Hydro, Wind and Solar PV

Some brief summary notes on hydro, wind and solar PV from various sources that I've read recently. I've prepared this to help me with my exams.

Low and zero carbon sources of energy generation accounts for approximately 15% of the global energy mix, with nuclear and hydropower around 6% each, and the rest of the renewables portfolio (biomass, wind, solar, wave etc.) making up the remaining 3%. While nuclear capacity has remained steady in the past 10 years, there has been steady growth in capacity of renewable energy, especially in hydro and wind.

In order to tackle climate change and to reach stabilisation levels of 550 ppm as advocated by policy makers, it is essential that low carbon technologies are ramped up to replace fossil fuels. For example in the UK, the UK Climate Change bill stipulates that GHG are to be reduced by 80% of 1990 levels by 2020, with 25-32% reduction goal by 2020. In order to reach this target, the government has mandated that by 2020, 20% of energy must come from renewable resources in line with its EU 20/20/20 obligations. This implies that the proportion of renewables generation in heating and cooling must increase from less than 1% to 10%, land transport from <1% to ~10%, and electricity production from <5% to ~40%. Similar targets are prevalent in other EU countries and in many states in America like California, who have mandatory renewable portfolios standards.

For the UK, this implies that by 2020, 57GW of renewable energy must be installed in order to reach the 20% target. Based on existing policies, it will be impossible to reach such levels due to the higher costs, political, social and logistical issues associated with renewables. The target can only be met with ambitious policies to promote same, backed up by finance and political and social support.

To reach the goals, there are a host of low carbon technologies at different levels of commercial development and potential. I will analyse 3 main technologies available today - hydro, wind, solar (both PV and concentrated).

HYDRO

Hydro is responsible for much of the growth in renewable energy generation globally in the next 10 years, especially in non-OECD countries in Asia and Central and South America. For example, China’s Three Gorges Dam project is expected to deliver 18.2 GW of new capacity and in India, 14.5 GW of hydropower is currently being constructed. In Brazil, 90% of electricity is generated from hydro and 12GW are on the pipelines to be installed.

Hydro is a mature technology that can provide baseload electricity and for large hydro, it is also dispatchable to meet peak demands. It also produces electricity at cost comparable with fossil fuels. However, there are large environmental and social concerns associated with damming rivers, such as displacement people and destruction of ecosystems. There are less environmental concerns with small scale hydro, which produce electricity based on water flow. However, since the river is not dammed, energy storage is not an option for small scale hydro. For example in Germany, CERs from large hydro projects are not eligible for compliance because of concerns over the environmental integrity of the credits (as reviewed by the World Commission on Dams).

In most of the developed world, hydro is no longer an option since most of the suitable sites have already been developed. There is therefore not much scope to exploit hydro for low carbon energy at least in developed countries.

SOLAR PV

There are broadly 3 types of solar, solar water heating, solar PV and concentrating solar power. I will concentrate on solar PV and CSP. Solar PV works by having solar photovoltaic cells converting the sun’s energy into electricity. Solar cells produce direct current from sunlight, and an inverter converts DC into AC current. The energy can then be distributed or stored in a battery. At the end of 2008, global cumulative solar PV capacity reach 15GW.

Although the PV sector has grown, it has not made a breakthrough in the market and contributes less than 1% of world energy production. With the exception of Germany, solar PV is not a significant source of energy even in sunny countries. The main stumbling block is the higher cost of producing solar cells and solar panels. With current technology solar PV can generate electricity at approximately 18-25 cents per kilowatt hour, compared to fossil fuel options which range between 3-7 cents per kilowatt. The installed cost today is around $8 a watt, meaning that to provide basic household needs it costs approcimately $30000 for solar panels. Amazingly, only half of the cost is due to production of solar cells. The rest is made up of panels, glass, inverter, labour and distribution costs. So even if the costs of solar cells decrease, it still needs to rely on the other costs to go down. It is therefore unlikely that silicon PV can ever become a low cost option.

There have been some recent technological breakthroughs, in the name of thin film solar cells. This technology has been able to cut costs down to $1-3 a watt, using less material and taking up less space. The problem is that all the materials that go into thin film are really rare – tellurium, indium, gallium, selenium. Therefore the ability to ramp up production is difficult.

Even if solar PV is price competitive, there are production restrictions associated with solar PV due to competition for basic raw materials like silicon with other industries such as the semiconductor industry. For example, the current cumulative production capability of the world solar PV industry is only around 6.85GW per year. To put that into perspective, NY city on a hot summer day uses around 12GW a day. Solar cells are also inefficient at converting the sun’s energy at around 12-23% conversion ratio, and take up large amounts of space for relatively low electricity generation. Even if solar PV grows by 50% per year for 10 years, a study has found that it would only contribute to 2.6% of the market. Therefore it can be questioned whether this technology can actually contribute to solving the problem in a meaningful timeframe.

Despite the prohibitive costs, the case study of Germany shows that solar PV may play a meaningful role if promoted by government policies. In Germany, form the 1990’s the government actively promoted solar PV through rebates, loans and feed-in-tariffs for excess electricity fed back into the grid. The market took off and by 2008 solar PV accounted for 1% of total electricity generation. Germany companies now account for 46% of the global solar PV market, generating over 10,000 jobs for the German workforce.

WIND

Wind energy is one of the most mature and fastest growing of all renewable technologies, and is now basically a production driven industry due to high demand of materials. The technology is now close to cost parity with fossil fuels at around 6 cents per kilowatt/hour, and can be scaled up as evidenced by current standard 5MW wind turbines. Wind now accounts for 1.5% of global electricity use and by 2008, capacity had reached 121 GW.

Wind turbines produce electricity by:
1. The wind blows on the blades and makes them turn.
2. The blades turns a shaft inside the nacelle (the box at the top of the turbine)
3. The shaft goes into a gearbox which increases the rotation speed enough for...
4. The generator, which uses magnetic fields to convert the rotational energy into electrical energy. These are similar to those found in normal power stations.
5. The power output goes to a transformer, which converts the electricity coming out of the generator at around 700 Volts (V) to the right voltage for distribution system, typically 33,000 V.
6. The national grid transmits the power around the country.

In Denmark, wind already contributes to 19% of total electricity generation and countries like Germany, Spain and Portugal are moving in the same direction. There are however some mentionable drawbacks to wind energy:

1. Capacity factor of 20-40% is far inferior to fossil fuel plants that can operate at 85% capacity. Therefore close to 3 times the capacity needs to be built to generate the same amount of electricity
2. Wind is intermittent and there is no available technology for large-scale storage of wind energy. It is therefore not a feasible solution for baseload electricity needs
3. wind resources are often distant from city centres where electricity demand is the highest. Exploitation of wind energy requires building of expensive transmission lines.
4. wind turbines may have negative impacts on local ecosystems and bird migration routes.
5. offshore wind is still a developing technology, with many uncertainties and technical difficulties relating to stability from strong winds and storms, and technological challenges in dealing with deeper water or less favorable soil conditions. It is therefore at least twice as expensive to develop as onshore wind.

The most effective policy instruments for further promotion of wind energy include feed-in-tariffs, mandatory long term power purchase contract to guarantee investment certainty, and assistance with high up-front capital costs through public-private partnerships. In terms of grid transmission, potential policies measures include direct funding for grid reinforcements and legal guarantee of grid access for renewables. These policies have been highly successful in Denmark, Germany and Spain and should be applied in all countries seeking to exploit this resource. It is also important to recognize that some of the barriers to wind are non-economic, such as protests from locals, land permits and environmental groups. This can be countered by policies that streamline application and permit procedures, as well as public engagement and education.

However, given current technology and grid systems, it has been argued that wind can only contribute up to 20% of electricity mix due to its inherent flaws such as intermittency and lack of storage. Technological breakthrough is needed in this area and more funding for R&D should be put in place.

To solve this problem and to increase wind’s share in the energy mix, improvements to the grid infrastructure through a smart grid will need to be built. This would consist of high voltage HVDC lines transmitting energy from distant wind farms to city centres. Another strategy, though not mutually exclusive, would be to set up microgrids for more distributed generation. A microgrid is an isolated grid with local generation; storage can operate autonomously, only connected to main grid when absolutely required. In each microgrid area, energy distributed through peer to peer technology where energy is transferred between peer to peer to create an aggregate supply of energy.

Wind energy will be especially important in the UK, where the RES targets will depend primarily on wind. In order to meet the target, it is envisioned that 14GW of onshore and 14GW of offshore wind capacity need to be built by 2025. This will require major transmission circuits, which traditionally take 10 years to permit and construct. Also, the effect of such a target means that more capacity needs to be built. In order to meet Britain’s demand of 61GW of energy, it is envisioned that 99GW of capacity will need to be built because of renewable energy’s lower capacity factors.

In terms of transmission, new routes will be required for both onshore and offshore wind, perhaps using submarine HVDC powerlines, connecting both on-land and offshore wind farms.