the Western US and then basically sampled the wind at two kilometre intervals every ten minutes at five different hub heights actually and made this gigantic wind data set. Then, from that, we picked out the best wind sites, we selected a wind turbine that we thought would be appropriate for out ten years or so, we looked at a hundred metre hub height and a three megawatt turbine, and used that to model our wind plan. We did something relatively similar but not as high resolution on the solar side. It was a huge effort and now these data sets are available on the internet so anyone else who is doing studies on wind and solar can go and tap in to these data sets to get time series  data for wind and solar plant production for these years.

Matthew Wright:

I assume the solar-photovoltaic was distributed throughout the entire study area?

Debra Lew:

That's correct. We don't know that much about large centralised PV plants and how they operate and what their characteristics are, especially on a sub-hourly basis when there might be a lot of fast-moving cloud so what we did instead, because we're still learning about that is we modeled rooftop PV. We modelled small systems, on roof-tops, in metropolitan areas, where we think they're likely to be proliferating. In the next follow-up work to this we hope to have models to model 200 megawatt PV plants, but at this time we just limited it to distributed generation roof-top PV.

Matthew Wright:

With the solar thermal, was that limited to the usual places, SouthWest, Nevada way, or Arizona?

Debra Lew:

We pretty much had the Concentrating Solar Thermal just in the New Mexico, Arizona, Colorado, Nevada, California, the South West and the desert areas.

Matthew Wright:

You said they had thermal storage, can you tell how much thermal storage was incorporated into those plants and why that figure was chosen?

Debra Lew:

We basically modelled six hours of thermal storage and the way we have selected that amount of thermal storage was to do an optimisation of where we thought it would be, basically in order to have six hours of thermal storage for say a hundred megawatt concentrating solar plant, you need to double the solar field size that you would have for a hundred megawatt solar thermal plant without the storage. Basically what we did was an analysis looking at different amounts of storage, different solar field sizes and found the optimum point, we decided that six hours provided the best price point. That's actually very similar to a plant that's been developed right now in Arizona by Abengoa, there's a solar thermal plant with six hours of thermal storage going in down there, so it actually ends up being very similar to what's going on in our region.

Matthew Wright:

I think that's the Solana plant isn't it?

Debra Lew:

Yes

Matthew Wright:

So you modelled that as a parabolic trough plant then, not as a central receiver plant?

Debra Lew:

Right, the parabolic trough plants.

Matthew Wright:

Did you find seasonally that certain seasons were harder to cater for in renewable energy than others, was the Winter the time that had less cumulative renewable resource, solar plus wind, or was that in the summer or some other season?

Debra Lew:

I should explain that when I said 35 percent wind and solar we actually broke that down, different penetration levels, 35 percent was the highest penetration level. Because we understand a lot more about the wind resource and believed that wind was more cost-competitive, we put a lot more wind in there than we did solar. We put in 30 percent wind energy penetration and only five percent solar. As a result, when you look at the monthly average energy coming out of the wind and solar facilities it's much greater in the Winter time, when the wind is peaking, than it is in the Summer time, when the solar is peaking, just because we've got so much more wind power in our study. So what we actually find is that there's probably the highest production in April, through out `Spring months, we get a lot of wind then and we also have pretty strong solar. In a lot of this region, even though you expect the solar to be best in the summer, we have these late afternoon thunder showers that come through that actually make the solar not quite as good in the summer as it might be in the spring time. So April, May, those months tend to have our peak wind and solar energy production and actually there are hours when the wind and solar output exceeds the load, so we're actually meeting the entire load of the area that we looked at with wind and solar, and trying to push out, export, that wind and solar to other balancing areas. It's quite a challenging thing, actually, to reach the 35 percent limit, because it's 35 percent on an average annual basis, but on a month by month basis, or on a day by day basis, or on an hour by hour basis the penetration levels can be much higher than that.

Scott Bilby:

Those times, those days or months when the renewable energy that you were talking about, it could potentially exceed load, what impact could that have further down the line for existing fossil fuel plants?

Debra Lew:

That's really the crux of why this is so challenging and what we're trying to model. You've got some plants that are must-run, for reliability reasons, you've got some base-load plants like nuclear units that you're just not going to ask to change their set-points at all, you've got some base-load plants that really can't ramp up and down all that much, or if you shut them down then you've got some minimum amount of down time for them. So there's a lot of constraints that we had to take into account with respect to those other units that are on line, and at the same time, there are good things, when you've got a lot of this wind and solar online you end up backing down some of those plants. On the one hand, you have to decommit, or essentially turn off some of those plants, but some of those plants you're just backing down. It does mean that when you're backing those plants down to lower set points you've got a lot of room to move up, so it's good in the sense that you've got a pretty big reserve margin to play with, in case you have any problems, you have a nice up reserve margin as a result of that backing down of other units. It's definitely one of the biggest issues, how the wind and solar affect the other plants, we don't know a whole lot, quantitatively, about the longer term impact of increased ramping and cycling of some of these other units, of some of these old coal units for example. There's going to be some cost, maybe increased operations and maintenance and maybe repair as a result of that increased ramping that we're asking them to do and we haven't really got good quantification of those costs and impacts yet.

Scott Bilby:

We're speaking with Dr Debra Lew, the National Renewable Energy Laboratory's project manager of the Western Wind and Solar Integration Study. Debra, you were saying that you only allowed for about five percent solar, but it seems that, potentially, a scenario could be where you could have vastly more than that, and then that starts really reducing the kind of, if you're exceeding the load, then by definition you're reducing the amount of coal fired plants anyway, is that correct?

Debra Lew:

Right. With very large penetrations we're reducing the amount of generation that we need from other plants. Because the wind and solar do provide some contribution to resource adequacy, what I mean is they contribute to the reliability of the system, maybe not full nameplate capacity reliability but they do contribute and they do provide some capacity value to the system. That means that there are some coal or gas or traditional plants that don't need to be built as a result of adding on all of this wind and solar.

Matthew Wright:

Against the average output of the wind, what was the capacity factors that you came up with? Was it like 20 percent could be considered firm wind, or 15 percent of the nameplate could be considered firm wind?

Debra Lew:

Our capacity values on the wind side were not real high, between 10 and 15 percent, but this is at, as I say, up to 30 percent wind penetration, and as you increase the penetration of wind that capacity value drops. Between 10 and 15 percent is what we saw for the wind. For the concentrated solar power it's actually extremely high, it's like 95 percent, that's equivalent to a natural gas plant or even better than traditional thermal plants, but on the wind side it's a bunch lower.

Matthew Wright:

I think potentially, 15 percent is quite high really, because the annual average that you expect in output is 30 percent of the nameplate, so 15 percent is really half of what you'd expect in terms of contribution to the grid's annual operating.

Debra Lew:

Right, we actually have some pretty good wind resources here in a lot of these regions, especially in the Colorado, Wyoming, New Mexico region, that sort of middle of the country, we've got much higher than 30 percent capacity factors, but in some of the other areas there more like 30 percent.

Matthew Wright:

So what was the average capacity factor across the grid?

Debra Lew:

I don't recall off hand what the average was across the whole area, but I'd say, for the studied footprint that we focused on, which is the Nevada, Arizona, New Mexico, Colorado, Wyoming area probably I'd guess around 35 percent.

Matthew Wright:

That sounds pretty good.

Scott Bilby:

Were there any states, Western states, that you would have ordinarily included in this sort of study but for one reason or another wasn't included in the study?

Debra Lew:

First off, we modeled the whole Western interconnection; you probably know the United States is divided into three interconnections, the West, East and Texas, and we modeled the whole Western interconnection, we modeled all of the West but we focussed in on a certain number of states that were part of this West Connect group of utilities, because West Connect was one of our main partners of the study. West Connect is a group of utilities that's trying to take those steps in co-operation that they think makes the most sense in terms of enhancing wholesale electricity markets in the West. They're already taking steps in the right direction, and we're helping them take more of those kinds of steps. One of the areas that is notably absent is Utah, that's because it's not part of this West Connect group of utilities, California also isn't - well it is part of this West Connect group of utilities but had just done their own integration study, so we didn't focus in on those areas, although in the overall modeling we do include them, but we don't focus in on them and do detailed modeling in those regions.

Matthew Wright:

If the interconnects were all included, how would that affect the firm capacity numbers; if you actually had California in there, if you had a connection to Texas,

Debra Lew:

Well California would probably lower some of these capacity values I would guess because their wind resources aren't as good as the middle of the country. Texas has excellent wind resources so that would probably help to boost things. It all, of course, depends on when the system peak is happening in those regions.

Matthew Wright:

Was forecasting included and how did that affect things?

Debra Lew:

Forecasting was a big part of this. We basically found that there was a large benefit from wind forecasting. We looked at forecasting in two different ways, first we ran the system without using any forecasts, then we ran the system using a forecast that we had one of the local forecasters provide for the different wind farms in the West, then we ran the system using a perfect forecast. The biggest increase, and we were looking at around five billion dollars worth of savings, comes from just using the forecast in the utilities, they had given a commitment to planning process. So just by using a forecast there's a huge saving, about five billion dollars in the high renewables case. Then when you move to a perfect forecast from that, there's about 500 million dollars of additional saving. So the most important thing that we tell folks is that they need to use a forecast in their planning processes. Right now some utilities still don't do that. As utilities get more and more experienced with wind in the US they start to hire forecasting services and even multiple forecasting providers incorporate forecasting. But a lot of utilities, when they don't have a lot of experience, they don't necessarily see the benefit of forecasting.

Scott Bilby:

If the forecasting is not very good or is quite poor, does that mean that you end up with low reserves, the sort of power that you have to keep in reserve, for these renewable plants, how does the forecasting affect that?

Debra Lew:

While the forecast generally looked pretty good, there are those times when you really miss the forecast badly. On average it looks good, but you've got those extremes where it looks really bad and if you under-forecast and there's a lot of wind and solar coming on the next day, then that's pretty easy to deal with, because you can just curtail the wind or solar and have them not produce. But if you over-forecast, and then the next day you find out that the wind doesn't show up or the solar doesn't show up, and you have one of those extreme over-forecasts, this can result in contingency reserve shortfalls, and in order to deal with these kinds of shortfalls there are different things that folks can do. They can commit more reserves, they can add storage, there's different options for dealing with this. However, I should note that we only find these kinds of shortfalls about one percent of the time, so if you install new storage or if you commit extra reserves for every hour of the year when these kinds of problems only occur one percent of the time, then it can be a really expensive way to address these reserve shortfalls. So instead, what we recommend, and what we find to be cheaper, is a demand response programme, which is a kind of programme where you would pay load to turn off. You would contract with industrial loads, maybe like a water pumping load, and at certain hours of the year you might send a signal to them and ask them to turn off for a couple hours, and they can turn back on after that. So we see that as being a much better way of dealing with this problem that only occurs for tens of hours out of year.

Matthew Wright:

Would the erection of the wind farms, as they're rolled out, and their on-board monitoring be fed back to forecasting services, so effectively we'd expect that forecasting would get closer and closer towards perfect all the time because there'd be lots more inputs at hub height?

Debra Lew:

That's actually being done, now, in some areas, like New York and Texas, California, where they are taking that data from the existing wind plants as well as the towers at the plants and feeding that directly into the forecasting models to improve the forecasting models. So that is something that is on-going. We think that there are probably a number of ways to increase forecasting accuracy. That could be one of them, another one could be improved resolution of our existing national weather service models. There's a bunch of different improvements that are in the works right now.

Scott Bilby:

There are many more questions that we could ask you, but I think we're going to have to ask a question that's starting to draw a conclusion because there's so much more that we could ask you, but the Western Wind and Solar Integration study, and the Eastern wind integration and transmission study. You've got the results from those now so what's the next step for the Department of Energy and NREL?

Debra Lew:

For one thing, these studies are one piece of a bigger puzzle that needs to be addressed before you'd install this much wind and maintain reliability. In these studies we look at hourly analyses, we look at down to a one-minute level, we do some statistical analysis. It's steady state analysis. We don't do any sort of dynamic analysis, we don't look at frequency, there's a whole bunch of other types of studies that need to happen before this actually becomes a reality. So those are some of the things that need to happen next, there's a lot more follow-up and detail that we'd like to follow-up these studies with, for example, as a result of the Western study, there's now a proposal in the Western US to have an energy imbalance market, which would essentially allow utilities to trade with each other on a five minute, or a ten minute or some sub-hourly basis. We want to try and support that as a movement in the right direction because that's one of the most important kinds of things that can happen in the West, where it's integrating wind and solar, so there's some analysis that needs to be done to support that. There's a lot of follow-on we're looking at for these two studies.

Scott Bilby:

We're looking very much towards the great conclusions from all that follow-on work because the work that you guys are doing so far is pretty impressive so we'd like to thank you very much

Debra Lew:

Oh thank you for having me!

Scott Bilby:

Thank you.

Matthew Wright:

That's fantastic

Scott Bilby:

We were just speaking with Dr Deborah Lew, the National Renewable Energy Laboratory's project manager of the Western Wind and Solar Integration Study. If you want to know more about the National Renewable Energy Laboratory go to "http://www.nrel.gov/", and if you want to know more about Beyond Zero Emissions, go to “http://www.beyondzeroemissions.org”