Thermal Storage and Heat Pumps Will be the Low Cost Peak Shaving Solution for Utilities and Users

With the Government of India (www.npcindia.gov.in) I gave two webinars to energy engineers on a proposal how to tackle it, helping them to deal with their weak grid. By the way, reading “The Grid” by Gretchen Bakke, also the USA has problems to keep pace with demand. Of course, our European Union, where I live, joined the club long ago. Today July 19 I heard on the news that London is hitting the historic temperature record with a peak of over 40°C.

Which impact will this have on power demand? Grid operators have a great interest in weather forecasts. So I thought it might be an idea to put the proposal in this article.  

If you are a decision-maker for a (large) energy user or you work at a utility and try to figure out how to deal with the demand peaks, you will be interested to know how a significant fraction of electricity can be stored with less capital but high technical safety, Security of Supply and sustainability.

Batteries are today considered by the most of us as the only way of storing electrical energy. Some of you will object: there is also electrical storage in gravity, like pumped water, or flywheels. But what about thermal storage? That is not really a way to store electrical energy and indeed it is not trivial to transform it back into the electrical form, but think again: how much electrical energy is used for cooling? The answer comes (for USA) from www.eia.gov. “The residential sector's electricity use for cooling was about 235 billion kWh in 2021, which was equal to about 16% of total residential sector electricity consumption and 6% of total U.S. electricity consumption”. For the whole world, www.iea.org writes: “Using air conditioners and electric fans to stay cool accounts for nearly 20% of the total electricity used in buildings around the world today.” These statistics are a bit different among them and in addition don’t include the cooling used by industry. So, maybe all cooling together takes close to 25% of all electricity and unfortunately is not a constant load on the grid. And we know how difficult peaks are to handle for the utilities.

My reason to bring a thermal process like cooling in relationship with electrical storage is based on two facts:

• If 1/4 of electricity is going into cooling, then it will be the same benefit for the grid if this fraction will be stored in batteries or in a tank of cold water (or ice);
• Thermal storage is way cheaper than electrochemical storage (batteries) and it is much easier to find Water (good material for thermal storage) than Lithium or Cobalt. It is also more sustainable.
• The advantage of thermal storage is also that the energy is already in the form you want. If it is in a battery, you still need a (big) chiller to meet a certain power demand. An example of this advantage I met in a metal factory in Zwitserland where the chiller was not big enough to keep the factory cool during the day. So they used this chiller to “charge” an ice bank (of 1400 kWh) with cheap night power and join the chiller during the day. In case of problems with the chiller or the battery, stored electrical energy is not going to be useful. It is too far from the form you need.

How can we make this idea useful?

Heat pumps produce cold and heat at the same time and ask a very limited amount of electrical power. One of the two (heat/cold) is usually discarded (!) but if you can use both, you are really in a nice situation. Imagine a factory where both heating and cooling processes are running. Imagine a hotel or hospital where space must be cooled, guests take a shower and the kitchen needs hot water. In this case, with 1 kW power a heat pump can deliver for example 4 kW of heat and 3 kW of cooling at the same time, so 7x multiplication of electric power. You can store both heat and cold in different storages and the heat pump will work between them. This will give you the flexibility to use heat and cold at different times. You can charge this coupled storage when power is cheap. If one or the other storage is full then of course you have to discard the cold or the heat as with usual heat pump configurations but at least you can try to make it an exception!

The heat pump with double storage can also be combined with CHP (Combined Heat and Power).

I am personally trying this concept in our holiday home in the hot Sicily (Italy) after trying to find a mini chiller (water/water heat pump). I didn’t find it so am forced to convert a standard air conditioner (air/air heat pump) and will use two tanks of 1000 litre for the cold and hot storage.

Which impact may have this concept on society?

What if all the grid operators would store their cheap power (night, surplus wind or solar power) into a form that can be sold as a commodity? That would work very well if much surplus power is available regularly available and where the demand on cold and heat is large and concentrated, so that a thermal grid is feasible.

An ideal scenario where this storage concept can be started before a broader introduction society is where Security of Supply of cold/heat is essential, for example an hospital, a fresh-food industry or supermarket. Also in the touristic sector cold and heat are important as my parents told after their trip to a tropical hotel with a black out, where the windows could not be opened. With a thermal storage, the cold & hot water are ready to use, even with high thermal power, just by starting a couple of pumps and control systems, which both ask little power. These are examples where decision-makers look much more to avoiding risk than to saving on the energy bill. And we can satisfy them in both.

So let’s start with example projects, partnering with ideal consumers that really need this solution and then roll it out to a broader market. With this concept there is so much energy that can be managed in a better way and will relieve the grids. I will update you with my personal realization of the idea.